Characterization of Wastewaters and Sludges
Potassium permanganate is used to determine the chemical oxygen demand
(CODp).lt is a very incomplete oxidation of organic matter, and the analysis should
therefore only be used to estimate the necessary dilutions in the BOD-analysis.
With potassium dichromate, a more thorough oxidation is obtained, including the
oxidation of different inorganic materials (N02 I 52 I 5zoj- I Fe 2 + I 5oj-). Ammonium and ammonia, which are released by the oxidation of organic nitrogen, are not
oxidized. The measured COD-value gives a good picture of the total content of
organic matter as the mentioned inorganic materials normally are not present in
significant concentrations in wastewaters.
The COD-analysis may be carried out automatically and relatively fast (1-2 hours).
The COD-values are suitable for the calculations of the mass balances in treatment
plants. Both COOp and COD are stated in the unit oxygen, for example g Oz/m 3 .
This means that the consumption of potassium permanganate or potassium dichromate is converted into an equivalent oxygen demand (the am~unt of oxygen which
will be consumed if the oxidation had taken place by using oxygen).
COD-fractionation
The COD-value covers a number of organic materials of varying biological qualities. For the purpose of calculations in biological treatment plants, COD may, for
example, be divided into the following fractions /13/:
Ccoo= 5s +51 +Xs+ X1
is (dissolved) easily biodegradable organic matter,
is dissolved biological inert organic matter,
is (suspended) slowly biodegradable organic matter,
is suspended biological inert organic matter.
(2.4)
The analysis and calculation work involved to determine these four fractions are so
extensive that the quantities cannot be used in the day-to-day management control
and operation of a treatment plant. In connection with the design of treatment
plants and operational tests of treatment plants, a COD-fractionation may be of
great importance. It is also included in the computer models which are used for the
design and optimization of plant operation.
The concept of inert matter covers substances which are degraded so slowly in
biological treatment plants that in practice they may be regarded as non-degradable.
For the two biodegradable fractions, Ss and Xs, the division into dissolved and
suspended solids is not accurate but the dissolved solids are dominated by easily
degradable organic materials whereas the suspended solids are dominated by
slowly degradable substances. The analytical determination gives two possibilities.
A rough estimate of the two types of substances can be made through filtration, or
they may be estimated by means of the biological degradation rate.
43
Potassium permanganate is used to determine the chemical oxygen demand
(CODp).lt is a very incomplete oxidation of organic matter, and the analysis should
therefore only be used to estimate the necessary dilutions in the BOD-analysis.
With potassium dichromate, a more thorough oxidation is obtained, including the
oxidation of different inorganic materials (N02 I 52 I 5zoj- I Fe 2 + I 5oj-). Ammonium and ammonia, which are released by the oxidation of organic nitrogen, are not
oxidized. The measured COD-value gives a good picture of the total content of
organic matter as the mentioned inorganic materials normally are not present in
significant concentrations in wastewaters.
The COD-analysis may be carried out automatically and relatively fast (1-2 hours).
The COD-values are suitable for the calculations of the mass balances in treatment
plants. Both COOp and COD are stated in the unit oxygen, for example g Oz/m 3 .
This means that the consumption of potassium permanganate or potassium dichromate is converted into an equivalent oxygen demand (the am~unt of oxygen which
will be consumed if the oxidation had taken place by using oxygen).
COD-fractionation
The COD-value covers a number of organic materials of varying biological qualities. For the purpose of calculations in biological treatment plants, COD may, for
example, be divided into the following fractions /13/:
Ccoo= 5s +51 +Xs+ X1
is (dissolved) easily biodegradable organic matter,
is dissolved biological inert organic matter,
is (suspended) slowly biodegradable organic matter,
is suspended biological inert organic matter.
(2.4)
The analysis and calculation work involved to determine these four fractions are so
extensive that the quantities cannot be used in the day-to-day management control
and operation of a treatment plant. In connection with the design of treatment
plants and operational tests of treatment plants, a COD-fractionation may be of
great importance. It is also included in the computer models which are used for the
design and optimization of plant operation.
The concept of inert matter covers substances which are degraded so slowly in
biological treatment plants that in practice they may be regarded as non-degradable.
For the two biodegradable fractions, Ss and Xs, the division into dissolved and
suspended solids is not accurate but the dissolved solids are dominated by easily
degradable organic materials whereas the suspended solids are dominated by
slowly degradable substances. The analytical determination gives two possibilities.
A rough estimate of the two types of substances can be made through filtration, or
they may be estimated by means of the biological degradation rate.
43