Effect of granular activated carbon adsorption and size of microbial aggregates in inoculum on stimulating direct interspecies electron transfer during anaerobic digestion of fat, oil, and grease

Enhancing proton-coupled electron transfer drives efficient methanogenesis in anaerobic digestion

The enhancement of electron or proton transfer between syntrophic microbes has been widely recognised as a means for improving methane generation. However, the uncoupled supplementation of electrons and protons in multiphase anaerobic environment hinders the balanced uptake of electrons and protons in the cytoplasm of methanogens, limiting methanogenesis efficiency. Herein, the cooperative effect of a proton-conductive material (PM) and an electron-conductive material (EM) in enhancing proton-coupled electron transfer (PCET) and driving efficient methanogenesis in anaerobic digestion was investigated. The cooperation of the PM and EM significantly increased methane production and the maximum methane generation rate by 78.9 % and 103.5 %, respectively, indicating enhanced methanogenesis efficiency. Analysis of the physicochemical properties, biochemical components, and microbial dynamics revealed that the cooperation of the PM and EM improved the metabolism of syntrophic microbes, which was critically dependent on electron and proton transfer. This enhancement was primarily due to the improvement in PCET, as mainly supported by hydrogen/deuterium kinetic isotope effect measurements, multi-omics integration analyses and reaction thermodynamics and kinetics analyses. Our findings suggest that the PCET enhancement stimulated efficient membrane-bound enzymatic reactions related to electron-driven proton translocation and facilitated electron and proton supply for CO2 reduction to realise highly efficient methane generation. These findings are expected to provide a new insight into effective electron and proton coupling transfer for methanogenic metabolism in multiphase anaerobic environments.

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.

A critical review of improving mainstream anammox systems: Based on macroscopic process regulation and microscopic enhancement mechanisms

Full-scale anaerobic ammonium oxidation (anammox) engineering applications are vastly limited by the sensitivity of anammox bacteria to the complex mainstream ambience factors. Therefore, it is of great necessity to comprehensively summarize and overcome performance-related challenges in mainstream anammox process at the macro/micro level, including the macroscopic process variable regulation and microscopic biological metabolic enhancement. This article systematically reviewed the recent important advances in the enrichment and retention of anammox bacteria and main factors affecting metabolic regulation under mainstream conditions, and proposed key strategies for the related performance optimization. The characteristics and behavior mechanism of anammox consortia in response to mainstream environment were then discussed in details, and we revealed that the synergistic nitrogen metabolism of multi-functional bacterial genera based on anammox microbiome was conducive to mainstream anammox nitrogen removal processes. Finally, the critical outcomes of anammox extracellular electron transfer (EET) at the micro level were well presented, carbon-based conductive materials or exogenous electron shuttles can stimulate and mediate anammox EET in mainstream environments to optimize system performance from a micro perspective. Overall, this review advances the extensive implementation of mainstream anammox practice in future as well as shedding new light on the related EET and microbial mechanisms.