Environmental Aspects of Nonionic Surfactants

L. Kravetz, J. P. Salanitro, P. B. Dorn K. F. Guin, and K. A. Gerchatio

Shell Development Company Westhollow Research Center

P.O. Box 1380 Houston, Texas 77251

Presented at the Am erica n Associa tio n

of Textile CC,emistsand Colorists

Atlanta, Georgia October37, 7986

. International Conference & Exhibition

0101 0632

8

' . Abstract #I

Environmental Aspects of Nonionic Surfactants

The biodegradation and resultant aquatic toxicity of several classes

of nonionic surfactants were investigated at concentration levels typical of

those found in textile biotreater influents. A linear primary alcohol eth-

oxylate (AE), a branched nonylphenol ethoxylate (NPE) and a tertiary thiol ethoxylate (TTE) were gradually adapted to microbial inocula in bench-scale biotreaters . These biotreater units were monitored for primary and ultimate

biodegradation, loss of foaming capabilities, BOD and COD removal, nitrifica- tion, biosolids growth, sludge settleability and aquatic toxicity of treated

effluents.

The results of these studies showed the AE was fully biodegraded as

measured by such primary biodegradation criteria as cobalt thiocyanate com-

plexing and foaming capacities. The NPE and TTE were only partially biode- graded by these criteria and the biotreated effluents contained significant

quantities of these surfactants. Plant parameters such as sludge settling,

presence of filamentous organisms and nitrification were affected adversely by

NPE and TTE at the higher concentration levels tested. These parameters were

not affected by AE at any of the concentrations tested. Effluent aquatic

toxicity was completely lost by the AE unit. Effluents from the NPE unit were the most toxic while effluents from the TTE unit showed toxicity levels

intermediate to those of the AE and NPE units. Upon chlorination, effluent

from the TTE unit completely lost its aquatic toxicity while effluent from the NPE unit retained its high toxicity level.

In a separate study comparing the ultimate biodegradation of AE, NPE

and TTE at 50 mg/liter, the AE was biodegraded to 70% of the theoretical

carbon dioxide yield, while the NPE and TTE yielded only 25-30% carbon dioxide under the same conditions.

Introduction

1

Environmental ASDeCtS of Nonionic Surfactants mm The biodegradation of nonionic surfactants has been studied exten-

sively in recent years.'-' For the most part, these studies have focused on

biodegradation under domestic waste treatment conditions in which influent

levels of nonionic surfactants ranged from 5-20 mg/l. The results of these studies have shown that the absence of alkyl chain branching and aromaticity

in the hydrophobe favored increased biodegradation kinetics as well as more

complete mineralization of nonionic to its ultimate biodegradation products,

CO, and water. These findings were observed in laboratory scale biotreaters

and in field trials in which surfactant levels were monitored at the influent

and effluent stages of a waste treatment plant receiving essentially domestic

waste .

However, little information is available on the biotreatability o f

nonionic surfactants under industrial use conditions where influent loadings

(ca 100 mg/l) to a biotreater frequently are 1-2 orders of magnitude greater than found in domestic waste treatment (ca 5 mg/l). Industrial wastes which

ultimately enter receiving waters are now being scrutinized intensely by state

regulatory agencies as a result of the potential for these wastes to impart

foam, toxicity to aquatic life and color to lakes, rivers and streams. In

particular, textile mill wastes, due to their high process chemical loadings,

are being monitored for aquatic toxicity, foam and color prior to entering

receiving waters or municipal treatment plants where they can increase organic

loadings and cause plant upsets. Surfactants used in textile processing cause

foaming and fish kills at relatively low levels. In order to be rendered

harmless, they must biodegrade to metabolites in which the surface active

properties of the intact surfactant are lost. In addition, these metabolites

must be considerably less toxic than their intact surfactant precursors.

This paper reports on the results of a treatability study of three

types of nonionic surfactants,, an alcohol ethoxylate (AE), a nonylphenol

ethoxylate (NPE) and a tertiary thiol ethoxylate (TTE) at concentration levels typical of those found in textile biotreater influents. The AE and NPE

u y .

. . , , * 2

.. represent two classes of nonionics used most extensively by the textile

industry. TTE is currently used at a much lower volume, mostly as a wool scouring agent. In the first phase of this study, bench-scale activated

sludge units were used and primary biodegradation (loss of properties of

intact surfactant) was determined. In addition, important operating para- meters, such as BOD, COD, nitrification and sludge floc characteristics were

followed. In the second phase, unchlorinated and chlorinated biotreated

effluents from the first phase were subjected to aquatic toxicity tests.

Chlorination of effluents is widely practiced at municipal waste treatment

plants in order to control human pathogens. In the third and final phase, a separate test for the ultimate biodegradation (conversion to GO, and water) of

the nonionic surfactants was performed.

