Environmentally compatible cooling water treatment chemicals · of cooling water biocides....

Environmental Research of theFederal Ministry of the Environment,

Nature Conservation and Nuclear Safety- Water Economy -

Research Report 200 24 233

Environmentally compatible cooling watertreatment chemicals

byDipl. Geogr./Hyd. Stefan Gartiser

Dipl. Hyd. Elke Urich

Hydrotox GmbH, Freiburg

On behalf of theFederal Environmental Agency

Berlin, April 2002

I

Report Cover Sheet1. Report No.

UBA-FB 200 24 2332.

Water economy3.

4. Report Title

Environmentally compatible cooling water treatment chemicals5. Autor(s) (Family Name(s), First Name(s))

Gartiser, Stefan; Urich, Elke6. Report Date

7. Publication Date

8. Performing Organisation(s) (Name, Address)

Hydrotox GmbH9. UFOPLAN-No.

200 24 233Boetzinger Str. 29D-79111 Freiburg

10. No. of Pages

106 + 91 (annex)11. No. of References

103 + 71 (annex)12. Sponsoring Agency (Name, Address)

German Federal Environmental Agency13. No. of Tables

20Postfach 33 00 22, D-14191 Berlin (Germany) 14. No. of Figures

1115. Supplementary Notes

This project was commissioned in the form of a grant on the basis of costs as partialfinancing to the recipients (Grant Decision Z 1.6-25106/182 of 31.01.00)In Germany about 32 billion m3/a cooling water are discharged from industrial plants andthe power industry. These are conditioned in part with biocides, scaling and corrosioninhibitors. Within the research project the significance of cooling water chemicals wasevaluated, identifying the chemicals from product information, calculating their loads fromconsumption data of more than 180 cooling plants and investigating the basic characteristicdata needed for an environmental hazard assessment. Additionally, the effects of coolingwater samples and products were determined in biological test systems. Batch tests (shocktreatments) were performed under defined conditions in order to measure the inactivationof cooling water biocides.Generally the cooling water samples only showed low ecotoxicity, upon considering theinactivation of the biocides with time. With systematic backtracking, the genotoxicity of thecooling water from one company in the umu test could be attributed to one biocide withisothiazolinones and Bronopol as ingredients. Measurement of the inactivation of biocides,with the luminescent bacteria toxicity test, revealed a strong correlation with the inoculumconcentration and enabled a better estimation of the importance of the elimination factorsdegradation and adsorption. An overall balance sheet of chemical loads confirmed that theprincipal amounts came from open recirculation cooling systems, whereas only <10% of theplants with once-through cooling water used conditioning chemicals at all. The extrapolationof consumption data for Germany gave total loads of about 4.000 t/a oxidative and 125 t/anon-oxidative biocides. Additionally inputs of about 1.500-2.200 t/a phosphonic acids, 45-135 t/a molybdate and 113-216 t/a zinc were calculated. Basic substance data sheets weredocumented for all chemicals applied, enabling first assessments of environmentalrelevance using several approaches of hazard assessment.17. Keywords

cooling water, treatment chemicals, biocide, degradation, elimination, phosphonates,phosphonic acids, polycarboxylates, polycarbonic acids, zinc, bioassay, ecotoxicity, geno-toxicity, Vibrio fischeri assay, Daphnia test, umu-assay, Ames test, balance, load18. Price 19. 20.

II

Contents

0 Summary .............................................................................................. 1

1 Introduction.......................................................................................... 5

2 Current knowledge .............................................................................. 6

2.1 Fundamentals ........................................................................................ 6

2.2 Cooling water flow ................................................................................. 7

2.3 Minimum requirements for cooling water discharges in Germany ......... 9

2.4 General environmental hazards from cooling systems ........................ 10

2.5 Cooling water conditioning................................................................... 12

2.5.1 Dispersants and hardness stabilizers .................................................. 122.5.2 Scale inhibitors .................................................................................... 132.5.3 Biocides ............................................................................................... 14

3 Goals and investigative strategy ...................................................... 18

4 Methods .............................................................................................. 20

4.1 Laboratory investigations ..................................................................... 20

4.1.1 Cooling water samples ........................................................................ 204.1.2 Product investigations.......................................................................... 244.1.3 Chemical parameters........................................................................... 244.1.4 Fluorescent bacteria test according to DIN 38412-34 and

Nr. 404 of the AbwV............................................................................. 244.1.5 Alga test according to DIN 38412-33 and Nr. 403 of the AbwV ........... 254.1.6 Daphnia test according to DIN 38412-30 and Nr. 402 of the AbwV ..... 254.1.7 Ames test in conformance with DIN 38415-4 ...................................... 254.1.8 umu test according to DIN 38415-3 and Nr. 410 of the AbwV ............. 264.1.9 Elimination of biocides ......................................................................... 27

4.2 Drawing up an overall balance sheet................................................... 28

4.2.1 Compilation of production information materials .................................. 28

III

4.2.2 Making a balance sheet of the emissions of cooling waterchemicals............................................................................................. 29

4.3 Literature and database-research........................................................ 33

5 Results................................................................................................ 36

5.1 Cooling water investigations ................................................................ 36

5.2 Product investigations.......................................................................... 38

5.2.1 Eco- and Genotoxicity.......................................................................... 385.2.2 Identifying the source of the genotoxicity in plant 6 ............................. 385.2.3 Decrease of the biocidal effect in the fluorescent bacteria test ........... 41

5.3 Evaluation of the product information sheets....................................... 52

5.4 Evaluation of the questionnnaires........................................................ 53

5.4.1 Open recirculation cooling systems ..................................................... 545.4.2 Once-through cooling systems ............................................................ 565.4.3 Closed circulation cooling systems ...................................................... 585.4.4 Estimation of the total loads for Germany............................................ 585.4.5 Overview and comparison ................................................................... 64

5.5 Elimination of chemicals in cooling systems and sewage plants ......... 70

5.6 Regulatory control of cooling water discharges ................................... 70

5.7 Literature and database research ........................................................ 71

6 Evaluation........................................................................................... 74

6.1 Composition of cooling water............................................................... 74

6.2 Emission route for cooling water chemicals ......................................... 75

6.3 Elimination behavior of cooling water biocides .................................... 75

6.4 Choice of active substances ................................................................ 77

6.4.1 Biocides ............................................................................................... 776.4.2 Cooling water conditioners................................................................... 82

IV

7 Recommendations............................................................................. 89

7.1 Energy conservation measures ........................................................... 89

7.2 Technical solutions .............................................................................. 89

7.3 Process operation................................................................................ 91

7.4 Evaluation and selection of cooling water chemicals ........................... 93

7.4.1 Water risk classes, the VCI-concept for open cooling systems ........... 937.4.2 "Benchmarking"-concept ..................................................................... 947.4.3 Plant specific evaluation of cooling water chemicals ........................... 957.4.4 TEGEWA-concept for indirect dischargers .......................................... 967.4.5 Outlook ................................................................................................ 96

8 Sources............................................................................................... 98

9 Ackknowledgements ....................................................................... 105

List of TablesTable 1: Cooling water discharge in river basins (1995) [Mio. m3] .............................. 7Table 2: River flow volume balance for Germany in 1992 .......................................... 7Table 3: Ratio of used/discharged cooling water (1995) ............................................. 9Table 4: Charateristic data for the investigated systems .......................................... 23Table 5: Determination of the elimination of cooling water biocides ......................... 28Table 6: Summary of the wastewater investigations ................................................. 37Table 7: Results of the product investigations .......................................................... 39Table 8: Source of the genotoxicity in the cooling water from plant 6 ....................... 40Table 9: Dosing of biocides in the circulation cooling ............................................... 42Table 10: Experimental overview of the elimination curves of cooling

water biocides ........................................................................................... 43Table 11: Elimination of BCDMH depending on the inoculum .................................. 50Table 12: Characteristic data for the cooling systems investigated .......................... 53Table 13: Total amounts of the investigated chemicals in open circulation

cooling ...................................................................................................... 55Table 14: Consumption data in plants with flow-through cooling .............................. 57Table 15: Cooling water use for thermal power plants (1995 ) ................................. 60

V

Table 16: Concentrations of continuously added conditioners (concentrationin the circulation water in mg/l) ................................................................. 61

Table 17: Chemical usage in open circulation cooling systems in Germany ............ 63Table 18: Total load of cooling water chemicals in the once-through cooling

of the foodstuffs industry........................................................................... 64Table 19: Comparison of the estimated consumption data for certain biocides

with data from other countries (data in kg/a on a substance basis) .......... 69Table 20: Summarized evaluation of the eotoxicity and degradability of cooling

water chemicals ........................................................................................ 73

List of FiguresFigure 1: Investigative strategy ................................................................................. 19Figure 2: Decrease of the fluorescent bacteria inhibition with isothiazolinone .......... 44Figure 3: Decrease of the fluorescent bacteria inhibition with QAV .......................... 45Figure 4: Decrease of the fluorescent bacteria inhibition with DBNPA (10 mg/l) ...... 46Figure 5: Decrease of the fluorescent bacteria inhibition with DBNPA (48 mg/l) ...... 46Figure 6: Fluorescent bacteria inhibition with glutardialdehyde (30-160 mg/l) .......... 48Figure 7: Fluorescent bacteria inhibition with glutardialdehyde (30-1000 mg d.s./l) . 48Figure 8: Decrease of the fluorescent bacteria inhibition with Bronopol ................... 49Figure 9: Decrease of the fluorescent bacteria inhibition with BCDMH (4 mg/l) ....... 51Figure 10: Decrease of the fluorescent bacteria inhibition with BCDMH (37 mg/l) ... 51Figure 11: Proportion of biocidal active ingredients in 101 products ......................... 52

VI

Abbreviations

AbwV Wastewater OrdinanceAMPA Aminomethylenephosphonic acidAOX Adsorbable organic halogens (X = Cl, Br, I)ATMP Aminotrimethylenephosphonic acidATV Abwassertechnische Vereinigung e. V.BAT Best available techniquesBCDMH 1-Bromo-3-chloro-5,5-dimethylhydantoinBgVV Bundesinstitut für gesundheitlichen Verbraucherschutz

und VeterinärmedizinBIG Brandweerinformatiecentrum Gevaarlijke StoffenBUA Beratergremium für umweltrelevante SchadstoffeCAS Chemical AbstractsCHEMIS Chemical information system of the BgVVCOD Chemical oxygen demandDBNPA DibromonitrilopropionamideDTPMP Dieethylenetriaminepentamethylenephosphonic acidDOSE Dictionary of Substances and Their EffectsECDIN Environmental Chemicals Data and Information NetworkEnviChem Data Bank of Environmental Properties of ChemicalsEC50 50% effect concentrationEDTA EthylenediaminetetraacetateEDTMP Ethylenediaminetetramethylenephosphonic acidEQS Environmental Quality StandardEC European CommunityGESTIS Gefahrstoffinformationssystem der gewerblichen

BerufsgenossenschaftenGSBL Gemeinsame Stoffdatenbank Bund/LänderGA Lowest ineffective dilution, alga test = lowest dilution

factor at which inhibition of algal biomass growth is below20%.

GEA Lowest ineffective dilution, Ames test = lowest dilutionfactor at which an induction difference as compared withnegative controls of <80 (TA100) resp. <20revertants/plate (TA98) is determined.

GEU Lowest ineffective dilution, umu assay = lowest dilutionfactor with an induction rate below 1.5.

VII

GL Lowest ineffective dilution, luminescent bacteria test =lowest dilution factor at which inhibition of luminescenceis below 20%

GD Lowest ineffective dilution, Daphnia test = lowest dilutionfactor at which 90% of Daphnia retain their mobility

HSDB Hazardous Substances Data BankHEDP Hydroxyethanediphosphonic acid

IR Induction rate in the Ames and umu tests

IUCLID International Uniform Chemical Information DatabaseIUPAC International Union of Pure and Applied ChemistryIPPC directive EC-directive Integrated Pollution Prevention and Control

KBwS Kommission zur Bewertung wassergefährdender StoffeLAGA Länderarbeitsgemeinschaft WasserLC50 50% lethal concentrationMW Molecular weightMQ Mean water flowNTA NitrilotriacetateOECD Organisation for Economic Co-operation and

DevelopmentOSPAR Oslo/Paris Convention for the protection of the marine

environment of the Northeast AtlanticPBTC Phosphonobutanetricarbonic acidPEC Predicted environmental concentrationsPNEC Predicted no effect concentrationQAV Quarternary ammonium compoundsRTECS Register of Toxic Effects of Chemical SubstancesSCAS-Test Semi-continuous activated sludge testTEGEWA Verband der Textilhilfsmittel-, Lederhilfsmittel,- Gerbstoff-

und Waschrohstoff-Industrie e.V.VCI Verband der Chemischen IndustrieVGB Technische Vereinigung der Großkraftwerksbetreiber e.V.WF Growth factor in the umu testWGK WassergefährdungsklasseVwVwS Verwaltungsvorschrift wassergefährdender Stoffe

1

0 Summary

In power plants and industrial processes non-recoverable heat released during the

use and conversion of energy is removed from the industrial processes by cooling

systems. Water is the most important coolant medium used. In Germany about 27

billion. m3 cooling water (109 m3) are discharged per year from power plants mainly

via once-through cooling systems. To this, about 5 billion m3 from industrial plants

must be added, of which about 376 million m3 comes from plants with open

recirculation cooling systems. The water consumption of open recirculation systems

amounts to only 2-5% of that of open cooling systems at equal cooling capacities.

Nevertheless, the water added to the system to compensate the loss of water due to

evaporation or blow down ("make-up water") regularly has to be conditioned with

biocides, scale inhibitors, dispersants and/or corrosion inhibitors, in order to prevent

disturbances of processes by depositions (scaling), corrosion or bio-mass growth

(fouling).

Within the research project the input of cooling water chemicals was evaluated,

identifying the chemicals from product information, calculating their loads from

consumption data of more than 180 cooling plants and investigating the basic

characteristic data needed for an environmental hazard assessment. Additionally, 12

water samples from 7 companies and 11 products have been evaluated in biological

test systems. The elimination of eight cooling water biocides has been determined,

using the luminescent bacteria assay and batch tests with defined inoculum

concentrations (30-1000 mg d.s./l).

Generally, the cooling water samples showed only low ecotoxicity in the algae,

Daphnia and luminescent bacteria assays if the elimination time of the biocides is

considered. With systematic backtracking, the genotoxicity of the cooling water from

one company in the umu-assay could be attributed to one biocide with

isothiazolinones and Bronopol as ingredients. No effects of the water samples have

been detected with the Ames test, although several products proved to be mutagenic

in the Ames test. The elimination of biocides in batch tests, as measured with the

luminescent bacteria toxicity test, showed that isothiazolinones and quarternary

ammonium compounds were better removed with higher inoculum concentration due

2

to their adsorption to activated sludge. In contrast, the elimination velocity for 2,2-

dibromo-3-nitrilopropionamide (DBNPA) increased with increasing pH. For the

oxidative biocide bromochlorodimethylhydantoin (BCDMH) only a weak dependence

on inoculum concentration was observed, while Bronopol showed a distinct toxicity at

low inoculum concentrations even after 8 days. Therefore, the test conditions for the

determination of elimination curves, which determine the period the circuit must be

closed after a shock treatment with non-oxidizing biocides according to Annex 31 of

the German Waste Water Ordinance, must be clearly defined. Inactivation curves

performed applying the test conditions of the VCI-working group "Biocides in cooling

systems" with high inoculum density (activated sludge with 500 mg d.s./l) favor

elimination by adsorption, and the test design corresponds to an inherent bio-

degradation test. Comparable biomass concentrations normally were not found in

cooling systems. If additional information is required, especially for directly

discharged cooling water, results about ready bio-degradation and/or elimination

curves at lower inoculum concentrations (i.e., 30 mg d.s./l corresponding to the test

conditions of the OECD 301 "Ready bio-degradability" tests) should be demanded.

The overall accounting of chemical loads in a balance sheet confirmed that the

principal amounts came from open recirculation cooling systems, whereas only

<10% of the plants with once-through cooling water used conditioning chemicals at

all. The extrapolation of consumption data for Germany gave total loads of about

4000 t/a oxidative (mainly chlorine, chlorine release agents, BCDMH and hydrogen

peroxide) and 125 t/a non-oxidative biocides (mainly isothiazolinones, DBNPA and

quaternary ammonium compounds). Additionally, inputs of about 1500-2200 t/a

phosphonic acids, 45-135 t/a molybdate and 113-216 t/a zinc were calculated.

The questionnaire for actual cooling systems in operation uncovered distinct

capacities for improvement. In 34 out of 110 facilities with open recirculation cooling

systems ground water was used for cooling purposes, and in 12 cooling systems

drinking water (in three systems more than 100,000 m3 drinking water per year!).

Divergent from the requirements of Annex 31, biocides were continuously added in

some open recirculation and flow-through cooling systems. Among these was one

3

power plant using salt water as coolant, as well as plants of the chemical and

foodstuff industries. Of course, for foodstuffs hygiene requirements (product safety)

are more important than the prevention of biofouling in the cooling system.

According to the operators’ statements, the recirculation water of closed cooling

systems is often discharged indirectly via municipal treatment plants and only in

isolated cases directly into the recipient water. No luminescent bacteria test results

were available for two thirds of the cooling systems, although 40% of them directly

discharged the cooling water. Only in some cases did operators indicate that

elimination curves of the biocides used have been submitted. As a rule, only the

period of time for which the circuit must be closed after a treatment with biocides is

documented as specified by the producers of conditioning chemicals. Concrete

examples have also been presented in which the usage of chemicals has been

reduced up to 90% by simple technical or organizational measures (cleaning,

shading of cooling towers from the sun).

Basic substance data sheets were documented for all chemicals applied, based on

extensive literature and data bank/database researches, enabling first assessments

of environmental relevance using several approaches of hazard assessment.

For some chemicals (e.g., butylbenzotriazole, chlorotolyltriazole, tetraalkylphos-

phonium chloride) considerable data gaps exist. With reference to the BREF-

document of the EU-Commission about "the application of best available techniques

to industrial cooling systems", different approaches regarding the selection and

optimizing of cooling water chemicals are described. There is a clear confirmation

that this issue cannot be examined separately from the complex thermodynamic

processes, the water quantity available and the site specific characteristics. A

combination of emission- and water-quality-based criteria is recommended to assess

cooling water chemicals. The advantage of emission-based approaches based on

the classification system of harmful water pollutants according to the European R-

phrases of the dangerous substances directive is that, along with the aquatic

ecotoxicity, other protection areas such as health aspects or soil conservation are

considered. Additionally, insufficient databases were considered for the assessment,

following the precautionary principle. However, in order to draw attention to the loads

emitted, both the consumption amount as well as the elimination in cooling systems

4

and (for indirectly discharged water) municipal treatment plants should be

emphasized, as described in the TEGEWA-concept for indirect discharges. The

advantage of water-quality based approaches such as the "benchmarking"-concept

based on the predicted environmental and effect concentrations is that the intrinsic

properties of chemicals such as bio-degradability and ecotoxicity are combined and

the site specific characteristics are considered. Nevertheless, this approach focuses

on the environmental quality standards for surface water derived from chemical risk

assessment, and the rule of load minimizing seems to be less important when the

water flow capacity of the recipient water is considered to be sufficient. The

determination of toxicity loads (=effect concentration multiplied by load) is a possible

further development of the "benchmarking"-concept. Prequisites for the assessment

of conditioning cooling chemicals are that chemicals can be identified unambiguously

in product descriptions and that data gaps will be closed.

5

1 Introduction

In power plants and industrial processes non-recoverable heat released during the

use and conversion of energy is removed from the processes by cooling systems.

Due to its high heat capacity water is the most important coolant medium used. Apart

from surface water from rivers and lakes also sea, ground or drinking water is used

for cooling purposes.

Along with the organic and inorganic constituent compounds of this water, non-

negligible amounts of air pollutants, which might cause scaling, growth of

microorganisms and corrosion, are also washed out by cooling water due to the high

air turnover of cooling towers. Hence, the cooling water often is conditioned with

dispersants, corrosion inhibitors and biocides. As wastewater treatment of cooling

water is usually not applied, these chemicals are discharged with the ”blow down”

into the sewer or (from directly discharging plants) into the receiving water.

Within the project a systematic evaluation of the input of cooling water chemicals into

German surface water was carried out. To accomplish this, the chemicals used were

identified from product information, their loads were calculated from consumption

data of more than 180 cooling plants, and the basic characteritic data needed for an

environmental hazard assessment were compiled. Additionally, the effects of cooling

water samples and products were determined in biological test systems. Batch tests

were performed under defined conditions in order to measure the elimination of

cooling water biocides.

6

2 Current knowledge

2.1 Fundamentals

Cooling systems can be distinguished as once-through systems, as well as open and

closed recirculation systems, and their combinations (Held and Schnell 2000,

Anonymous 2001c). In once-through cooling systems cooling water is used without

recirculation, i.e., the warmed water is directly discharged into the receiving water.

Often once-through cooling is applied in combination with a cooling tower, where the

cooling water is trickled in order to remove part of the heat via evaporation cooling.

Once-through cooling systems demand a large water supply. For instance, power

stations with a difference between in- and outlet temperature of 10°C consume, as a

rule, about 3.5 m3 cooling water per 100 MW installed electric capacity (Fichte et al.

2000).

Open recirculating cooling systems are wet cooling circuits open to the air, where the

water used for cooling purposes is cooled down by evaporation. As a first

approximation one can assume that in open recirculating systems 70% of the heat

amount is removed by evaporation. The evaporation loss depends on the cooling

capacity and the climatic conditions. As a rule of thumb it can be assumed that, per

10°C temperature elevation, 1.1% to 1.6% of the circulating water flow evaporates in

Central Europe (Fichte et al. 2000, Sommer 1988). Additionally, droplet losses of

about 0.1% of the circulating water flow are emitted. Hereby, cooling water

ingredients are usually concentrated by a factor of 2-4. The concentration factor is

adjusted via the blow down (draining of cooling water to the recipient water body or

municipal treatment plant). The evaporation losses and the blow down are

compensated by the make-up water. The fresh water supply of open recirculating

systems amounts to only 2-5% of that from once-through cooling systems at equal

cooling capacity.

Besides the above mentioned, there are also closed circuit cooling systems (dry air-

cooling), which are operated without wastewater emissions and are usually applied

at high process temperature levels above 50°C. Hybrid cooling systems combine the

wet and dry cooling principles.

7

2.2 Cooling water flow

The discharge of cooling water into surface water has substantial significance for

water economy. The water resource balance shows that about 40% of the

precipitation drained off in Germany is used for cooling purposes, whereas significant

differences in the river basins can be observed because of to regional industrial main

areas and the varying water flow of the principal water recipients. For example, the

proportion of cooling water from the total flow of the Elbe and Rhine Rivers is above

60%, while the proportion from the Danube River amounts only to about 10% (Table

1; Table 2).

