RESUMO
Heavy metals such as zinc in untreated industrial effluents cause diseases and disorders in living organisms. They cannot be degraded like organic contaminants and hence have to be removed. Though physical and chemical methods are available for their removal, most of them are not economical and eco-friendly. Hence, a suitable technique is necessary to minimize the deleterious effects of dispersion of heavy metals in ecosystems. Though zinc serves as a micronutrient, it becomes toxic in higher concentrations. Bacteria can be used in the removal of zinc and the process is economical and ecofriendly. Hence, in the present study, we tested zinc removal efficiency of Bacillus subtilis (MTCC 2423) for various concentrations viz. 100, 200, 300, 400 and 500 ppm of zinc in nutrient broth for a period of 10 days. Samples were tested for the zinc level every two days in each concentration and the maximum removal was noticed after six days of treatment. With the increase in zinc concentration, both biomass and zinc removal efficiency showed an increase. Autoclaved cells showed maximum zinc removal when compared with other cell types. Among the other heavy metals tested, iron enhanced the biomass of B. subtilis during zinc treatment and the results are discussed.
RESUMO
Effluent samples from an electroplating industry located at Madurai, India were collected and analysed for chosen physico-chemical parameters. Among the heavy metals tested, zinc exhibited highest level with 739 ppm with a pH of 4.83. The bacterial strain isolated from the effluent contaminated site was identified as Escherichia coli and it was subjected to 15, 20 and 25% of effluent in minimal broth for 20 days. Optical density and pH changes were recorded daily and the levels of chromium, nickel and zinc were analysed after ten and twenty days of treatment. Significant reduction in the level of zinc was observed and the results are discussed.