Materials and Methods

Bench-Scale Biotreaters

Five continuous bench-scale (one control and four test surfactant

units) activated sludge biotreaters were seeded primarily with mixed liquor

suspended solids (MLSS) obtained from a small domestic sewage treatment plant

in Harris County, Houston, Texas. Eighty percent of the MLSS was from the domestic plant and 20% from the biotreater at the Shell Development Westhollow

Research Center Laboratories. The bench units consisted of a three liter

stirred, air-sparged aerator and a one liter clarifier (Figure 1). Feed

vessels and effluent receivers were maintained at refrigerated temperatures.

The operating conditions for the units are given in Table 1. The synthetic

sewage was similar to that described by Painter and Kings except that the peptone and beef extract components were doubled. This feed contained ap-

proximately 230-300 mg/l TOC, 150-200 mg/l BOD, 400 mg/l COD, 65-80 mg/l total

Kjeldahl nitrogen (TKN) , 1.5-3 .O mg/l NH3 and 20-30 mg/l PO4=.

Test Surfactants

Surfactant addition tp the biotreaters was accomplished by pumping

(Gilson Minipuls 2 peristaltic metering pump) concentrated solutions through

VITONO and TEFLON@ tubing at a constant flow rate (50 ml/day). Filter

3

sterilized solutions (0 .045 pm Millipore) were kept sealed in graduated

cylinders. Table 2 lists the structures of the surfactants tested. Each

bench biotreater was adapted to increasing doses of surfactant from 0 to 100 mg/l over a period of five months. Table 3 gives the concentrations o f

surfactants during the adaptation phases. The control biotreater was not fed

with surfactant.

Analvsis of Biotreatment Parameters

Influent and effluent samples from each activated sludge unit wer2

taken once or twice per week and analyzed for total organic carbon ( T O C ) ,

chemical oxygen demand (COD), biochemical oxygen demand (BOD - 5 days), total

nitrogen (TN) , ammonia (NH,+), phosphate (PO,=), nitrate (NO,-), nitrite

(NO,-), and CTAS (intact ethoxylate surfactant). TOC was determined using a

Beckman Model 915 TOC analyzer and NH, , PO, , NO, and NO, were estimated by

DIONFXB liquid chromatography. BOD and COD were analyzed by Edna Wood

Laboratories, Houston, according to methods outlined in Standard Methods.g

Total nitrogen (organic nitrogen + NH, -N) was determined by a combustion

chemiluminescence detection method. The amount of intact surfactant in

effluents was analyzed by the CTAS (cobaltothyiocyanate active substances)

method.1° Effluent samples for CTAS were preserved in 1% formalin and kept refrigerated before analysis.

+ i

+

Aerator suspended solids were monitored for total suspended solids

(TSS) and volatile (organic) suspended solids (VSS) as given in Standard

method^.^ Dissolved oxygen levels in biotreaters were determined with an

Orbisphere oxygen electrode. Settleability of biosolids (sludge volume index,

SVI) in activated sludge units was estimated by determining the settled volume of one liter of suspended solids in a graduated cylinder for 30 minutes. SVI = Settled vol (ml)/TSS (g/l). Morphological observations of sludge flocs were

made with a phase contrast light microscope (Zeiss) and usually viewed at 160X

magnification under dark-field illumination.

Aauatic Toxicitv Tests on Unchlsrinated and Chlorinated Effluents

Effluents from the control and TTE units were sampled from days

239-247 of operation while those from the NPE and AE units were samples from days 256-264. Effluents were composited (ca 8 l/day) over 4 consecutive days

and filtered (0.45 pm Millipore) and maintained at 4°C prior to aquatic

toxicity testing. Free chlorine was determined with a CHEMETRICSe chlorine

test kit (Cl-5 0-5 ppm) and total organic halide (TOX) analyzed by EPA Method 9020. Residual Ammonia (NH,) in effluent was estimated using a CHEMETRICS

Ammonia test kit (AN-10, 0-10 ppm).

Composited effluents (ca 8 gal) contained 60-70 mg/l NH, and repre- sented a significant oxidation demand in the chlorination process. Prior to

chlorination, therefore, effluents were brought to room temperature, adjusted

to pH 10-10.5 with 5 N NaOH and flushed for 3-4 days with a sterile stream of air to remove NH, down to a few mg/l. Samples were then adjusted back to pH

7.0 with 5 N HC1 and sufficient sodium hypochlorite (different batches ana-

lyzed as 1.5 or 3.75% free chlorine, AR Mallinckrodt) added with stirring to give 1-3 mg/l free chlorine. Chlorinated effluent was kept covered at room

temperature for 30 minutes and monitored for chlorine. Dechlorination was

accomplished by addition of NaHSO, (1000 mg/l stock solution) at doses of ca

1.5 x concentration of residual chlorine. Contact time was 5-10 minutes with stirring. (Dechlorination with NaHSO, is a common practice in the reduction

of chlorine species to chloride).

