Evaluation of pilot scale moving bed biofilm reactor and stripping process for sulfate reduction from real high-sulfate waste activated sludge: Effect of HRT and return sludge

Finding an appropriate strategy to enhance the methane content of biogas and reduce the level of produced H2S simultaneously from waste activated sludge (WAS) are of importance. In this study, a pilot-scale biophysical process was used for pretreating of municipal sulfate-rich WAS in Karbala wastewater treatment plant. The process uniquely integrates a moving bed biofilm reactor (MBBR) for biological sulfate reduction and a stripper for removing H2S physically. The MBBR operated in two scenarios: with and without sludge recycling line, each with different hydraulic retention time (HRT) of 36, 24, and 12 h. The findings from both scenarios were impressive in terms of sulfate reduction and H2S removal at different residence time. In the MBBR system without recycling, the sulfate reduction efficiency varied between 75.6 % and 100 % as HRT increased, whereas with recycling system, it ranged from 81.2 % to 100 %. These findings demonstrated the efficiency of the process in reducing sulfate levels from sludge. Also, in the system without recycling, the H2S removal efficiency ranged from 78 % to 83 %, whereas in the system with recycling, it ranged from 72 % to 81 %. These results highlight the effectiveness of the stripper in physically eliminating H2S, further enhancing the overall treatment process. This research presents a pioneering approach by combining MBBR technology with a stripper, on a pilot scale in treating sulfate-rich sludge and its applicability for sulfate reduction and H2S removal from various industrial and municipal sludge.