Table 1: Cooling water discharge in river basins (1995) [Mio. m3]

Table 2: River flow volume balance for Germany in 1992

The power plants for public supply, with 84% of all cooling water discharges, are the

most important dischargers. Only 219 million m3 cooling water from mostly small

companies were indirectly discharged via municipal sewage treatment plants, so the

cooling water proportion of municipal wastewater amounts to only 2-3 % of the total

by volume. Thus, nearly all the volume of cooling water (>99%) is discharged directly

River basin Donau Rhein Maas Ems Weser Elbe

coast and sea Oder sum

Cooling water discharges of mining and industry 536,7 3.621,7 17,1 34,8 175,9 597,4 16,7 45,5 5.045,9

direct dischargers 500,5 3.527,7 15,1 33,0 156,4 532,8 15,6 45,4 4.826,4indirect dischargers 36,3 93,9 2,0 1,8 19,6 64,6 1,2 0,1 219,4

Cooling water discharges from power industry for public supply 1.974,6 12.603,0 n.a. 62,1 4.647,8 7.178,9 880,3 1,0 27.347,7Source: Statistisches Bundesamt Fachserie 19, Reihe 2.2, 1998Maas=sum of cooling water of the Rur, Schwalm and Niers Rivers

River basin Donau Rhein Maas Ems Weser Elbe

coast and sea Oder sum

Average runoff into BRD [m3/s] 579 1225 253 n. a 2057Average runoff from BRD [m3/s] 1346 2043 32 111 347 610 201 11 4701Runoff from area of BRD [m3/s] 767 818 32 111 347 357 201 11 2644Cooling water effluents in total [m3/s] 80 514 1 3 153 247 28 1 1027Proportion of cooling water from MQ with runoff into BRD 6% 25% 40% 14% n. a 22%Proportion of cooling water from MQ from area of BRD 10% 63% 2% 3% 44% 69% 14% 13% 39%Source: Statistisches Bundesamt Fachserie 19, Umweltökonomische Gesamtrechnungen, August 1994

Statistisches Bundesamt Fachserie 19, Reihe 2.2, 1998, changed to m3/sMQ = Average runoff in 1992 of the respective draining areas of rivers; BRD=Federal Republic of Germany

8

into the receiving water course. Conequently the chemicals used for cooling water

conditioning immediately enter the receiving water, so that a particular risk potential

might arise, unless the chemicals are inactivated in the cooling system itself.

Considering the different industrial sectors of cooling water dischargers (cf., table 3)

it is evident that, next to the power plants for public supply, in particular the chemical,

mining and metal industries are the principal dischargers of cooling water. From the

proportion of "used" and "discharged" cooling water a "utilization factor" can be

calculated. This factor gives an indication of the importance of open recirculating

cooling systems in the respective industrial sector. (The data on cooling water

utilization also contain the recirculated volume and multiple-shift uses for different

purposes.)

9

Table 3: Ratio of used/discharged cooling water (1995)

2.3 Minimum requirements for cooling water discharges in Germany

In Germany the discharge of cooling water is regulated in Annex 31 of the

Framework regulation for wastewater. Here inter alia the following requirements are

given:

• With the exception of phosphonates and polycarboxylates exclusively complexing

agents which are readily bio-degradable may be used,

• The wastewater must not contain chromium, mercury or organometallic

compounds,

• The concentrations for chlorine, AOX, COD, phosphorus and zinc are limited,

Water used for cooling purposes

Water used for cooling

Discharged cooling water

without treatmentUtilisation factor *)

*1000 m3 *1000 m3

Power plants for public supply 61.759.994 27.347.665 2,3

Mining industry 5.616.335 812.998 6,9Foodstuff and tobacco industries 905.610 161.889 5,6Textile industry 176.554 145.123 1,2Leather industry 4.170 317 13,2Wood manufacturing 41.723 11.609 3,6Paper and printing industry 683.511 390.528 1,8Coking plant and petroleum processing 2.415.387 127.419 19,0Chemical industry 11.333.036 2.488.627 4,6Rubber ware production 640.606 65.111 9,8

Glass, ceramics and stone commerce 382.479 28.497 13,4Metal products and manufacturing 5.091.455 616.186 8,3Engine construction 236.904 26.284 9,0Production of office machines, electrical engineering 393.444 59.964 6,6Vehicle construction 1.143.730 108.069 10,6

Production of furniture etc., recycling 50.581 3.261 15,5Sum of industrial cooling systems 29.115.525 5.045.882 5,8

Grand total of all cooling systems 90.875.519 32.393.547 2,8Reference: Statistisches Bundesamt Fachserie 19, Reihe 2.2, 1998*) The Utilisation factor here refers to the discharged cooling water and not to the make-up water!

10

• For fresh water cooling systems a shock treatment with microbicidal substances

is limited to oxidative biocides (chlorine, chlorine dioxide, hydrogen peroxide,

ozone).

• After a shock treatment with a biocidal substance the blow down of recirculating

cooling systems is only allowed if the luminescent bacteria toxicity does not

exceed GL =12 (GL= Lowest ineffective dilution factor, LID).

Annex 31 currently is being revised and will be in force in 2002 (Anonymous 2001). A

background paper (draft of the Bund/Länder GK 21/41 from 17.12.2001) will also be

published in 2002.

In the course of the implementation of the EC-directive 96/61/EC concerning

Integrated Pollution Prevention and Control (IPPC-directive) an extensive "Reference

Document on the Application of Best Available Techniques to Industrial Cooling

Systems" was elaborated, which is available in the internet (http://eippcb.jrc.es). The

aim of the IPPC-directive is to optimize the operation of industrial plants, so that

while considering energy efficiency and waste avoidance no substantial pollution of

the environment will be generated. Hereby measures for the improvement of one

environmental compartment (e.g., water) shall not lead to additional stress of another

compartment (e.g., air). The reference document offers a comprehensive

documentation for the selection of cooling systems, technical descriptions and

potential environmental effects. It is clear that the cooling system cannot be

considered separately from the industrial process and location. By optimizing the

overall process substantial amounts of energy can often be saved. In addition, the

excess energy should be used insofar as possible, for example for hydrothermal

heating projects. Although in the reference document approaches for evaluating the

chemical additives in cooling systems are described (cf., sect. 7.4), until now there

has been no systematic presentation of the basic data required for this, both on the

input side (consumption data), as well as on the material, chemical side

(degradability, ecotoxicity, genotoxicity, bioaccumulation).

2.4 General environmental hazards from cooling systems

In the operation of cooling systems a complex field of tensions between various

usage interests and environmental conflicts arises. The water consumption is highest

11

for once-through cooling systems and for larger power plants this can exceed several

m3/s. Depending on the mesh width of the inflow rates to the cooling system and the

flow rate, substantial numbers of fish, especially young ones, can be sucked in and

killed (up to 25 fish per 1000 m3; Anonymous 2000). The temperature increase in the

surface water leads to a reduction of the oxygen solubility in the water together with

an increase in the metabolic activity. Since this can lead to a shift in the species

spectrum in the waters (LAWA 1991), heat load plans have been prepared for the

waters. The EU-Guideline 78/659/EWG specifies for Salmonid and Cyprinid waters,

among other things, the maximal permissible temperature elevations (1.5°C and 3°C)

and maximal temperatures (21.5°C and 28°C, and, during the spawning period of

cold-water fish, for certain waters 10°C; 78/659/EWG 1978).

For cooling towers a large part of the heat burden is released as latent heat

(evaporation) and causes an increase of the air temperature, which can lead to

changes in the local microclimate (VDI 3784: 1986). For large power plants natural-

draft wet cooling towers are used, for which the construction height provides

sufficient force to drive the air current. For ventilator cooling towers the necessary

amounts of air are, in contrast, introduced by forced air blowers, for which electrical

energy must be provided (corresponding to 0.5-2% of the amount of emitted heat

energy, Anonymous 2000). For open recirculation cooling systems the water

consumption is usually reduced by ca. 95%-98% compared to once-through cooling

systems at equal cooling capacity. At the same time, however, the electrical energy

needed for the pumps is increased by ca. 50% thus amounting to ca. 1.5% of the

amount of emitted heat energy. The evaporation losses can be taken to be ca. 0.4-

0.7 l/s per 1000 MW of output electricity (Wunderlich 1978b). This leads to an

increase in the concentration of the constituent compounds in the water, so that

often a purification of the water and/or a conditioning of the cooling water is

necessary, which then requires the addition of chemicals to the receiving waters.

The most urgent goal of the plant management of cooling systems, however, is their

efficiency and protecting the system against depositions (scaling), corrosion and

biomass growth (fouling). The formation of depositions on the cool water side of a

heat exchanger or pipeline interferes with heat transfer and increases the loss of

pressure, so that the performance is substantially reduced. Ultimately, this leads to a

12

higher water consumption and must be compensated by an increased application of

energy. Thus, a calcium deposit 0.5 mm in thickness reduces heat transfer in

condensers by ca. 20% (Todutza and Steinlein 1990). Corrosion processes not only

damage the system, but also increase the risk of leaks on the production side. In

addition, the corrosion products endanger the waters.

A control of the biomass growth is performed with the additional goal of minimizing

the microbiological risks arising from the cooling plant. It is known, for example, that

thermophilic human pathogens, especially Legionella pneumophilia, which causes a

severe pneumonia (Legionnaire’s disease), can be found in cooling systems (States

et al. 1987, Kusnetsov et al. 1997, Werner and Pietsch 1991, Howland and Pope

1983, Kusnetsov et al. 1993). Guidelines for controlling Legionella in cooling systems

are available (Anonymous 2001a).

2.5 Cooling water conditioning

For the prevention of scaling in recirculation cooling systems, dispersants and

hardness stabilizers are added. In addition, corrosion inhibitors and biocides are

used, whereby there are overlaps between the individual groups (e.g., phosphates

act both as hardness stabilizers and corrosion inhibitors).

2.5.1 Dispersants and hardness stabilizers

The precipitation of salts due to their exceeding their solubility limits is termed

scaling. Of particular interest in cooling systems is the precipitation of calcium

carbonate and calcium phosphate, and to a limited extent also calcium sulfate and

silicates. The hardness of the water can also be reduced by active decalcification

(precipitation with calcium hydroxide). The residual hardness is either removed by

conversion of the carbonate hardness into non-carbonate with acids (primarily

hydrochloric and sulfuric acid) or stabilized through the addition of hardness

stabilizers such as orthophosphate, polyphosphates and phosphonic acids. The

ready hydrolysis of polyphosphates to orthophosphate and the associated danger of

calcium phosphate deposition led to the development of stable phosphonic acids,

which are added in sub-stoichiometric amounts (Andres et al. 1980). The most

important phosphonic acids used in the field of cooling water treatment are aminotri-

methylenephosphonic acid (ATMP), hydroxyethanediphosphonic acid (HEDP) and

13

phosphonobutanetricarbonic acid (PBTC). Organic polymers based on polyacrylic

acid, polymetacrylic acid, polymaleic acid and polyacrylamide (so-called

polycarboxylates) also have a certain hardness stabilizing effect and are often used

in combination with phosphonic acids.

The calcium carbonate hardness can be stabilized with, e.g., carboxymethylcellulose.

To a limited extent complex formers (NTA) are used; EDTA is however excluded de

facto from use because of its poor degradability.

Further depositions can also be caused by the precipitation of suspended organic

and inorganic particles and iron oxides. To prevent this, dispersants based on the

above mentioned polycarboxylates as well as low-molecular weight anionic acids

(e.g., succinates) are added. These are to be distinguished from natural products,

such as lignins and tannins, and from synthetic polymers of the polyacrylic,

polymetacrylic, and polymaleic acids as well as sulfonates. The transition between

the hardness stabilizers and the dispersants is not clear-cut.

2.5.2 Scale inhibitors

The corrosion of metals is enhanced by the presence of oxygen, salt content

(especially chlorides) and a low pH, but also by deposits. During oxygen corrosion

metal ions are dissolved at the metal surface, which acts as the anode, while in the

cathodic reaction oxygen is reduced to hydroxide ion and a high pH is produced

locally (Anonymous 1991). Of particular importance is microbially induced corrosion,

which is caused by acidic metabolic products as well as the anoxic/anaerobic

conditions within biofilms. Sulfate-reducing bacteria of the genus Desulfovibrio act

corrosively, by reducing the sulfate while forming hydrogen sulfide. These bacteria

are among the most important in cooling systems (Koppensteiner 1973). However,

corrosion can also be induced by sulfur bacteria (Thiobacillus), iron bacteria

(Ferrobacillus, Gallionella) and nitrifying bacteria (Nitrosomonas, Nitrobacter).

Passive (anodal) corrosion inhibitors, such as phosphates, phosphonates, nitrite,

silicates and molybdates form a passive protective layer on the metal surface. The

use of chromate is no longer permitted. In contrast, cathodic inhibitors like zinc or

calcium carbonate, and to a limited extent also orthophosphate, form insoluble

deposits which protect the metal surface by reacting with the corrosive hydroxyl ions.

14

Especially for copper and copper alloys, 1,2,3-triazoles are used as inhibitors.

Mercaptobenzthiazoles may no longer be used for this purpose according to Annex

31 of the AbwV regulations.

2.5.3 Biocides

The mean temperature in water cooling systems is ca. 35°C and thus lies just below

the temperature optimum of most microorganisms (Mattila-Sandholm and Wirtanen

1992). Biocides are used to control biologically induced deposits and corrosion

processes. For cooling water systems algicides, fungicides and molluscicides are

relevant.

2.5.3.1 Biology in cooling systems

The growth of autotrophic algae is dependent on the presence of mineral nutrients,

carbon dioxide and light energy, while the growth of heterotrophic bacteria requires

organic material, which is composed of dead algae and/or the existing burden of the

water or air. In principle, bio-degradable conditioning agents can also function as a

carbon source. Many bacteria secrete a highly hydrated slime consisting of

polysaccharides, which leads to the formation of biofilms on surfaces (biofouling).

Biofilms decrease heat exchange, promote corrosion and hinder control by means of

biocides. Protozoa such as Ciliates or Amöbae colonize affected cooling towers as

consumers, as do higher organisms such as mussels and snails, which can lead to

serious disturbances.

In once-through cooling systems, because of the short retention time and the

requirement for a rapid elimination, fast-acting oxidative biocides are used; and in

open cooling systems, non-oxidative, more stable organic biocides are called for.

2.5.3.2 Oxidative biocides

The most commonly used oxidative biocide, owing to its effectiveness and low price,

is chlorine or cholorine bleach (sodium hypochlorite). At the pH-values of > 8 typical

for cooling system circulation, there is a reduction of the biocidal effect of the active

substance, hypochlorous acid (HOCl), while hypobromous acid is still effective at pH

9. Hypobromous acid is generally generated on site by adding sodium bromide to

sodium hypochlorite (NaOCl). The use of free halogens as biocides may, depending

15

on the water composition (e.g., DOC- and ammonium concentration), pH-value and

contact time, lead to the formation of disinfectant by-products such as

trihalomethanes, chloro- and bromoamines as well as absorbable organic halogen

compounds (AOX).

In the purification of drinking water chlorine is replaced in part by chlorine dioxide, in

order to minimize the formation of AOX, especially halogen methanes. Chlorine

dioxide reacts noticably more weakly with complex organic molecules and

ammonium, consequently forming less AOX. Chlorine dioxide is also occasionally

used in the cooling water field, whereby it is usually generated on location through

the reaction of chlorine gas with sodium chlorite (NaClO2). Organic chlorine and

bromine release agents are used especially in open recirculation cooling systems.

Here, above all, the rapidly hydrolyzing biocide 1-bromo-3-chloro-5,5-

dimethylhydantoin (BCDMH) should be mentioned. Related compounds like 1,3-

dichloro-5,5-dimethylhydantoin or 1,3-dichloro-5-ethyl-5-methylhydantoin are also

occasionally used.

Ozone is a highly effective oxidatively acting biocide. Usually, ozone is continuously

added to the cooling water in very low concentrations of 0.1 to 0.3 mg/l (Wasel-

Nielen and Baresel 1997, Viera et al. 1999). Production is achieved directly on

location using high voltage, In comparison with the other oxidative biocides,

hydrogen peroxide is only effective at higher concentrations (> 15 mg/l; cf., van Donk

and Jenner 1996) and has a short half-life. Rarely, peracetic acid is also used as an

organic oxygen release agent in cooling systems. Under unfavorable conditions,

peracetic acid is corrosive. This chemical is readily bio-degradable.

2.5.3.3 Non-oxidative biocides

Non-oxidative biocides are used nearly exclusively in open recirculation cooling

systems, where the contact time of the cooling water with the biocide suffices for a

satisfactory effect. As a rule, here the biocide is added batchwise in a shock

treatment.

One of the most important non-oxidative cooling water biocides, a mixture consisting

of a chemical belonging to the isothiazolinone family, 5-chlorine-2-methyl-4-

isothiazolin-3-one, together with 2-methyl-4-isothiazolin-3-one, is already effective at

16

concentrations below 1 mg/l. Isothiazolinones hydrolyze slowly (t1/2 = 7 d at 30°C and

pH 8) and are not readily bio-degradable. Quarternary ammonium compounds (QAV)

act through their binding to the cell membrane and are also not readily bio-

degradable. During passage through the sewage treatment plant they are largely

eliminated by adsorption on the activated sludge. The most important representative

in the cooling water area is alkyldimethylbenzylammonium chloride.

The addition of dibromonitrilopropionamide (DBNPA) is also widespread in the

treatment of cooling water. This compound hydrolyzes rapidly to the still partially

biocidally active compounds dibromoacetonitrile, dibromoacetamide, monobromo-

nitrilopropionamide and cyanoacetamide. Further members of the organic bromine

compound group include 2-bromo-2-nitropropan-1,3-diol (Bronopol) and beta-bromo-

beta-nitrostyrene.

Glutardialdehyde is also rather frequently used in the cooling water field. The

mechanism of action is based on the denaturation of proteins. Glutardialdehyde is

less toxic for aquatic life forms as compared to the other biocides, and the

concentration added is correspondingly higher. This compound is readily bio-

degradable. Specifically for the control of algal growth additional biocides are used,

such as copper sulfate, as well as photosynthesis inhibitors based on triazine-

derivatives.

To reduce the risk of the appearance of microorganisms resistant to the added

biocides combination products containing several biocides are used.

2.5.3.4 Elimination of the biocidal effects

A basic requirement for cooling water biocides is that their damaging action or

biocidal effects must diminish in a relatively short time, since otherwise there might

be toxic effects on the surface waters, especially after the direct discharge of cooling

water. This calls for a rapid hydrolysis and/or biological degradability of the biocides.

For indirect emissions via municipal sewage treatment plants it has to be proven that

the biological wastewater treatment is not inhibited and that the biocides are retained

in the treatment plant. Preferably, the biocides should be biologically degraded.

While elimination through adsorption on the activated sludge (cf., QAV) protects the

17

receiving water, this merely shifts the problem, when the collected sludge is spread

on the land for agricultural or forestry use.

The elimination of the biocidal effects can be assayed either in the laboratory or on

site at the actual treatment plant. For the completion of such so-called ”elimination

curves” in the laboratory there are, however, no generally acceptable specifications

to date. Here the manufacturers have proposed static experiments with relatively

high concentrations of activated sludge (0.5 g d.s./l), in order to simulate the

influence of a hypothetical biofilm in the cooling system circulation (Scheidel et al.

1996). Other authors, on the other hand, determine an elimination curve without

adding any inoculum (Gartiser and Scharmann 1993, Gellert and Stommel 1995,

Baltus et al. 1999).

18

3 Goals and investigative strategy

In accordance with the project description, the following goals have been set:

• Estimation of the emission of cooling water conditioners in flowing surface waters

of the Federal Republic of Germany

• Determination of the introduced cooling water chemicals and investigation with

respect to their ecotoxicity, genotoxicity, bioaccumulation and degradability

• Determination of current practices of the governmental control agencies in the

individual Bundesländer

• Extension of the data status on ecotoxicity, genotoxicity and biological

degradability of the cooling water chemicals in use through measurements of our

own

• Develop suggestions/proposals for the reduction and optimization of the addition

of cooling water chemicals

• Develop a recommendation for the selection of cooling water chemicals based on

the present technical state of the art

The investigative strategy is based on three pillars (see Fig. 1):

• Literature and database research on the active ingredients/substances of the

standard commercially used cooling water conditioners

• Drawing up of an overall accounting balance sheet of the loads and

concentrations of cooling water conditioners in treatment systems

• Direct testing of cooling water samples, products and active ingredients with

respect to their ecotoxicity and genotoxicity, as well as determining the rate of

elimination of biocides (elimination curves)

19

Figure 1: Investigative strategy

- Products- Active substances- Elimination of biocides- Ecotoxicity, Biodegradability Genotoxicity

- Consumption data of plants- Wastewater concentration- Total volume loads in BRD- Total loads of active Subst.

Cooling water

Active substances/Products

Comparision of data

Elimination of biocides/

Products

Research Overall Balance

Tests

Practice of regulatorycontrol

State of the art

20

4 Methods

4.1 Laboratory investigations

4.1.1 Cooling water samples

Cooling water samples from 7 treatment plants in Southern and Northern Baden

were investigated. All these plants have open recirculation cooling systems.

Collection of the samples was as qualified test samples direct from the investigated

cooling vessel or from the return flow of the circulation (DIN 38402 1991). The

descriptive data of the investigated cooling water with respect to water consumption

and the products added are presented in Table 4.

a) Plant 1, Electroindustry

The operation of a semi-conductor manufacturer has six cooling towers with a total

cooling capacity of 2.5-3 MW. The cooling tower investigated has a cooling capacity

of 1.2 MW and removes the heat produced by a refrigeration system. As a special

feature, the concentrate of the water treatment (reverse-osmosis system with a

capacity of 700 µS/cm) is used as cooling water. For hardness stabilization and

corrosion inhibition a product based on sodium phosphonates, sodium molybdate,

sodium polycarboxylates and triazoles is added continuously. As a biocide,

isothiazolinone is added in summer as needed. Through regular mechanical cleaning

of the cooling vessel and an adequate shading of the cooling tower the amount of

this chemical added was reduced by more than 90% compared to the previous

years. The yearly consumption of isothiazolinones in the year 2000 was ca. 0.4 kg/a

of active substance. At the time of sampling no biocides were being added.

b) Plant 2, Plastics manufacturing industry

The company manufactures molded plastic parts for the automobile industry and has

several cooling towers with a total capacity of 6700 kW, which are fed with ground

water. As biocide a quarternary ammonium compound is added batchwise as

needed and then the outflow is closed for the next three days. The time of addition is

decided upon by visual examination of the algal growth. In addition, corrosion

21

inhibitors and hardness stabilizers based on phosphonic acids, zincchloride and

dispersants are continuously added.

