Unabhängige, beratende und planende Ingenieure

für Wasser-, Abwasser-, Abfall- und Umwelttechnik

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General Introduction

• Sum parameters can be determined easier.

• Organic pollution loads must be determined.

• Measurement results should be repeatable.

• Measurement methods should be available to all.

• Measurement results should be unbiased.

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Sum-Parameter Definition

• A term to summarize the effect and substance

characteristics.

• Summarizes one or several groups of substances under

defined analytical conditions.

• Used in environmental analysis to describe the quality of

water samples (drinking water, surface water, ground

water, waste water.

• No statement about the proportion of individual elements

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Sum-Parameter Definition (2)

• Simple overall recording and reporting of environmental

pollutants in environmental samples such as content of

organic compounds, organically bound halogens and the

salt contents.

• Some of sum parameters are:

– COD

– BOD

– Permanganate index (PI)

– TOC

– Total Dissolved Organic Carbon (DOC)

– Conductivity

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Chemical Oxygen Demand (COD) Topic Contents

1. Introduction

2. Analysis history

3. Methods for COD determination

4. Field of application und disturbances

5. Conclusion: Advantages and disadvantages of

measuring COD parameter

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1.Introduction

Why this topic?

• Sum parameters are easy and uncomplicated to handle.

• Results can be easily accepted without being questioned.

• However, the background of the sum parameter is not obvious.

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COD Definition

• According to DIN 38409 :

The chemical oxygen demand (COD) of water is the volume-related mass of oxygen equivalent to

the mass of potassium dichromate which reacts with the oxidizable substances contained in the

water under the operating conditions of the processes.

• According to W.Gujer :

The chemical oxygen Demand is a sum parameter that expresses how much oxygen is required

for the complete oxidation of organic substances to CO2 and water.

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COD Calculation

• Example : A sugar solution with a density of (C6H12O6) = 200 g/m3

C6H12O6 + 6 O2 => 6 CO2 + 6 H2O

M(C6H12O6)= 180g/mol ; M(O2) = 32 g/mol

• From the Stochiometry it can be seen that 1 mol of sugar needs 6 mol of

oxygen for the reaction.

200g = 1,11 mol Zucker

COD = (1,11mol * (6*32g))/ 1 mol

COD= 213 g/m3 > 213 mg O2 /l

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2. Analysis History

Marqueritte discovered

the permanganate as

an oxidizing agent.

1866 1846 1987

1849 1924 2003

Development of the

‘’Kubel’’ method.

Development and

standardization of COD

Development of BOD5 Forchammber discovered that

organic substances can be

oxidized by permanganate.

Standardization of the

COD cuvette test for

easier determination.

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3.Methods for COD Analysis

Determination based on:

• DIN 38409 Methods

• ISO DIN 15705 (cuvette test)

• UV absorption

• Oxidation over OH radicals

• Correlation measurement via TOC

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3.1 Determination of COD According to DIN 38409

Long Term Processes Measuring Range (mg/l) Chloride Content(mg/l)

H 41-1 15-300 < 1

H 41-2 15-300 > 1

H 42 >15

H 44-1 5-50 < 0,3

H 44-2 5-50 > 0,3

Short Term Process

H43-1 5-50 < 1

H43-2 5-50 > 1

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3. Determination of COD Test Description

The water sample is added to sulfuric acid,

silver ions (catalyst) and potassium

dichromate (oxidizing agent).

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3.Determination of COD Test Description

Cooling water The water sample is boiled under reflux for

two hours at boiling temperature (148 º C)

for the oxidation of organic contents

Cr2O72- + 14 H+ + 6 e-

–Ag+ 2Cr3+ + 7 H2O

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3.Determination of COD Test Description

After cooling, unused oxidising

agent is determined with the

Fe+2(back titration). The amount of

the dichromate converted during

the oxidation of the water contents

can be calculated from this. The

result is COD which is indicated in

mg o2/l.

Cr2O72- + 14 H+ + 6 Fe2+

2Cr3+ + 6 Fe3+ + 7 H2O

Before After

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4. Field of Application

Substances Oxidation Products Extent of the reaction

Organic substances CO2, H2O

Partial to complete

Nitrogen-organic compounds (with N in

reduced form)

CO2, H2O, NH4+

Partial to complete

N from hydrazine and its derivatives N2

Practically complete

N from nitrite and derivatives of nitrous

acid

NO3-

Practically complete

N from nitroso and nitro compounds NO3-

Practically complete

S from reduced. Sulfur compounds (such

as sulfide, sulfite, thiosulfate, mercaptan ,

etc.