Approximately 7-7.5 gallons of effluent were sent to TRAC labora-

tories of Denton, Texas for static acute aquatic toxicity testing using

PimeDhales oromelas (fathead minnow) and DaDhnia Dulex (water flea) bioassays.

C02 Evolution

The apparatus used in the CO, evolution assay is given in Figure 2 and is similar to that described by Sturm'l except that biodegradation reac-

tions were performed in 500 ml v o l w e s in one liter glass bottles fitted with

rubber stoppers containing inlet and outlet connections. Reaction vessels

contained (1) 500 ml of mineral salts medium [containing (mg/l) KH2P0,(17),

K2HOP4(43.5), Na2HP0,*2H,0(66.8), MgSO+*7H20(22.5), CaC1,(27.5), NH,C1(3.4),

(NH4)2S04(4C)-, + FeC1,*6H20(1)], (2) 59 mg/l surfactant or sodium benzoate

5 #, (positive control, readily degradable substrate) ( 3 ) composited mixed liquor

suspended solids from four activated sludge units treating nonionic su r fac -

tants. The mineral salts medium was prepared with C0,-free distilled water.

Dow Corning antifoam emulsion (DB 31, 30% silicone defoamer) was added at 10 mg/l to inhibit surfactant foaming in the reaction vessels. Previous experi-

ments with DB 31 alone in the Sturm test showed that the antifoam material was not biodegradable and did not contribute to BaCO, formation in the absorbers.

Experiments were initiated by sweeping C0,-free air through the reaction units

and collecting biologically formed CO, in the Ba(OH), absorbers as BaCO,. It

was determined that at least 90% of the dissolved CO, (50 mg/l as NaHCO,)

could be recovered in the absorber traps upon acidification of the reaction

vessels. Reactions proceeded at room temperature (23-25°C) for 14 days. At

1, 4 and 7 days, the CO, absorber proximal to the reaction unit was removed

and each subsequent absorber advanced a position; a fresh Ba(OH), absorber was

placed in the third position. After 14 days incubation, dissolved oxygen

measurements were made of the reaction solution and samples taken for viable

microbial counts. Five ml of concentrated H2S0, were added to the reaction unit (pH12) and trapping of residual GO, was continued for 60 minutes. All traps were analyzed for residual Ba(OH), by titration with 0.100N HC1 to the

phenolphthalein endpoint.

The theoretical yield of CO, from complete biodegradation (miner-

alization) of the test material is given by the following equation:

No. of carbons in compound x Molec. wt of CO, mg CO,/mg compound - Molec. wt of compound

Table 4 gives the calculated values for the theoretical amount of CO, that

could be formed from each test surfactant and the positive control substrate,

benzoate. The percent of the theoretical CO, formed during the test was

determined by the formula:

% theoretical - mg CO, formed x 100 C02 yield Theoretical C 0 2

6

Results and Discussion

Characteristics of Biotreater Influent Feed

Early in the adaptation phase of the activated sludge inoculum to

synthetic sewage it was observed that biosolids yield was less than expected

(as analyzed by TOC, COD and BOD) from previous studies of Painter and King.8

The feed components, peptone and yeast extract, were doubled. This increase

in feed concentrations of BOD, COD, TOC and TN was reflected in the period of run days 30 to 40 . Influent feed composition as given in Table 5 was main-

tained throughout this study. However, differences in the daily preparation

of synthetic sewage for the units resulted in variations in feed BOD (200-300

mg/l), COD ( 3 5 0 - 4 5 0 mg/l), TOC (150-200 mg/l), TN ( 5 5 - 7 5 mg/l) and NH,+ (2-10

mg/l) *

Biotreatment Efficiency and Effluent Characteristics

BOD. COD and TOC Removal

During the detergent adaptation period effluent BOD (a measure of

undegraded feed and/or surfactant carbon escaping activated sludge treatment)

remained <10 mg/l in the control and AE units. This indicates that nearly all

( > 9 5 % ) of the biodegradable organics in the synthetic feed were removed.

Breakthrough of readily degradable feed constituents appeared in the effluent

(BOD 2 0 - 5 0 mg/l) of the TTE unit upon step-increase to 80 and 100 mg/l surfac- tant. This indicates that high TTE levels or its metabolites are apparently toxic to activated sludge microbes in the metabolism and breakdown of ordinary

feed components. A smaller increase in BOD (10-20 mg/l) was noted when the

surfactant level in the NPE biotreater was increased to 80 and 100 mg/l.

