Screening parameters in water analysis

Screening parameters in water analysis

31.08.2015

Ralf Dunsbach

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Screening parameters in water analysis


Water analysis

The main focus within environmental analysis is the subject of water. Our instruments are used to carry out routine analysis of organic impurities in the water industry.


Introduction

H2O Contains

• Inorganic compounds (salts like NaCl)

• Organic compounds (humic substances + man-made waste)

Only 0,3% of the global water resources is availble as drinking water

Water protection, technology and analysis gain more and more importance!

One of the most important quality criteria for water is Pollution with organic compounds

How to determine organic pollutants

Pollution with organic compounds - how to determine?


Single compound analysis

by chromatographic methods?

Drawback:

Nearly impossible due to the huge number of possible compounds – applicable only for certain classes of substances (e.g. polycyclic aromatic hydrocarbons)

Screening parameter analysis

for all organic compounds

- BODx - biological oxygen

demand

- COD - chemical oxygen

demand

- TOC -total organic carbon

How to determine organic pollutants

BODx and CSB are indirect methods to determine the amount of

organic carbon by the determination of the biological and chemical oxygen demand during the decomposition of its compounds.

Disadvantage:• slow

• insufficient or wrong oxidation

• depending from biological activity

• heavy metal containing reagents

• no automation



BOD5 - biological oxygen demand after 5 days

DIN 38 409 H51DIN 38 409 H52

Disadvantage:

particulates are not sufficiently oxidized slow (5 days)

Reference: Fonds der chemischen Industrie - Umweltbereich Wasser

BOD


DIN 38 409 H41

Disadvantage:

higher or fluctuating results, if dichromate is consumed due to the oxidation of sulfur containing compounds

Reagents:concentrated sulfuric acid H2SO4 – corrosive!potassium dichromate K2Cr2O7 - toxic!mercury substance (masking of chloride) – toxic!

Analysis time: > 2 hours, automation very difficult

Dichromate out of use in EU latest 2017!!

Reference: Fonds der chemischen Industrie - Umweltbereich Wasser

COD


Recovery rates COD

According to Janicke (WaBoLu report 1/1983):

n-hexane 2% Urea 82%

Cyclohexane 5% benzene 63%

Chloromethane 8% EDTA 78%

Trimethylamine 1% starch 91%

Nicotinic acid 12% stearic acid 60%

Poor recovery for alcanes, amines

False COD readings

• High false readings by chlorides, bromides, iodides, certain sulfur compounds, nitrites and certain metal compounds

• False low readings by chromium (VI)-compounds, nitrates, peroxides


TOC

EN 1484 - European Standard Water analysis - Guidlines for the determination of the total organic carbon (TOC) and dissolved organic carbon (DOC)

The EN 1484 approves the determination of TOC and DOC as appropriate method to determine the contamination of water with organic compounds.


R-C + O2 CO2 + H2O + further products


TC

TC [total Carbon] = TIC [total inorganic carbon] + TOC [total organic carbon]

TOC = POC [purgable organic carbon] + NPOC [non-purgable organic carbon]

TOC + TIC

POC + NPOC

TOC


TC [total Carbon] Oxidation

Detection

Sample [R-C-R + CO3 2-] + O2 CO2 + H2O + ...

Total carbon can be determined by oxidation and decomposition of the sample and detection of the deriving CO2

How to determine TC


Detection

Acidified Sample: CO3 2- + 3 H+ CO2 + H3O+

TIC

Total inorganic carbon can be determined by degradation of the carbonates by acid, purging and detection of the deriving CO2

Gas

How to determine TIC


NPOC [total Carbon] Oxidation

Detection

Acidified and purged Sample [R-C-R ]

Non-Purgable Organic Carbon can be determined by purging the acidified sample in advance to remove TIC and POC, oxidation of the remaining components and detection of the deriving CO2

Oxidation: R-C-R(non vol.) + O2 CO2 + H2O + ...