The first sample collection on 19.07.00 took place two months after a shock

treatment with biocides, and the second and third samples were taken either directly

after the biocide was added and after an elimination time of three days resp. Besides

the cooling water, the wastewater produced from the released steam, to which

hydrazine was added, was also examined.

c) Plant 3, Plastics manufacturing industry

The plant manufactures PVC-foils and has a cooling tower with a capacity of 2.3-9.2

MW. Ca. 250 m3 of completely desalted cooling water are added weekly. In the non-

shaded cooling tower problems with algae arise. In this event, a "heterocyclic

sulfur/nitrogen-compound" (Isothiazolinone) is added batchwise in a shock treatment

(total load 0.8 kg/a active ingredient).

d) Plant 4, Plastics industry

The plant of a manufacturer of adhesive foils has four cooling towers, whose function

is to thermally reclaim solvents from activated charcoal filters. About four times a

year a preparation based on isothiazolinones is added batchwise (ca. 30 liters of

product/a). After a retention time of 24 h according to statements from the operator,

the GL-value is ascertained to be below 12. As hardness stabilizers polycarboxylates

and phosphonocarboxylates are added continuously. At the time of the collection of

the first sample, there was no addition of biocide, and the second sample was taken

24 h after a biocide treatment just after the outflow was reopened.

e) Plant 5, Plastics manufacturing industry

The plant manufactures foamed polystyrene- and polypropylene-packaging and has

three cooling towers. For the foaming of the plastics 10-12 t/h of desalted boiler

feeder water (steam) is needed. The boiler feeder water is treated with a corrective

material and the condensed steam (condensate) enters the open cooling system

during the production process. Thereby solid materials from the production process

are also carried over and are removed from the cooling water circulation with bag

filters (towel filters). These filters are cleaned daily. Twice weekly 60 liters of a

22

biocidal product based on hydrogen peroxide and quarternary ammonium

compounds are added. The cooling water sample was taken in the filter outflow 7 h

after a batch treatment.

f) Plant 6, Chemical industry

The plant has two cooling water systems, which were both sampled. The plant

cicrculation (KW1) has four forced-aeration cooling towers and is operated with a low

compression ratio of 1.1. The second circulation (KW2) handles the central cooling

system and is run at a high cycle of concentration of 3.0. Both circulations are

treated continuously with the biocide 1-bromo-3-chloro-5,5-dimethylhydantoin. As

needed, a product based on 2-bromo-2-nitropropan-1,3-diol and isothiazolinones is

added. For corrosion inhibition phosphonic acids and tolyltriazole are continuously

added.

g) Plant 7, Chemical industry

This pharmaceuticals producing operation set up a new cooling system for the

expansion of the refrigeration plant. A portion of the drinking water needed for

feeding this system is completely desalted by an ion-exchanger. The cooling water is

treated twice weekly for several h with the biocide 1-bromo-3-chloro-5,5-

dimethylhydantoin. To inhibit corrosion phosphonic acids and triazoles are added

continuously. The sample was collected 24 h after the last biocide treatment after

opening the outflow.

23

Table 4: Charateristic data for the investigated systemsFirm Water consumption Principle Products Active

ingredient 1

Active

ingredient 2

Active

ingredient 3

Active

ingredient 4

Branch [kW] [m3/a]

[m3/(a*KW)]

Concentrationratio

Pro-ducts

Biocide-addition

Pro-duct[kg/a]

Discharge

Conc.[%]

Load[kg]

Conc.[%]

Load[kg]

Conc.[%]

Load[kg]

Nr. 1 2.500 14.402 5,8 RO OK Biocide 1 10 KA CMI 2,4 0,2 MI 2,4 0,2Electro- TW Product S 457 Triazoles 2,5 11,4 NaOH 2,5 11,4 Phosphonate Na.molybdateindustry Product 90 HCl 21,0 18,9 (without conc.)Nr. 2 6.700 1.761 0,3 G OK Biocide 3 S 660 KA QAVPlastics manufacturing 1,8 Product 2250 HEDP 15,1 339,8 ATMP 20,1 452,3 Polyoxy-

carbonacid10,1 227,3 Zinc chloride

(without conc.)Product 4145 HCl 30,0 1243,4 HEDP 9,9 1,4-Butindiol 9,9 410,3

Nr. 3 3.000 13.000 4,3 VE OK Biocide 4 S 40 KA CMI 0,9 0,4 MI 0,9 0,4Plastics manufacturing ? PO4

3- 24 Ortho-phosphate

100,0 24,0

Nr. 4 18.710 23.579 1,3 G OK Product 900 O Poly-carbonates

Phosphon-carbonate

Foil production 3,0 Biocide 2 S 30 CMI/MINr. 5 4.000 2.600 TW OK Biocide 5 S 6240 KA H2O2 QAVPlastics manufacturing NaOH 3120 NaOH 25,0 780,0

Product 1200 Polyethoxylate Non-ion.Tenside

Nr. 6 Chemical Industry 7020 NaOH 3,5 245,7 Tolyltriazole 3,0 210,6 Phosphonicacid

7,5 526,5

Circulation1

6.300 720.000 114,3

G OK/1,1 1600 Phosphonicacids

Biocide 6 K 644 O and BCDMH 25,1 161,6Biocide 7 S 125 KA Bronopol 9,0 11,3 MI 1,8 2,3 CMI 1,8 2,3NaOCl 2000 Sodium-

hypochlorite13,0 260,0

Circulation2

43.500 120.000 G OK/3,0 Product 7350 NaOH 3,5 257,3 Tolyltriazole 3,0 220,5 Phosphonicacid

7,5 551,3

Product 1000 Phosphonicacids

Biocide 6 K 2323 KA BCDMH 25,1 583,1Biocide 7 S 25 Bronopol 9,0 2,3 MI 1,8 0,5 CMI 1,8

Nr. 7 6.000 58.000 9,7 TW OK Product Planning KA Polycarbonicacid

17,5 Phosphonicacid

6,3 Triazole 2,5

Chemical Industry max. 4.0 Biocide 8 S stage BCDMH 75,0Water consumption: G=Ground water; RO=Reverse osmosis; VE=completely desalted water; TW=Drinking water; Biocide added: K= continuous; S=Batch treatment; Source: O=surface water; KA=municipal waterpurification plant; ingredients: CMI: 5-chloro-2-methyl-2H-isothiazolin-3-one; MI: 2-methyl-2H-isothiazolin-3-one; BCDMH: 1-bromo-3-chloro-5,5-dimethylhydantoin; Bronopol: 2-bromo-2-nitropropan-1,3-diol; HEDP: 1-Hydroxyethan-1,1-diphosphonic acid; ATMP: Aminotrimethylphosphonic acid

24

4.1.2 Product investigations

Altogether five biocides and one corrosion inhibitor were tested. All of these active

substances are used in the plants investigated. They were tested with respect to

their mutagenicity, genotoxicity and ecotoxicity. At a later time four more products as

well as the biocide Bronopol were investigated in the umu test, in order to to

determine the source of the genotoxicity in the wastewater of one plant by systematic

"backtracking". An additional emphasis was the determination of the elimination

behavior of the most important biocides applied in the cooling water field, using the

fluorescent bacteria test (cf., sect. 4.1.9).

4.1.3 Chemical parameters

pH-value: pH 196 pH-meter from WTW GmbH in Weilheim.

Conductivity: Measuring instrument pH-LF 3001 from Neukumelektronik GmbH in

Straubenhardt.

CSB: Round cuvette test (Dr. Lange Co.): Two-hour oxidation with potassium

dichromate, sulfuric acid, silver- and mercury sulfate at 148 °C in conformance with

DIN 38409 H41.

Chlorine (free and total): Round cuvette test (Dr. Lange Co.): reaction with diphenyl-

p-phenylendiamine (DPD) witih the formation of a colored substance; total chlorine

determined after addition of potassium iodide.

4.1.4 Fluorescent bacteria test according to DIN 38412-34 and Nr. 404 of theAbwV

The toxicity of wastewater contaminants is detected on the marine bacteria of the

species Vibrio fischeri, which show a natural light production (bioluminescence) that

is closely coupled with their metabolic activity. The decrease of the light intensity

provides a quantitative measure of the toxic effect on the bacteria. The test is

performed with the LUMIS-tox system of the company Dr. Lange, Düsseldorf. The

lyophilized bacteria of the strain Vibrio fischeri NRRL-B-11177 were obtained from

the same company (LCK 482). The wastewater samples were tested without further

pre-treatment after salinizing with sufficient sodium chloride to give a 2% solution

25

and adjusting the pH-value to 7.0 +/- 0.2. The test result is given as the least

stepwise dilution (GL-value), for which the light emission is inhibited less than 20%.

4.1.5 Alga test according to DIN 38412-33 and Nr. 403 of the AbwV

The chronic inhibitory effect of the cooling water samples on the growth of

Scenedesmus subspicatus, a planktonic fresh-water alga, was determined. For this

purpose, a dilution series of the cooling water sample was made, without any further

preparation, but adding an algal nutrient solution inoculated with a defined algae

suspension (corresponding to 104 cells/ml) and incubating under defined light and

temperature conditions. After 72 h, the number of cells was determined

microscopically as a measure for the biomass. The result given is the least dilution

step (GA-value), after which the measured inhibitory effect on biomass production is

less than 20%.

4.1.6 Daphnia test according to DIN 38412-30 and Nr. 402 of the AbwV

The acute toxic effect of wastewater on Daphnia magna STRAUS (Crustacea, clone

5 of the German Federal Health Agency) was determined. The value measured is

the dilution factor GD beyond which no acute toxicity for Daphnia is detected within

24 h. The GD-value corresponds to the least dilution factor by which a wastewater

sample must be diluted in order for 90% of the Daphnia to maintain their ability to

swim. The pH-value of the sample was adjusted with hydrochloric acid or sodium

hydroxide solution to 7.0 – 7.5. No other pre-treatment was performed.

4.1.7 Ames test in conformance with DIN 38415-4

The Ames test is a bacterial mutagenicity test with Salmonella typhimurium. The

Salmonella-bacterial strains used are deficient mutants, which are unable to grow in

histidine-free medium. These histidine-requiring mutants can back-mutate (reversion)

and then are able to form colonies on minimal-agar plates. Each of the Salmonella-

strains has a specific spontaneous mutation rate. The number of back-mutated

bacteria (revertants) above this level provides a measure of the mutagenic potential

of a substance or a sample. Certain mutagens in higher organisms are first activated

by being metabolized (promutagens) or are thereby inactivated. Therefore, to the

bacterial system the needed enzymes are added in the form of rat liver extract S9

26

(Moltox Co.). The test version used is based on a simplified version of the OECD-

Guideline 471 with the test strains TA98 and TA100. The strain TA98 detects

frameshift mutagens; strain TA100 in contrast is for base pair substitution mutagens

(point mutations). The cooling water samples were sterilized over a membrane filter

(0.45 µm). Up to 1 ml of cooling water per Petri dish could be added. Because of the

substantial effort involved, the samples were initially investigated in the Screening-

Test at only one test concentration. A sample is then classified as mutagenic

according to DIN 38415-4 if in one of the strains with or without S9 an induction

difference compared to the control (solvent alone) of 80 (for TA100) or 20 revertants

(for TA98) is induced and a dose-effect relationship is found. The GEA-value

corresponds to the last dilution step at which the induction difference established for

that strain is not exceeded. Since the wastewater sample in the test is diluted by a

factor of 3 with medium/inoculum, the lowest possible GEA-value = 3 (non-

mutagenic). The number of revertants of the negative controls should be: for TA100

in the range of 80-180 and for TA98 in the range of 15-40 revertants per plate.

In testing substances or products a sample was evaluated as being mutagenic in

accordance with the relevant OECD-guideline if the induction rate (ratio of the

number of revertants in the test plates to the negative controls) exceeded a factor of

2 and a dose-effect relationship existed.

4.1.8 umu test according to DIN 38415-3 and Nr. 410 of the AbwV

The umu test is a genotoxicity test with the gene-technologically modified bacterium

Salmonella typhimurium strain TA1535/pSK 1002. The bacteria are exposed to

various concentrations of the cooling water. Here gene toxins induce the so-called

umuC-gene, which belongs to the SOS-repair system of the cell and which acts to

prevent damage to bacterial genetic material. Through the coupling of the umuC-

gene promoter with the lacZ-gene for ß-galactosidase the activation of the umuC-

gene can be indirectly measured spectrophotometrically at 420 nm through the

formation of a colored product from the ß-galactosidase substrate o-nitrophenyl-

galactopyranoside (ONPG). The induction rate (IR) corresponds to the increase of

the extinction at 420 nm relative to the negative control. In calculating the induction

rates one must take into account the growth factor, which is determined

turbidometrically from the optical density at 600 nm. An inhibition of bacterial growth

27

is expressed as a reduced growth factor ("Wachstumsfaktor" or WF) compared to the

controls. For growth factors below 0.5 (50% growth inhibition) the results are not

evaluated. The result given is the smallest dilution step G (GEU-value), at which an

induction rate < 1.5 is measured. If a different induction rate is seen upon addition of

S9, the higher of the two values is taken (=GEU-value).

4.1.9 Elimination of biocides

Until now there have been no generally accepted specifications for a procedure to

determine elimination curves in the laboratory. On the part of the producing

companies there have been proposals for static experiments with a relatively high

concentration of activated sludge (0.5 g d.s./l), in order to simulate the influence of a

hypothetical biofilm in the cooling circulation (Scheidel et al. 1996). However, at an

UBA-Workshop on the present project the consensus was arrived at that such high

biomass concentrations in cooling circulation are not usual (cf., table 5, (Gartiser and

Urich 2001).

In order to determine the effect of the inoculum concentration on the elimination

behavior of biocides, various inocula were introduced. As a test-system the Zahn-

Wellens test according to DIN EN 29888 or Nr. 408 of the AbwV was

correspondingly adapted. The tests with activated sludge were supplemented with an

inorganic nutrient solution according to DIN EN 29888; all tests were continuously

stirred and aerated with an aquarium pump.

28

Table 5: Determination of the elimination of cooling water biocides

Inoculum Concentration Comments

Activated sludge 1 g d.s./l Upper conc. Zahn-Wellens test

" 0.5 g d.s./l Proposal by VCI AG"Microbiocides in Annex 31"

" 0.2 g d.s.//l Lower conc. Zahn-Wellens test

" 0.03 g d.s./l OECD 301 A, B, C and F"ready bio-degradation"

Outflow final-clarifier

- Model for microbiologically activeinoculum with low d.s.-content

Tap water - predominantly abiotic hydrolysis

The starting concentrations of the biocides were selected on the basis of various

information provided on the effective concentrations of the active ingredients in the

cooling water (Baltus and Berbee 1996; Anonymous 1994, Fielden and Iddon 1997)

and in part reduced further according to updated information from the manufacturers

(Klautke 2001) (Table 9). As the end point, after filtration through a folded paper filter

a bacterial fluorescence toxicity test was performed at dilution step 12 (based on

Annex 31 to the AbwV). For low toxicity, dilution step 2 was also tested.

4.2 Drawing up an overall balance sheet

4.2.1 Compilation of production information materials

Letters were sent to a total of more than 100 firms in the chemical industry that also

offer product groups used in the cooling water field (including algicides, antifouling

agents, bactericides, corrosion inhibitors, dispersants, biocides, inhibitors, and water

chemicals). Addresses were obtained in some cases from the relevant handbooks

but also to a large extent through information provided by the operators of the

cooling plants. Altogether, 49 firms replied that they were not engaged in the cooling

water field. Product information was sent by 22 firms. These materials were of

29

varying quality (from safety data sheets with little useful information to detailed

product descriptions with ecological evaluations). In order to learn more about the

substances in the products investigated in the context of preparing the balance (cf.,

sect. 4.2.2) the operators of ca. 50 cooling plants were requested to provide the

corresponding safety data sheets. In this way information on 418 products from 35

manufacturers was obtained and evaluated. The active substances documented in

these materials served as the basis for our literature- and database-research (cf., sect.

4.3).

4.2.2 Making a balance sheet of the emissions of cooling water chemicals

The yearly emissions of cooling-water chemicals by the firms considered in the

cooling water sampling were determined on site. In order to extend the data base a

questionnaire was prepared for the operators of the cooling plants, including

questions about the cooling system used, the cooling capacity, the source of the

water, the annual consumption of cooling water chemicals (on a product basis), the

mode of addition of biocides and the parameters controlled. Initially, this was sent to

all business-controlling governmental agencies in Baden-Württemberg and then to

the environmental agencies in all the Bundesländer (usually to the Environmental

Ministry). After the questionnaires had been passed on to the local sub-authorities

and/or the operators of the cooling plants, they were then returned to us either

directly or through the authorities. In some cases, Hydrotox was also provided by the

authorities with lists of addresses of operators of cooling plants, and we then

contacted them directly. Ultimately, 182 questionnaires from 176 operators were

evaluated. Because of incorrect or incomplete data, ca. 1/3 of the firms had to be

contacted again by telephone or by e-mail. In most cases, we ultimately succeeded

in obtaining consistent data sets.

We did not ask about and consequently did not make any systematic balance sheet

for chemicals added in treating the water (decarbonizing, flocculation, production of

VE-water, regeneration of the ion-exchanger). Nonetheless, such consumption data

were provided by some of the operators and were evaluated.

Based on the annual consumption data for cooling water conditioners (on a product-

basis) and the recipes for preparation in product information sheets, the loads of

30

defined ingredients and chemicals could be estimated. In cases where only an order

of magnitude of the substance concentrations was documented, the following

procedure was followed. Where “less than” or “more than” was given, the next lower

or higher concentration after the decimal was used for the balance. Where

concentration ranges were given, the mean was used. Example:

Given in the production information Assumed for the balance

< 10% 9.9%

> 10% 10.1%

10% - 20% 15%

When no concentration was given, and only the product group was listed in the

product information, typical concentrations from the literature or the available additive

concentrations and product recipes were used. For example, for quarternary

ammonium compounds and polycarboxylates no concentration could be obtained

from the product information sheets.

All data were subjected to a plausibility control. Thereby the annual water

consumption per installed kW of cooling capacity was calculated as a basic

parameter and the following classification was made:

Cooling system spec. water consumption [m3/(kW*a)]

Once-through cooling system 100 - 1000

Open recirculation cooling system 1 - 100

Closed cooling system 0 - 1

Deviations from this rule of thumb classification indicated incorrect data or special

features such as the use of hybrid cooling towers, a limited running time during the

year or the like. In addition, the calculated concentrations of introduced substances

in the wastewater of the individual plants were compared with the concentrations to

be added as given in the literature (Anonymous 1994, Baltus and Berbee 1996,

Fielden and Iddon 1997). For implausible concentrations the operators of the plants

were contacted.

31

Estimating the annual loads for Germany:

In order to calculate to an order of magnitude the total consumption of cooling water

chemicals for Germany the questionnaires of the 176 plants were evaluated in

separate categories of once-through, open recirculation, and closed cooling systems.

The addition of chemicals in closed cooling systems was assumed to be irrelevant

for the wastewater since the amounts added at the time of initial filling can only with

some reservation be assigned to any year’s consumption (instead usually being

disposed of as a concentrate in the garbage when the water is changed). Because of

fundamental differences between industrial cooling systems and power plants (cf.,

sect. 5.4.4.1), the two categories were calculated separately. For the remaining

cooling plants the percentage of plants that used a particular substance or a

substance group was determined. Then the means and medians of the

concentrations (on a substance basis rather than a product basis) were calculated

from the annual water- and substance-consumption. Here the relationship of the

amounts consumed to the added water volumes is a parameter which makes it

possible to take into account the temporal components. (In principle, the substance

consumption could also be derived from the wastewater volumes, but usually these

were not known). For substances which were not continuously added, the calculated

mean concentration generally lies well below the actual concentrations in practice.

However, in individual cases, such as the shock treatment by batchwise addition of

oxidative biocides to the circulation water, higher concentrations could also be

calculated when the system volume is larger than the added water volume (cf., sect.

5.4.5). The estimation of the total loads of the non-continuously added chemicals

(biocides) for Germany was then obtained from the following formula:

Fx = Concx * AX * Qx / 1000

where

Fx Substance load [kg/a]

Concx Median of the balance concentration [mg/l]

Ax Relative proportion of the plants that use the substance

32

(e.g., 0.01 represents 1%)

Qx Water consumption for cooling purposes [m3/a]

x Cooling principle (x = D for flow-through cooling and x = OK for open

circulation cooling)

This estimation is based on simplifying assumptions, which are briefly explained

below:

• The classification of the plants as once-through, open recirculation, and closed

cooling systems is not always unequivocal. There are substantial overlaps so as

to give more of a continuum.

• The estimation of the total loads from the proportion of the plants that use this

substance, based on the available data set provided by the operators, assumes

that the specific consumption values are independent of the size of the cooling

plant. This is only true to a certain extent. Thus, for example, larger plants tend to

use oxidative and smaller plants non-oxidative biocides. However, because of the

limited database at hand, a further sub-classification into various size classes,

going beyond the separate consideration of industrial cooling and power plants,

was not deemed appropriate.

• In general, it can be assumed that in the various industry branches, different

requirements are placed on cooling water conditioning. Thus in the foodstuffs

industry, because of hygiene requirements, a tendency to higher consumption

amounts for biocides compared to other branches can be observed. However, the

limited database does not permit a separate consideration of each branch.

Although we asked the manufacturing firms to calculate the total loads on the basis

of their product sales for cooling water conditioners in combination with the

preparation recipes and the individual share of the market, we did not succeed in

obtaining the desired results (Gartiser and Urich 2001).

For continuously added conditioners (phosphonates, polycarboxylates) instead of the

balance sheet values, the concentrations to be added in normal practice, as provided

by industry, were used (cf., table 16). The annual loads of auxilliary additives (N-

33

methyl-2-pyrrolidone, alcohols) as well as inorganic pH-regulators and flocculation

agents such as Fe(III)Cl3 for additional water treatment were not calculated for the

Federal Republic of Germany, because the consumption in the plants was not

systematically determined.

4.3 Literature and database-research

The cooling water chemicals for which literature- and database-research was to be

performed were determined on the basis of the product information. We did not

consider chemicals for water treatment (inorganic acids and bases, salts for

regeneration of the ion-exchanger) as well as auxilliary additives, e.g., solubilizing

aids such as alcohols, which have no specific biocidal, dispersive or corrosion

inhibiting effect. With the help of the following data banks/collections and databases,

research was carried out on the individual substances:

Substance data collections and fact databases

• Roth: Wassergefährdende Stoffe, ecomed-Verlag, Landsberg

• Verschueren: Handbook of Environmental Data on Organic Chemicals, vanNostrand Reinhold (1996)

• Kommission zur Bewertung wassergefährdender Stoffe (KBwS): Dokumentationwassergefährdender Stoffe, Hirzel-Verlag, Stuttgart

• Merck Index 12th Ed. (1996)

• Ash: Handbook of Water Treatment Chemicals, Gower House (1996)

• Paulus: Microbicides for the Protection of Materials, Chapman & Hall (1993)

• Rossmoore: Handbook of Biocide and Preservative Use, Chapman & Hall (1995)

• Chemfinder, ECDIN and other Internet-Databases

• Dictionary of Substances and Their Effects (DOSE)

• International Uniform Chemical Information Database (IUCLID)

• Hazardous Substances Data Bank (HSDB)

• Data Bank of Environmental Properties of Chemicals (EnviChem)

• Register of Toxic Effects of Chemical Substances (RTECS)

34

• Gefahrstoffinformationssystem der gewerblichen Berufsgenossenschaften(GESTIS)

• PhysProp and Biolog/Biodeg (On-Line Databases of the Syracuse ResearchCooperation, SRC, http://esc.syrres.com)

Literature databases

• Biological Abstracts

• Current Contents

• MEDLINE

The hazard risk statements (R-Phrases) in the dangerous substance regulations

were researched in the GESTIS database. Here, in addition to the official

classification according to Annex I of the Guideline 67/548/EWG, are also found self-

evaluations by the producers (http://www.hvbg.de/d/bia/fac/zesp/zesp.htm). We went

beyond this information and performed – with varied success – additional internet-

searches of the databases of the U.S. Environmental Protection Agency (EPA), the

U.S. National Institutes of Health (NIH) and the National Library of Medicine

(including the database GENE-TOX). The available data were compared with the

internal substance-database shared by Bund/Länder (GSBL), which includes the

UBA-Neustoffdatenbank for new substances, the databases of the KBwS

(RIGOLETTO), the BgVV Chemis and BIG of the Feuerwehrinformationszentrum in

Geel (Belgium). Additional information so obtained substantially extended our

database.

