Effect of S/N Ratio on the Removal of Hydrogen Sulfide from Biogas in Anoxic Bioreactors

Both biogas desulfurization and wastewater denitrification can be achieved simultaneously, when nitrate/nitrite is used as the electron acceptor for H₂S oxidation. The main objective of this study was to investigate the influence of the molar ratio of sulfide/nitrate (S/N) on biogas desulfurization performance in a biotrickling filter (BTF) and a biobubble column (BBC). The results show that with the decrease of the S/N ratios from 3.6 to 0.7, the removal efficiencies of H₂S increased from about 66 to 100 %, while the removal of nitrate decreased from 100 to 70 % in the two bioreactors. The BTF has a better and more stable desulfurization performance than the BBC does, which could be attributed to their different gas-liquid contacting modes. With the increase of the S/N ratios from 1.0 to 2.5 in the BTFs, the removal of H₂S in biogas was affected slightly, while the percentages of the produced sulfate decreased evidently. In addition, different supplying methods of nitrate wastewater, i.e., intermittent and continuous, did not affect the removal of H₂S significantly, while the intermittent addition of nitrate wastewater increased the percentages of sulfate and denitrification performance.