Absorption removal of hydrogen sulfide from recirculated biogas

This study is focused on the effect of biogas recirculation with hydrogen sulfide removal on anaerobic treatment of sulfur-enriched synthetic wastewater in a UASB reactor. The presence of hydrogen sulfide in biogas causes problems in its further energy recovery while sulfides inhibit the anaerobic process. The reactor was gradually loaded with sulfates and their effect on the reactor operation was monitored. At the same time, external absorption of hydrogen sulfide from biogas with absorbent regeneration was operated. The results show that low concentrations of added sulfates support biogas production. At the sulfate concentration of 125 mg l⁻¹, biogas production increased by approximately 2 l d⁻¹. However, further increasing of the amount of sulfates in the substrate led to the opposite effect. At twice the amount of sulfates, the biogas production decrease by 1 l d⁻¹ and its adverse effects on the removal of N-NH₄, N_C and P-PO₄ were observed. Biogas recirculation through the absorption column ensured a decrease in the hydrogen sulfide concentration from 19 960 ppm to 4 030 ppm and an increase in the methane content from 59.2 % to 83 % and also a decrease in the sulfides concentration in the reactor. From the measured data it can be concluded that this method reduces sulfides inhibition.