A preliminary listing of the results of our research was distributed to participating

firms in preparation for the UBA-Workshop on the present project with the request

that they fill in any gaps in the data (Gartiser and Urich 2001). As a result, the data

pool was enlarged further. Whenever there were no citable published data available,

the product-specific entries on the safety data sheets of the manufacturers were

taken into account after consulting with them. The research results are presented in

the Annex to this report. It remains to be noted that it was not the aim of this report to

carry out a comprehensive and complete evaluation of all substances in the sense of

a “Risk Assessment” in accordance with the laws on chemicals or biocide-

35

regulations. Consequently, as a standard for the selection of substance data we

relied on the wastewater relevance of the data. In addition, we looked at the oral

toxicity for mammals and the risk statements (R-Phrases), which are the prerequisite

for classification in water-hazard classes (Anonymous 2000). Those organisms that

are of importance in governmental control and are included in the list of parameters

of the wastewater regulations were given a higher significance. Hereby it was sought

to make a comparison possible with the practical investigations on wastewater

sidestreams, products and active ingredients.

36

5 Results

5.1 Cooling water investigations

The results of the investigated wastewater samples are presented in Table 6. A total

of 12 cooling water samples and one condensate from steam production were

tested. The pH of the cooling water samples lay between 7.9 and 9.5; the

conductivity was between 121 µs/cm (for VE-water in plant 2) and 10,130 µS/cm (for

the concentrate of the reverse-osmosis system in plant 1).

The ecotoxicity of the cooling water samples in the algae, fluorescent bacteria and

Daphnia tests was in most cases low (GA/L/D -values from 1 to 3). After a shock-

treatment with quarternary ammonium compounds (plant 2) and isothiazolinones

(plant 6), values up to a dilution factor of GL=196 were determined. However, after

the elimination times of 1 to 3 days typically observed in practice, the ecotoxicity in

the cooling water of plants 4, 7 and 2 was completely eliminated. In the cooling water

of plant 5, 7 hours after the addition of QAV and hydrogen peroxide a slightly

elevated ecotoxicity was measured, but this can be largely attributed to the input of

solid materials during production. Also in the case of the continuous addition of

bromochlorodimethylhydantoin, no ecotoxicity of the cooling water was observed. In

the Ames test (screening) there was no mutagenic effect. However, one cooling

water sample was toxic after a shock treatment with isothiazolinones (plant 6). The

same sample turned out to be the only one that was genotoxic in the umu test

(GEU=6).

37

Table 6: Summary of the wastewater investigations

Nr. 1 Nr. 2 Nr. 3 Nr. 4 Nr. 5 Nr. 6 Nr. 7

Company No./ BranchElectro industry Plastic manufacturing Plastic

manufacturingPlastic

manufacturingChemical industry

KW KWKW after

biocide shock dosage

Blow-down after inacti-

vation period

Steam condensate KW KW KW KW KW 1 KW 2 KW2 KW

Biocide (shock treatment)

(Isothia-zolinone) (QAV) QAV (Isothia-

zolinones)(Isothia-zolinones)

24 h after shock treatment with Isothiazolinones

H2O2/QAV

BCDMH, (Bronopol, Isothia-zolinones), NaOCl

BCDMH, Bronopol, shock-dosage with Isothia-zolinones

BCDMH Isothia-zolinones

Sampling 27.06.00 19.07.00 11.10.00 14.10.00 19.07.00 19.07.00 12.07.00 17.07.01 27.07.00 11.12.00 11.12.00 16.07.01 17.07.01

pH pH 9,5 8,7 8,60 9,00 7,6 8,1 8,8 8,6 8,7 8,3 7,9 7,8 9,0

Conductivity µS/cm 10130 1640 2160 121 31600 130 720 831 240 735 2170 2220 1620

COD mg/l 52 24 67 501721

(filtered) 17 14 11302 (unfilt.)

138 (filtered) <15 138 55 23

Ames test TA98 - S9 IF 1,0 1,0 1,1 1,0 0,9 1,0 0,8 1,1 0,9 0,86 tox. 0,87 1,01

Ames test TA98 + S9 IF 1,0 1,3 1,0 0,7 1,0 1,2 1,0 0,8 1,0 0,87 1,04 0,95 0,93

Ames test TA100 - S9 IF 1,1 1,1 0,8 1,1 1,1 1,1 1,0 1,1 1,1 1,12 tox. 1,09 1,09

Ames test TA100 + S9 IF 1,0 0,9 0,9 1,1 1,1 1,0 0,9 1,0 0,7 0,92 1,07 1,14 1,1

umu test - S9 GEU 1,5 3 tox. 1,5 1,5 1,5 1,5 1,5 1,5 1,5 6 1,5 1,5umu test + S9 GEU 1,5 1,5 tox. 1,5 1,5 1,5 1,5 1,5 1,5 1,5 6 1,5 1,5Algae toxicity GA 2 2 192 2 4 2 2 1 32 (unfilt.) 3 64 2 1Luminescent bacteria toxicity GL 2 2 48 2 2 2 2 2 4 2 192 2 2

Daphnia toxicity (24 h) GD 2 1 96 1 4 1 1 1384 (unfilt.) 2 (filtered) 1 24 1 1

IF: Induction factorKW: Cooling water

Chemical industryPlastic film manufacturing

38

5.2 Product investigations

5.2.1 Eco- and Genotoxicity

The results on the mutagenicity, genotoxicity and ecotoxicity of the products used in

the plants are presented in Table 7. Biocidal product 1, based on isothiazolinone,

was found to be mutagenic or genotoxic in the Ames- and umu tests. The maximal

induction factor was determined to be 11.1 (TA100). Biocidal product 2, based on a

not further specified "heterocyclic sulfur/nitrogen compound," had a similar action

spectrum and consequently is presumably also assignable to the isothiazolinone

group. Biocidal product 3 also showed an increase in the induction factor in TA98

and in the umu test, although such an effect is not known for the group of the

quarternary ammonium compounds (cf., annex); presumably, another component of

this product is responsible. The effective concentrations (EC50) in the fluorescent

bacteria and Daphnia tests lie roughly in the range from 1 to 34 µl/l; the corrosion

inhibitor used in plant 1 turned out to be only slightly ecotoxic.

5.2.2 Identifying the source of the genotoxicity in plant 6

In the cooling water of circulation #2 of plant 6 a genotoxic effect was obtained in the

umu test. At the time the sample was taken the cooling water was being continuously

treated with 1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH) as well as with two

additional products containing tolyltriazole, phosphonic acid and

nonylphenolethoxylate. On the day of sampling there had been an additional shock

treatment with a combination preparation based on 2-bromo-2-nitropropan-1,3-diol

(Bronopol) and isothiazolinone (5 liters to a 50 m3 system volume). In order to assign

the cause of the genotoxic effect, all these products were investigated in the umu

test. Since no umu test results were available for Bronopol, it was also tested as the

pure substance (Fluka-Chemika 17728). The results are shown in Table 8.

39

Table 7: Results of the product investigations

Maximum IF Maximum IF Maximum IF EC10 EC50 EC10 EC50 -S9 + S9 -S9 + S9 -S9 + S9 [µl/l] [µl/l] [µl/l] [µl/l]

Biocide 1 1 Isothiazolinone 200-500 1,6 1,4 11,1 1,7 3,2 2,0 1,15 3,74

(20 µl/Pl) (20 µl/Pl) (20 µl/Pl) (4 µl/Pl) (42 µl/Pl) (42 µl/Pl)

Corrosion inhibitor 1 1 NaOH, Triazoles 100-200

makeup water 1,2 1,7 1,5 1,3 1,0 1,5 100-500 500-1000

(80 µl/Pl) (20 µl/Pl) (500 µl/Pl) (160 µl/Pl (333 µl/Pl)

Biocide 2 4 100 shock dosage 1,3 1,9 10,1 1,5 2,9 2,9 0,6 2,3 1,6 5

(20 µl/Pl) (20 µl/Pl) (20 µl/Pl) (4 µl/Pl) (21 µl/Pl) (42 µl/Pl)

Biocide 3 2 QAV 10-100 1,4 2,1 1,0 1,1 0,9 1,8 1,3 2,8 0,1 0,6

(100 µl/Pl) (100 µl/Pl) (5,2 µl/Pl) (42 µl/Pl)

Biocide 4 3 not known 100-250 1,5 1,7 1,4 1,0 1,6 1,3 5,8 29,5 0,2 34

(20 µl/Pl) (10 µl/Pl) (20 µl/Pl) (333 µl/Pl) (21 µl/Pl)

Biocide 5 5 H2O2, QAV 100-200 1,6 1,8 1,2 1,0 1,6 1,6 0,6 2,5 0,8 1,8

(20 µl/Pl) (5 µl/Pl) (5 µl/Pl) (21 µl/Pl) (333 µl/Pl)IF: Induction factor

Daphnia testumu test

Heterocyclic sulfur/nitrogen

compound

Luminescent bacteria test

Ames test TA98 Ames test TA100Name

Usage in plant No.

Active substance

Dosage µl/l

40

Table 8: Source of the genotoxicity in the cooling water from plant 6

Induction-factor IF Dilution factor G (- S9) Dilution factor G (+ S9)Growth-rate

WR 1,5 3 6 12 24 48 96 192 1,5 3 6 12 24 48 96 192

Biocide 6 50 mg/l IF 0,53 0,54 0,78 0,77 1,00 1,00 1,11 0,96 0,69 0,87 0,93 0,85 0,84 1,05 0,96 0,90

WR 1,38 1,35 1,23 1,24 0,95 1,04 0,91 1,12 1,13 1,01 1,01 1,04 1,05 0,97 0,92 0,93

Solubility aid 50 µl/l IF 0,84 0,77 1,03 0,94 0,93 0,82 0,85 1,00 0,76 0,83 0,82 0,98 0,78

for biocides WR Turbidity 1,17 1,24 0,89 1,04 1,06 1,00 1,01 1,00 1,19 1,13 1,07 0,98 1,05Corrosion inhibitor 2 Tolyltriazole 200 µl/l IF 0,71 0,80 0,86 0,80 0,72 0,73 0,78 0,75 0,73 0,78 0,93 0,94 0,79 0,80 0,66 0,79

Phosphonic acid WR 1,21 1,23 1,21 1,16 1,10 1,00 0,98 1,01 1,00 1,03 0,99 0,94 1,07 1,03 1,01 1,04

Biocide 7

2-Bromo-2-nitropropan-1,3-diol (Bronopol) 100 µl/l IF 2,09 1,12 1,18 1,19 1,11 1,03 0,94 0,83 2,05 1,21 1,11 1,05 1,09 0,93 1,10 1,06

2-Methyl-4-isothiazolin-3-one WR 0,50 0,73 0,78 0,85 0,94 1,05 0,89 0,92 0,55 0,79 0,94 0,96 1,02 1,03 0,89 0,965-Chloro-2-methyl-4-isothiazolin-3-one

Commercial chemical 20 mg/l IF tox. tox. 2,63 1,78 1,35 1,04 1,24 1,02 tox. 2,20 1,53 1,26 1,13 1,05 1,09 1,06

WR 0,15 0,39 0,58 0,87 0,99 0,98 0,88 0,93 0,39 0,73 0,88 0,97 1,01 1,01 0,99 0,94

Product

Nonylphenol-ethoxylate

Concen-tration

1-Bromo-3-chloro-5,5-dimethyl-hydantoin

2-Bromo-2-nitropropan-1,3-diol (Bronopol)

Active substance

41

It turned out that neither the biocide 1-bromo-3-chloro-5,5-dimethylhydantoin, the

corrosion inhibitor, nor the solubilizing agent could explain the observed gentoxic

effects. But biocide 7 proved to be weakly genotoxic, whereby the maximal induction

factor of 2.0 was accompanied by a strong decrease in the growth factor (growth

factor >0.5). From the product testing it is known that the isothiazolinones 2-methyl-

4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one are genotoxic (cf.,

sect. 5.2.1). However, here induction factors up to 3.2 were determined. The

substance testing of Bronopol yielded the result that this non-oxidative biocide also

induced a weak effect in the umu test (up to an induction factor of 2.6), whereby also

here the toxic effect must be taken into account in explaining the result.

Thus, the genotoxic effect in circulation #2 of plant 6 is with high probability due to

biocide 7, whereby the effect could be explained by both isothiazolinone as well as

Bronopol.

5.2.3 Decrease of the biocidal effect in the fluorescent bacteria test

5.2.3.1 Starting concentration

According to Annex 31 of the wastewater regulations, after a shock treatment with

biocides the outflow may only be opened when for fluorescent bacteria toxicity the

dilution step GL=12 is not exceeded. Since until now no generally accepted standard

procedure was available for the determination of the elimination behavior of cooling

water biocides in a batch experiment, various conditions with respect to the starting

and inoculum concentration were simulated (cf., sect. 4.1.9). Our aim was to

determine the influence of the biomass on the elimination factors degradation and

adsorption.

The starting concentration of the biocides was chosen based on the effective

concentrations to be added according to values in the literature and manufacturers’

recommendations (cf., table 9).

42

Table 9: Dosing of biocides in the circulation cooling

An overview of the experiments carried out and the most important results can be

found in Table 10. In Figures 2-10 the elimination curves are presented.

Active substance Concentration of active substance[mg/l]

Reference 1) 2) 3) 4)O x i d a t i v e b i o c i d e sChlorine 5) 0,1 - 0,2 0,1 - 0,2Sodium hypochlorite 1 - 5 1-51-Bromo-3-chloro-5,5-dimethylhydantoin 2 - 7 0,2 - 5 0,2 - 5 1 - 4

Ozone 0,015 - 0,2 0,015 - 0,2 0,02 - 0,2 0,1 - 0,2Hydrogen peroxide - 1 - 5 1 - 5 >50N o n - o x i d a t i v e b i o c i d e sGlutardialdehyde 25 - 50 11 - 200 1 - 50 25 - 502,2-Dibromo-3-nitrilopropionamide 4 - 10 1 - 50 1 - 50 4 - 10

2-Bromo-2-nitropropan-1,3-diol (Bronopol) 1 - 25 1 - 25 200 - 1500

(?) 1 - 25

ß-Bromo-ß-nitrostyrene 1 - 5 4 - 20 1 - 5Isothiazolinone 1 - 5 1 - 30 1 - 30 1 - 2Methylenebisthiocyanate 2 - 6 0,8 - 5 0,75 - 5 2 - 6Quarternary ammonium compounds 3 - 50 5 - 40 6 - 10 3 - 151) Baltus and Berbee: Het gebruik van biociden in recirculatiekoelsysteme. RIZA, 1996 2) Consultants in Environmental Sciences: Biocides in Cooling Water Systems, April 19943) Fielden and Iddon: Use Category Document - Water Treatment Chemicals, Env.Agency, 1997 4) Personal communication Dr. Klautke, BetzDearborn GmbH, from 06.07.015) Required concentration without consideration of chlorine depletion

43

Table 10: Experimental overview of the elimination curves of cooling waterbiocides

5.2.3.2 Non-oxidative biocides

Isothiazolinones

The biocide based on isothiazolinones (biocide 2) was tested at the concentration to

be used according to the manufacturer’s recommendation. There is a clearly

discernible dependence on the density of the inoculum. While the fluorescent

bacteria toxicity at the highest inoculum concentration was already completely

reduced within one day, at the lowest concentration (post-settling outflow of a

municipal sewage treatment plant) no elimination was observed even after 7 days

(Figure 2). In a Daphnia test performed in parallel the product showed a similar

elimination behavior at a dilution step of 12 (data not shown). Adsorption is a

particularly important elimination factor here.

Concentration active

substance

Time until < 20% inhibition at dilution factor G12

cf., Figure

mg/l 0,5 g TS/l 30 mg TS/l No.N o n - o x i d a t i v e b i o c i d e s

Isothiazolinones

100 µl/l (used

concentration)2 d >7d 2

Quarternary ammonium compounds

50 µl/l (used

concentration)3 h 3 h not shown

Quarternary ammonium compounds with hydrogen peroxide

100 µl/l (used

concentration)3 h 3 h not shown

Alkyldimethyl-benzylammonium chloride 10 2 d 3 d 3

2,2-Dibromo-3-nitrilopropionamide (DBNPA)

10 48 h 48 h 4

48 7 d >14 d 5Glutardialdehyde 30 3 d 6

60 3 d120 6 d160 7 d 7 d 7

2-Bromo-2-nitro-propan-1,3-diol (Bronopol) 35 4 d >8 d 10

o x i d a t i v e b i o c i d e s1-Bromo-3-chloro-5,5-dimethylhydantoin 4 1 h (G2) 1 h (G2) 8

37 44 h (G2) 44 h (G2) 9TS: dry solids

44

Figure 2: Decrease of the fluorescent bacteria inhibition with isothiazolinone

Quarternary ammonium compoundsTwo products with quarternary ammonium compounds (biocide 3 and biocide 4 as a

combination product with hydrogen peroxide) were tested at the concentration

recommended by the manufacturer. However, already at 3 h after the beginning of

the test both products showed no further fluorescent bacteria toxicity (cf., table 10).

Another product was tested at a defined concentration of 10 mg alkyldimethylbenzyl

ammonium chloride. Depending on the inoculum concentration, 2 typical curves were

obtained. Above 200 mg d.s./l a 70% decrease in the fluorescent bacteria inhibition

was already achieved 3 h after test begin, while in contrast, the time for a decrease

at 30 mg d.s./l and in the outflow of the final-clarifier increased to 3 days (Figure 3).

As a first approximation, biological de

gradation and the adsorption of the quarternary ammonium chloride can be regarded

as equally important elimination factors.

Isothiazolinone, Starting concentration 100 µl product/l

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Time [h]

Inh

ibit

ion

at

dilu

tio

n f

acto

r 12

[%

]

1000 mg TS/l

500 mg TS/l

200 mg TS/l

30 mg TS/l

Nachklärung

TS: Dry solids; Nachklärung: Outflow final clarifier

45

Figure 3: Decrease of the fluorescent bacteria inhibition with QAV

Dibromo-nitrilopropionamide (DBNPA)

The biocide dibromo-nitrilopropionamide was investigated at two different

concentrations. At a concentration of 10 mg/l the fluorescent bacteria inhibition for all

inoculum concentrations decreased rapidly within 3 h, but then more slowly

thereafter. The threshhold of 20% inhibition was already reached after only 1 h in the

experiment with the final-clarifier water. In contrast, in the tests with activated sludge

up to 48 h were required (Figure 4). This difference is even more striking with the

higher starting concentration of 48 mg/l; here the fluorescent bacteria inhibition in the

final-clarifier water was completely eliminated within 24 h, while in tests with

activated sludge at higher concentrations up to 14 days were required (Figure 5).

The grounds for this can be found in the pH-dependence of the rate of hydrolysis of

the compound. It is known that DBNPA is hydrolyzed substantially faster in the

alkaline range than under neutral conditions. While the pH-value in the experiments

with final-clarifier water lay between 7.6 and 8.2, in the tests with activated sludge a

pH of 7.4 to 7.6 was measured (data not shown).

Alkyldimethylbenzylammonium chloride,Starting concentration 10 mg/l

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Time [h]

Inh

ibit

ion

at

dilu

tio

n f

acto

r 12

[%

]

1000 mg TS/l

500 mg TS/l

200 mg TS/l

30 mg TS/l

Nachklärung


46

Figure 4: Decrease of the fluorescent bacteria inhibition with DBNPA (10 mg/l)

Figure 5: Decrease of the fluorescent bacteria inhibition with DBNPA (48 mg/l)

2,2-Dibromo-3-nitrilopropionamide (DBNPA),Starting concentration 10 mg/l

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Time [h]

Inh

ibit

ion

at

dil

uti

on

fa

cto

r 1

2 [

%]

1000 mg TS/l

500 mg TS/l

200 mg TS/l

30 mg TS/l

Nachklärung


2,2-Dibromo-3-nitrilopropionamide (DBNPA), Starting concentration 48 mg/l

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400

Time [h]

Inh

ibit

ion

at

dil

uti

on

fac

tor

12 [

%]

1000 mg TS/l

500 mg TS/l

200 mg TS/l

30 mg TS/l

Nachklärung


47

Glutaraldehyde

Initially the influence of the glutaraldehyde concentration was investigated at a

constant inoculum-content (30 mg d.s./l activated sludge). While the fluorescent

bacteria inhibition at concentrations below 60 mg/l glutaraldehyde was fully

eliminated within 3 days (Figure 6), the lag-phase at higher concentrations increased

to 6 (at 120 mg/l) or 7 days (at 160 mg/l). In a second experiment the influence of the

inoculum concentration at a constant concentration (160 mg/l) of glutraldehyde was

determined. As was later noticed, this concentration was given in only 1 of 4

reference sources (Table 9). In the final-clarifier the fluorescent bacteria inhibition at

this glutaraldeheyde concentration had not decreased after 7 days. At the highest

inoculum concentration of 1 g d.s./l, in contrast, the inhibitory effect was completely

eliminated after 3 days (Figure 7).

48

Figure 6: Fluorescent bacteria inhibition with glutardialdehyde (30-160 mg/l)

Figure 7: Fluorescent bacteria inhibition with glutardialdehyde (30-1000 mgd.s./l)

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Time [h]

Inh

ibit

ion

at

dilu

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n f

ac

tor

12

[%

]

160 mg/l

120 mg/l

60 mg/l

30 mg/l

Glutardialdehyde; inoculum: activated sludge 30 mg dry solids/l

Glutardialdehyde, Starting concentration 160 mg/l

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180

Time [h]

Inh

ibit

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at

dilu

tio

n f

ac

tor

12

[%

]

1000 mg TS/l500 mg TS/l200 mg TS/l30 mg TS/lNachklärung


49

Bromonitropropandiol (Bronopol)

The formaldehyde releasing biocide 2-bromo-2-nitro-propan-1,3-diol was

investigated at a concentration of 25 mg/l. The results showed a strict dependence of

the elimination behavior on the inoculum density. At an inoculum concentration of 1 g

d.s./l the fluorescent bacteria inhibition was largely eliminated wilthin 1 day, while at

30 mg d.s./l or in the outflow of the final-clarifier the inhibitory effect remained stable

even after 8 days.

