unabhängige, beratende und planende ingenieure für wasser...
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Unabhängige, beratende und planende Ingenieure
für Wasser-, Abwasser-, Abfall- und Umwelttechnik
Hannover
Bremen
Erfurt
Hannover ∙ E
rfurt ∙ Oldenburg
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