Kinetic Study of Removal of Toxic Metals by a Mixed Bacterial Culture Isolated from East Calcutta Wetlands

Abstract

Nowadays, one of the most prominent contributors in environmental pollution, specifically in case of soil and ground water pollution is industrial effluent which is laden with heavy metals like lead, cadmium, mercury etc. Heavy metals in hazardous waste cause serious health issues. Removal of heavy metals by chemical= processes results in residual toxicity. Thus, bioremediation is much more beneficial as an economic and environment friendly method. The present study deals with lead and cadmium. Mixed bacterial cultures were obtained from the soil collected from East Calcutta Wetlands. The cultures were acclimatized in presence of lead and cadmium separately. The pure cultures capable of growing in presence of lead or cadmium were isolated from the mixed bacterial culture. After isolation, the strains were identified to be Stenotrophomonasmaltophilia (tolerating lead) and Bacillus subtilis (tolerating cadmium) by 16s rRNA sequence data analysis method. The µmax (maximum specific growth rate) value, without lead inhibition, was found to be 0.321 hr-1 and with lead inhibition, was found to be 0.182 hr-1. Growth kinetic study was done for cadmium tolerating culture as well. For the culture tolerating cadmium, µmax value, without cadmium inhibition, was found to be 0.241 hr-1 and with cadmium inhibition, was found to be 0.187 hr-1. Metal removal kinetic study of the corresponding pure cultures were done in presence of respective metals. Atomic absorption spectroscopy (AAS) was used to determine the concentration of the metals. The removal kinetics of lead by Stenotrophomonasmaltophilia was investigated. With respect to lead concentration, the order was found to be 1.63 and the rate constant was 0.01967 mg-0.63l 0.63h-1. By Similar experiment, the removal rate of cadmium by Bacillus subtilis with respect to cadmium concentration was determined and the order of the reaction was 1.43 and the rate constant was found to be 0.01076 mg-0.43l 0.43h-1.