COD Scoping Study - circabc.europa.eu Industries/Library...•Biochemical oxygen demand - BOD 5 •Total suspended solids - TSS ... • COD is a chemical test, defined as a chemical

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COD Scoping Study

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• Under the Urban Waste Water Treatment Directive requirements for discharges of organics are set out:

• Biochemical oxygen demand - BOD5

• Total suspended solids - TSS

• Chemical Oxygen Demand – COD

• The reference method for COD uses a homogenised, unfiltered, undecanted water sample, using of potassium dichromate.

• REACH-Commission Regulation (EU) No 348/2013 of 17 April 2013 bans Potassium Dichromate and its use for analysis purposes under the Urban Waste Water Treatment Directive 91/271/EEC.

UWWTD and COD measurement

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COD in UWWTD, Table 1, Annex 1

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• An exemption allowing the use of 1 tonne per year per legal entity was granted, with an additional requirement for carefully controlled conditions. This exemption is understood by manufacturers (e.g. Hach, Merck) and laboratory users (e.g. ALS Global) to enable continued use of the small scale closed cuvette measurement method, which for any legal entity enables many millions of COD tests per year using the small scale, enclosed, cuvette method (see also section 5 of this report).

• As the European Commission aims to avoid use of Potassium Dichromate in future and to fulfil the REACH Commission Regulation 348/2013 a change of the parameter COD, or of the method to determine its value for the purpose of the UWWTD, is required.

COD analysis using CrVI exempt

from ban, but aim to replace

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This study includes four main technical tasks to achieve the overall objective:

• Task 1: Overview of parameters and methods

• Task 2: Preparation of a suggestion for future analysis replacing the Cr VI-COD method

• Task 3: Assessment of simplification and costs

• Task 4: Presentation at UWWTD Expert Group

The overall expected output of the contract is to propose a replacement of the parameter Cr VI-COD in the UWWTD, i.e. to amend Table 1 of Annex I of the Directive.

WRc Tasks

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Tasks and outcomes

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Final report headings

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Project timetable

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Some examples of wastewater treatment works use of COD measurements are:

Regulatory measurements of wastewater effluents and influents;

Process management within treatment works;

Load determination of incoming organic materials including industrial wastewaters and outlying works sewage sludge;

Effectiveness of dewatering of sewage sludge;

Design of new treatment works, assessing load, potential recoveries and costs;

Optimisation of existing and new treatment works using modelling tools – the most important of which currently include the IAWQ COD models;

Meeting stabilisation criteria for sludge and other organic wastes, including productisation measurements.

Usage of COD measurements

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• To make no amendment and for individual EU

Member States to use an alternative

• For EU Member States to use a different standard

• Replace COD with TOC in UWWTD

• Set a ratio between a measurement parameter and

COD

• Modify UWWTD by replacement of BOD and SS with

single lumped measurement method

• Other?

Management options

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• BOD is a biological test method that uses a seed bio-culture mixed with the sample, to find the amount

of oxygen used due to the bio-culture metabolism of substances in the sample, over a 5 day (or 7 or 10

day) period. Although it is standardised, it does not adapt to the particular liquor under test in the same

way as a treatment plant, or a bio-flora in a catchment.

• COD is a chemical test, defined as a chemical oxidation of the sample material. The Cr VI-COD method

measures close to the maximum possible oxygen demand of a sample, but generally at least 50% of the

demand is from organic material that is not readily degradable in short-term biological processes such

as the BOD test.

• TOC (total organic carbon), measures the amount of carbon in a sample after removal of inorganic

carbon (alkalinity, carbonate, carbon dioxide). It does not provide any direct measure of potential or

actual impact of the carbon containing material on oxygen demand in a catchment.

• TOD (total oxygen demand), measures the amount of oxygen required to oxidise material in a sample

by means other than wet chemical methods. Instruments that carry out this determination have been

offered by manufacturers since the 1970s, but have not been widely used. Use of TOD measurement

methods has been increasing in the USA, but has not been validated in European conditions.

• The suspended solids measurement provides an indication of the turbidity of an effluent as well as

possible organic load. The turbidity affects clarity of the water column in a catchment and therefore

potential loss of transmission of light to oxygen releasing plant matter in a water column.

