Anaerobic co-digestion was conducted on the solid residues after three-phase separation of kitchen waste (KWS) and waste-activated sludge (WAS), the synergistic effects and process performance were studied during co-digestion at different ratios of KWS to WAS. KWS and WAS mix ratios of 0:1, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1 and 1:0 (based on TS). The results showed that a ratio of KWS to WAS of 1:1 got a very high methane recovery with a methane yield of 310.45 ± 30.05 mL/g VSadded. The highest concentration of free ammonia among all reaction systems was only 70.23 ± 5.53 mg/L, which was not enough to produce ammonia inhibition in the anaerobic co-digestion system. However, when the KWS content exceeded 50%, methane inhibition and prolongation of the lag phase were observed due to the accumulation of volatile fatty acids (VFAs), and during the lag phase. Microbial community analysis showed that various bacterial groups involved in acid production and hydrolysis were mainly dominated by phylum Firmicutes, Chloroflexi, Proteobacteria and Bacteroidetes. Hydrogenotrophic methanogen was found to dominate all archaeal communities in the digesters. Co-digestion of KWS with WAS significantly increased the relative abundance of Methanobacterium compared with anaerobic digestion of WAS alone.

Nitrogenases are the only known enzymes that reduce molecular nitrogen (N2) to ammonia. Recent findings have demonstrated that nitrogenases also reduce the greenhouse gas carbon dioxide (CO2), suggesting CO2 to be a competitor of N2. However, the impact of omnipresent CO2 on N2 fixation has not been investigated to date. Here, we study the competing reduction of CO2 and N2 by the two nitrogenases of Rhodobacter capsulatus, the molybdenum and the iron nitrogenase. The iron nitrogenase is almost threefold more efficient in CO2 reduction and profoundly less selective for N2 than the molybdenum isoform under mixtures of N2 and CO2. Correspondingly, the growth rate of diazotrophically grown R. capsulatus strains relying on the iron nitrogenase notably decreased after adding CO2. The in vivo CO2 activity of the iron nitrogenase facilitates the light-driven extracellular accumulation of formate and methane, one-carbon substrates for other microbes, and feedstock chemicals for a circular economy.

Measuring greenhouse gas (GHG) fluxes and pools in ecosystems are becoming increasingly common in ecological studies due to their relevance to climate change. With it, the need for analytical platforms adaptable to measuring different pools and fluxes within research groups also grows. This study aims to develop a procedure to use portable optical spectroscopy-based gas analyzers, originally designed and marketed for gas flux measurements, to measure GHG concentrations in aqueous samples. The protocol involves the traditional headspace equilibration technique followed by the injection of a headspace gas subsample into a chamber connected through a closed loop to the inlet and outlet ports of the gas analyzer. The chamber is fabricated from a generic mason jar and simple laboratory supplies, and it is an ideal solution for samples that may require pre-injection dilution. Methane concentrations measured with the chamber are tightly correlated (r2 > 0.98) with concentrations determined separately through gas chromatography-flame ionization detection (GC-FID) on subsamples from the same vials. The procedure is particularly relevant for field studies in remote areas where chromatography equipment and supplies are not readily available, offering a practical, cheaper, and more efficient solution for measuring methane and other dissolved greenhouse gas concentrations in aquatic systems.

This study assessed the effects of the addition of biochar prepared at 700 °C with different dosages on the anaerobic digestion of food waste. The biochar addition at a concentration of 10.0 g/L increased the cumulative methane yield by 128%, and daily methane production was also significantly promoted. The addition of biochar derived from poplar sawdust significantly increased the relative abundance of dominant bacteria for anaerobic digestion by 85.54-2530% and promoted the degradation of refractory organic matter and the transfer of materials between the hydrolysis and acid production stages. Further analysis has demonstrated that Bathyarchaeia and hydrogenotrophic methanogens were enriched by the biochar addition. Meanwhile, the relative abundances of functional genes, including C5-branched dibasic acid metabolism, and pyruvate metabolism, were increased by 11.38-26.27%. The relative abundances of genes related to major amino acid metabolism, including histidine metabolism, lysine biosynthesis, and phenylalanine, tyrosine, and tryptophan biosynthesis, were increased by 11.96-15.71%. Furthermore, the relative abundances of genes involved in major replication and repair were increased by 14.76-22.76%, and the major folding, sorting, degradation, and translation were increased by 14.47-19.95%, respectively. The relative abundances of genes related to major membrane transport and cell motility were increased by 10.02 and 83.09%, respectively.

Sewage sludge (SS) is a potential source of bioenergy, yet its management is a global concern. Anaerobic digestion (AD) is applied to effectively valorize SS by reclaiming energy in the form of methane. However, the complex floc structure of SS hinders hydrolysis during AD process, thus resulting in lower process efficiency. To overcome the rate-limiting hydrolysis, various pre-treatment methods have been developed to enhance AD efficiency. This review aims to provide insights into recent advancements in pre-treatment technologies, including mechanical, chemical, thermal, and biological methods. Each technology was critically evaluated and compared, and its relative worth was summarized based on full-scale applicability, along with economic benefits, AD performance improvements, and impact on digested sludge. The paper illuminates the readers about existing research gaps, and the future research needed for successful implementation of these approaches at full scale.

