COD values of the standard substances and effluent treated human excrement were determined by 13 methods and the influence of Cl
- on the COD values was investegated. The results are as follows ; 1. When KMnO
4 was used as an oxidant (KMnO
4 method), COD values of standard substances were zero or very low comparing with the values obtained by methods using K
2Cr
2O
7 as an oxidant (K
2Cr
2O
7 method). Low COD value was also obtained on the effluent of treated human excrement by KMnO
4 method. Therefore, the COD value by KMnO
4 method is meaningless as an indicater of sewage pollution. 2. By K
2Cr
2O
7 method, especially with Ag
2SO
4 as a catalyst, high COD values were obtained for almost every standard substances and effluent of treated human excrement. In this case, COD values were also obtained by the inorganic substances such as NH
3 and Cl
-. 3. KMnO
4 method was slightly affected by Cl
-, while K
2Cr
2O
7 method was greatly influenced by Cl
-. The influence of Cl
- in K
2Cr
2O
7 method can be eliminated by adding HgSO
4 to the sample.
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