Abstract
Removal of heavy metals (Zn, Pb, Cu, Ni and Cr) from municipal raw sewage by extended aeration activated sludge treatment process and the effects of the treated effluent in relation to the raw sewage on the heavy metal contents of water of the receiving water body, Buckingham canal at Kalpakkam was monitored seasonally during pre-monsoon, monsoon, winter and summer. It was found that the concentrations of Zn, Pb, Cu, Ni and Cr were 0.12, 0.063, 0.57, 0.63 and 0.019 ppm, respectively in the raw sewage, which were reduced considerably at each phase of the treatment, at aeration tank with a removal efficiency (RE) of 17, 13, 14, 33 and 31%, respectively, and in secondary clarifier with RE of 67, 73, 72, 87 and 47%, respectively. The concentrations of these heavy metals have increased in the downstream compared to that of its upstream of the canal in both treated as well as untreated sewage outfall zones, and were higher in the later zone. The concentrations of these heavy metals were higher during pre-monsoon and monsoon seasons followed by that of summer and winter in the canal water.
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