Effective bioremediation and toxicity assessment of tannery wastewaters treated with indigenous bacteria

This study evaluated the bioremediation capacity of indigenous bacteria isolated from tannery sludge for two different tannery wastewaters collected from Kanpur and Chennai. To identify bacteria which can efficiently degrade a mixture of different pollutants, the isolates were grown in hazardous 100% tannery wastewaters. The reductions in toxicants such as chromium, sulphate, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the wastewater were analysed post-bioremediation. Amongst the isolates, Citrobacter freundii was able to reduce the concentration of multiple toxicants such as chromium by 73% and sulphate was reduced by 68% bringing down the level much below the permissible limit stipulated by Bureau of Indian Standards (BIS). Notably, the organic load characterized by BOD and COD was also lowered by 86 and 80%, respectively. The indigenous isolates, not only bioremediated the Kanpur effluent but, also significantly detoxified the Chennai effluent having higher toxicant load. An interesting observation made during the study was better survival and growth along with the development of appendages of Artemia nauplii in the treated wastewaters which thus further confirmed reduction in toxicity of the effluents. The results thus demonstrate that the tested indigenous strains are promising for bioremediation of tannery wastewater and effectively improve the water quality for safe discharge.