Sunlight-driven biogas biodesulfurization in an alkaline bioscrubber at low gas residence time coupled to an open photobioreactor.

This study addresses the application of an alkaline bacteria-microalgal process for biogas desulfurization. The bacterial consortium, composed of the genus Thioalkalivibrio, in conjunction with the microalgae Picochlorum sp. and Scenedesmus sp., fosters hydrogen sulfide (H2S) removal from biogas and promotes its conversion to sulfate. The performance of a bioscrubber (BS) coupled with a high-rate algal pond (HRAP) exposed to outdoor conditions for the removal of various H2S loads from synthetic biogas was analyzed. During diurnal period, the oxygen produced by the microalgae in the HRAP, in conjunction with controlled dissolved oxygen loading rates to the bioscrubber enhanced (three times respect to data published elsewhere) the removal rates of H2S from biogas up to 15.2 g/m3 h at gas residence time (GRT) of 4 min with H2S and CO2 inlet concentrations of 5000 ppmv and 30% vol, respectively, achieving efficient H2S and CO2 removal efficiencies of 99.9% and 80%, respectively. During the night, the supply of crude biogas was stopped to prevent sulfide accumulation and a decrease in pH. This sunlight-driven biodesulfurization process operates only during daylight hours, as it requires high external irradiance to sustain high oxygenic photosynthetic activity. Thus, the proposed microalgae-based desulfurization technology could serve as a supplementary unit to conventional systems, partially fixing CO2 into biomass and increasing the methane concentration of the purified biogas.