Purging: [R-C-R (volatile and non volatile) + CO3 2-] + 3 H+ CO2 + H3O+ + R-C-R (vol.)

if POC = 0

NPOC = TOC

How to determine NPOC


Method Advantages Disadvantages

Differential:

TOC=TC - TIC

includes volatile organic compounds

Less suitable for high TIC concentrations

(TOC << TIC)

long measuring times

Direct: NPOC

Non-purgeable organic carbon = TOC in case no volatile compounds are present

suitable for high TIC concentrations

(TIC >> TOC)

fast results

Does not include volatile organic compounds if

present in the sample

How to determine TOC


EN 1484 - European Standard

Determination of TOC and DOC by:

• Wet chemical - UV-persulfat method (DOC only)

• Combustion method




Wet chemical - UV-persulfat method

Quelle: Deutschen Bundesstiftung Umwelt (DBU)

R-C + O2 CO2 + H2O + further productsUV-light +oxidation agent

Advantage:• large sample volume (up to 20mL)• high sensitivity

Disadvantage:• insufficient oxidation of particulates• not applicable for electrolytes or

chlorine containing samples• not for highly contaminated samples • not for solid samples• not for nitrogen


Combustion method

R-C + O2 CO2 + H2O + further products

Advantage:• quantitative oxidation of all carbon

containing compounds• low matrix influence• applicable for waste water and solids• applicable for TNb as additional parameter

Disadvantage:• lower injection volume• problematically with salts• lower sensitivity

High temperature in presence of catalyst


State-of-the-art TOC analyzer



The Concept

Easy maintenance


• Temperatur programmable up to 1100°C

• Matrix separation (patent pending) to keep salt away from the catalyst

• Multiway valve on top of the combustion tube for fast and easy injection

• All maintenance parts easily accessible

Solids analysis


• Only TOC in water analyzer worldwide with automatic sample feeder for solids

• Sample feeding by reliable ball valve technique

• Sample carousel with 80-120 positions

• Solids expansion kit for carbon amounts up to 20mg C abs.


Drinking water: 0.5 ppm – 2 ppm TOC

Surface waters: 0.5 ppm – 10 ppm TOC

Waste waters: 5 ppm – 10,000 ppm TOC

Waste and soil: upper ppm to percentage range of TOC

Waters in pharmacy: 0.05 – 0.5 ppm TOC

Waters in power plants: 0.05 – 1 ppm TOC

Waters in semiconductor industries: 0.005 – 0.5 ppm TOC

Typical TOC contents


Correlation TOC/COD

Oxalic acid

Ethanol

Both compounds have the same TOC (in mol/l), but COD is 5* higher than oxalic acid.


COD/TOC of certain compounds


COD/TOC in different samples I

Origin COD/TOC SD

Influent MWWTP <1000 r 3,23 0,42

Influent MWWTP 1000-5000 r 3,16 0,41

Influent MWWTP 5000-10000 r 2,99 0,37

Influent MWWTP 10000-100000 r 2,99 0,37

Influent MWWTP >100000 r 2,92 0,39

Edible oil refinery 3,64 0,70

Fish processing 3,51 0,45

Meat industry 3,26 0,41

Glue production 4,28 1,62

MWWTP: municipal waste water treatment plant


COD/TOC in different samples II

Origin COD/TOC SD

Ore processing 4,05 0,15

Sugar production 2,92 0,36

Paper production 2,75 0,18

Iron+steel production 3,78 1,02

Textile production 3,05 0,27

Glas and inorganic fiber production 2,62 0,25

Chemical cleaning 3,64 0,24

Waste deposit 3,04 0,2

Oil refineries 3,32 0,25

Source: Verbesserung der Einleiterüberwachung durch die Einführung der Meßgrößen TOC, TNb and Pges., Wasserwirtschaft Forschungsbericht 296-22-322

Summary

• TOC analysis require minimum manpower

• TOC can be measured within 4 minutes

• The only chemicals required for TOC are diluted, non-oxidizing mineral acids

• No special workbench (fume) required for TOC

• Therefore: it needs some work to replace COD by TOC, but it‘s worth it!

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Screening parameters in water analysis

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