Copper-exchanged zeolite omega (Cu-omega) is a potent material for the selective conversion of methane-to-methanol (MtM) via the oxygen looping approach. However, its performance exhibits substantial variation depending on the operational conditions. Under an isothermal temperature regime, Cu-omega demonstrates subdued activity below 230 °C, but experiences a remarkable increase in activity at 290 °C. Applying a high-temperature activation protocol at 450 °C causes a rapid deactivation of the material. This behavioral divergence is investigated by combining reactivity studies, neutron and in situ high-resolution anomalous X-ray powder diffraction (HR-AXRPD), as well as electron paramagnetic resonance spectroscopy, to reveal that the migration of Cu throughout the framework is the primary cause of these behaviors, which in turn is governed by the degree of hydration of the system. This work suggests that control over the Cu migration throughout the zeolite framework may be harnessed to significantly increase the activity of Cu-omega by generating more active sites for the MtM conversion. These results underscore the power of in situ HR-AXRPD for unraveling the behavior of materials under reaction conditions and suggest that a re-evaluation of Cu-zeolites priorly deemed inactive for the MtM conversion across a broader range of conditions and looping protocols may be warranted.

Livestock production significantly contributes to greenhouse gas (GHG) emissions particularly methane (CH4) emissions thereby influencing climate change. To address this issue further, it is crucial to establish strategies that simultaneously increase ruminant productivity while minimizing GHG emissions, particularly from cattle, sheep, and goats. Recent advancements have revealed the potential for modulating the rumen microbial ecosystem through genetic selection to reduce methane (CH4) production, and by microbial genome editing including CRISPR/Cas9, TALENs (Transcription Activator-Like Effector Nucleases), ZFNs (Zinc Finger Nucleases), RNA interference (RNAi), Pime editing, Base editing and double-stranded break-free (DSB-free). These technologies enable precise genetic modifications, offering opportunities to enhance traits that reduce environmental impact and optimize metabolic pathways. Additionally, various nutrition-related measures have shown promise in mitigating methane emissions to varying extents. This review aims to present a future-oriented viewpoint on reducing methane emissions from ruminants by leveraging CRISPR/Cas9 technology to engineer the microbial consortia within the rumen. The ultimate objective is to develop sustainable livestock production methods that effectively decrease methane emissions, while maintaining animal health and productivity.

Urban environments are recognized as main anthropogenic contributors to greenhouse gas (GHG) emissions, characterized by unevenly distributed emission sources over the urban environments. However, spatial GHG distributions in urban regions are typically obtained through monitoring at only a limited number of locations, or through model studies, which can lead to incomplete insights into the heterogeneous spatial distribution of GHGs. To address such information gap and to evaluate the spatial representation of a planned GHG monitoring network, a custom-developed atmospheric sampler was deployed on a UAV platform in this study to map the CO2 and CH4 mixing ratios in the atmosphere over Zhengzhou in central China, a megacity of nearly 13 million people. The aerial survey was conducted along the main roads at an altitude of 150 m above ground, covering a total distance of 170 km from the city center to the suburbs. The spatial distributions of CO2 and CH4 mixing ratios in Zhengzhou exhibited distinct heterogeneities, with average mixing ratios of CO2 and CH4 at 439.2 ± 10.8 ppm and 2.12 ± 0.04 ppm, respectively. A spatial autocorrelation analysis was performed on the measured GHG mixing ratios across the city, revealing a spatial correlation range of approximately 2 km for both CO2 and CH4 in the urban area. Such a spatial autocorrelation distance suggests that the urban GHG monitoring network designed for emission inversion purposes can have a minimal spatial resolution of 4 km. This UAV-based measurement approach demonstrates its capability to monitor GHG mixing ratios across urban landscapes, providing valuable insights for GHG monitoring network design.

Septic tanks are widely adopted in decentralized household wastewater treatment systems serving billions of people globally. Due to the lack of effective electron acceptors, insufficient nutrient removal and the emission of harmful gases, e. g. H2S, CH4, etc., are the common drawbacks. In the present work, we attempted to supplement nitrite into septic tanks as an electron acceptor, via nitrifying human urine source-separated from blackwater, to overcome these drawbacks. Partial or complete nitritation of source-separated urine was achieved in a sequencing batch reactor. The addition of nitrified urine into septic tanks improved organic and nitrogen removals in blackwater up to 90 % and 70 %, respectively. The emission of harmful gases from the septic tanks was stably diminished, with more than 75 % of CH4, CO2 and H2S reductions. Nitrite addition significantly reduced the abundance of hydrogenotrophic methanogens in septic tanks. Though the activity of sulfate-reducing bacteria recovered after the initial inhibition upon nitrite addition, the bio-generated H2S was retained in water since the increased wastewater pH after nitrite addition promoted the disassociation of H2S in aqueous solution.

The thermodynamic effect of octyl-β-D-glucopyranoside (OGP) on the formation of methane-1,3-dimethylcyclohexane (DMCH) hydrate was studied in this work. The thermodynamic equilibrium hydrate formation pressures between 275.15 K and 283.15 K were measured by the isothermal pressure search method. Different OGP aqueous solutions (0, 0.1, and 1 wt%) were used in this work. The experimental results show that OGP had no obvious thermodynamic inhibition on methane-DMCH hydrate formation when its concentration was low (0.1 wt%), whereas it had an inhibition on methane-DMCH hydrate formation when its concentration was high (1 wt%). The phase equilibrium hydrate formation pressure of the methane-DMCH-OGP system is about 0.1 MPa higher than that of the methane-DMCH system. The dissociation enthalpies of methane hydrate in different solutions remained uniform, which indicates that OGP was not involved in methane-DMCH hydrate formation. This phenomenon is explained from the perspective of the molecular structure of OGP. As a renewable and biological nonionic surfactant, the concentration of OGP in the liquid phase is low, so OGP can be added to the methane-DMCH system without significant thermodynamic inhibition.