SO42-

Practically complete

Chloride and chlorine from organochloro

compounds

Cl2

Partial to complete, occasionally with

over-stoichiometric oxidant consumption

Bromide and bromine from

organobromine compounds

Br2

Practically complete

ATV Landesgruppentagung 1979

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4.Field of Application

Substance

TOD in mg/L

Total Oxygen Demand

COD mg/l (H41-1)

Share of COD in total

oxygen demand %

Harnstoff(CH4N2O) 800 653 82

Benzol(C6H6) 3077 2003 65

Phenol(C6H6O) 2383 2362 99

ATH(C4H8N2S) 2069 1855 90

DDT(C14H9CL5) 1465 39 3

More recovery rates (K2Cr2O7)

N-Hexan 2% Starch 91%

Cyclo-hexan 5% Stearic acid 60%

Chloroform 8% Trimethylamin 1%

Nicotinic acid 12% EDTA 78%

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4. Disturbances

• No detection of pyridines, quaternary nitrogen compounds, organosilicon

compounds and other substances which are very difficult to oxidise.

• Alkanes (paraffins), haloalkanes and alkenes, amines and compounds

which have an oxidizing effect, e.g. Chromium (VI) compounds were below

the level of detection.

• Substances which are higher than the level of detection: – Chloride, bromide and iodide ions

– Hydrogen peroxide and its adducts

– Certain sulfur compounds e.g. Sulfite ions

– Nitrite ions

– Certain metal compounds

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4. Disturbances Advantages and Disadvantages

Advantages Disadvantages

Standardized procedure Long reaction time

Legally valid Relatively high effort and labor is

needed

Lots of experience reports are available Handling of hazardous chemicals

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3. COD Determination Determination with Cuvette test

• According to DIN ISO 15705 since 2003

• High work safety and user friendly

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4. Field of Application

• Field of application is very similar to DIN 38409

• Can be used for the measurement of up to 1000 mg / l

yellow chromium (III) at a wavelength of 600nm ± 20nm

• For measuring smaller values of chromium (VI)

– Up to 150 mg / l with a wavelength of 440nm ± 20nm

– 50 mg / l with a wavelength of 348nm ± 15nm

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4.Disturbances

• The same as disturbances in DIN 38409

• Further disturbances due to manganese, which becomes

non detectable at 600 nm and more wavelengths.

• Batch production with quality fluctuations

• Quality assurance is thereby predominantly an external

factor.

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4. Field of Application Round Robin Test

probe L N NAP

WWTP outlet 1 35 136 6.62

WWTP outlet 2 34 132 7.58

Industrial wastewater 1 32 124 4.03

Industrial wastewater 2 32 124 7.26

Industrial wastewater 3 35 136 1.47

KHP 850 32 123 12.2

KHP 20 + Chloride 2000 33 127 20.47

L: Number of labroratories participiting

N: Number of measured values

NAP: percentage of outliers

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4.Field of Application Overview of Different Suppliers

Manufacturer Measuring Range Accuracy DIN ISO Conformity

Merck 4.0-40 mg/l ±1.8 mg/l Yes

10-150 mg/l ±6mg/l Yes

15-300 mg/l ±7mg/l Yes

25-1500 mg/l ±30mg/l Yes

Hach Lange 5-60 mg/l ±0.7mg/l ns

15-150 mg/l ±1.5mg/l ns

50-300 mg/l ±3.9mg/l ns

0-1000 mg/l ±4.2mg/l Yes

0-150 mg/l ±1.9mg/l Yes

Machery und Nagel 5-60 mg/l ± 2mg/l Yes

15-160 mg/l ±3 mg/l Yes

50-300 mg/l ±5mg/l Yes

100-1500 mg/l ±21mg/l Yes

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–http://vsa.labeaux.ch/docs_public/06%20MT%20C-Parameter%20DP.pdf

Wave length

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Area of Application

–http://vsa.labeaux.ch/docs_public/06%20MT%20C-Parameter%20DP.pdf

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Oxidation on Radical OH

• UV irradiation with the addition of hydrogen peroxide

– Photolysis of the peroxide to form OH radicals:

H2O2 + hv 2OH-

Oxidation of the pollutant molecule by the OH radicals

OH- + M MOX

• Side reaction 1: Reaction of the OH radicals with undissociated

peroxide with oxygen formation:

OH- + H2O2 H2O + HO2-

OH- + HO2- H2O + O2

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Measuring Apparatus

http://vsa.labeaux.ch/docs_public/06%20MT%20C-Parameter%20DP.pdf

Instrument outlet

Probe Inlet

Oxygen Electrodes

UV Reactor

Dosing Pump

Reagent

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Area of Application and Disturbances

• Side reaction 2: reaction of radical OH with other water contents

• Side reaction 3: Reaction of radical OH with so-called scavengers

These substances include vitamin C, vitamin E, betacarotene, selenium and

phytoestrogens

• No further studies on the correlation with the laboratory COD

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5. Conclusion: Advantages and Disadvantages of

Measuring COD Parameter

• Objective: Determination of the pollutant load that is emitted in the

receiving water

• Problem: The COD does not necessarily consist of 100% pollutants

But it is clear that :

• How and where the sample was taken / pretreated

• Which analysis method was used

• Which treatment procedure has been sampled

• When the sample matrix looks roughly, there may be impurities

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Section 2:TOC

• Structure

1) What is TOC?

2) Where TOC is measured?

3) Sampling

4) Sample decomposition

5) Non - dispersive infrared spectroscopy

6) Determination methods according to DIN

7) Process flow chart

8) Cuvette test

9) TOC - conductivity determination

10) Conclusion on TOC

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1. What is TOC?

