Enhancement of anaerobic digestion by adding elemental sulfur

In this study, a new approach to enhance methane (CH₄) production from organic substrates in anaerobic digestion (AD) has been discovered. That is, the addition of elemental sulfur (S⁰) particles into the AD system promotes the synergistic growth of elemental sulfur disproportionation bacteria, acidogenic bacteria and methanogenic archaea, thus facilitating hydrolysis, acidogenesis and methanogenesis. The efficacy of this AD enhancement pathway was confirmed in AD experiments with glucose as a model organic substrate. The results demonstrated that CH₄ production in the AD system increased considerably with S⁰ dosages ranging from 20 mg/L to 300 mg/L. Two gas production peaks appeared at dosages of 20 mg/L and 180 mg/L, where the total CH₄ production increased by 2.1 times and 2.5 times, respectively compared with the control group. However, inhibitory effect was observed for S⁰ dosages above 300 mg/L. The chemical states of S, the microbial community and the abundance of key functional enzymes in the AD system were analyzed. The results showed that S⁰ addition increased the relative abundance of Dethiobacteraceae, Caldatribacterium, Anaerolineaceae, Methanobacterium and Methanosaeta and considerably increased the abundance of key functional enzymes, such as dehydrogenase, D-glucosidic glucosidase, pyruvate synthase and acetyl-CoA deacetylase. The enrichment of these microorganisms and functional enzymes was strongly positively correlated with the production of volatile fatty acids and CH₄, demonstrating that S⁰ addition effectively enhances methanogenesis during AD.