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Microbial electrosynthesis is a promising technology that recovers energy from wastewater while converting CO 2 into CH 4 . Constructing a biocathode with both strong H 2 -mediated and direct electron transfer capacities is crucial for efficient startup and long-term stable CH 4 production. This study found that introducing carboxyl groups onto the cathode effectively enhanced both electron transfer pathways, improving the reduction rate and coulombic efficiency of CH 4 production and increasing the CH 4 yield by 2-3 times. Carboxyl groups decreased the overpotential for H 2 evolution and increased current density, thereby enhancing H 2 -mediated electron transfer. Additionally, carboxyl groups increased the relative abundance of Methanosaeta by 3%-10%, doubled the protein content in extracellular polymeric substances, and boosted the expression of cytochrome c-related genes, thereby enhancing direct electron transfer capacity. These findings present a novel and efficient approach for constructing a stable, high-performance biocathode, contributing to energy recovery and CO 2 fixation., 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., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The productivity and efficiency of two-chamber microbial electrolysis cell and anaerobic digestion integrated system (MEC-AD) were promoted by a complex of anaerobic granular sludge and iron oxides (Fe-AnGS) as inoculum. Results showed that MEC-AD with Fe-AnGS achieved biogas upgrading with a 23%-29% increase in the energy recovery rate of external circuit current and a 26%-31% decrease in volatile fatty acids. The energy recovery rate of MEC-AD remained at 52%-57%, indicating a stable operation performance. The selectively enriched methanogens and electroactive bacteria resulted in dominant hydrogenotrophic and acetoclastic methanogenesis in the cathode and anode chambers. Mechanistic analysis revealed that MEC-AD with Fe-AnGS led to specifically upregulated enzymes related to energy metabolism and electron transfer. Fe-AnGS as inoculum could improve the long-term operation performance of MEC-AD. Consequently, this study provides an efficient strategy for biogas upgrading in MEC-AD., 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., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The performance and microbial community dynamics in anaerobic co-digestion (ACoD) of chicken manure and corn stover with different modification methods and trace element supplementation strategy were investigated in this study. KOH and liquid fraction of digestate (LFD) were applied for modification; Fe, Co, Mn, Mo, and Ni were used for supplement. Results showed that the selected trace element was insufficient in the partial or whole digestion process. When trace element supplement was combined with KOH or LFD modifications, the ACoD obtained biomethane yields of 245.3-258.0 and 254.0-261.8 mL N ·gVS -1 , 26.0%-32.5% and 30.5%-34.5% more than that of the control, respectively. Microbial community analyses indicated that the composition and diversity of archaea and bacteria varied at genus level. Main pathways involved in ACoD were affected accordingly, which in turn affected co-digestion performance. This study demonstrated that the combining modification and trace element supplement could improve the digestion performance and achieve higher biomethane yield., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Liquid fraction of digestate (LFD) was used to pretreat corn stover to enhance the biomethane production of anaerobic co-digestion (AcoD) with cattle manure. The effects of LFD concentration and water content (WC) for pretreatment on co-digestion performance and microbial community structure were investigated in a batch system. Results showed that the cumulative biomethane yield (CBY) for co-digestion was improved by 16.85%-41.78% compared with the control. The highest biomethane yield of 238.25 mL g VS -1 was obtained at 85% WC for pretreatment and a 5 M LFD concentration, and this yield was 41.78% higher than that in the control. The LFD pretreatment enriched the dominant bacterial phyla (Firmicutes and Bacteroidetes), but had little influence on the prevalent archaeal genus (Euryarchaeota). This study demonstrated that LFD pretreatment can greatly enhance the biomethane yield of co-digestion of corn stover and cattle manure under optimal parameters., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Biological and chemical pretreatment methods using liquid fraction of digestate (LFD), ammonia solution (AS), and NaOH were compared in the process of mesophilic anaerobic co-digestion of cattle manure and corn stover. The results showed that LFD pretreatment could achieve the same effect as the chemical pretreatment (AS, NaOH) at the performance of anaerobic digestion (AD). Compared with the untreated corn stover, the cumulative biomethane production (CBP) and the volatile solid (VS) removal rate of three pretreatment methods were increased by 25.40-30.12% and 14.48-16.84%, respectively, in the co-digestion of cattle manure and corn stover. T80 was 20-37.14% shorter than that of the control test (35 ± 1 days). LFD pretreatment not only achieved the same effect as chemical pretreatment, but also reduced T80 and improved buffer capacity of anaerobic digestion system. Therefore, this study provides meaningful insight for exploring efficient pretreatment strategy to stabilize and enhance AD performance for practical application., (Copyright © 2015 Elsevier Ltd. All rights reserved.)