Figure 8: Decrease of the fluorescent bacteria inhibition with Bronopol

2-Bromo-2-nitro-propan-1,3-diol (Bronopol), Starting concentration 25 mg/l active substance

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250

Time [h]

Inh

ibit

ion

at

dilu

tio

n f

acto

r 2

[%]

1000 mg TS/l

500 mg TS/l

200 mg TS/l

30 mg TS/l

Nachklärung


50

5.2.3.3 Oxidative biocides

Bromochlorodimethylhydantoin (BCDMH)

Bromochlorodimethylhydantoin is used as a solid granulate with a sidestreamwater

flow channeled through a filter filled with BCDMH. Because the granulate proved to

be poorly soluble in the mineral salts nutrient solution needed for the Zahn-Wellens

test, the substance was dissolved in tap water. The elimination behavior was

determined for two starting concentrations. Because of the known instability of the

compound, additional total chlorine determinations were carried out. At the required

dilution step 12 there was no detectable fluorescent bacteria inhibition for either

starting concentration, so the undiluted samples (G=2) were investigated. At a

substance-concentration of 4 mg/l (1 mg total chlorine), for all inoculum

concentrations there was no more measurable fluorescent bacteria toxicity after 3 h

(Figure 8). At a substance-concentration of 37 mg/l (10 mg/l total chlorine) already

within the first 6 h a clear dependence of elimination on the inoculum concentration

could be observed. Thereafter, the inhibitory effect for all tests with inoculum lay

between 10 and 30%, while the fluorescent bacteria inhibition in the test with tap

water still lay at 90% even after 45 h (Figure 9). The decrease in the fluorescent

bacteria toxicity accompanied the decrease in the total chlorine concentration (cf.,

table 11).

Table 11: Elimination of BCDMH depending on the inoculum

F r e e c h l o r i n e [ m g / l ]500 mg

TS/l200 mg

TS/l30 mg TS/l

Outflow final clarifier

Tap water

0 h 2,08 0,48 0,17 0,98 4,983 h 1,11 0,13 0,15 0,49 5,5520 h 0,12 0,05 0,10 0,30 4,7844 h 0,11 0,07 0,05 0,04 0,57T o t a l c h l o r i n e [ m g / l ]

500 mg TS/l

200 mg TS/l

30 mg TS/l

Outflow final clarifier

Tap water

0 h 4,92 3,81 2,62 4,09 8,303 h 2,70 2,48 0,82 2,92 8,6520 h 0,72 0,49 0,17 1,13 6,4544 h 0,14 0,09 0,07 0,07 0,61Start concentration 9,9 mg/l total chlorine

51

Figure 9: Decrease of the fluorescent bacteria inhibition with BCDMH (4 mg/l)

Figure 10: Decrease of the fluorescent bacteria inhibition with BCDMH(37 mg/l)

1-Bromo-3-chloro-5,5-dimethylhydantoin, Starting concentration 1 mg/l total chlorine

0

10

20

30

40

50

60

70

80

90

100

0 0,5 1 1,5 2 2,5 3 3,5

Time [h]

Inh

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dil

uti

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fac

tor

2 [%

]

1000 mg/l

500 mg TS/l

200 mg TS/l

30 mg TS/l

Nachklärung

Leitungswasser

TS: Dry solids; Nachklärung: Outflow final clarifier; Leitungswasser: Tap water

1-Bromo-3-chloro-5,5-dimethylhydantoin,Starting concentration 9.9 mg/l total chlorine

0

10

20

30

40

50

60

70

80

90

100

110

120

0 5 10 15 20 25 30 35 40 45 50

Time [h]

Inh

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2 [

%]

500 mg TS/l

200 mg TS/l

30 mg TS/l

Nachklärung

Leitungswasser

TS: Dry solids; Nachklärung: Outflow final clarifier; Leitungswasser: Tap water

52

5.3 Evaluation of the product information sheets

In the course of the study documentation was compiled for a total of 418 products for

cooling water conditioning from ca. 35 manufacturing firms. A total of 101 products

therefrom contained biocides. The qualitity of the documents ranged from poorly

documented safety data sheets to detailed ecological evaluations. Very few

elimination curves for cooling water biocides were provided. Since all the leading

producers in the field sent us information, an estimated 80% of the total market has

been surveyed.

In Figure 11 the product groups for the cooling water conditioners are documented.

Figure 11: Proportion of biocidal active ingredients in 101 products

Chlorine releasers8%

Bromine releasers16%

Oxygen releasers8%

Aldehydes6%

Organic bromine compounds

10%

Isothiazolinones26%

Organic sulfuric compounds

8%

Quaternary ammonium compounds

9%

Guanidines3%

Others3%

Not known3%

53

5.4 Evaluation of the questionnnaires

Altogether 182 questionnaires on the cooling systems of 176 plants were evaluated.

Of these, 110 had open circulation cooling, 48 had once-through cooling, and 24

could be classified as closed-circulation cooling. The most important characteristic

data from the data set are given in Table 12.

Table 12: Characteristic data for the cooling systems investigated

The water consumption for cooling purposes of ca. 6 billion m3 represents 19% of the

total untreated discharged cooling water (Stat. Bundesamt 1998). Only 76 Mio. m 3

are assigned to open circulation cooling. Overall, it could be established that in most

cases it was not possible to make an unequivocal assignment of the continuously

added substances as well as their concentration ranges from the product

information; often only the substance group was indicated. For the batchwise added

biocides, in contrast, the names of the active substances and their concentration

ranges are better documented, because these are listed as hazardous substances in

the safety information sheets.

Cooling systems with

Cooling systems

Cooling capacity

Water consumption

Mean specific water

consumption

Products used Biocides Condition-

ingBiocides and conditioning

[n] MW [1000 m3/a] [m3/(kW*a)] [t/a] [n] [n] [n]Power plants 10 4.817 40.380 6 83 5 8 4

Industrial cooling systems

100 2.051 35.421 20 778 69 72 62

48 18.936 5.985.084 501 23 4 4 2

24 198 13 0,6 7 *) 4 16 4

Sum 182 26.002 6.060.898 891 82 100 72[n]: Number *) Partly once-only filling not attributable to annual amount

Open recirculation cooling

Once-through cooling

Closed circulation cooling

54

5.4.1 Open recirculation cooling systems

In the cooling systems investigated a total of 891 t of cooling water conditioners

(weight on a product basis) was used. This does not include the chemicals used for

treatment of raw water (de-carbonizing, flocculation and pH-adjustment) such as

inorganic acids and bases. For these latter purposes, a total of 53 t of sulfuric acid, 4

t of hydrochloric acid, 0.2 t of sodium hydroxide, 145 t of ferric(III) chloride (weights

of the pure substances) as well as 2 t of organic flocculation aids (weight of the

products) were consumed. The total loads of defined substances which were used in

the 110 plants for open circulation cooling are given in Table 13. Here products were

not considered if they could not be assigned to a group or if the concentrations used

were not given, so the values given are minimal values. For the 10 power plants with

open circulation cooling investigated, no zinc or molybdate was used, in agreement

with Annex 31. Therefore, it seems justified to consider these separately from the

industrial cooling systems.

55

Table 13: Total amounts of the investigated chemicals in open circulationcooling

Industrial cooling systems

Power plants

[t/a] 1) [t/a] 2)

Oxidative biocidesChlorine 52,3Sodium hypochlorite 27,7 8,2Calcium hypochlorite 0,01Trichlorisocyanuric acid 0,03Ammonium bromide / sodium bromide ?Sodium hypobromite 0,51-Bromo-3-chloro-5,5-dimethylhydantoin 1,6 0,7Hydrogen peroxide 9,7Ozone 0,2Potassium peroxymonobisulfate 0,1Peracetic acid 0,3Non oxidative biocides

2,2-Dibromo-3-nitrilopropionamide 0,12-Bromo-2-nitropropan-1,3-diol (Bronopol) 0,01Isothiazolinones 0,6S-Triazine ?Dodecylguanidine hydrochloride (DGH) 0,01Methylenebisthiocyanate 0,1

Quaternary ammonium compounds ?Conditioning chemicalsPhosphonic acids 6,6 1,7Phosphates 0,7Triazoles 2,4 ?Polycarboxylates >7,7 >0,3Sodium molybdate 1,0Zinc salts 11,9

N-methyl-2-pyrrolidone 0,2Alcohols 2,4Fe(III)Cl3 145,2inorganic lyes 1,6 0,1inorganic acids 42,2 4,9

2) 10 power plants with open recirculation cooling

1) 100 industrial cooling systems with open recirculation cooling

Auxiliary additives/water treatment

56

5.4.2 Once-through cooling systems

The 48 investigated plants with once-through cooling systems include about 20%

each from the branches foodstuffs industry, chemical industry and energy

production, with the remaining plants belonging to the plastics, metal and paper

industries, as well as other areas. Only 6 of the 48 plants used cooling water

conditioners. These plants should be considered separately (see Table 14). In one

food processing plant the canned goods were cooled with water after sterilization. In

order to prevent contamination or corrosion of the cans, fatty alcohol ethoxylates,

sodium ethyl-hexanoate and chlorine in the form of sodium hypochlorite were

continuously added to the cooling water. In another plant manufacturing canned

foodstuffs, corrosion inhibitors (sodium molybdate; alcohol ethoxylates) and

hardness stabilizers (phosphocarbonic acids) were continuously fed into the cooling

water. In one plant, which manufactures packaging materials, the cooling water is

treated with isothiazolinone and phosphonic acids. The provision of cooling waters

here is made more difficult by the very high hardness (25 °dH) and manganese

content.

In one plant of the chemical industry chlorine was continuously added to the cooling

water. Sodium hypochlorite is used in a thermal power plant cooled by sea water. In

one large thermal power plant iron(II) sulfate is used, since in low concentrations

(0.05-1 mg/l) in sea water and brackish water it acts anticorrosively through the

formation of a protective layer of iron hydroxide (Wunderlich 1978a).

All in all, the use and selection of conditioners in plants with once-though water

cooling presents a very heterogeneous picture.

57

Table 14: Consumption data in plants with flow-through cooling

Nr. Branch Capacity Water consumption Origin of Biocide Product Active ingredient 1 Active ingredient 2 Active ingredient 3 Active ingredient 4

[MW] [1000 m3/a] [m3/(a*KW)]water dosage consump-

tion [kg] [kg] [kg] [kg] [kg]

37 Foodstuffs ? 17 other Product 1 2.400 KA

Sodium molybdate dihydrate 132,0

Cocoimino-propionate 132,0

Alkanol-ethoxylate 132

Phosphon-carbonic acids 132

industry none

65 Foodstuffs ? 314 O Product 2 1.300O and

KAEthoxylated alcohols 258,7

Sodium 2-ethylhexanoate 63,7

industry 240 G Product 3 S 502 NaOCl 50,7 NaOH 49,7Chlorine K 300 Chlorine 300,0

68 Power 3.400 420.000 124 M Sodium S 12.000 M NaOCl 1560,0plant hypochlorite

Ferrous(II)-83 1.486 1.040.000 700 (M) sulfate 450.000 O Ferrous(II)sulfate

120 Bandage 0,2 55 275 G Product 4 K 430 O

5-Chlor-2-methyl-4-isothiazolin-3-one 6,5

2-Methyl-4-isothiazolin-3-one 2,2

material

Product 5 1.200 Phosphonic acids

Butanephos-phonotricar-bonic acid

134 Chemical ? 7.000 O Chlorine K 4.380 O Chlorine 4380,0industry

Origin of water: G=ground water; O=surface water; M= marine water; (M)=brackish waterBiocide dosage: K=continuously, S=batchwise (shock) dosingDischarge: O=surface water; KA=municipal treatment plant; M=sea

Power plant

Dis-charge

58

5.4.3 Closed circulation cooling systems

The 24 closed circulation cooling systems investigated were mostly small plalnts with

less than 10 MW cooling capacity. In 8 plants the cooling water is not conditioned. In

all, the chemicals added weighed 13 t (on a product basis), but only a small

proportion (< 0.5 t) could be attributed to defined chemicals. A large proportion of the

products consists of not further characterized antifreeze agents. To inhibit corrosion,

molybdate and zinc salts are used, as well as phosphonic acids and triazoles. As

biocides, quarternary ammonium compounds, organobromine compounds and

isothiazolinone are used. The estimation of the total amounts used was made even

more difficult by the fact that in some cases the first filling of the closed systems was

involved and as a rule the circulation water is only changed at intervals of several

years. According to the operators’ responses on the filled out questionnaires, ca. 1/3

of the plants have the cooling water taken away for disposal after use, while 2/3 of

the plants release it into the municipal sewage treatment plants, in individual cases

also over the surface water.

5.4.4 Estimation of the total loads for Germany

5.4.4.1 Water consumption for cooling purposes

In keeping with our originally stated aims, on the basis of the consumption data of

the cooling plants surveyed an overall balance sheet calculation is to be made of the

total annual loads for conditioners (on a substance basis) for Germany as a whole.

Here the water consumption data for cooling purposes collected by the German

Federal Statistics Office is directly applied (Stat. Bundesamt 1998). However, the

Statistics Office does not distinguish between plants with flow-through cooling and

those with open circulation cooling, so that several assumptions must be made.

a) Mining and processing activities

In 1995 376 Mio. m3 of cooling water were discharged after recirculation cooling and

4.981 Mio. m3 without recirculation cooling (Stat. Bundesamt 1998). While in a first

approximation the discharged amount without recirculation cooling equals the

amount of water used, for the plants with recirculation cooling the evaporation losses

must be considered. For a concentration factor of 3 ca. 1/3 of the make-up water is

re-emitted, while 2/3 evaporates. Thus a total water use for recirculation cooling

59

plants of 1.1 billion m3 (109 m3) can be calculated. However, hereby once-through

cooling systems with outflow cooling are included.

An alternative procedure is based on the data given by the Statistics Office for the

total use of cooling waters and the utilization factor for multiple and recirculation use

(Stat. Bundesamt 1998). In calculating the “total use” the recirculation water is

included repeatedly with a factor corresponding to the number of times it recirculates.

"Multiple use" is understood to mean the further use of the cooling waters for other

purposes (e.g., for cleaning). From the total use of the cooling water (29.1 billion m3)

and the utilization factor of 4.8 (Statistisches Bundesamt, Fachserie 19, Reihe 2.2

(1995), 3.1) it can be calculated that ca. 6 billion m3 fresh water were used for

cooling purposes in 1995. If one subtracts from this value the amount of water used

only once (i.e., without recirculation cooling), then ca. 1 billion m3 water were used

for open recirculation cooling and 5 billion m3 water for once-through circulation

cooling. By and large, these data agree with the rule of thumb numerical

classification given above. Using these values we then performed the calculations to

obtain the overall estimates.

b) Cooling water provision for the thermal power plants for the public power supply

The thermal power plants supplying the public have a special position and are

treated separately by the Federal Statistics Office and also in Annex 31. The

operations of the plants are more uniform in comparison to the industrial cooling

systems. The principal demand for cooling water is for the turbine condensors, and

secondary cooling locations are usually operated in closed systems. For large

cooling systems of modern power plants with condensors made of stainless steel or

titanium the addition of corrosion inhibitors is not necessary. Large cooling towers of

power plants should be so constructed and operated that the regular use of

microbiocides is not necessary (Fichte et al. 2000). The total amount of cooling water

used in 1995 (including multiple use and circulation use) was ca. 61 billion m3, and

the utilization factor was ca. 2.2 (Stat. Bundesamt 1998). In response to our enquiry,

the Federal Statistics Office provided us with the data for the proportion of multiple

use and circulation use, as this could not be ascertained from the published

information (Mr. Knichel 2001). From the total amount of discharged cooling water,

by subtracting the water used only once, the proportion used for multiple use and

60

circulation cooling water was calculated in the first approximation to be 4% of the

total discharged cooling water (cf., table 15).

Table 15: Cooling water use for thermal power plants (1995 )

Sources: (Mr. Knichel 2001); (Stat. Bundesamt 1998)

Based on these considerations, it was assumed for further calculations that 1 billion

m3 cooling water are discharged from open circulation cooling and 27 billion m3

cooling water from once-through cooling. Assuming a concentration factor of 2, this

represents ca. 2 billion m3/a of fresh water consumed for open circulation cooling of

power plants.

5.4.4.2 Open circulation cooling

The procedure for calculating the concentrations of chemicals and the proportion

(percentage) of the plants which use a particular chemical or chemical group is

described in Sect. 4.2.3. The total loads are obtained from the total amount of 1

billion m3 cooling water used for mining and processing industries. The thermal

power plants, which use ca. 2 billion m3 of additional water, were calculated

separately.

Continuously added conditioners

A preliminary version of the balance drawn up from these data was sent to the

participants of the workshop of 18.05.01 for their comments. Several participants

expressed skepticism about the level in the balance for the added concentrations

and loads, especially for the continuously added cooling water conditioners such as

the phosphonates. In response, an accounting for this compound was additionally

undertaken on the basis of the concentrations added in normal practice (cf., table 16)

Since the standard concentrations are based on the circulation water, the estimation

of the total load here is not made on the basis of the fresh water volumes, but rather

Cooling water used[1000 m3] [1000 m3] [%]

Multiple use 458.861Circulation use 34.354.663Single use 26.946.470 26.946.470 96Sums 61.759.994 28.072.725 100

1.126.255

Cooling water discharged

4

61

on the actually discharged cooling water (376 Mio. m3 from industrial cooling plants,

1 billion m3 from power plants). The consumption of auxiliary aids (N-methyl-2-

pyrrolidone, alcohols) as well as inorganic pH-regulators and flocculants like

Fe(III)Cl3 was not systematically surveyed and thus not included in the calculation for

total consumption for all of Germany. In the substance group polycarboxylates

several differently named compounds were included (polycarboxylate, polycarbonic

acid, alkylepoxycarboxylate, polyoxycarbonic acid, polymaleic acid, maleic acid/co-

polymer, acrylic acid-co-polymer, acrylic acid-Ter-polymer). The less important low

molecular weight acids were omitted here.

Table 16: Concentrations of continuously added conditioners (concentration inthe circulation water in mg/l)

Shock treatments by batchwise addition of cooling water biocides

The balance sheet calculations used for continuously added chemicals could not be

applied for the biocides which are usually added batchwise, as this would have led to

a gross overestimation of the loads. In order to take into account the time factor, the

total loads were calculated as described in sect. 4.2.3 from the consumption

numbers and the documented fresh water use.The concentration calculated here

represents a helpful parameter, which does not necessarily correspond to the

concentration in the circulation water (after a shock treatment).

Active substance Industrial cooling-water circulation Power plants 2), 3) Corrosion

inhibitors 4)Hardness

stabilizers/Dispersants 4)Cooling water

5)

Phosphonate (~ ppm P) 6)

3 - 8 (~ 0.8 - 2)

1.5 - 3 (~ 0.4 - 0.8)

5 - 20 (~ 1.3 - 5)

2 - 10 (~ 0.5 - 0.8)

6 - 12 (~ 1.5 - 3)

Phosphate (~ ppm P)

12 - 15 (~ 4 - 5)

6 (~ 2)

5 - 25 (~ 1.6 - 8) n.a. 7 - 15

(~ 2.2 - 4.8)

Polycarboxylates and Polycarbonic 6 - 12 2 - 7 - 5 - 20 20 - 50

Zinc 1 - 3 - 2 - 10 - 3 - 4

Molybdate 5 - 7 - 2 - 15 - n.a.

Triazole derivatives 1 - 2 1 - 2 1 - 5 - n. a.

n.a.= no information available; "-" = not used for this purpose1) Personal communication from Dr. Klautke, BetzDearborn GmbH , 09.01.022) Personal communication from Dr. Olkis, ONDEO Nalco GmbH, 10.12.013) Personal communication from Dr. Hater, Henkel Surface Technologies, 13.12.024) Fielden et al. (1997)5) Wunderlich (1978)6) The usual P-content of phosphonates lies between 10 and 30%, due to the substances present in the largest amounts, HEDP and ATMP, with 30% P-content assumed to be present at an average content of 25%.

62

For the biocide groups of quarternary ammonium compounds (QAV), triazine

derivatives and guanidine, no information on concentrations was available for the

products involved. It was assumed that these biocides as well as isothiazolinones

were usually added batchwise at long intervals. The median of the calculated

substance concentration for isothiazolinones is 0.08 mg/l (cf., table 17). To take into

account the higher concentrations used for QAV and triazine derivatives this value

was adjusted upward, to 0.26 mg/l (QAV) and 0.533 mg/l (triazine/guanidine). Here it

was assumed that the effective substance concentrations of isothiazolinones, QAV

and triazine/guanidine correspond to 3, 10 and 20 mg/l (cf., also table 9). In Table 17

the balance of the total amounts of cooling water chemicals in open circulation

systems are presented for Germany, with industrial cooling systems and power

plants given separately. For continuously added conditioners the loads are

calculated in two ways for comparison, from the concentrations usually applied in

practice and from the concentrations inferred from drawing up the balance.

63

Table 17: Chemical usage in open circulation cooling systems in Germany

5.4.4.3 Once-through cooling

The database for an estimation of the total loads of chemicals used in once-through

cooling systems is not adequate for a reliable calculation, because in most plants

conditioners are not used. An extrapolation of total loads from the 6 plants given (cf.,

table 14) is very unreliable, since these represent individual examples.

SumMedian of active

subst. concentration

[mg/l]

Proportion of plants

[%]

Load [t/a]

Median of active subst. concentration

[mg/l]

Proportion of plants

[%]

Load [t/a]

Total load [t/a]

Oxidative biocides 1)

Chlorine 4,6 4 184 184Sodium hypochlorite 2,4 11 264 2,05 10 (410) (674)Calcium hypochlorite 14,6 1 (146) (146)Trichlorisocyanuric acid 1 1 (10) (10)Ammonium bromide / sodium bromide ? 2 ?Sodium hypobromite 1,1 4 (44) (44)1-Brom-3-chloro-5,5-dimethylhydantoin 3,4 11 374 3,64 20 (1456) (1830)Hydrogen peroxide 23,6 5 (1180) (1180)Ozone 0,3 1 (3) (3)Potassium peroxymonobisulfate 1,1 1 (11) (11)Peracetic acid 5 1 (50) (50)Non-oxidative biocides 1)

2,2-Dibromo-3-nitrilopropionamide 0,66 3 20 202-Bromo-2-nitropropan-1,3-diol (Bronopol) 0,02 2 0,4 0,4Isothiazolinones 0,08 26 21 21S-Triazines 0,53 2 11 0,5 10 (100) (111)Dodecylguanidine hydrochloride (DGH) 0,69 1 (7) (7)Methylenebisthiocyanate 0,08 3 2 2

Quaternary ammonium compounds 0,267 4 11 0,267 10 (53) (64)Conditioning chemicals, concentrations used in practice 1)

Phosphate 14 8 421 6 0 0 421Phosphonic acids 6 42 948 2,3 30 690 1638Triazoles 1,5 22 124 1,5 30 450 574Polycarboxylates 9 36 1218 4,5 10 (450) (1668)Molybdate 6 6 135 - - 135Zinc 2 15 113 - - 113Conditioning chemicals, balanced concentration 1)

Phosphate 2 8 160 - 0 160Phosphonic acids 4,6 42 1932 0,4 30 240 2172Triazoles 1,1 22 242 ? 30 242Polycarboxylates ? 36 ? ? 10Molybdate 0,752 6 45 - - 45Zinc 1,44 15 216 - - 2161) With reference to the fresh water consumption (1000 Mill. m3 for industrial ccoling, 2000 Mill. m3 for power plants)2) With reference to the discharged water (376 Mill. m3 for industrial systems, 1000 Mill. m3 for power plants) Values in brackets are based on unreliable data basis

Industrial cooling systems Power plants

64

At best, an evaluation of the foodstuffs industry sector seems permissible, although

even these numbers have only limited validity (Table 18). In the foodstuffs industry,

based on the data documented in Table 3, ca. 3.2% of the cooling water is

consumed in the processing industry. This corresponds to ca 160 Mio. m3 cooling

water for once-through cooling (3.2% of 5 billion m3). In one thermal power plant 1.6

t/a active chlorine is added for the treatment of sea water from the Baltic. However,

this value is not representative for once-through water cooled thermal power plants.

