The effect of biofilm growth on the sulfur oxidation pathway and the synergy of microorganisms in desulfurization reactors under different pH conditions.

Biofilm growth affects the oxygen transfer in biofilm and thus the oxidation pathway of sulfur and the synergy of microorganisms. In this study, the effect of biofilm growth on the oxidation pathway of H2S and the synergy of microorganisms in desulfurization reactors under different pH conditions was first discussed to enhance the understanding of desulfurization process. A biotrickling filter (BTF) was operated for 168 days under acidic condition (pH<4.7) and 32 days under alkaline condition (7.0 <pH<10.2). In acidic period, the average growth mass (AGM) of biofilm was 0.04 g/L-BTF/d, and most of S-H2S was converted to S-SO42- (>89.0%). In alkaline period, the AGM raised to 0.97 g/L-BTF/d, and 77.0% of S-H2S was transferred to elemental sulfur (S0) and polysulfanes (R-Sx-R) accumulated in biofilm. The increase of biofilm and sulfur-oxidizing bacteria activity limited the oxygen transfer in alkaline biofilm, leading to the accumulation of S0 and the emergence of an obligate anaerobe- Acetoanaerobium (8.1%). The formation of R-Sx-R may be due to the reaction of S0 with thiols produced by a thiol-producing bacterium- Pseudomonas (6.7%). The uneven distribution of oxygen in biofilm caused by biofilm growth complicated the transfer pathway of sulfur and the synergy of microorganisms in desulfurization system.