Sulfate bioreduction and elemental sulfur formation in a packed bed reactor

•97% removal from 1500 mg/L SO42∧, at 0.70 COD/SO42∧ ratio, 24 h HRT by mixed bacterial culture.•S0 formation in absence of DO.•Port profile sampling for better discussion.

A laboratory scale packed bed reactor (PBR) was fabricated and operated to study its feasibility on SO42∧ reduction. The reactor was packed with polyurethane foam cubes and operated under different feeding and operating conditions of HRT, COD/SO42∧ ratio and SO42∧ concentration. Microbial community characterization showed the presence of sulfate reducing bacteria (SRB) Desulfovibrio species in the bioreactor. The reactor performance was found to be highly efficient than those previously reported at COD/SO42∧ ratio below 0.7 and HRT of 24 h. A maximum SO42∧ reduction of 97% was achieved in the PBR when operated at an HRT of 24 h with SO42∧ concentration of 1500 mg/L and COD/SO42∧ ratio of 0.67. Formation of elemental sulfur was noticed even in absence of any dissolved oxygen which might probably be due to oxidation of sulfides by the intermediate sulfite.