Effective Treatment of Tannery Effluent by Biofilm-Forming Bacteria and Evaluation of their Toxicity Reduction

This study investigates the treatment efficiency of biofilm immobilized MBBR (moving bed biofilm reactor) system for tannery effluent compared to suspended cells system. A mixed culture of biofilm-forming strains Bacillus vallismortis, Bacillus haynesii, Alcaligenes aquatilis, and Enterococcus faecium showed increased biofilm formation and Cr(VI) reduction compared to individual strains. The MBBR carriers were shown to have a greater biofilm formation (cell viability = 8.255 log units) and EPS yield (58 mg/g total solids) compared to the PUF (polyurethane foam) carriers (cell viability = 6.806 log units, and EPS yield = 36.4 mg/g total solids). The COD removal efficiency of the biofilm immobilized MBBR was higher (82.5%) compared to suspended cells treatment (61.3%) in the fed-batch treatment method. GC–MS analysis showed that 2,6-Bis(tert-butyl) phenol and 1-monopalmitin compounds were either diminished or transformed during treatment with biofilm immobilized MBBR. Furthermore, phytotoxicity and genotoxicity tests confirmed the lower toxicity of biofilm stabilized MBBR treated effluent compared to treated suspended cells on fenugreek plant and Allium cepa L. roots, respectively. The study indicates that treating tannery effluent with a mixed culture of B. vallismortis, B. haynesii, A. aquatilis, and E. faecium immobilized on MBBR effectively removes both organic and inorganic contaminants along with genotoxic effects.