Effluent COD also increased (20-140 mg/l above control) during this time in

the TTE and NPE units. Lower COD concentrations (20-80 mg/l above control)

were observed in effluent from the AE unit. Increases in effluent organic

carbon (TOC) above the control were noted in all units during adaptation to

higher surfactant levels. The.elevations in TOC and COD values (as observed with BOD) in the TTE and NPE units is also associated with a breakthrough of feed organic material and undegraded surfactant.

e .

7

S u r f a c t a n t D e n a d a t i o n and Removal

Est imat ion of t he ex ten t o f s u r f a c t a n t degradat ion (primary) i n the

b i o t r e a t e r s w a s determined by CTAS ana lys i s of e f f l u e n t s . Each s u r f a c t a n t

u n i t w a s f ed i n c r e a s i n g concentrat ions o f de t e rgen t ( 1 0 , 20 , 4 0 , 80 and 100

mg/l) Over a 150 day adap ta t ion per iod. During the i n i t i a l accl imat ion phases

a l l u n i t s degraded t h e 10, 20 and 40 mg/l i n f l u e n t s u r f a c t a n t doses; e f f l u e n t

CTAS values were similar t o the con t ro l b i o t r e a t e r r ece iv ing no s u r f a c t a n t

(Figure 3 ) . However, s i g n i f i c a n t breakthrough of i n t a c t s u r f a c t a n t was

observed i n t h e TTE and NPE u n i t s when i n f l u e n t de t e rgen t concentrat ions were

increased t o 80 and 100 mg/l. High e f f l u e n t s u r f a c t a n t concentrat ions (30-65

mg/l) were maintained i n t h e TTE u n i t during t h e 20 days following feeding the

100 mg/l l e v e l . Over the next 80 days (run day 230) , biodegradation of TTE

f l u c t u a t e d as observed by the high (40 -65 mg/l) and low (10-20 mg/l) e f f l u e n t

CTAS values . S i g n i f i c a n t concentrat ions of CTAS were a l s o de t ec t ed i n t h e NPE

e f f l u e n t (up t o 4 0 - 5 5 mg/l) during t h e 80 day pe r iod ( run day 230) i n which

NPE was f ed cont inuously a t 100 mg/l. I n t a c t s u r f a c t a n t concentrat ions were

usua l ly 4-10 mg/l and never approached C1 mg/l during t h i s time. I n c o n t r a s t ,

t he a c t i v a t e d s ludge u n i t t r e a t i n g the AE r e a d i l y adapted t o a l l concentra-

t i o n s of i n f l u e n t s u r f a c t a n t (10-100 mg/l); e f f l u e n t CTAS va lues were s i m i l a r

(4 mg/l) t o t h e c o n t r o l .

Foam h e i g h t tes ts on b i o t r e a t e d e f f l u e n t s (Fivure 4 ) a l s o confirmed

t h a t s i g n i f i c a n t amounts of undegraded ethoxylate ( e f f l u e n t foam h e i g h t , 3 - 2 3

m l a f t e r 3 minutes) were p r e s e n t i n t h e TTE and NPE u n i t s during adaptat ion t o

100 mg/l s u r f a c t a n t . Smaller amounts of foam (2-6 m l af ter 3 minutes) were

noted during acc l ima t ion of a l l u n i t s t o 10-80 mg/l de t e rgen t . The AE b i o -

t r e a t e r c o n s i s t e n t l y produced e f f l u e n t s with low l e v e l s of foam ( 0 - 4 m l )

dur ing adap ta t ion t o a l l levels of t he e thoxy la t e .

These d a t a i n d i c a t e t h a t adap ta t ion and u l t i m a t e degradation by

activated sludge of t h e TTE and NPE e thoxy la t e s are incomplete and f l u c t u a t e

widely from p e r i o d s o f low removal (high e f f l u e n t CTAS, 140 mg/l) t o i n t e r -

mediate removal ( e f f l u e n t CTAS 120 mg/l). The AE degraded r ap id ly with l i t t l e

o r no r e s i d u a l s u r f a c t a n t d e t e c t e d i n the e f f l u e n t . 'p4- 1

Nitrification

8

Nitrification is a microbial process in which ammonia (NH,+ is

converted to nitrate (NO,-). Although nitrifying bacteria present in acti-

vated sludge are some of the more sensitive species to toxic compounds present

in feeds, this conversion is important for removing potential effluent fish

toxicity due to high feed NH,+ concentrations. In these experiments most of the NH,+ for nitrification is derived from the degradation (hydrolysis,

deamination) of organic nitrogen material present in the synthetic sewage feed

(e.g., urea, peptone, yeast extract). Effluent from the control unit consist-

ently produced low levels of MI,+ ( 5 2 0 mg/l) and high NO,- ( 1 5 0 - 2 8 0 mg/l)

indicating that a significant portion (>go%) of the feed nitrogen had been

mineralized. It was calculated that if all the feed nitrogen (total nitrogen

ca 5 5 - 8 0 mg/l) was nitrified about 2 4 0 - 2 8 0 mg/l NO,- would be formed. This

estimate agrees well with the amount of NO,- analyzed in the control effluent.

