EFFECT OF HEXAVALENT CHROMIUM ON THE KINETIC PARAMETERS OF ACTIVATED SLUDGE PROCESS

Abstract

Chromium ions are very commonly found in waste-water coming from large number of process industries namely electroplating, paints, photochemicals, refinery, dys etc. Because of toxic nature of hexavalent chromium ions to biological systems, mixing of these wastes with municipal waste or other high BOD wastes, hinder the performmance the biological waste treatment plants. In the present work experiment were conducted to study the effect of hexavalent chromium ion [Cr (VI)) on the aerobic biological treatment of organic waste under batch conditions. The influence of process parameters such as temperature, pH and initial chromium ion doses, on the COD reduction rate and specific growth rate of biomass have been studied. The results indicate that chromium ions hinder the growth rate of biomass in the reactor resulting in the net performance of the biological system. The Cr(VI) doses up to 50 mg/L are not very detrimental to the system, however Cr(VI) doses above 50 mg/L, have substantial adverse effect on both COD reduction rate and specific growth rate of biomass. The optimum pH and temperature for the system were found to be 7.0 and 37°C respectively. There was no effect of Cr(VI) ions on the optimum pH and temperature of the system. The maximum specific growth rate was observed at 37°C and pH 7 as 1.8 day-1 in the absence of Cr(VI) ions. This value decreases propoti-onally with the addition of Cr(VI) ions to the system.