Photoautotrophic removal of hydrogen sulfide from biogas using purple and green sulfur bacteria

Biogas desulfurization based on anoxygenic photosynthetic processes represents an alternative to physico-chemical technologies, decreasing the risk of O2 and N2 contamination. This work aimed at assessing the po-tential of Allochromatium vinosum and Chlorobium limicola for biogas desulfurization under different light intensities (10 and 25 klx) and H2S concentrations (1 %, 1.5 % and 2 %) in batch photobioreactors. In addition, the influence of rising biogas flow rates (2.9, 5.8 and 11.5 L d-1 in stage I, II and III, respectively) on the desulfurization performance in a 2.3 L photobioreactor utilizing C. limicola under continuous mode was assessed. The light intensity of 25 klx negatively influenced the growth of A. vinosum and C. limicola, resulting in decreased H2S removal capacity. An increase in H2S concentrations resulted in higher volumetric H2S removal rates in C. limicola (2.9-5.3 mg L-1 d-1) tests compared to A. vinosum (2.4-4.6 mg L-1 d-1) tests. The continuous photo-bioreactor completely removed H2S from biogas in stage I and II. The highest flow rate in stage III induced a deterioration in the desulfurization activity of C. limicola. Overall, the high H2S tolerance of A. vinosum and C. limicola supports their use in H2S desulfurization from biogas.