Development of enhanced sulphidogenesis process for the treatment of wastewater having low COD/SO42− ratio

An upflow hybrid sulphidogenesis reactor of 1.75 L volume was developed (at oxidation-reduction potential (ORP) = −225 ± 25 mV) using flocculent extended aeration process sludge (selected based on screening study at COD/SO42− ratio = 1) for enhanced sulphidogenesis and COD removal. The reactor was subjected to various loading rate studies at a hydraulic retention time (HRT) of 1 day with COD/SO42− ratio of 1.3. At loading rate of 2.5 kg COD/(m3 day), excellent performance with more than 97% removal of sulphate was achieved within bottom 40% volume of the reactor. At a higher loading rate of 3.75 kg COD/(m3 day), there was a decrease in both sulphate (70-75%) and COD (50%) removal efficiencies. A controlled and continuous air injection (0.19 L/(L min)) given at 40% volume of the reactor affected sulphide oxidation inside the reactor and enhanced the sulphate reduction in the reactor. The specific sulphate reduction capacity of mixed culture drawn from the bottom part of the reactor was 0.35 kg SO42−/(kg VSS day). The results of this study showed that enhanced sulphidogenesis with sulphide inhibition control can maintain sulphate-reducing bacteria (SRB) in anaerobic reactor at low COD/SO42− ratios between 1 and 2, with efficient simultaneous removal of COD and SO42−. The sulphide generated in the system can be recovered as elemental sulphur and/or oxidized back to sulphate.