The AE unit also converted feed nitrogen to NO,- similar to the control during adaptation to high detergent levels. Although effluent NH,+ reached 2 0 - 3 5

mg/l during acclimation to 10, 20 and 40 mg/l AE, nitrification continued and

increased to high levels ( 2 2 0 - 2 5 0 mg/l effluent NO,-) even after step in-

creases of 80 and 100 mg/l detergent. The TTE and NPE units nitrified during the 20 and 40 mg/l surfactant adaptation phases. However, higher detergent

levels (80 and 100 mg/l) were apparently toxic to nitrifying organisms and

these biotreaters lost their nitrification ability producing effluents with

high NH,+ (60-80 mg/l) and little or no detectable NO,-. The TTE and NPE units never regained nitrification even after 6 0 - 8 0 days feeding of 100 mg/l

surfactant. These data indicate that nitrifying microbes present in activated

sludges are not affected by high concentrations ( 8 0 - 1 0 0 mg/l) of AE; however,

the TTE and NPE ethoxylates and/or their metabolites are toxic or inhibit the growth and activity of these bacteria at similar high doses.

Aerator and Effluent Suspended Solids

At waste rates of 1 5 0 - 2 0 0 ml/day from the aerators, total suspended

solids (TSS) in the biotreaters varied during the adaptation phases from

2 0 0 0 - 4 0 0 0 mg/l. The decrease and subsequent increase in TSS during the first .a I

. . 9

40 days of opera t ion represents b ioso l id s growth fol lowing the inc rease of

feed organics (prev ious ly noted) a t about day 25. V o l a t i l e suspended s o l i d s

(VSS) was usua l ly 85-90% o f the TSS f o r a l l u n i t s i nd ica t ing t h a t most of the

measured suspended s o l i d s (SS) was biomass (da ta not shown). Aerator SS i n

the de te rgent u n i t s decreased s i g n i f i c a n t l y from the c o n t r o l during acclima-

t i o n a t 10 mg/l (TTE u n i t ) and 40 and 80 mg/l (NPE and AE u n i t s ) . This

decrease i n SS i n d i c a t e s t h a t b ioso l id s growth was temporar i ly i n h i b i t e d and

co inc ides with the s i g n i f i c a n t breakthrough of feed BOD and TOC observed i n

the u n i t s . Aerator SS w a s g i f f i c u l t t o maintain over long per iods when the

TTE and NPE de te rgen t s were f ed a t 100 mg/l r a t e s . (The usual waste r a t e o f

150-200 ml/day had t o be decreased t o 1200 ml/week t o maintain a t l e a s t 2000

mg/l T S S . )

Ef f luent SS increased markedly (300-500 mg/l) during accl imat ion of

t h e TTE and NPE (20-40 mg/l) u n i t s . However, i n t e r m i t t e n t e l eva t ions i n

e f f l u e n t s o l i d s (50-100 mg/l) a l s o occurred during the 150 day adapta t ion

per iod . The c o n t r o l and AE e f f l u e n t s u sua l ly had 1200 mg/l S S . The increase

i n e f f l u e n t SS i n the TTE and NPE u n i t s i n d i c a t e s t h a t these s u r f a c t a n t s

a f f e c t e d aggregat ion and growth o f t he biosludge f l o c s . Deflocculat ion

occurred and caused increases i n d ispersed b a c t e r i a and p in-poin t f l o c s

( e f f l u e n t TSS) as w e l l as sludge bulking i n the c l a r i f i e r . The bulking and

d ispersed b a c t e r i a may be due t o a sur face e f f e c t by the s u r f a c t a n t on d i s -

rup t ing b i o f l o c formation and/or growth i n h i b i t i o n ( t o x i c i t y ) of f loc-forming

and f i lamentous b a c t e r i a . The imbalance of growth of f loc-formers and f i l a -

mentous organisms i n a c t i v a t e d sludges has been e s t ab l i shed as a model t o

account f o r t h e formation of bulking s ludges , d i spersed b a c t e r i a and p in-poin t

f l o c s . 12

Sludge bulking as measured by s ludge volume index ( S V I ) on b ioso l id s

f r o m t h e a e r a t o r s showed h igh va lues f o r t he TTE (SVI-200) u n i t s . However, SS

f r o m the c o n t r o l , AE and NPE u n i t s showed good s e t t l i n g c h a r a c t e r i s t i c s with

SVI’s 550. Bulking, poor ly s e t t l i n g s ludges usua l ly have S V I 2150 i n s tud ie s

f r o m municipal b i o t r e a t e r s . 1 3 , 1 4

10

Macroscopic and Microscopic Observations of Suspended Solids from

Biotreaters

The TTE and NPE sludges changed from a brown color to a white or cream-colored solids compared to the control and AE units which remained brown

throughout the study. The change in color occurred during adaptation to the

20 and 40 mg/l surfactants. In addition, the TTE and NPE units produced sludges with large visible aggregated flocs especially during acclimation to

80 and 100 mg/l detergent. The control and AE units produced smaller flocs.

