Response of BOD, COD and TOC of secondary effluents to chlorination

The behavior of BOD, COD, and TOC of secondary effluents under varied concentrations of chlorine, was investigated. The three parameters were measured in final effluents treated with chlorine dosages in the range of 2–50 mg l−1 and 30 min contact time followed by dechlorination with sodium thiosulfate. Chlorine dosages above 10 mg l−1 resulted in increased BOD and COD levels of the effluent, with chlorine dosages above 30 mg l−1 resulted in almost double the original BOD and COD values. TOC measurements showed obvious stability against chlorine impact, which makes TOC a better indicator for the organic content of wastewater. Almost all the observed increase in BOD measurements could be attributed to modification of the dissolved part of the organic matter by chlorine. Effects of chlorine on BOD and COD were also confirmed by actual data reported by the treatment plant. The results also show that the response of BOD and COD to chlorination is a function of chlorine dosage and the organic content of wastewater.