Organic matter
Total oxygen demand
By oxidizing at a high temperature and by using a suitable catalyst, a total chemical
oxygen demand may be determined, called TOD. By using this analysis, the few
organic compounds are oxidized which are not oxidized by the COD-analysis.
Besides, ammonium is oxidized. TOD-values are therefore somewhat higher than
COD-values, see Table 2.1
Total organic carbon
By using this analysis, organic matter is oxidized to carbon dioxide by heating. The
difference between the carbon dioxide concentration before and after oxidation is
used for the calculation of the TOC.
TOC is not unambiguously tied to other parameters for organic matter as it states
the amount of carbon atoms, but does not say anything about their state of oxidation, and hence nothing as to how much oxygen should be used for the oxidation.
In Tables 2.2 and 2.3, the TOD, BOD and BODz~rvalues are given for a number of
materials.
46
Example2.2
Two wastewater analyses both have a TOG-value of 12 g/m 3 . One test contains methane and the other acetic acid.
Calculate the COD-values of the two samples (if everything is oxidized by the CODanalysis)
1. Methane CH4.
1 mole of CH4 contains 1 mole of carbon = 12 g, signifying that the wastewater contains 1 mole of CH4.
Oxidation of methane:
CH4 + 2 02 ---> C02 + 2 H20
(2.6)
Oxygen demand = 2 0 2 = 2 · (16 · 2) = 64 g oxygen.
COD= 64 g/m 3 .
2. Acetic acid CH3COOH
%mole contains 1 mole of carbon= 12 g, signifying that the wastewater contains%
mole of acetic acid.
Oxidation of % mole of acetic acid:
1
2 CH3 COOH + 02 ---> C02 + H20
(2.7)
Oxygen demand= 0 2 = 16 · 2 = 32 g
COD =32 g/m 3
It appears that in spite of the same TOG-value, the two water types have very different
COD-contents.
Total oxygen demand
By oxidizing at a high temperature and by using a suitable catalyst, a total chemical
oxygen demand may be determined, called TOD. By using this analysis, the few
organic compounds are oxidized which are not oxidized by the COD-analysis.
Besides, ammonium is oxidized. TOD-values are therefore somewhat higher than
COD-values, see Table 2.1
Total organic carbon
By using this analysis, organic matter is oxidized to carbon dioxide by heating. The
difference between the carbon dioxide concentration before and after oxidation is
used for the calculation of the TOC.
TOC is not unambiguously tied to other parameters for organic matter as it states
the amount of carbon atoms, but does not say anything about their state of oxidation, and hence nothing as to how much oxygen should be used for the oxidation.
In Tables 2.2 and 2.3, the TOD, BOD and BODz~rvalues are given for a number of
materials.
46
Example2.2
Two wastewater analyses both have a TOG-value of 12 g/m 3 . One test contains methane and the other acetic acid.
Calculate the COD-values of the two samples (if everything is oxidized by the CODanalysis)
1. Methane CH4.
1 mole of CH4 contains 1 mole of carbon = 12 g, signifying that the wastewater contains 1 mole of CH4.
Oxidation of methane:
CH4 + 2 02 ---> C02 + 2 H20
(2.6)
Oxygen demand = 2 0 2 = 2 · (16 · 2) = 64 g oxygen.
COD= 64 g/m 3 .
2. Acetic acid CH3COOH
%mole contains 1 mole of carbon= 12 g, signifying that the wastewater contains%
mole of acetic acid.
Oxidation of % mole of acetic acid:
1
2 CH3 COOH + 02 ---> C02 + H20
(2.7)
Oxygen demand= 0 2 = 16 · 2 = 32 g
COD =32 g/m 3
It appears that in spite of the same TOG-value, the two water types have very different
COD-contents.