In dark-field photographs of bioflocs during acclimation to 10 and 80 mg/l

surfactant, filamentous bacteria were clearly visible in all flocs from units

receiving >10 mg/l; many higher forms such as ciliates, flagellates, and

rotifers were observed in the control and AE units. The AE biosludge also

formed compact, dense and good settling flocs. Fewer protozoa and filamentous

organisms were evident in the TTE and NPE units during the period in which 10 mg/l surfactant was fed. The appearance of the white or cream-colored bio- solids also coincided with the loss of filamentous bacteria (e.g., Nocardia) in these units. Substantial deflocculation (broken flocs) and the formation

of small pin-point flocs and dispersed bacteria were evident when the TTE and NPE surfactants were fed at 80 mg/l. Filamentous bacteria and protozoa

(ciliates) with compact dense flocs were present in the control and AE units

while little or no filaments or higher organisms were observed in the TTE and NPE units. The NPE and TTE biosolids contained a significant fraction of dispersed bacteria and small flocs. Similar types of biosludge floc mor-

phology were noted when units were treating 100 mg/l detergent.

These microscopic results confirm observations on the formation of

substantial effluent SS, bulking sludges and dispersed bacteria in the TTE and NPE units when activated sludges are adapted to high surfactant levels.

Furthermore, these data indicate that the formation of poorly formed bioflocs

and disaggregated biosludge by the treatment of wastes containing high surfac-

tant levels (40-100 mgil) may adversely impact the activated sludge process in

biosolids handling and biodegradation efficiency.

11

- Aauatic Toxicitv of Unchlorinated and Chlorinated Effluents

Acute toxicity of neat surfactants and their corresponding bio-

treated effluents are shown in Table 6 for two aquatic species, Daphnia

Pulex and fathead minnow. As shown, all surfactants studied showed fairly

high toxicities in their unbiodegraded form. Toxicity was greatest for AE and

least for TTE. However, after biotreatment, AE had lost all of its toxicity

while the NPE and TTE were still toxic. These data highlight the importance

of rapid biodegradation of surfactants as a most important criterion in

reduction of aquatic toxicity. Biodegradability should be a more important

criterion than aquatic toxicity of neat surfactants.

Table 7 lists aquatic toxicity of chlorinated effluents (following dechlorination) for those surfactants showing effluent toxicity (NPE and TTE). It should be noted that TTE effluent lost all of its toxicity and foaming capacity following chlorination while the NPE effluent remained toxic and

foaming. This loss of TTE effluent toxicity following chlorination is be-

lieved due to formation of sulfone which has considerably less surface active

characteristics compared to TTE itself.

RS(CH,CH,O)nH c1, H2O

Toxic- & Foaming Non-Toxic, Non-Foaming

Chlorination prior to or following biotreatment appears to be an

attractive process for removal of undesirable surface active properties of

surfactants like TTE.

Ultimate Biodegradation Potential

Comparison of nonionic surfactant biodegradability in the CO,

evolution test is given in Fiaure 5 . Benzoate (50 mg/l), the readily bio-

degradable control, was transformed rap'idly to CO, in the first few days and w .

1 2

reached a maximum degradation rate at 7 days of 8 5 - 9 5 % of the theoretical

yield. These data are consistent with rates of mineralization of benzoate in

sewage reported by Rubin, et. a1.I' in the range of 9 5 - 9 9 % for concentrations

of <60 p g / l . This very high degradation rate has been attributed to microbial

transformation of an organic compound mainly to CO, with little or no sub-

strate carbon being assimilated into cellular material. The OECD chemicals

study group has indicated that there is scientific evidence (collective

experience and literature findings) demonstrating that compounds are con-

sidered completely degraded if ca 60% of the organic carbon is converted to

C02; the remainder being incorporated into the cellular matrix. 1 6

NPE and TTE were mineralized similarly in the Sturm test; about 2 5 - 3 0 % of the surfactant carbon was degraded to CO, in 14 days. In contrast,

the AE was more extensively mineralized (70-75s of the theoretical CO, yield)

in the same incubation period. Sturm reported' that branched-chain alkyl-

phenol ethoxylates (similar to NPE) were degraded in acclimated sewage cul- tures from <30 to 40% while primary alcohol ethoxylates were at least 70%

mineralized in 28 days in the CO, evaluation test. Kravetz, et &17'18 also

reported that the ultimate degradation of AE was extensive ( 6 0 - 8 5 % ) at 1 5 mg/l

in 1 4 - 2 8 days in activated sludge shake flasks where CO, evolution was meas-

ured. In these same studies NPE-carbon was degraded to only 10% of the

theoretical C02 yield in 28 days.

