Biological Co-treatment of HS and reduction of CO to methane in an anoxic biological trickling filter upgrading biogas.

This study investigated the feasibility of co-treating HS and CO in a biological trickling filter (BTF) inoculated with hydrogenotrophic methanogens (HMs) and nitrate-reducing, sulfur-oxidizing bacteria. This was accomplished by introducing a pure culture of Thiobacillus denitrificans in a BTF that was successfully upgrading a biogas mimic (60:40 CH:CO) to >97% methane using an enriched HM consortium. Nitrate was fed as the electron acceptor to oxidize HS. The results revealed that a severe competition for hydrogen's electrons occurred between carbon dioxide and nitrate. Due to this competition, N:S loading rates of 16:1 were required to achieve >98% HS removal, a ratio which is four times greater than the theoretical N:S ratio for complete sulfur oxidation. However, such high nitrate loading rates (>50 g N-NO m h) had a negative impact on the BTF's biogas upgrading performance. An electron balance illustrated the increasing diversion of H electrons towards nitrate reduction as nitrate loading increased. Overall, this study showed that simultaneous biogas upgrading and HS removal in a single bioreactor is possible, but that achieving high yields for both reactions requires further research in process and culture optimization.