Enhanced propionate degradation and CO 2 electromethanogenesis in an up-flow dual-chamber electrocatalytic anaerobic bioreactor (UF-DC-EAB): Leveraging DIET-mediated syntrophy for microbial stability.

Anaerobic digestion faces numerous challenges, including high CO ₂ content in biogas and volatile fatty acids (such as propionate) accumulation in digestate. To address these issues, an up-flow dual-chamber electrocatalytic anaerobic bioreactor (UF-DC-EAB) was developed to enhance propionate degradation through microbial symbiosis while improving biogas quality via CO ₂ electromethanogenesis. Under the extreme conditions with propionate as the primary carbon source at 6-h HRT, the UF-DC-EAB achieved a propionate removal efficiency of 72.1 ± 9.4 % and a faradaic efficiency of 25.5 ± 5.1 %. Microbial community analysis revealed an enrichment of acetoclastic methanogens (Methanosarcinales, 5.4 %) and syntrophic propionate-oxidizing bacteria (Syntrophobacterales, 13.9 %) in the anode, which facilitated propionate degradation. In the cathode, hydrogenotrophic methanogens (Methanobacterium, 13.6 %) and electroactive bacteria (Geobacter, 6.2 %) were predominant, further promoting CO ₂ electromethanogenesis and biogas upgrading. Co-occurrence network and structural equation modeling indicated that the electrocatalytic regulation roused the intrinsic capability of the microbial community to oxidize propionate and provoked the occurrence of direct interspecies electron transfer (DIET) among the enriched functional microorganisms, by regulating the synthesis of key molecules like F ₄₂₀ and cytochrome c in response to propionate-induced changes. The DIET-mediated syntropy increased the net energy output by 212.5 %. This study presents a novel electrochemical system combining CO ₂ electromethanogenesis with propionate-rich digestate degradation, offering an efficient approach for anaerobic post-treatment.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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