According to an estimate made by the Bund/Länder working group on cooling water

ca. 50 t/a of chlorine are used in thermal power plants with once-through cooling

(Piegsa 2001a). Only in one plant of the chemical industry is chlorine continuously

added. In the discharge of this plant, according ot the operator, there is no

detectable chlorine and the AOX-value of ca. 50 µg/l lies substantially below the

threshhold value.

Table 18: Total load of cooling water chemicals in the once-through cooling ofthe foodstuffs industry

5.4.5 Overview and comparison

The balance sheet of the chemical usage in open circulation cooling shows a

consumption of ca. 4100 t/a for oxidative and 125 t/a for non-oxidative biocides. For

once-through cooling systems there are, in addition, ca. 50 t of chlorine/chlorine-

releasers. The balance shows chlorine concentrations in 4 plants with open

circulation cooling of ca. 4 to 5 mg/l, substantially higher than the value of 0.2 mg/l

given in Table 9. However, the concentration added depends primarily on the

chlorine removal, and the value of 0.3 mg/l pertains to the targeted residual chlorine

concentration in the circulation water. The balance for the chlorine concentration of

4.6 mg/l was based on data reports from only 3 operators, so these values are quite

Chemical Proportion of Total load 1)

concentration companies[mg/l] [%] [t/a]

Sodium molybdate dihydrate 7,8 8 104Chlorine and chlorine releasers 0,6 8 8Ethoxylated alcohols 0,5 8 6Cocoiminopropionate 7,8 8 104Phosphono-carbonic acids 7,8 8 1041) Cooling water demand of the branch 160 Mill. m3

65

possibly non-representative. The sodium hypochlorite-concentration (2.1-2.4 mg/l

active chlorine) was, in contrast, calculated from 10 reports and is thus more valid.

However, more extensive research on the cooling plants in which chlorine was used

revealed that the hydraulic conditions also had to be considered. As examples, 2

cases are described:

In one plant of the chemical industry with 2 open cooling systems (Cycles of concentration 2.5 – 3.0)

100 kg of liquid chlorine are added batchwise daily to a total circulating volume of 48.000 m3/h and the

outflow is closed for 4 h. The measured chlorine concentration after the shock treatment is 0.3 to 0.8

mg/l. However, if one relates the annual consumption of active chlorine of 30.000 kg/a to the amount of

fresh water used of 6.5 Mio. m3/a, the hypothetical concentration "in the inflow" is increased to 4.6 mg/l.

The ground for this lies in the fact that the amount of fresh “make-up” water introduced is less than the

system volume (which is not known to the operator).

In another plant, also from the chemical industry, ca. 20 kg of liquid chlorine is automatically added

daily to each of 3 cooling circulation systems (concentration factor 2.0 - 2.5) , until a free chlorine

content in the circulation water of 0.3 mg/l is reached (corresponding to a total amount added of 2.9

mg/l of circulation water). The overall system volume is 21.000 m3, and the mean amount of make-up

water added is 9.378 m3/d. From this it can be calculated that the system volume (neglecting the

evaporation) is only exchanged once every 2 days. Thereby the hypothetical chlorine concentration "in

the inflow" increases to 6 mg/l.

Thus for batchwise addition of chemicals to the circulation water when the

consumption is based on the volume of added make-up water, substantially higher

hypothetical concentrations may be calculated than the corresponding applied

concentration.

While the consumption of sodium hypochlorite (including chlorine) in Germany is at

about the same level as in the neighboring European countries, the consumption of

hydrogen peroxide and peroxyacetic acid in Germany is notably higher (cf., table 19,

after Anonymous 2000). However, the loads for Germany have been extrapolated

from only 5 reports on the use of H2O2 and one mention of the use of peroxyacetic

acid. Hydrogen peroxide is used at high substance concentrations (up to 50 mg/l)

and is frequently added continuously, so the large loads seem plausible at first

inspection. However, the calculated consumption numbers for Germany are probably

too high, since hydrogen peroxide is for the most part used in small to medium-sized

cooling systems. A restriction of its use to selected branches of industry, as

supposed by certain employees of the manufacturers, could not be confirmed.

66

It was noted by the producers that the loads calculated for BCDMH are also too high,

because this biocide is primarily used in smaller plants. The balance drawn up

revealed that BCDM was used in 13 of 110 plants with open circulation cooling with a

total cooling capacity of 140 MW and a total water consumption of 1.5 Mio m 3. In the

largest plant (chemical industry), comprising 2 cooling towers, for a total capacity of

50 MW and a water consumption of 840,000 m3, ca. 750 kg/a of BCDMH were

consumed. Both power plants were small thermal power plants, with a cooling

capacity under 25 MW.

The production of sodium hypobromite generally takes place on site, through the

reaction of sodium bromide with sodium hypochlorite. The consumption of sodium

hypochlorite was taken into account in Table 17, but for sodium bromide no

concentration data were available. The total load of sodium hypobromite in the

balance in Table 17 is based on one product based with stabilized sodium

hypobromite. The extrapolation of the consumption data for calcium hypochlorite is

just as inaccurate. Its use (as a solid) in cooling systems is unusual, but is

documented in one actual case.

For non-oxidative biocides the consumption data for quarternary ammonium

compounds, isothiazolinones, dibromonitrilopropionamide and methylene-

(bis)thiocyanate are comparable with the values for England. For some biocides

such as ß-bromo-ß-nitrostyrene or glutardialdehyde no consumption values for

Germany were provided, although products with these active ingredients are on the

market. On the other hand, other biocides such as triazine derivatives, guanidine and

Bronopol, for which relevant loads were determined in this study, were not

investigated in neighboring countries. The total load for triazines was substantially

influenced by its rather untypical use in one of the surveyed power plants, and the

high water consumption of power plants over all, which appears unrealistically high.

In a first approximation, the total consumption should be maximally of the same

order of magnitude as for the other non-oxidative biocides (ca. 10-20 t/a).

For hardness stabilisation and corrosion inhibition ca. 1,600-2,200 t of phosphonic

acids were consumed in open circulation cooling. In an earlier study a consumption

of ca. 3.900 t of phosphonates was reported for Europe (without indicating the year)

for cooling water conditioning (Gledhill and Feijtel 1992, Meerkerk and Puijker 1997).

Horstmann et al. (1986) estimated the phosphonate load from cooling circulation for

67

Germany (the old Bundesländer) to be 3,400 t/a, assuming for all cooling water

circulation a phosphonate concentration of 5 mg/l and for indirect dischargers a 50%

elimination of the phosphonates (Horstmann and Grohmann 1986). Since in this

estimate the concentration factor was not taken into account, the number was later

corrected to 1,200 t/a (Hässelbarth 1987). The amount of PBTC produced in

Germany is given as 1,000-10,000 t/a, and consumption is estimated to be 500-

1,000 t/a. Of this amount, 40% is used in cooling systems (UNEP 1996). Thus the

total load of phosphonates calculated in this project lies at a realistic level. (The total

consumption of phosphonates in all areas of application for the entire U.S.A. is

estimated to be ca. 20,000 t/a; cf., Nowack and Stone 1999). Knepper et al. (2002)

used the data in the Register for washing detergents and cleaning agents to estimate

the consumption of ATMP, HEDP, EDTMP, PBTC and DTPMP as complex-formers

for this purpose in Germany at 11.100 t/a. For the areas of textile-, leather- and

paper-aids another 472 t/a are used. However, these values are also inaccurate

because they fail to include changes in the formulations to be found in the database

and are probably substantial overestimates (Kleinstück 2002).

Heavy metals used in open circulation cooling include ca. 45-135 t molybdenum in

the form of sodium molybdate and 110-220 t zinc, mostly in the form of zinc chloride.

On the other hand, a survey of the emissions of zinc from the cooling water area for

Nordrhein-Westfalen gave a total load of only 5 t zinc/a from cooling water emissions

for the drainage basins of the Rhine, Lippe and Ruhr Rivers (Piegsa 2001a).

However, there are altogether only very few comparative numbers which could be

used to evaluate the reliability of the balance drawn up. Wunderlich (1978) estimated

the consumption of hardness stabilizers, corrosion inhibitors and dispersents in

cooling water conditioning at 12,000 to 20,000 t/a (on a substance-weight basis). To

this total, the biocides must be added, whereby 95% of the biocides were used in

circulation cooling. The applied biocides included chlorine and inorganic chlorine

compounds (95%), acrolein (1%), quarternary ammonium compounds (2%) and

others (together 2%, Wunderlich 1978a). The estimate was based on the then

available cooling systems (flow-through and open circulation cooling), as well as the

concentration of substances corresponding to the most likely used doses and

procedures (Wunderlich 2002).

68

In principle the size of the cooling plants could also be considered in estimating total

loads of cooling water conditioners, so as not to overestimate the load of, for

example, biocides like hydrogen peroxide or BCDMH, which are primarily used in

smaller plants. However, data on the size in terms of the water volumes are only

available for the 314 thermal power plants supplying the public (from < 5 Mio m3/a to

>500 Mio. m3/a; cf., Stat. Bundesamt 1998). So as to preserve the systematic basis

of and the plausibility or validity of the balance, it was consciously decided not to

attempt to include any, at best rather arbitrary, “size factor” in assuming the total

water consumption. In order to introduce such a factor, the database would have to

be substantially enlarged. Instead, doubtful data in the balance data in Table 17 are

suitably marked.

69

Table 19: Comparison of the estimated consumption data for certain biocideswith data from other countries (data in kg/a on a substance basis)

Active substance UK 1) NL 1) F D 2)

o x i d a t i v e b i o c i d e sChlorine based Chlorine 184.000

Sodium hypochlorite 731.000 2.100.000 817.000 674.000Calcium hypochlorite 146.000Sodium dichlorisocyanuric acid 19.300 10.000Chlorodioxide 13.000

Bromine based Sodium bromide 356.0001-Brom-3-chlor-5,5-dimethylhydantoin (BCDMH) 286.000 1.830.000Sodium hypobromite 44.000Ozone 0 3.000Hydrogen peroxide 910 1.180.000

Potassium peroxymonobisulfate 11.000Peracetic acid 975 50.000

1.407.185 2.100.000 817.000 4.132.000n o n - o x i d a t i v e b i o c i d e s

QAVDimethylcocobenzyl-ammonium chloride 23.400Benzylalkylammonium chloride 21.400Total amount of QAV 71.152 64.100

Isothiazolinones5-Chlor-2-methyl-4-isothiazolin-3-on 13.200

Total amount of Isothiazolinones 18.000 2.250 20.800halogenated Bisphenols (Dichlorophen, Fentichlor) 12.150Thiocarbamate 56.800

Others Glutardialdehyde 56.400 15.000Tetraalkylphosphoniumchloride 9.5002,2-Dibromo-3-nitrilo-propionamid 17.200 10.000 19.8002-Bromo-2-nitropropan-1,3-diol 400S-Triazine 11.000Dodecylguanidinehydrochloride 6.900Methylenbisthiocyanate (MBT) 2.270 2.400ß-Bromo-ß-nitrostyrene 231Fatty amines 3) 20.000Others 4.412

248.115 27.250 20.000 125.400Reference:UK, F: IPPC Reference Document on the Application of BAT to Industrial Cooling Systems (11/2000)

NL: IKSR Synthesebericht Antifoulings und Kühlwassersysteme (Entwurf 15.11.2001)

D: This study (F+E 200 24 33, Januar 2001) 1) All cooling water systems2) Only recirculation cooling systems, NaOCl is indicated as Cl23) Consumption of fatty amines in a costal power plant

Total amount of non-oxidative biocides

Total amount of oxidative biocides

70

5.5 Elimination of chemicals in cooling systems and sewage plants

Alongside the intended reaction, the greater part of the biocides and conditioners is

eliminated in the cooling system through hydrolysis, adsorption, biological

degradation or evaporation and is thus not relevant for surface waters. This is

especially true for oxidatively acting biocides, whereby the in part more stable

disinfectant side-products (including trihalomethane, AOX, and bromate) must still be

considered. For the non-oxidatively acting biocides the elimination of fluorescent

bacteria toxicity is used as the criterion for inactivation, whereby the elimination

factors involved can usually not be distinguished.

Organic corrosion inhibitors, dispersents and hardness stabilizers are usually not

developed with ready biological degradability in mind, rather it is intended that they

should be stable in the cooling system. The addition of readily degradable carbon

sources in cooling systems would be counterproductive, since these serve as a

substrate for the formation of biomass. Nonetheless, poorly or non-degradable

compounds undergo some degree of elimination in cooling systems. Thus, for the

phosphonic acid 2-phosphono-1,2,4-butantricarbonic acid (PBTC), for example, it is

reported that in the presence of oxidative biocides (chlorine, bromine, ozone) as well

as through photolysis an average of 20% of the PBTC is degraded after its addition

in cooling systems (BUA 1996).

For indirectly discharged cooling waters the elimination ability of the municipal

sewage plant must also be taken into account, for which some examples are given in

Sect. 6.4.2. In the Annex the substance-specific data are presented for hydrolysis,

adsorption tendency (water solubility, log Pow) as well as for the elimination or

biological degradability. From this information, the behavior in cooling towers and in

municipal sewage plants can be estimated, at least roughly.

5.6 Regulatory control of cooling water discharges

The discharge of cooling water is regarded as wastewater emission and accordingly

regulated through the still valid Annex 31 to the Framework-wastewater-

administrative procedures, which was revised in 2002 and is to be included again as

Annex 31 in the German Wastewater Ordinance (Anonymous 2001). In the course of

surveying the companies (cf., sect. 5.3) the responsible authorities were asked to

provide information on the usual practices in controlling cooling water discharges. Of

71

special interest here was the experience with the fluorescent bacteria test, since it

has been used since 1994 as the legally established standard test for determining

the outflow shut-off pauses for cooling systems with non-oxidative biocides. The

answers of the representatives of the agencies (as a rule, the local water authorities)

were very non-uniform. In some districts only direct dischargers were considered,

while in others all plants above a certain flow-volume were considered. Data on

fluorescent bacteria toxicity were often only requested for direct dischargers. A

systematic presentation of the experiences and results is not available. In personal

discussions with representatives of the agencies it was reported to us that in general

no significant pollutant loads were expected from cooling water emissions. Moreover,

cooling water discharges were often sampled together with partial flows from other

parts of the commercial operations, so that a separate compilation of the data for

cooling systems would require a rather substantial effort.

In our questionnaire distributed to the plants the persons responsible were also

asked about the measured wastewater parameters (governmental agency control or

their own). Of 156 plants with open circulation cooling or flow-through cooling that

provided the corresponding data, for only 23% were data on fluorescent bacteria

toxicity given. Some based their answers on single measurements taken several

years previously, which were not regularly repeated. And even when only those

cooling systems were considered for which biocides were known to have been used,

a similar picture is seen. For only 1/3 of these cooling plants (n=52) were fluorescent

bacteria-test results available. In 2/3 of the cooling systems with biocide use no

fluorescent bacteria tests were performed, even though 40% of these discharged

directly. Only in isolated cases was it mentioned that elimination curves for the

biocides used were even on hand.

In summary, it can be concluded from these data that there is a notable deficit in the

performance of fluorescent bacteria tests for the evaluation of cooling water

discharges.

5.7 Literature and database research

The results of the research on the environmentally relevant substance properties of

the cooling water chemicals are presented in the Annex. Along with the literature-

and database research the information provided by the producers is documented as

72

“personal communications”. As a rule, the data provided by the manufacturers could

not be verified from original data.

The comprehensive evaluation of the ecotoxicity and degradability is presented in

Table 20. As expected, the aquatic ecotoxicity of the biocides is quite high, while the

corrosion inhibitors and hardness stabilizers can be described as relatively "non-

toxic". With the exception of glutaraldehyde a ready degradability has not been

shown for any of the organic biocides or conditioners. Only for quarternary

ammonium compounds was a complete degradation reported in several studies

(without respecting the 10-day window). In some cases there are still some

significant data gaps. For some of the applied triazole compounds (e.g.,

butylbenzotriazole, chlorotolyltriazole) and phosphonic acids

(hydroxyphosphonoacetic acid, tetraalkylphosphonium chloride) there are virtually no

data available. For PBTC and ATMP, in contrast, there are extensive substance

dossiers (UNEP 1996, UNEP year not indicated). Also, little is known about several

biocides such as the BCDMH-related 1,3-dichloro-5-ethyl-5-methylhydantoin or the

QAV dimethylcocobenzylammonium chloride.

73

Table 20: Summarized evaluation of the eotoxicity and degradability of coolingwater chemicals

Daphnia Fish Bacteria Biol.Degradation

Biocides

Chlorine 3 3 3

Sodium hypochlorite 2 2-3 1-0

BCDMH 3 3 + (DMH)

Ozone 3 3

Hydrogen peroxide 2 1 1-2

Glutardialdehyde 2 2 2 +++

Org. Bromocompounds

2-3 1-3 3 +

Isothiazolines 3 3 3 +

Org. sufluriccompounds

2-3 2-3 +

QAV 3 1-2 1-3 +-++

Corrosion inhibitors and Hardness stabilizers

Phosphonic acids 0 0 0 +

Triazoles 0 1 0 +

Polycarboxylates 0 0 0 +

Triethanolamine 0 0-1 0 +

Zinc- /copper salts 3 2-3 1

Molybdate 0 0

Silicate 0 0 0

The classification of ecotoxicity was performed following the criteria of the GefahrstoffVO:

Classificationnumber

Classification LC50 or EC50

0 Non-hazardous >100 mg/l

1 Hazardous 10-100 mg/l

2 Toxic 1-10 mg/l

3 Very toxic <1 mg/l

The classification of bio-degradability was made following the criteria:

+++ Readily bio-degradability proven ++ Bio-degradable without 10 days window + Poorly bio-degradable or inconsistent results

74

6 Evaluation

6.1 Composition of cooling water

As a rule no ecotoxicity could be found for the cooling waters investigated. After a

shock treatment with biocides a higher toxicity was measured, but this was

completely eliminated within the prescribed inactivation period. Only in one plant with

continuous addition of biocides (BCDMH) was a high toxicity found after an

additional batch treatment with isothiazolinones. Although the outflow was not closed

during treatment in this case, an indirect discharger was involved, so that no direct

hazard for the surface waters was anticipated.

In Germany the first results on the ecotoxicity of cooling water samples treated with

biocides were presented by Börnert and Hagendorf (1992). For one indirect

discharger the effectiveness of a not further specified biocide was inactivated after 4

h, but for another, also after 4 h, a GL- or GA-value of up to 192 was still measured

(Börnert and Hagendorf 1992). Gellert and Stommel (1995) investigated the cooling

water from 41 production plants and found among plants with flow-through cooling

none exceeding the legally prescribed threshhold valules for fluorescent bacteria

toxicity (GL≤12). For plants with circulation cooling with sodium hypochlorite shock

treatments the fluorescent bacteria toxicity correlated with the chlorine concentration

(up to 2.75 mg/l). The highest toxicity was measured immediately after the treatment

of a circulation water with methylenebisthiocyanate (GL=1024). After 5 days the

fluorescent bacteria toxicity of this biocide was also completely eliminated (Gellert

and Stommel 1995). In the most extensive data collection on the ecotoxicity of

cooling water up to that point, Diehl and Hagendorf (1998) presented 248 test

results. The medians for the Daphnia, fluorescent bacteria and algae toxicity lay at

GD=6, GL=1 and GA=6, the maxima at GD=128, GL=16 and GA=32. In comparison to

the other biotests the fluorescent bacteria test was found to be less sensitive (Diehl

and Hagendorf 1998). In a Dutch study the cooling water from 14 plants was

investigated and a clear relationship was demonstrated between the substance

concentration and the ecotoxicity of cooling water samples. In general, cooling

waters treated with the non-oxidative biocides isothiazolinone, DBNPA, ß-bromo-

nitrostyrene and methylenebisthiocyanate showed higher toxicity (up to a dilution

75

factor of 769) than those treated with the oxidative biocides sodium hypochlorite and

ozone (< dilution factor of 2; cf., Baltus et al. 1999).

6.2 Emission route for cooling water chemicals

The most important emission route for cooling water chemicals or their reaction-

products (e.g., AOX) is the outflow, or for indirect dischargers the municipal sewage

plant. In open cooling circulations a portion of the oxidative biocides can be stripped

out in the cooling tower (cf., sect. 6.4.1 for the example of chlorine, chlorine dioxide).

In addition, chemicals dissolved in water are emitted in the form of expelled water

droplets (ca. 0.01% of the water flow). Along with the chemicals added for

conditioning, these also contain salts and microorganisms from the cooling waters

(VDI 3784: 1986).

6.3 Elimination behavior of cooling water biocides

Having information on the elimination time, for which period the outflow is to remain

closed after a shock treatment with a non-oxidative biocide, provides an opportunity,

according to Annex 31 of the AbwV regulations, to limit the effort involved in direct

on-site measurements of fluorescent bacteria toxicity. This makes it all the more

important to specify precisely the conditions for performing these tests. The results of

the present study show that predictions about the decline in the biocidal effects

should not be considered separately from the inoculum concentration. At a lower

activated-sludge concentration (30 mg d.s./l) the fluorescent bacteria inhibition from

isothiazolinone and Bronopol was not completely eliminated even after 7 days, while

at the highest concentration (1 g d.s./l) a decrease within 1 day to GL<12 was

observed; here elimination through adsorption played an important role. According to

statements from cooling tower operators and manufacturers of cooling water

conditioners, a closure of the outflow for more than 24 h is usually not practical.