Presence of Toxic Metabolites

Giger et. a1.19 recently reported the presence of 4-nonylphenol

(4-NP), a highly toxic chemical in aerobic and anaerobic sludges obtained from domestic waste treatment plants. These workers state that toxicity tests with

Daphnia mama show an effective concentration (EC,,) for 4-NP of 0.18 mg/l. The maximum permissable concentration in sludge for chemicals of similar

toxicity, such as cadmium (EC,, = 0.35 mg/l) is set at 0.03 g/kg. These

workers found 0.08-2.53 g/kg of 4-NF in sludge-far in excess of the maximum concentration permitted for chemicals having similar levels of toxicity. The

4-NP is not present normally as an impurity in commercial NPE, but arises as a bioresistant metabolite of NPE biotreatment.

'.'B- I

Using the separation and determination procedure of Ahel and

Giger,2O sludge samples from 10 mg/l NPE biotreatment described above were

subjected to anaerobic digestion. Stabilized aerobic and anaerobic sludges

were found to contain 0 . 1 3 g/kg and 0 .85 g/kg, respectively, of 4 - N P , well

within the range found by Giger and coworkers.

J*

Additional information on the identification of metabolites from

nonionic surfactant biodegradation will be published separately.

Conclusions

The biodegradation of three nonionic surfactants, AE, NPE and TTE, was studied under high surfactant loadings typical of those found in textile

mill waste. The AE was fully biodegradable losing its foaming and other

surfactant characteristics to yield non-toxic effluents. Under these condi-

tions, the NPE and TTE were degraded incompletely yielding foaming, toxic

effluents. Upon chlorination, effluents containing TTE completely lost their

foaming and acute toxicity characteristics. Foaming and acute toxicity of the NPE effluents remained high after chlorination. Chlorination, in the case of TTE, offers the useful option of facile removal of its surface active charac- teristics following its function as a processing surfactant.

Sludge characteristics were affected adversely by the NPE and TTE at

the higher concentrations, but were unaffected by AE at any of the concentra-

tions tested. It appears that the presence of surface active materials at appreciable levels in activated sludge changes surface properties of the

solids leading to difficulties in maintenance of good bioflocs.

14

. . Re f e renc e s

1. Patterson, S.C. C . C. Scott and K. B. E. Tucker, J. Am. Oil Chem. S o c . ,

- 4 7 , 37 ( 1 9 7 0 )

2 . Rudling, L. and P. Solyom, Water Research 8 , 115 ( 1 9 7 4 ) .

3. Kravetz, L. et al., Household and Personal Products Industry, l.9, 46 and

62 ( 1 9 8 2 ) .

4 . Kravetz, L. et al., Tenside Detergents, 2l, 1 ( 1 9 8 4 ) .

5 . Schoeberl, P., E. Kunkel and K. Espeter, Tenside Detergents, 18, 18

( 1 9 8 1 ) .

6 . Huddleston, R. L. and R. C. Allred, J. Am. Oil Chem. SOC., 41, 7 2 3

( 1 9 6 4 ) .

7 . Cook, K. A., J. of Appl. Microbiol., 44, 297 ( 1 9 7 8 ) .

8 . Painter, H. A . and E. F. King, Water Res., 12, 9 0 9 ( 1 9 7 8 ) .

9. Standard Methods for the Examination of Water and Wastewater (American

Public Health Association), Washington, D.C. ( 1 9 8 0 ) .

10. Boyer, S. L. et al., Env. Science and Technol., 11, 1 1 6 7 ( 1 9 7 7 )

11. Sturm, R. N., J. Am. O i l Chem. S O C . , 5 0 , 159 ( 1 9 7 3 ) .

1 2 . Lau, A . 0 . et al., J. Water Poll. Contr. Fed., 56, 5 2 ( 1 9 8 4 ) .

1 3 . Tomlinson, E. J . , Techn. Rep. TR35, Water Res. Centre, Stevenage, U.K. ( 1 9 7 6 ) .

14 . Wagner, F., Water Sci. Techn., 16, '1 ( 1 9 8 4 ) . BP

15

15. Rubin, H. E., et al., A p p l . Environ. Microbiol, 43, 1133 (1982).

16. OECD Report on Chemicals Testing Programme. Degradation/Accumulation

(Final Report). Berlin and Tokyo, December 1979 and 1980.

17, Kravetz, L. et al., Proceedings of the Am. Oil Chem. SOC. 70th Annual

Meeting, San Francisco (1979).

