Sulfur Metabolism and Its Inhibition Alleviation in Anaerobic Digestion Ecosystems

Sulfate reduction mediated by sulfate-reducing bacteria (SRB) significantly impacts the efficiency of anaerobic digestion, particularly due to the inhibitory toxicity of its metabolite, hydrogen sulfide, on the microbial community of anaerobic digestion. Sulfate reduction occurs through the assimilatory sulfate reduction and/or the dissimilatory sulfate reduction, and the produced hydrogen sulfide can inhibit methanogenesis. Generally, two types of SRB exist in anaerobic digestion systems, with incomplete SRB converting organic carbon to acetate and complete SRB converting organic carbon to carbon dioxide. The competition between SRB and methanogens is affected by diverse factors, especially the carbon to sulfate ratio. Furthermore, alleviation strategies for the inhibition of hydrogen sulfide were proposed. Specifically, the potential of optimizing the substrate ratio and the addition of adsorbent conductive materials (such as biochar and zero-valent iron) to regulate the competition and collaboration between SRB and methanogens were detailed.