Deciphering microbial responses to H2S inhibition of typical functional microorganisms in anaerobic digestion ecosystems
Wenhui Shu, Bang Du, Guangxue Wu
Abstract
Hydrogen sulfide (H 2 S), a product of sulfate reduction in anaerobic digestion (AD) systems, poses severe challenges by reducing methane production and destabilizing system performance. Despite extensive studies on H 2 S toxicity, the specific responses and adaptation mechanisms to H 2 S stress of key functional microorganisms in AD systems remain insufficiently elucidated. Four reactors were operated with sequencing batch reactor (SBR) and continuous flow reactor (CFR) configurations under varying COD/sulfate ratios (2 and 1) to investigate microbial response to H 2 S inhibition. Long-term experiments demonstrated that CFRs combined with a COD/sulfate ratio of 1 achieved superior sulfate reduction and ethanol degradation rates under H 2 S stress, while SBRs with a COD/sulfate ratio of 2 facilitated methanogenic activity. Batch inhibition experiments revealed that ethanol-oxidizing bacteria (EOB) and incomplete oxidizing sulfate-reducing bacteria (IO-SRB) exhibited greater H 2 S tolerance in CFRs, with EOB (IC 50 = 51.2–185.1 mg/L) generally outperforming IO-SRB (IC 50 = 47.4–97.7 mg/L). While acetoclastic methanogens (AM) and complete oxidizing sulfate-reducing bacteria showed enhanced H 2 S tolerance in SBRs compared to CFRs, particularly AM in SBR with the COD/sulfate ratio of 2 (IC 50 = 113.2 mg/L). Microbial adaptation analysis demonstrated that SBRs promoted Methanothrix enrichment, enhancing detoxification capacity by specifically increasing the relative abundance of genes encoding thiosulfate sulfurtransferase to mitigate H 2 S toxicity. Desulfomicrobium and Geobacter were significantly enriched in CFRs, and they mitigated H 2 S inhibition through increased cytochrome bd oxidase and cysteine synthase genes, respectively. Furthermore, thioredoxin and cysteine desulfurase protein repair genes sustained microbial metabolism under H 2 S stress. This study provides critical insights into microbial tolerance and adaptive strategies to H 2 S under different reactor configurations, offering guidance for optimizing AD processes in sulfate-rich wastewater treatment.