18. Kravetz, L. et al., Text Chem. and Colorist, l5, 57 (1983).

19. Giger, W., P. H. Brunner, C. Schaffner, Science, 225, 623 (1984).

20. Ahel, M. and W. Giger, Anal. Chem., 57, 1577 (1985).

Table 1. Biotreater Operating Conditions

Pa ra m et e r ~~

Synthetic Feed

Feed Influent Flow Rate

Surfactant Flow Rate

Sludge Residence Time (Waste Rate)

Aerator Mixed Li uor Suspended Soli a s (MLSS)

PH

0 i s o I ved Oxygen

Temperature

Mod if i ed 0 E C DIE E C Synthetic Sewage

8 literslday

50 ml/day

15-20 Days (1 60-200 ml/day)

2000-3000 mgA

6.5-7.5

2-4 mgfl

23-25°C

01 0 1 06-33

'6 .

Table 2. Surfactants Evaluated

Alcohol Ethoxylate (AE-7)a)

Surfactant I General Structure ~ ~ ~~-

RO(CH2CH20)7H R = Blend of 80% Linear C12,13,14,15

Nonylphenol Ethoxylate (N P E -9)M

Tertiary Thiol Ethoxylate (TTE 2-9)C)

RS(CHzCH20)gH R = BranchedCl2

a) NEODOL@ 25-7; Shell Chemical Company. 6) lgepal CO-630; GAF Corporation. c) Development surfactant; Shell Chemical Company; hydrophobe derived from

butylene trimer.

01010C37

Table 3. Surfactant Adaptation Phases

Run Day

0

25

64

87

100

127

Surfactant Concentration

Stock Solution,

%

0

0.16

0.32

0.64

1.28

1.60

Biotreater In flu en t,

mgll

0

10

20

40

80

100

*Added to bench unifs at 50 mlldayl8 liters in t7ucn t synthetic waste.

0101 0634

Table 4. Comparison of the Theoretical C 0 2 Yields from Biodegradation

Compound

Sodium Benzoate (Control Substance)

Tertia ryth i 01 Ethoxyl ate WE)

No n y I p h en o I Ethoxy I ate “E)

Alcohol Ethoxylate (AE)

Average Mol. Wt.

144

616

61 2

536

No. of Carbons

7

30

33

29

Theoretical C02 Yield

mg C02/mg Mate rial

-

2.14

2.14

2.37

2.38

*Based on the stoichiometric amount of CO2 formed upon complete biological oxidation.

01 0 106-35

Table 5. Modified OECD/EEC Synthetic Sewage

Component 1 Concentration, mgll I

Peptone (Difco)

Beef Extract (Difco)

320

220

Laboratory Dist. Water 1000 ml pH (Unadjusted) 6.8-7.0

010106-36

.

t

Neat Surfactant, m g l l

Surfactant

Table 6. Acute Aquatic Toxicities of Neat Surfactants and Their Biotreated Effluents

14.7

43.6

> 100.0

7.3

8.8

> 100.0

NPE

7TE

AE

2.9

28.4

1.6

6.8

I 0.76 I 0.50

Control (No Surfactant)

- -

Biotreated Effluent, %

Da hnia Pime hales &T [.+I I

82-7 I 'loo-o 1 I I

010 106-38

. -

Surfactant

NPE

NPE

7TE

7 T E

Chlorine Effluent Addition LCSO* Foam Height,

ml

No 7.3 1 1

Yes 6.3 12

No 8.8 14

Yes >loo 0

'96 hour LCso in % cfffucnt.

01 010639

Mixer 0

Surfactant Vessel

Aerator (3 a

p- Vessel

Sludge Recycle Pump

E uent Receiver

Figure 1. Bench-Scale Activated Sludge Biotreater y1

09424-1

CO2-Free I

3

1

Air In - c

4

r\ I

2

. v

3

b

1 = Rotameter, 80-100 cdmin 2 = Silica Drying Tube with Indicating Drierite 3 = C 0 2 - Drying Ascarite 4 = C02 Absorber, 100 ml Ba(OH)2,0.05N

-

Figure 2. Diagram of a Modified Sturm Test Unit for the Determination of Ultimate Biodegradation by C02 Formation

-

- I - T

0 10 106 19

ppm Surfactant Added 0 10 20 40 80 100

1 1 V I 60 A - I \

I \ A L I \

40 _ - CTAS,

20 ic\x \/ I I I

I I I I

NPE \

\ \ "@-v -.- . - J , I' 1 Surfactant) ,AE ' Control (No v t

120 160 200 240 Run Day

Figure 3. Measurement of Intact Surfactant (CTAS) in Biotreater Effluents

0101 0617

t

. 100

80

60 % of

Theoretical C 0 2 Formed

140

I ,................................... . . - * *

Benzoate - \ .. . * - *

0 0 .

e - . - * - .

0 # . L * - = . . .e* 0 . .

/

- AE . . I.@* 0

0

.)* . ) *@ .. -: . . / * )

: r '