Simultaneous removal of chromium and sulphate from tannery waste using microbes

Abstract

Leather industry contributes to one of the major industrial pollution problems our country is facing today. Microbes (bacteria/fungi) are the most important eco-friendly agents for the degradation and detoxification of industrial pollutants along with organic waste removal. Extensive research has been carried out to find suitable, resistant and efficient microbes to treat the tannery effluent. In the concerned study, we have tried to isolate the organisms from the tannary effluent acclimatized them to increasing Chromium and Sulphate rich environment which may later be utilized towards bioremediation of both the pollutants. In this direction, bacteria resisting 240mg/l Cr and 280mg/l and others with 170mg/l Cr and 200mg/l sulphates have been obtained and tested for growth rates and Cr removal capacity. A maximum of 99.8% Cr removal have been achieved in four days of submerged culture by Micrococcus yunnanensis. The consortium of Pseudomonas aeruginosa & Micrococcus yunnanensis microbes is found to be best performing interms of biomass growth and removal of Cr than the individual isolate. These two microbes also remediated about 24% sulphate from the culture. The optimal parameters for treatment process were pH 7, temperature 35oC, rpm 100 and Cr concentration 150 mg/l. Laboratory scale fermenter study maintaining the optimized parameters showed 97.5 % removal of Cr in just 48 hours and the highest of which is 98% achieved in 56 hours. In a second step, the effluent was treated by a consortium of SRBs (Desulfovibrio desulfuricans, D. vulgaris and D. gigas) that utilize Cr(VI) as an electron acceptor for sulphate reduction and hence both Cr(VI) and sulphates get removed from the broth. From the initial concentrations of 150mg/l and 200 mg/l of Cr(VI) and sulphate in the simulated wastewater, it was brought down to 0.1 mg/l and 70.2 mg/l for Cr and sulphate respectively. Hence in a two stage biological treatment process for tannery waste, an excellent 99.9% Chromium and 63.9 % sulphate removal was achieved.