Simultaneous methylmercaptan and hydrogen sulfide removal in the desulfurization of biogas in aerobic and anoxic biotrickling filters

Abstract Hydrogen sulfide (H 2 S) and methylmercaptan (CH 3 SH) are the most common sulfur compounds found in biogas. The simultaneous removal of H 2 S and CH 3 SH was tested at neutral pH in two biotrickling filters, one operated under aerobic conditions and the other one under anoxic conditions. Both reactors were run for several months treating a H 2 S concentration of around 2000 ppm v . Then, the effect of CH 3 SH loading rate (LR) on H 2 S and CH 3 SH removal was investigated in both reactors maintaining a constant H 2 S LR of 53–63 gS-H 2 S m −3  h −1 , depending on the reactor. Initially, CH 3 SH concentration was stepwise increased from 0 to 75–90 ppm v . Maximum elimination capacities (ECs) of around 1.8 gS-CH 3 SH m −3  h −1 were found. After that, the CH 3 SH LR was increased by testing different empty bed residence times (EBRTs) between 180 and 30 s. Significantly lower ECs were found at short EBRTs, indicating that the systems were mostly mass transfer limited. Finally, EBRT was stepwise reduced from 180 to 30 s at variable CH 3 SH and H 2 S loads. Maximum H 2 S ECs found for both reactors were between 100 and 140 gS-H 2 S m −3  h −1 . A negative influence was found in the ECs of CH 3 SH by the presence of high H 2 S LR in both biotrickling filters. However, sulfur mass balances in both reactors and batch tests under aerobic and anoxic conditions showed that CH 3 SH chemically reacts with elemental sulfur at neutral pH, enhancing the overall reactors performance by reducing the impact of sulfur accumulation. Also, both reactors were able to treat CH 3 SH without prior inoculation because of the already existing sulfide-oxidizing microorganisms grown in the reactors during H 2 S treatment. Co-treatment of H 2 S and CH 3 SH under aerobic and anoxic conditions was considered as a feasible operation for concentrations commonly found in biogas (2000 ppm v of H 2 S and below 20 ppm v of CH 3 SH).

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