Geochemistry and mass balance of selected heavy metals in East Kolkata Wetlands, a Ramsar site of West Bengal, India

A geochemical profile of the East Kolkata Wetlands and its efficiency in treating municipal and industrial wastewater is presented in this study. The mean concentration (mg/L) of some of the trace metals in the un-treated pond waters decreased in the order of Mn (12.6) > Cr (11.8) > Fe (8.0) > Ni (6.2) > Zn (2.7) > Cu (2.6) > As (2.0) > Pb (1.8) > Cd (0.2). The corresponding mean concentration (mg/kg, dry weight) of the sediment trace metals decreases in the order of Fe (446.2) > Mn (114.1) > As (112.4) > Cr (30) > Zn (9.0) > Ni (6.8) >Cu (5.7) > Pb (3.0) > Cd (0.5). Our study found that the bioremediation of the wastewaters containing Al, Cr, Mn, Fe, Pb, Ni, Cu, and Zn was not uniform in all the ponds. Although reduced concentrations of Mn and Fe were found in 98% of the treated pond waters, 56% of the ponds could not remove Zn and As. Mass balance calculation showed that the differential load after microbial treatment of the wastewaters decreased in the order of Cr (differential load 3463 kg/day), Ni (1743 kg/day), Cu and Zn (681, 684 kg/day, respectively).