In the publication from German et al. (1996) 4 elimination curves for cooling water

biocides in the fluorescent bacteria test are presented. The static experiments were

inoculated with activated sludge from a municipal sewage plant (0.5 g d.s./l), and the

determination of the fluorescent bacteria inhibition was made at a dilution of 12, as in

the present study. Methylenebisthiocyanate (20 mg/l) showed an inhibitory effect of

ca. 80%, which was also not completely eliminated after 24 h. In contrast, a

76

quarternary ammonium compound, isothiazolinone, and a

dibromonitrilopropionamide-formulation (at product-concentrations of 10, 70 and 100

mg/l) showed inhibitory effects even at the start of only 27% to 50%, so that under

these experimental conditions no effective biocidal effect was detected even by using

individual species such as the fluorescent bacteria. After 2 to 3 h, all 3 compounds

were below the threshold value of 20% inhibitory effect (German et al. 1996).

In a Dutch study the decrease in the fluorescent bacteria inhibition by cooling water

biocides was investigated specifically with regard to hydrolysis as an elimination

factor. Here the surface water used for cooling was tested, without any additional

inoculum, after removing zooplankton by filtration through 25 µm pores. Within 96 h

the fluorescent bacteria inhibition from DBNPA (12.5 mg/l), ß-bromo-ß-nitrostyrene

(2.5 mg/l) and ß-bromo-ß-nitrostyrene/methylenebisthiocyanate (4 and 2.2 mg/l) was

completely inactivated, while for isothiazolinone (1.5 mg/l) and glutardialdehyde (50

mg/l) only minimal elimination was observed (Baltus et al. 1999).

Gartiser and Scharmann (1993) utilized unconditioned cooling water without addition

of any further inoculum to determine the inactivation kinetics of 3 biocides at their

usage concentration. For the biocide based on isothiazolinone the G L-value indeed

decreased within 13 days from GL=128 to GL=16., but did not reach the legally

prescribed threshhold value GL=12. The fluorescent bacteria toxicity of the biocide

based on hydrogen peroxide was completely degraded in 3-6 days. A dye used

against algal growth was already below the threshhold value of GL=12 when tested at

its application concentration (Gartiser and Scharmann 1993).

The question of establishing the experimental conditions for the determination of

"elimination curves" for cooling water still remains open. Elimination curves obtained

under the experimental conditions of the VCI-working group "Biocides in cooling

circulations" with a higher inoculum concentration (activated sludge, 500 mg d.s./l),

favor elimination through adsorption and correspond to the design of an inherent

degradation test. Comparably high biomass concentrations are not normally found in

cooling circulations. The biomass in water channeling systems is sessile, primarily in

the form of biofilms; the microbe count in the water is 103 to 104 fold lower. Biofilms

in water-channelling systems seldom exceed a thickness of more than 1 mm and

contain 98% to 99% water. The greater part of their dry mass consists of

extracellular polysaccharides, and only maximally 10% of the dry mass is present in

77

the form of cells (Cloete and Brözel 1992). A comparative measurement of the

elimination behavior of cooling water biocides in a laboratory test and in real plants is

important, in order to interpret the data correctly. However, here there are scarcely

any published results available. For all such measurements at real plants it is

important that the decrease in the fluorescent bacteria toxicity is not caused by

dilution with added make-up water. Therefore, the outflow must be closed during

such an experimental series. When additional information on the biological

degradability is called for, especially when evaluating direct dischargers, results on

ready biological degradability and/or elimination curves with lower inoculum

concentrations (e.g., 30 mg d.s./l in conformance witih the conditions for the OECD

301 Test of "ready bio-degradability") should be called for.

6.4 Choice of active substances

6.4.1 Biocides

The choice of a biocide depends in part on the organisms whose growth is to be

controlled. Especially for preventing algal growth, copper sulfate, quarternary

ammonium compounds and photosynthesis inhibitors based on triazine derivatives

are used. There are also some contradictory reports on experience concerning the

effect spectrum of cooling water biocides. Thus, for example, it was reported that

glutardialdehyde and quarternary ammonium compounds can only be effectively

used against algae, while isothiazolinones showed the best effect against bacteria.

With methylenebisthiocyanate biofilm formation could not be effectively prevented

(Mattila-Sandholm and Wirtanen 1992). Mussels cannot be effectively combatted in

cooling systems with chlorine-releasers, because they protect themslves by closing

their shells. In these cases non-oxidative biocides such as QAV are used. In one

investigation isothiazolinone but also QAV and thiocarbamate also proved ineffective

against several amoebae isolated from cooling water thought to be causing the

spread of pathogenic Legionella (host organism). On the contrary, a growth-

promoting effect was even observed in some cases (Srikanth and Berk 1993).

In the following, the most important biocides will be described.

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Chlorine and sodium hypochlorite

Active chlorine added in the form of chlorine and sodium hypochlorite is the most

important oxidative biocide for cooling plants. For cooling plants that use sea water

as a heat carrier, usually 0.5-1.5 mg/l chlorine is continuously added. In conformance

with the reference document on the IPPC-directive, this is also BAT (Anonymous

2000). Because of the bromides contained in the saltwater, different disinfectant by-

products are produced here than those found for fresh-water chlorination. In a

French study bromoform, dibromoacetonitrile, tribromophenol and dibromoacetic

acid were identified as the main components (Allonier et al. 1999). The VGB-cooling

water guideline recommends a level for continuous addition of 0.1 mg/l free chlorine

(for brackish water) and 0.25 mg/l (for sea water), and for batchwise shock-treatment

chlorination concentrations of 2-3 mg/l free chlorine (Fichte et al. 2000). At the usual

pH-values > 8 in cooling circulation, the biocidal effect of chlorine in the water is

reduced, because the dissociation equilibrium is shifted away from hypochlorous

acid in favor of the less effective hypochlorite-ion (OCI-). In this case it is better to

use the more weakly dissociating hypobromous acid (HOBr), which dominates over

the only weakly microbiocidally acting hypobromite-ion (OBr -) up to pH 9.

Hypobromous acid is, as a rule, generated on site from sodium bromide by adding

sodium hypochlorite (NaOCl). With decreasing pH an increasing proportion of the

hypochlorous acid is stripped out during cooling tower passage (ca. 30-40% at pH 6

and ca. 10% at pH 8.5, Holzwarth et al. 1984, Baltus and Berbee 1996); therefore, it

is recommended to use chlorine-releasing biocides in open circulation cooling in

spite of their lower effectiveness at pH-values above 8 (Anonymous 2000).

Depending on the water composition (including DOC- and ammonium

concentration), pH-value and contact time, the use of free halogens as biocides

leads to the formation of disinfectant by-products such as trihalomethane, chlor- and

bromamine as well as adsorbable organic halogen compounds (AOX).

79

Chlorine dioxide

In the treatment of drinking water chlorine is in part replaced by chlorine dioxide, in

order to minimize the formation of AOX, especially halogenmethanes. Chlorine

dioxide reacts substantially more weakly with complex organic molecules and

ammonium and thus forms less AOX. Ocasionally, chlorine dioxide is also used in

the cooling water field, whereby it is usually produced on site through the reaction of

chlorine gas with sodium chlorite (NaClO2). Chlorine dioxide is considerably more

volatile than hypochlorous acid and consequently can be more easily stripped out

from open cooling plants (Anonymous 1991, Groshart and Balk 2000).

BCDMH

Among the organic chlorine- and bromine-releasers, 1-bromo-3-chloro-5,5-

dimethylhydantoin (BCDMH) is preferentially used. Here the actual active compound,

hypobromous or hypochlorous acid, is released after a time delay.

BCDMH hydrolyzes rapidly and because of its limited water solubility it is usually

added over a separate sidestream (over BCDMH filtered cooling water) (van Donk

and Jenner 1996). The organic residue after hydrolysis, 5,5-dimethylhydantoin, is

poorly bio-degradable, but has a weak tendency to adsorption (Anonymous 1994). It

has been reproted that the biocidal effect of 1-bromo-3-chloro-5,5-dimethylhydantoin

is 10 to 20 fold higher than that of chlorine-releasers (Mattila-Sandholm and

Wirtanen 1992). Related compounds such as 1,3-dichloro-5,5-dimethylhydantoin or

1,3-dichloro-5-ethyl-5-methylhydantoin are also occasionally used.

Ozone

Ozone is a highly effective oxidative biocide. While ozone holds a firm position in the

treatment of swimming-pool water, there is little practical epxerience available on the

use of ozone in cooling water treatment (Schmittecker et al. 1997, Schmittecker et al.

1999, Wasel-Nielen and Baresel 1997). In the data we compiled on cooling water

practices (cf., sect. 5.3), there was only one plant that used ozone. In a study of the

Landesanstalt for Environmentschutz Baden-Württemberg the following advantages

of treating cooling water with ozone, as compared to chlorine and non-oxidative

biocides, were listed: effective inhibition of biogrowth, no storage necessary since

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ozone is produced on site, no formation of AOX, attainment of the CSB-threshhold,

elevation of the ozone concentration in the air near the ground by maximally 1 µg/m 3

(Schweitzer 1995). The chemical reactions of ozone in water have been described by

Rice and Wilkes (1992). It is reported that ozone decomposes at pH-values above 8

to free hydroxyl radicals. These have a stronger oxidizing effect than ozone itself, but

at the same time they also have a very short half-life of a few microseconds.

Especially with high concentrations of hydrogen carbonate as a radical-trap, the

disinfectant effect of ozone at pH-values >9 is poor. In the ozonation of bromide-

containing water, the bromide is oxidized to hypobromite-ion (OBr -), which is rapidly

hydrolyzed to the equally biocidal hypobromous acid (HOBr) or to the genotoxic

bromate (BrO3-) ion. As disinfectant by-products compounds such as bromate,

bromoform or monobromoamine are formed, some of which show a genotoxic effect

(Rice and Wilkes 1992, Gunten and Hoigné 1994). Comparative measurements with

the Ames test on the mutagenicity of disinfectant-by-products of ozone, chlorine and

chlorine dioxide in the treatment of drinking water, showed a substantially higher

mutagenicity after disinfection with chlorine. At a dose of 3 mg/l ozone a slight

increase in the mutation rate was found, but at higher ozone concentrations (10 mg/l)

this was eliminated (Kool and Hrubec 1986).

Usually, ozone is added to the cooling water continuously in very low concentrations

of 0.1 to 0.3 mg/l (Wasel-Nielen and Baresel 1997)(Viera et al. 1999). Production

occurs directly on site using high voltage, with an energy expenditure of ca. 10 kWh

per kg ozone. Thus, for cooling systems in energy generation, up to 0.1% of the

energy generated must be used for the production of ozone (Anonymous 2000). Due

to the high oxidative potential of ozone decomposition, when used at high

concentrations, the intermediate hydroxyl radicals formed may attack structures

made of plastic or wood. Organic conditioners, for example dispersents, can also be

degraded by ozone. In order to keep the ozone content low, the cooling water should

have the lowest possible content of organic material.

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Hydrogen peroxide

In comparison to the other oxidative biocides, hydrogen peroxide is only effective at

higher concentrations (>15 mg/l; cf., van Donk and Jenner 1996). Reports of lower

effective concentrations were questioned on the part of industry (cf., table 9). Due to

iron- or copper-catalyzed decomposition, it only has a very short half-life. In some

cases, the effectiveness of hydrogen peroxide was improved through the use of

special catalysts.

Rarely, peracetic acid is used as an organic oxygen-releaser in the cooling field. This

compound is readily biologically degradable, but under unfavorable conditions it is

corrosive.

Isothiazolinones

One of the most important non-oxidative cooling water biocides consists of a mixture

of compounds from the isothiazolinone substance group: 5-chloro-2-methyl-4-

isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one. They are already effective in

the concentration range below 1 mg/l. The mechanism of action involves an inhibition

of cellular proteins (Groshart & Balk, 2000). The isothiazolinones hydrolyze slowly

(t1/2 = 7 d at 30°C and pH 8) and are biologically not readily degradable. In

experiments with laboratory sewage treatment plants a limited mineralization of the

compounds (<25%) was demonstarted (Baltus & Berbee, 1996; Krzeminski et al.,

1975). Unpublished test reports from Thor GmbH in simulation tests

(Water/Sediment-test according to BBA IV 5-1) confirm the rapid primary

degradation of the investigated isothiazolinones, but only ca. 10% was mineralized to14CO2. Thus, 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-

one form stable metabolites, which are to a large part adsorbed in the sediment in

the test system (Schoester 2001).

Isothiazolinones are rapidly bound to biomass. Adsorption and bioaccumula tion in

the biomass are major elimination factors. Investigations with the bacteria

Pseudomonas aeruginosa and P. fluorescens showed that the concentration of 5-

chloro-2-methyl-4-isothiazol-3-one inside the cells was a factor of 400 higher than

outside (Diehl and Chapman 1999).

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Quarternary ammonium compounds

Quarternary ammonium compounds (QAV) act by binding to the cell membrane and

are also not readily biologically degradable. In sewage plant passage they are largely

eliminated by adsorption to the activated sludge. With an adapted inoculum or after

longer incubation times, an extensive mineralization of QAV has been reported. The

most important representative in the cooling water field is alkyldimethylbenzyl-

ammonium chloride.

Organic bromine compounds

The non-oxidatively acting dibromonitrilopropionamide (DBNPA) is hydrolyzed rapidly

to the in part still biocidal compounds dibromoacetonitrile, dibromoacetamide,

monobromonitrilopropionamide and cyanoacetamide. Only substance-specific

degradation data are available (Blanchard et al., 1987). The substance itself is

presumably poorly biologically degradable (Groshart & Balk, 2000). Other members

of this group include 2-bromo-2-nitropropan-1,3-diol (Bronopol) and ß-bromo-ß-

nitrostyrene, but no degradation data on these compounds is available. Bronopol is

hydrolyzed slowly (t1/2=14 d at 30°C and pH 8), but in contrast ß-bromo-ß-

nitrostyrene hydroyzes rapidly (t1/2=20 min at 30°C and pH 8) (Baltus and Berbee

1996).

Glutardialdehyde

Glutardialdehyde is only used occasionally in the cooling water field. The mechanism

of action is based on the denaturation of proteins. Glutardialdehyde is less toxic for

aquatic living organisms as compared to the other biocides, and the concentration

used is correspondingly higher. The compound is readily bio-degradable.

6.4.2 Cooling water conditioners

Phosphates

Phosphates and polyphosphates have been used for a long time as corrosion

inhhibitors. For very soft waters a cooling water treatment with zinc ions or inorganic

phosphates is often used for steel as a satisfactory protection against corrosion. The

concentration of orthophosphate used to inhibit corrosion is maximally 15 mg/l. This

corresponds to a concentration of phosphorus of ca. 5 mg/l. In the opinion of several

83

of the manufacturing companies, in the present study the balance sheet loads of

inorganic (poly)phosphates are probably underestimates. However, this could not be

confirmed. Even if the consumption of phosphoric acid is assigned to the phosphates

(as was the case), in comparison to the organic phosphonic acids substantially fewer

plants report the use of inorganic phosphorus compounds. The evaluation of product

information showed that phosphates were primarily used in combination with

phosphonic acids and/or polycarboxylates, as well as with zinc or molybdates. This

explains why the overall balance gave phosphate concentrations lower than would

correspond to the concentration added if used alone. Thus, for example, a good

protective effect was achieved for non-alloy steel in cooling circulations using sodium

polyphosphate as well as sodium polyphosphate or polyacrylate in combination with

zinc sulfate. The exclusive addition of zinc sulfate did not reduce the rate of corrosion

(Naumann and Schimke 1991). Hence, the calculated concentrations (1.8 mg/l) also

are lower than the values that would be necessary for the sole addition of phosphate

(cf., table 16). Of note is the frequent use of inorganic phosphates in the water added

to the heating vessel.

Phosphonic acids

Phosphonic acids are used in very sub-stoichiometric concentrations for hardness-

stabilsation (treshold-effect) and in higher concentrations as corrosion inhibitors.

They are biologically poorly degradable and stable against hydrolysis. In the

concentration range of 5-20 mg/l some phosphonic acids have good properties as

corrosion inhibitors for steel (all-organic operation). In conjunction with zinc, however,

only one-half the phosphonic acid concentration is needed for a corrosion inhibiting

effect.

Under the phosphonic acids which could be unequivocally identified in the product

information provided, the frequency distribution was HEDP >

hydroxyphosphonoacetic acid > PBTC >> ATMP and DTPMP. By and large, this

agrees with the frequency of the surveyed phosphonic acids

(hydroxyphosphonoacetic acid > HEDP >> ATMP = PBTC = DTPMP). However,

owing to the poor documentation, the predominantly consumption numbers for

phosphonic acids could not be assigned to particular substances.

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The elimination of PBTC in sewage plants appears to occur, according to laboratory

experiments, 0-60% through adsorption, as well as 60-100% through flocculation (P-

elimination (BUA) 1996). Metzner et al. measured the elimination capacity for HEDP

and ATMP in municipal sewage plants to be ca. 50% (Metzner 1990).

The elimination of some other phosphonates in municipal sewage plants is reported

to be on the order of 50%. Adsorption experiments with radioactively labeled

phosphonic acids at environmentally realistic concentrations showed that 23-70% of

EDTMP and 80-90% of DTPMP was adsorbed to various activated sludges (Gledhill

and Feijtel 1992). In general, phosphonates influenced the phosphate-precipitation,

as the third purification step, since they form complexes with iron(III)-ions. However,

this influence is compensated by the higher concentrations of flocculants (Horstmann

and Grohmann 1986). The dependence on pH-value and the concentration of heavy

metals for the adsorption of phosphonic acids onto clay minerals was investigated by

Nowack et al. (1999). They found that the adsorption decreased substantially above

pH 8. While copper and iron ions only had a limited influence on adsorption, it

increased noticeably in the presence of calcium (Nowack and Stone 1999). In the

outflow of 7 municipal sewage plants with phosphate-precipitation, phosphonate

concentrations were generally below the detectability limit (ca. 2 µg/l). The

elimination in the sewage plant was over 80% (Nowack 1998).

Only a few studies considered the behavior of the metabolites of phosphonic acids.

In a recent Dutch study the in- and outflow-concentrations of aminomethylene-

phosphonic acid (AMPA), a degradation product of ATMP, were determined in 5

municipal sewage plants. In some cases, higher concentrations were measured in

the outflow. (Meerkerk and Puijker 1997). The proportion of the cooling water

conditioners (for direct dischargers) in the total load of AMPA in a part of the

drainage basin of the Maas River was estimated at 28%. The contribution by

municipal sewage plants was in the same range. An additional source for AMPA is

the degradation product of the herbicide Glyphosat (Meerkerk and Puijker 1997).

Nowack et al. (2001) investigated 2 diphosphonates which are formed in the catalytic

degradation of ATMP in the presence of manganese(II)-ions and molecular oxygen.

These compounds were also effectively eliminated in the sewage plant (>80%)

(Nowack 2001).

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In the surface water the photodegradation of phosphonic acids surpasses bio logical

degradation by far, especially when they are present in the form of iron complexes

(Gledhill and Feijtel 1992, Steber and Hater 1997). It should be noted, however, that

only the primary degradation of the substances was determined. Several studies

document a substantial photodegradation of phosphonic acids in the presence of

equimolar amounts of iron ions (ca. 44% to 82% at pH 7 in 17 days with natural

sunlight illumination; Gledhill and Feijtel 1992). Unpublished data of the Bayer AG on

the photodegradability of PBTC, HEDP and ATMP at a test concentration of 10 mg/l

in the presence of 0.2 mg/l iron-ions indicate a PBTC-degradation of 53-81% within

24 h, but a negligible degradation of HEDP and ATMP over this time. Without the

addition of the iron-ions no photodegradation of PBTC was detected. The presence

of nitrate also favored photodegradation. Adsorption experiments with radioactively

labeled PBTC (1 mg/l) showed that 95% adsorbed to the activated sludge

(Kleinstück 2001). However, the photolysis of the iron(III) complexes of ATMP and

DTPMP, unlike that of the iron(III)complex of EDTA does not lead to biologically

degradable compounds (Nowack and Baumann 1998). As an additional, relevant

degradation mechanism in natural surface waters, the catalytic oxidation in the

presence of manganese-ions and oxygen has been discussed (Nowack and Stone

2000).

The analytical determination of phosphonic acids and their metabolites in surface

waters has so far been limited by the relatively high detection threshold of ca. 2-13

µg/l with the method of Klinger et al. (1999) and Nowack (2001). However, since it

can be expected that phosphonic acids will be found in surface waters, their

elimination in the treatment of drinking water has been investigated. The results

show that all phosphonates are removed by precipitation with iron(III)- or aluminum-

salts under practically relevant conditions. Using ozone only the nitrogeneous

phosphonic acids are completely converted, whereby the herbicide Glyphosat and its

main degradation product aminomethylphosphonic acid (AMPA) are formed as

oxidation products (Klinger et al. 1998).

Polycarboxylates

Polycarboxylates are generally regarded to include the water-soluble negatively

charged polymers (polyelectrolytes) which are primarily used (alongside zeolites) as

phosphate substitutes in the wash-detergent field. These are homopolymers of

86

acrylic acid as well as co-polymers of acrylic acid and maleic acid with a mean

molecular weight (MW) of ca. 70,000 (Opgenorth 1992). These are not classified as

defined compounds with their own CAS-numbers, so no direct substance searches

could be carried out, and reference had to be made to more general studies. This

substance group is consequently not included in the Annex.

In Germany ca. 20,000 t/a polycarboxylates are used in wash detergents (Kaiser et

al. 1998). In the cooling water field, hardness stabilizers and dispersants of

polyacrylates, polymethacrylates and polymaleinates, sulfonated copolymers and

polyacrylamides are all grouped together under polycarboxylates (Piegsa 2001b).

Polycarboxylates with MW of 500-20,000 are used in the cooling water field for

hardness stabilizing, and higher molecular forms (up to MW 50,000) as dispersents

(Andres et al. 1980). In the product information these compounds are often listed

under polycarbonic acids. All these compounds are poorly bio-degradable, whereby

a low molecular weight favors degradation. Thus, the copolymer of acrylic acid and

maleic acid at a MW of 70,000 is only degraded 20% after 30-90 days, and at a MW

of 1000 up to 45% (Opgenorth 1992). In municipal sewage plant polycarboxylates

are primarily eliminated through precipitation with calcium and magnesium hardness

and adsorption to the activated sludge, whereby in laboratory experiments (Zahn-

Wellens-test, SCAS-test, laboratory sewage plant) values up to 98% were

determined for higher molecular weight compounds. Below a MW of 10,000 the

adsorption tendency of a copolymer of acrylic acid and maleic acid decreases

substantially (Opgenorth 1992). In a recent study on the degradability of 2

radioactively labeled polycarboxylates based on acrylic and methacrylic acid and

styrol at a MW of 55,000 and 7,000 only negligible mineralization in the CO2-

evolution-test (OECD 301 B) was measured. In the SCAS-test (semi-continuous

activated sludge test according to OECD 302 A) < 1% of the polycarboxylates was in

the aqueous phase, and the bulk (96-99%) was adsorbed to the activated sludge

(Jop et al. 1997).

