Boosting thermophilic anaerobic digestion with conductive materials: Current outlook and future prospects

Intermittent electrostimulation-modified direct interspecies electron transfer for enhanced methanogenesis in anaerobic digestion of sulfate-rich wastewater

Methane recovery and organics removal in sulfate (SO42-)-rich wastewater anaerobic digestion are hindered by electron competition between methanogenesis and sulfidogenesis. Here, intermittently electrostimulated bioelectrodes were developed to facilitate direct interspecies electron transfer (DIET)-driven syntrophic methanogenesis, increasing substrate competition among methanogenic archaea (MA). By optimising the electrochemical environment, MA was able to employ electron transfer more efficiently than sulfate-reducing bacteria (SRB), resulting in significant methane accumulation (58.1 ± 1.0 mL-CH4/m3reactor) and COD removal (90.5 ± 0.5 %) at lower COD/SO42- ratio. Intermittent electrostimulation improved the metabolic pathway for electroactive bacteria to utilize acetate and direct electrons to electrotrophic MA, decreasing SRB abundance and affecting the sulfate reduction pathway. Intermittently electrostimulated biofilms significantly increased gene levels of key enzymes in electron transport for cytochrome and e-pili biosynthesis, crucial for DIET, demonstrating enhanced DIET-driven syntrophic methanogenesis. This study provides a strategic approach to optimize methanogenesis in sulfate-rich wastewater anaerobic digestion.

Adding Granular Activated Carbon and Zerovalent Iron to the High-Solid Anaerobic Digestion System of the Organic Fraction of Municipal Solid Waste: Anaerobic Digestion Performance and Microbial Community Analysis

Anaerobic digestion (AD) performance and microbial dynamics were investigated in a high-solid anaerobic digestion (HSAD) system of the organic fraction of municipal solid waste (OFMSW). 1, 5, 10, and 15% (w/w, dry weight of the OFMSW) of granular activated carbon (GAC) and zerovalent iron (ZVI) were added to the HSAD system. The results showed that adding ZVI and GAC can improve the methane yield of the OFMSW. Notably, R-(GAC + ZVI) exhibited the highest cumulative methane yield of 343.0 mL/gVS, which was 57.1% higher than that of the R-control. At the genus level, the dominant bacteria included norank_f__norank_o__MBA03, norank_f__norank_o__norank_c__norank_p__Firmicutes, Fastidiosipila, norank_f__Rikenellaceae, and Sphaerochaeta, while Methanoculleus, Methanobacterium, and Methanosarcina were the dominant archaea. The highest relative abundance of norank_f__norank_o__norank_c__norank_p__Firmicutes was 30.8% for the R-(GAC + ZVI), which was 71.4% higher than that of the R-control. The relative abundance of Methanoculleus and Methanobacterium for the R-(GAC + ZVI) and the R-control group accounted for 79.0 and 90.8% of the total archaeal abundance, respectively. Additionally, the relative abundance of Methanosarcina was 10.6% for R-(GAC + ZVI), which was higher than that of the R-control (1.1%). After the addition of GAC and ZVI, the electron transfer capacity of the HSAD system was enhanced, resulting in promoted methane production. Thus, the simultaneous addition of GAC and ZVI to the HSAD system can be an effective strategy to promote the cumulative methane yield of the OFMSW.