• Definition according to DIN EN 1484

Total organic carbon (TOC) is a measure of carbon content in dissolved

and undissolved organic substances in water. However, It provides no

indication of the nature of organic matter.

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1. What is TOC?

TC

Total Carbon

Sum of inorganic and organic bounded carbon in dissolved and

undissolved compounds

TIC

Total anorganic Carbon

TOC

Total organic carbon

DOC

dissolved organic carbon

POC

Undissolved organic carbon

VOC

Volatile organic carbon

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2) Where TOC is measured?

• In the outlet of WWTPs

• For direct industrial dischargers

• In pharmaceutical companies

• In industrial plants where pure or ultrapure water is used

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3. Sampling

• Sampling according to DIN EN 1484

• Representative probe

• Acidification of the sample with expected biological activity

• Pre-treatment or storage of the sample for a longer retention time

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4.Chemical Decomposition of the Sample

• Two standardized procedures (DIN EN 1484)

• Used to dissolve carbon particles from the aqueous

matrix

• In some cases, solid particles must be separated

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4. High Temperature Processes

• Thermal-catalytic reaction

• Combustion of the sample at more than 800 ° C

• Inert gas stream transports gas to the detector

Advantage Disadvantage

Complete sample decomposition Corrosion

No chemical is needed Maintenance and cost-intensive

systems

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4. Sample Decomposition-Wet Chemical

Infection (nasschemischer)

• Wet-chemical- or UV - persulphate method

• Inorganic carbon content is blown out

• Oxidizing agent: persulphate, sodium peroxide sulfate

Advantages Disadvantages

• Low maintenance

• Large sample volumes

• Low detection limits

• Problematic with strongly

salty and particle-containing

samples

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5. Non-Dispersive Infrared Spectroscopy

• IR beam goes through a

measuring cuvette to the

detector.

• Concentration of the sample

gas is deduced from the

strength of the absorption

–http://www.fresenius-ut.com/de/download/messprinzipien/DB_MePri1.pdf

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6.Determination methods

According to DIN

1) Direct Processes

• Removal of all inorganic carbon particles

• Decomposition of the sample

• Measurement of the TOC

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6.Determination methods According to DIN

Differential Measurement Processes

• Decomposition of the sample

• Determination of TC and TIC

• Calculation of the TOC from:

TC - TIC = TOC

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7. Process Flow Chart

(High Temperature Decomposition) Degassing

Gas pumping

HCL acid

Sample

preparation

Reaction Tank

850 º C

C5H12+ 8 O2→ 6 H2O + 5 CO2

CO2 absorber

Gas cooling

Acid filters

Acid filters

CO2

measurement

device (NDIR)

Exhaust air Siphon

Outlet

Carrier gas (air) Strip gas

TIC

measurement

Dosing pump

multi-channel

Gas outlet

TC

measurement

Gas Route

Liquid Route

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8.Cuvette test

Three components:

• Cuvette Indicator,

• Cuvette Boiler,

• Membrane

Sample decomposition in the

cuvette boiler

Carbon dioxide concentration is

determined photometrically

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8.Cuvette test

TIC determination: Using acid for expelling in the cuvette decomposer

TC determination: Decomposition of the sample, subsequent

determination

Limitations and Disturbances:

• TIC ions interference- Determination: formate, acetate, sulfite, sulfide, nitrite

– nitrogen

• TC ions Interference - Determination: chloride, ammonium nitrogen

• PH value: between pH 4 and pH 10

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8. Cuvette test – Direct method

• Direct TOC determination by expelling the inorganic carbon fraction

or oxidation by means of sodium peroxosulfate in the cuvette boiler

• Then boil and determine the TOC photometrically

–http://www.hach-lange.de/shop/action_q/highlights/highlight_id/479/lkz/DE/spkz/de/TOKEN/nsU05J9HcgbkinjA-i0qwRVcDgg/M/vzv6vA

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9. TOC Determination by means of

Conductivity

• Online procedure

Exposure of the sample to UV light with a wavelength of 185 nm

Double conductivity measurement

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9. TOC Determination by means of

Conductivity

• Two conductivity sensors

• Sample flow through spiral of quartz glass

• Integrated UV lamp

• Measuring range: 0.05 to 1000 ppb

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10. Conclusion for TOC

• Automated measuring methods are suitable for different types of

WWTPs.

• No knowledge of the expected impurities or measuring ranges is

needed

• The chosen process should match the sample

• Little to no chemicals

• Used to determine the organic load of the sample

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11. TOC and COD Comparison

Pro Cons

• Only a few

Procedures are possible to

be measured Online.

• Standardized procedure

• Legally valid

• Lots of experience reports

available

• Analysis takes

about three hours

• High analysis costs,

especially for

laboratories

research

• Use of toxic

chemicals

Pro Cons

• Easy automation

• Analysis time of approx.

20 min

• Low analysis costs

• Low personnel costs

• Almost free of chemicals

• Can be synchronized

with other parameters

• High initial-

costs

• No knowledge of

oxygen requirement

COD TOC