Influence of S/N Ratio on Biogas Desulfurization Performance Using Conventional Anoxic Bioreactor (ABR) and Membrane Bioreactor (AMBR)

The increasing energy crisis is becoming a difficult problem for the sustainable development of human being, and the demand for renewable energy, like biogas, is becoming more and more vital. The presence of hydrogen sulfide (H2S) in biogas is extremely hazardous to human health, poisonous to process catalysts, and corrosive to equipment. In this study, alternative techniques for anoxic biogas desulfurization using chemically produced nitrate as an electron acceptor was developed. The objective of this study was to investigate the influence of different biogas flowrate and S/N molar ratio on desulfurization and denitrification performance in a conventional ABR and AMBR. The results show that the AMBR has a better and more stable desulfurization and denitrification performance than the ABR does, which could be attribute to their different gas-liquid contacting trends. At low biogas flowrate, the AMBR is able to enrich the CH4 contents from 60% to 75%, whereas the CO2 contents dropped from 39% to 20%; moreover, it effectively removed almost all gas phase H2S from 10,000 ppm to 100 ppm (up to 99%). However, in the conventional ABR, the gas-phase H2S removal efficiency attained only about 62%. With the increase of the S/N ratios from 1.9 to 4 in the AMBR, the biological oxidation efficiencies of dissolved sulfide was affected slightly, while the percentages of the produced sulfate decreased evidently; but the removal of nitrate increased from about 75% to 100%. It can be conclude that the high S/N molar ratio had a significant negative effect on denitrification and favors biological elemental sulfur generation. Therefore, the AMBR process developed in this study is an easy-to-operate and effective alternative than conventional ABR for simultaneous desulfurization and autotrophic denitrification.