The aquatic ecotoxicity of polycarboxylates is generally low. The EC50 for Daphnia,

and fish was > 200 mg/l for the copolymer of acrylic acid and maleic acid with MW=

4500 or 70,000 (Kaiser et al. 1998, Opgenorth 1992). In the activated sludge-

respiration-inhibition test (OECD 209) up to a concentration of 3,200 mg/l no

significant inhibitory effect against the activated sludge could be detected (Jop et al.

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1997). Similar data were reported by Guiney et al. (1996). Also the polycarboxylates

used in the wash-detergent field have a low ecotoxicity. A potential to remobilize

heavy metals and for bioaccumulation was not observed (Schöberl and Huber 1988).

Dispersants based on acrylic acid with a MW of 45,000 were weakly ecotoxic in the

activated sludge respiration-inhibition test, fluorescent bacteria test and algae test

with EC50 values <100 mg/l. However, for aquatic crustaceans of the species

Ceriodaphnia dubia chronic effects due to physical damage have been reported, the

NOEC (no effect concentration) here was 1 mg/l (Guiney et al. 1996).

Triazoles

Triazoles are predominantly used as corrosion inhibitors for copper and its alloys.

The most important compounds are benzotriazole and tolyltriazole (Andres et al.

1980). The triazoles generally have low aquatic ecotoxicity. Few data are available

on the degradability or elimination, but triazoles are generally regarded as not readily

degradable. The degradability of tolyltriazoles appears to depend on the position of

the methyl group. While 5-methyl-1H-benzotriazole reported to be degraded in

cooling towers, 4-methyl-1H-benzotriazole is stable (Cornell et al. 2000). These data

agree with the Zahn-Wellens test results (96% elimination for 5-methyl-, 0% for 4-

methyl-1H-benzotriazole; cf., annex). For other compounds there are serious data

gaps as regards the ecotoxicity and eliminability.

Heavy metals

Zinc and molybdenum are also used as corrosion inhibitors in open industrial cooling

circulations. When these heavy metals are indirectly discharged, elimination in the

sewage plant through adsorption should also be taken into account. It is well known

that adsorption to the activated sludge occurs, and consequently threshold limits

have been established according to the sewage-sludge regulations (for removal for

spreading on agriculturally used soils, for zinc 200 mg/kg).

Zinc

According to Annex 31, zinc salts may not be used in open cooling systems of power

plants. The evaluation of the questionnaires confirmed that this restriction was

respected. In industrial cooling systems zinc is often used in combination with

phosphates or phosphonates. In combination with phosphate the pH in the

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circulation water is maintained in the neutral range through the addition of mineral

acids, in order to avoid excessive deposition of poorly soluble zinc hydroxides or

calcium phosphate. In contrast, when using phosphonates the addition of acid is not

necessary (Piegsa 2001b).

A balance for the zinc loads in the in- and outflows of municipal sewage plants

revealed that ca. 50% was eliminated with the excess sludge and 50% passed with

the wastewater in the final settling tank (pond) (Kroiss and Zessner 2001). Zinc is an

essential trace element for animals and plants, but in higher concentrations is toxic.

The zinc content in the outflow of industrial cooling circulations is limited to 4 mg/l

according to Annex 31.

Molybdenum

Several manufacturers remarked that molybdate is primarily used in closed systems.

Nonetheless, its use in open systems is documented for 6 plants (from the foodstuffs

industry, automobile industry, chemical industry and one steel plant), so its loads

may not be neglected. The use in open systems also agrees with the producer’s

information for several products. Molybdenum is an essential trace element for plants

and is contained in the enzyme for nitrogen fixation (nitrogenase), as well as in

several animal enzymes. Consequently, small amounts of molybdates are added to

some fertilizers. However, higher concentrations can be toxic for both plants and

grazing animals (Parker 1986). In comparison to zinc salts, the aquatic ecotoxicity of

molybdates is substantially lower. Investigations on the adsorption of molybdates to

activated sludge are not available, but it can be supposed that there is an enrichment

on the activated sludge.

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7 Recommendations

Cooling plants are components of complex thermal technical processes and

furthermore are dependent on the available water and the local conditions.

Consequently, an optimization of the cooling and the selection of the conditioners

should always take into account the whole process.

7.1 Energy conservation measures

Cooling plants are used to remove from the industrial process excess heat produced

during the consumption of primary energy. Hence, a rational use of the energy leads

not only to cost savings, it also reduces the emissions of greenhouse-gases and the

effort required of the cooling plants including the amount of chemicals. In optimizing

the process internal measures to save energy should thus have the highest priority.

In addition, the use of the industrial waste heat for thermal energy is by far the most

environmentally friendly system for the provision of low-temperature heating. For this

reason, an increased development of thermal energy production with the utilization of

industrial excess heat is being sponsored (Roth et al. 1996).

7.2 Technical solutions

In the reference document "Industrial cooling systems" the various technical

possibilities for the optimization of cooling plants are comprehensively presented, so

here only the essential elements need to be mentioned. The choice of the cooling

system depends on the local givens, such as, e.g., the capacity of the surface water

to be used. From the questionnaire to the cooling plants it was surprisingly learned

that, in 34 of the 110 surveyed plants with open circulation cooling, ground water was

used for cooling purposes and in 12 plants drinking water. Indeed, in 3 plants more

than 100,000 m3 drinking water were used annually for cooling. Thus, the water

supply can be a significant cost factor and influence the site selection.

Regarding the choice of basic materials, it seems that because of the complexity of

cooling water systems there is no ideal basic material. Nonetheless, the choice must

be made according to the specific requirements. In the VGB-cooling water guideline

recommendations for basic materials for pipes, heat exchangers and water

90

chambers are provided with considerations of the water composition (chloride

content).

From the experiences reported by the employees of the plants included in this study,

it became clear that already through simple measures the cost intensive use of

cooling water biocides could be reduced, in some cases by 90%. Thus, for example,

the orientation of the cooling tower with respect to the sun plays a decisive role for

the growth of algae, the primary producer of biomass. Already through the placement

of the cooling tower and/or its subsequent shading, algal growth can be substantially

reduced.

Pre-treatment of cooling water: Through treatment of the added water dispersed

material can be removed by filtration procedures, or the carbonate hardness and/or

the salt content of the added water reduced with an ion-exchanger. Thereby, the

amount chemicals required can be reduced and higher concentration cycle factors

can be adjusted downward. However, in making a comparative evaluation, the

chemicals required for the decarbonization and regeneration of the ion-exchanger

must also be taken into account. Thus, the regeneration requirements for

hydrochloric acid and sodium hydroxide fluctuate between 110% and 250% of the

stochiometrically called for amounts, and for sodium chloride solution (NaCl)

between 150% and 300% (Greiner et al. 1987, Kohler 2000). For power plants,

because of the large demand for water, the treatment of the added water is generally

limited to the primary interfering substances (mechanical prurification by filtration,

decarbonation with sulfuric acid or calcium hydrate) (Fichte et al. 2000).

Side-stream filtration: The addition of chemicals in open circulation cooling can also

be reduced by continuously cleaning a partial-stream using filter technology. Thus

concepts were developed to reduce the potential for biofouling in cooling systems by

removing the nutrient materials. By introducing a reverse-flow washable sand filter

upstream, the formation of the biofilm can be specifically limited to an easily

controllable system and thereby protecting the downstream cooling plant. The

biologically degradable carbon could be reduced in one plant with this technique to

1/4 of the original value. The thickness of the biofilm was corresponding reduced by

90% (Griebe and Flemming 1996). By cleaning just 1-3% of the circulating water

over a continuously operating sand filter the consumption of sodium hypochlorite was

reduced by 70-80% (Daamen et al. 2000). The VGB-cooling water guideline

91

recommends where appropriate the filtration of a side-stream of up to 5% of the total

flow through the use of gravel-filters (Fichte et al. 2000). According to Kunz (1993)

water circulations “should be regarded as bioreactors in which growth should not

take place". Based on the observation that many organisms protect themselves from

colonization with bacteria by keeping their milieu iron-free, his biotechnological

concept for limiting the biomass growth consists of seeking to specifically reduce the

concentration of iron ions in the cooling system (Kunz 1993).

Water-flow velocity: Periods of standing, stagnation phases and too low flow

velocities are to be avoided, in order to minimize the risk of biomass formation,

corrosion and scaling. In the reference document of the EU on industrial cooling

systems current velocities of 1.8 m/s are described as a BAT-measure to protect

condensers and heat-exchangers (Anonymous 2000). On the other hand,

excessively high flow should also be avoided to prevent possible erosion corrosion

phenomena and the formation of a protective layer. In the VGB-cooling water

guideline a current-flow velocity range of 0.5-3 m/s is recommended (Fichte et al.

2000).

Chemical-free operation: Occasionally, there are reports of attempts to introduce

physical procedures for cooling water treatment. Thus, for example, in laboratory

experiments electrical impulses were successfully used to control salt-water polyps

(Hydrozoa arge) (Abou-Ghazala and Schoenbach 2000). Brief treatments with heat

or microwaves are supposed to control the biology in cooling systems (Anonymous

2001c). However, corresponding descriptions of practical experience here are not

available.

7.3 Process operation

In the course of our visits to the plants, various employees reported to us that the

amounts of chemicals to be added could be substantially reduced by regular

cleaning of the cooling pans and sprinkling structures. It is known that biofilms are

substantially more resistant to biocides than planktonic microorganisms. Moreover,

killing the organisms present does not remove the biofilm itself, so that the possibility

of a rapid recolonization and a continuation of the biofouling exists. Therefore,

attempts are made to remove the dead biofilm with dispersants, but often this only

partially succeeds (MacDonald et al. 2000). Insofar as the formation of biofilms with

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acceptable thicknesses cannot be prevented in advance, mechanical cleaning

methods are more effective. The VGB-cooling water guideline recommends the

continuous cleaning of the cooling pipes with beads or brushes. A number of bead-

carriers (sponge, granulate or polishing beads), coated with various materials

(pumice, plastic, natural rubber, corundum), are available on the market (Fichte et al.

2000).

There are also self-cleaning heat-exchangers available on the market in which

particles 1 to 3 mm in diameter are carried with the cooling water current and before

emission are reclaimed, e.g., via hydrocyclones (internal circulation, e.g. Klarex

Technology B.V., the Netherlands). Fully automatic systems for the cleaning of

condensers with compressed air have been developed. Larger surfaces are cleaned

with high-pressure water streams (50-200 bar), and for pipes automatic cleaning

systems are offered (brush-cleaning, sponge-bead-cleaning, swab-cleaning) (Paikert

1986).

Closing the blow-down after a batch treatment with biocides until their demonstrated

inactivation is an important instrument for protecting the sewage plant and the final

tanks. Another advantage of closing the outflow is that the contact time of the

biocides with the cooling water is increased and at the same time also their

effectiveness.

Carefully measuring the added cooling water chemicals to match the amount actually

needed can potentially bring a great savings. For example, quick methods were

developed for surveillance (monitoring) of the microbiological activity of cooling water

samples. One possible measureable endpoint for this is the content of adenosine

triphosphate (ATP) in the cooling water, which can be measured with luciferin as

released light (Marczewski et al. 1995, Hild 2000). In addition, fluorescent bacteria

toxicity is also used to monitor the effect of a present biocide. At GL-values >2 there

was a distinct reduction of the total number of colonies (Schaaf no year given).

Several companies offer measuring instruments for the determination of the

fluorescent bacteria toxicity (e.g., Dr. Lange Lumismini, Merck ToxAlert®, FH-

Furtwangen, BetzDearborn BioscanTM). However, based on previous experience,

these techniques are hardly ever applied in practice. Instead, a continuous

conductance measurement in the outflow of open circulation cooling plants is state of

the art in order to permit adjustment of the blow-down and with it the concentration

93

factor. Moreover, the dosing of the addition of chemicals can be guided by online

measurements. Phosphonic acids can also measured with online phosphate

analyzers (Elfering and Schmitz 1995).

7.4 Evaluation and selection of cooling water chemicals

There are essentially 4 approaches with which the hazard potential from cooling

water chemicals can be evaluated and applied as an instrument for the selection of

an active ingredient. In the reference document of the European Commission 3 of

these are presented in detail, so here only the basic outlines and possible

associations will be mentioned (Anonymous 2000).

7.4.1 Water risk classes, the VCI-concept for open cooling systems

The concept of the Verband der Chemischen Industrie was not developed for the

evaluation of cooling water chemicals, rather for taking measures during possible

leakages with water-hazardous substances. It proposes measures for monitoring and

adjusting fresh-water and open circulation operation, as well as alternatives to once-

through cooling, depending on the water-risk presented by the substances which

could be introduced by leakages of cooling water. The basis is a derivation of water-

hazard classes in conformance with European laws on hazardous substances from

the Risk- or “Gefahren-“Phrases (R-Phrases), which are presented in the

“Verwaltungsvorschrift wassergefährdender Stoffe" from 17 May 1999 (VwVwS) and

expounded by the Commission for the evaluation of water-endangering substances

(Kommission zur Bewertung watergefährdender Stoffe 1999). Here each R-Phrase

relevant for the protectable natural resource aquatic environment in combination with

the protectable natural resources human health and soil protection is assigned a

certain point value. The points for all the R-Phrases given to a particular substance

are added up to give a total number of points. Here data gaps on ecotoxicity,

degradability/bioaccumulation or acute oral/dermal mammalian toxicity are

compensated with additional default assigned values. With this total point value the

water-risk class of a substance in accordance with the VwVwS can be determined.

For prepared mixtures a water-risk class for the product is then generally determined

from the consideration-limits (the sum of proportional values for each of the WGK-

substances present, scaled on a percentage basis corresponding to its proportion in

the mixture) (Annex 4 VwVwS).

94

The VCI-concept links the total point value with the necessary cooling water safety

measures (Anonymous 2001b, Anonymous 2000, Piegsa 2001b). For substances

with a total point value > 5 (corresponding to WGK 2) depending on the

contingencies of each individual case, measures for the monitoring of once-through

cooling systems should be immediately undertaken and where appropriate the

cooling water should be directed into wastewater treatment facilities (usually

municipal sewage plants). However, the concept is only valid for direct dischargers.

Although the VCI-concept is not intended for the selection of cooling water chemicals

based on environmental aspects, the emission based approach for considering

water-risk classes could be a possible instrument for a comparative evaluation of

cooling water chemicals.

However, since the assignment of water-risk classes especially considers the

accident situation, the concept requires further development, e.g., in order to

relativize the high ecotoxicity of a chemical to a known rapid elimination in cooling

systems or sewage plants. In addition, for mixtures the consideration-limits (the sum

of proportional values for each of the WGK-substances present based on the

composition of the mixture) must be incorporated for the determination of WGK-

classes.

7.4.2 "Benchmarking"-concept

Benchmarking is a continuous process, in which a defining evaluation parameter is

compared with a reference situation (benchmark). Here data from comparable

situations are collected and compared with the target data of the reference situation

in the form of a relative "ranking" so that every participant can recognize "where he

stands", i.e., how far he is from the benchmark. In the reference-document of the EU

"Industrial cooling systems" this instrument was applied to the procedure of risk

evaluation for chemicals usually followed in the EU, as described in the Technical

Guidance Document (Commission 1996). This is based on the ratio of the

environmental concentration to be expected (predicted environmental concentration,

PEC) to the threshold-concentration, below which no effects would be expected

(predicted no effect concentration, PNEC). Here the PEC is calculated from emission

scenarios from the discharged amounts, the elimination factors and the dilution; the

PNEC is generally determined from laboratory ecotoxicity tests assuming certain

95

safety factors (up to a factor of 1000). In special cases the PNEC is also extended

using model ecosystems as well as field studies. In Annex V of the Water-

Framework-Directive of the EU (2000/60/EG) the procedure for obtaining the PNEC

is to be introduced in order to define the chemical quality standards to be established

by the member states. Here data on persistence and bioaccumulation are to be

considered (environmental quality standards, EQS). The "benchmarking"-concept

only envisages a relative evaluation of the cooling water chemicals, corresponding to

their ratios for PEC/PNEC or PEC/EQS. A conceivable further development of the

concept for the evaluation of substance mixtures exists in the introduction of an

Index-Number (=sum of the PEC/PNEC-ratios of the individual components).

The advantages of this immission-based procedure are that substance-inherent

properties of the chemicals can be used and the local conditions taken into account.

However, the focus is on the aquatic ecotoxicity. Indirect negative effects on humans

are not considered, insofar as there are no official EQS derived from the chemical

evaluations of the EU available. A further disadvantage is that the PEC depends on

the flow of the receiving river, so that there is a tendency to view dilution as solving

the problem ("dilution as solution"), while the real goal of limiting the load recedes

from view. In addition, the additional burden on the receiving river through other

emissions upstream can only be taken into account with great effort. While the

elimination in sewage plants is fully considered, also for adsorptively bound

chemicals, other exposure paths, e.g., through an agricultural utilization of the

activated-sludge ase not considered. The "benchmarking"-concept thus remains only

a promising approach, which still should be further developed.

7.4.3 Plant specific evaluation of cooling water chemicals

The benchmarking-concept was further developed by Baltus et al., among others,

especially to provide an instrument with which the use and selection of cooling water

biocides could be optimized (Baltus and Berbee 1996, van Donk and Jenner 1996,

Baltus et al. 1999). The basis for this is an extension of the benchmarking-concept to

actual cooling plants. While in the benchmark-process the inital pre-selection of the

biocide is made on the basis of relative "rankings", in the optimization phase all

available techniques for process operation, dosing, treatment and control are

considered. Thereafter the local effects on the environment are estimated and

96

measures for their reduction, for example through treatment of the added water,

dosing, closing the outflow or monitoring, are established.

7.4.4 TEGEWA-concept for indirect dischargers

The TEGEWA, together with the Gesamtverband der Deutschen Textilver-

edelungsindustrie developed an evaluation concept for the classification of textile

treatment aids. Based on their relevance for surface waters and in 1997 in this was

established as a self-commitment to be followed voluntarily (Noll and Reetz 1998).

The basis is a classification of textile additives in 3 classes from slightly to strongly

relevant for emitted water depending on their composition of bio-accumulable

substances (classification in R 53), their toxicity for surface waters (LC50 Daphnia),

their ready bio-degradability (OECD 301 tests) and their eliminability in sewage

plants (Zahn-Wellens test). Certain problem substances (cancerogenic, genotoxic

and reproduction toxic substances) a priori lead to classification in Class 3, while on

the other hand textile chemicals, which are hazardous to water organisms (R 52) and

are not readily degradable (R 53) are still assigned to Class 1 if substantial

elimination in sewage plants occurs. In its structure the TEGEWA-concept resembles

a classification of water-endangering substances, but it takes into account the

elimination in municipal sewage plants.

7.4.5 Outlook

From the viewpoint of the researcher a combination of an emission-based approach

based on the classification in water-endangering classes or the TEGEWA-concept

with the immission-based "benchmarking"-approach would be a possible instrument

for making a pre-selection of suitable cooling water chemicals. The assignment to

water-endangering classes also includes health aspects, along with aquatic

ecotoxicity. Moreover, any lacking data are compensated by default values following

the precautionary principle. However, in order to place priority attention on the

emitted loads, both the used amounts as well as the elimination in the cooling

system and (for indirect dischargers) in the municipal sewage plant must be more

strongly considered. Thus the TEGEWA-concept tends more to include the

elimination in the wastewater treatment facility. The total load should, however, also

be considered, so that, for example, effective biocides with higher aquatic toxicity but

a lower use concentration are not a priori rated as worse than less effective biocides

97

with higher loads. The total load is included in the evaluation in the "benchmarking"-

concept, but is also relativized through the dilution in the final settling pond. However,

the goal should be the minimizing principle, in introducing hazardous substances

while at the same time maintaining the goal of environmental quality. In order to

direct the idea of "benchmarking" in this direction, a relative ranking of cooling water

chemicals in the direction of toxicity loads (=effect concentrations x load) should be

possible.

In general, the emission-based wastewater-evaluation is regarded as the stricter,

precautionary principle-bound approach, while the immission-based approach first of

all requires the definition of quality criteria. Of course, there have been attempts to

link the two strategies. Also in the EU-Water Framework guideline the "combined

approach" has elements of emission- (emission controls for prioritary substances)

and immission-based criteria (environmental quality standards), (cf., also Reemtsma

and Klinkow 2001).

More advanced concepts for the evaluation of wastewater inputs on the basis of

ecotoxicity, bioaccumulation, degradability and genotoxicity have been developed by

Reemtsma and Klinkow, among others, and are currently being discussed at the

OSPAR (Reemtsma and Klinkow 2001, Commission 2000).

In order to undertake a qualified evaluation of cooling water chemicals their identity

and properties must be known. In the Annex some essential data regarding

ecotoxicity, genotoxicity and biological degradability, which were obtained in

extensive substance-based searches, are listed together with the R-Phrases and the

physico-chemical properties. It should be emphasized that this data set is only

sufficient to permit an initial estimation of the environmental relevance of cooling

water chemicals to be made and is not sufficient for a complete evaluation in

accordance with chemical laws.

In any case, the optimization of the use of cooling water chemicals must be made

with a consideration of the local conditions and the available techniques for process

management, dosing, treatment and monitoring. The various evaluation strategies

described above can only reflect general basic principles. In order to achieve the

needed linkage of the emission- and immission-based approaches, these strategies

must be further developed.

98

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9 Ackknowledgements

The successful completion of the F+E-Project was only possible through thecooperation and assistance of numerous persons, whom we would like to thank heremost sincerely:

• Mr. Mehlhorn, Fachbereichsleiter Abteilung II 3.2 "Stoffhaushalt Gewässer",Environmentbundesamt and Leiter des IKSR-Expertenkreises "Antifouling andKühlwaterkreisläufe" for outstanding support, advice and coordination of theproject,

• Mr. Seelisch, FG II 3.1 "Übergreifende Angelegenheiten Gewässergüte andWaterwirtschaft", Environmentbundesamt for research in internal data banks,

• The otehr employees of Hydrotox GmbH for conscientious performance of thetests, especially Mrs. Stiene (Daphnia-, algae-tests), Mrs. Welsch (umu test,Ames test) as well as Dr. Schnurstein (coordination in the area of mutagenicity),

• Mrs. Knieß for the secretarial work and for correcting the manuscript,

• Mr. Piegsa, Staatliches Environmentamt Herten and Obmann des Bund-/Länder-Gesprächskreises "Kühlwater",

• The representatives of the agencies of the Länder and Bezirke for their supportwith the questionnaire on the use of cooling water chemicals in the operatingfacilities,

• Dr. Ungeheuer, TEGEWA, for the organisation of the Workshop,

• The employees of the facilities considered for providing information and samplesand for filling out the questionnaire,

• The representatives of the companies manufacturing conditioners for providingproduct information, safety data sheets and additional, in part unpublishedinformation, especially Dr. Klautke, BetzDearborn GmbH; Dr. Hater, HenkelSurface Technologies GmbH; Dr. Kleinstück, Bayer AG; Dr. Weindel, BK-GiuliniChemie GmbH & Co OHG; Dr. Olkis, Fa. ONDEO Nalco Deutschland GmbH; Dr.Heinl, Drew Ameroid Deutschland GmbH; and Dr. Schoester, Thor GmbH.

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