Main measurement types

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Pollutant assessment methods,

usage and type

Method Usage Type of test

COD-CrVI

Widespread, plant operations,

regulator Chemical

COD-MnIII Limited Chemical

COD-MnVII Obsolete? Chemical

TOD, total oxygen demand Developing in USA Chemical (combustion)

PeCOD Patented, TiO2 / UV Advanced oxidation

BOD, biochemical oxygen

demand Widespread, regulatory Biological

Suspended solids

Widespread, regulatory,

operation Mass

TOC / NVOC, total organic

carbon, non-volatile organic

carbon

Some operational & regulatory,

including online Chemical (combustion)

Turbidity Online site operations Light scatter

UV absorbance Online site operations Photometric

Electrochemical COD Online site operations Electrochemical

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• Closed reflux, cuvette method

• 2 ml sample, prepared reagent

• Heat for 2 hours, 150°C

• Colour measured

• Automated methods available for semi-continuous

sampling

COD-Cr(VI)

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• Hach patent 1995

• Purple Mn(III) oxidised to colourless Mn(II)

• Concentrated H2SO4 solution

• Test kits available (20-1000 mg/l, Method 10067)

• 1 h at 150°C

• Chloride and ammonia interference

COD-Mn(III)

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• Purple Mn(VII) oxidised to colourless Mn(II)

• ISO 8467:1993 Water quality - Determination of

permanganate index

• Titration with oxalate

• Not recommended for wastewater

• Research – FIA-FAAS

• No test kits available

COD-Mn(VII)

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• Total Oxygen Demand

• ASTM D6238 - 98(2011)

• 3 minute analysis time

• Analytical instruments available, incl. on-line

• TOD > COD

TOD

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• TiO2/UV (photo-oxidation)

• Analytical instrument available, patented

• Chloride interference >400 mg/l

• High particulate concentration can cause blockages

• Good correlation with BOD according to manufacturer

• 15 minutes reaction time

PeCOD

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• Electrochemical oxidation

• Analytical instrument available

• Good correlation to COD-Cr(VI) according to

manufacturer

• 4 minute analysis time

• For low COD

Electrochemical COD

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• Biological Oxygen Demand

• Typically 5 days

• DO measured before and after incubation

• Tryptophan-like fluorescence instruments developed

as a surrogate

• BOD<COD

BOD

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• Total Organic Carbon

• C oxidised to CO2

• IR detector

• Well established lab & on-line method

• TOC correlate with COD-Cr(VI) but correlation to be

established for each WwTW

TOC

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• Relates to aromatic carbon content

• Need to be compensated for particulates or filtered

• Correlates with DOC but correlation to be established

for each site

UV absorbance

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• Measure solids captured on filter (slow, hours)

• On-line and handheld instruments (quick, seconds)

• Optical

• Attenuation of ultrasound

• Any correlation with COD would be site specific

Total suspended solids (TSS)

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• Light scattering

• Handheld, bench top and on-line instruments

• Quick (seconds)

• Site specific correlation with TSS

Turbidity

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• Range of methods

• Biological

• Chemical

• Physical

• Each has particular application

• Need to demonstrate reliability, accuracy

• Limits of detection

• Economy to be taken into account

• Application to range of circumstances

Methods summary

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Comparisons between COD

BOD/COD TOC/COD

high 0.40 0.25

average 0.24 0.17

low 0.21 0.12

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Final effluent, COD vs BOD, TSS

y = 0.5504x - 3.6487 R² = 0.2956

y = 0.0544x + 1.1719 R² = 0.2163

0

5

10

15

20

25

30

35

40

0

20

40

60

80

100

120

140

160

0 50 100 150 200

BO

D, m

g/l

TSS,

mg/

l

COD, mg/l

COD vs BOD, TSS, final effluent

TSS (mg/l)

BOD (mg/l)

Linear (TSS (mg/l))

Linear (BOD (mg/l))

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• COD to other methods relationships and variability

• Austria has been tracking TOC measurements – these will

become available to us

• WRc has some limited data

• Literature has some data

• Practical data highly desirable

• Understand other country uses of measurements

• Summary initially provided has been reviewed and updated

• All countries in review use standard COD-CrVI measurement.

• Some have additional / alternative

Information to be found

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• What is happening in your country?

• What method is used for COD measurements?

• Any alternative COD-methods or alternatives to COD measurements being investigated?

• Do you have access to, or aware of, any comparative data for different COD methods, e.g. trials, round-robin inter-lab tests?

• What is COD used for? For example design of works, works operation, regulatory.

• Can COD be dropped and replaced? What would the implications be?

Questions to group

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• To make no amendment and for individual EU

Member States to use an alternative

• For EU Member States to use a different standard

• Replace COD with TOC in UWWTD

• Set a ratio between a measurement parameter and

COD

• Modify UWWTD by replacement of BOD and SS with

single lumped measurement method

• Other?

Management options

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• Gather information and views from this meeting

• Seek further information

• Research sources of information,

• Collate outcome of consultation enquiries for Expert sub-group

• member country issues,

• determinand analysis methods,

• environmental regulatory impacts of changes,

• Develop options.

Next stage(s)

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• Reporting and discussion on:

• Development of data relationships

• Member state issues, practice and evidence

• Analytical methods

• Environmental and industrial management consequences of different measurements

• Agreements on:

• Issues resulting from consultations

• Development of analysis

• Preliminary approach to revision of UWWTD

• Next stages of consultant analysis

• Requests for costing and practice information

Next meeting