The main objective of this study was to establish the metabolic pathway of a biogas fermentation system active at low temperature, and to describe the bacterial and archaeal methanogenic species responsible. A biogas fermentation inoculum adapted to be active at 9°C was used in a 10‐L batch‐type temperature‐controlled fermentor, using pig manure as the raw material. Fermentation at 9°C was followed for 120 days. A combination of nonbiological and biological factors was analyzed. Species were identified from OTU analysis based on 16S rDNA amplicon sequencing, and correlation analysis was used to study the effect of nonbiological factors, bacterial communities, and archaea communities. Biogas production was most effective between days 50 and 90, where gas production was above 0.70 L/d and the CH₄ yield was above 0.36 L/g‐volatile solid. The relative abundance of the first dominant bacterial OTU with 99% identity to Clostridium cellulovorans varied between 16.17% and 27.30%. These bacteria typically degrade cellulose and hemicellulose. The second dominant bacterial OTU (relative abundance 15.23%‐27.15%) was 99% identical to Terrisporobacter petrolearius, a typical fermentative species. The most abundant (4.15%‐37.14%) archaeal OTU was 98% identical to Methanocorpusculum sinense, which is a typical hydrogenotrophic methanogen. A low‐temperature biogas metabolic pathway was constructed, based on abundant bacterial and methanogen OTUs. The most suitable metabolic pathway describes that hydrogen is produced by one part of the community and then used to reduce the produced carbon dioxide into CH₄; this seems to be the major pathway by which biogas is produced under low‐temperature conditions.

Anaerobic digestion is widely used to simultaneously generate biogas while treating different organic wastes. It is difficult to determine the source of CH₄ from the complex microbial community structure using traditional microbiological pure culture techniques. Therefore, this study aimed to elucidate the microbial source of CH₄ in low-temperature anaerobic digestion systems using the recently developed high-throughput sequencing technology. Herein, anaerobic digestion microbes were domesticated at 15°C and then inoculated into pig manure-containing raw materials in a batch anaerobic digester to form a low-temperature anaerobic digestion system with fermentation controlled at 15°C. Several analytical approaches including abiotic factor analysis and biotic factor analysis (high-throughput sequencing) were applied to investigate the abiotic factors, bacterial communities, and archaeal communities in the low-temperature anaerobic digestion system. The results showed that: 1) The anaerobic digestion lasted for 120 days, with 68.65 L total gas production and 31.19 L CH₄ production. 2) The relative abundances of the primary and secondary dominant bacterial operational taxonomic units ranged from 8.02 to 22.84% and 5.62–17.09%, respectively, with 99% similarities to Clostridium cellulovorans (a typical cellulose- and hemicellulose-degrading bacterium) and Terrisporobacter petrolearius (a representative fermentation bacterium), respectively. Moreover, the relative abundance of the primary dominant methanogenic archaeal operational taxonomic unit ranged from 1.03 to 16.85%, with 98% similarity to Methanobacterium beijingense, which is a typical hydrogenotropic methanogen. Based on the low-temperature CH₄-producing metabolic pathways of bacterial and methanogenic operational taxonomic units, Methanobacterium beijingense was found to be the primary functional microbe for CH₄ production in the 15°C anaerobic digestion system.

To improve the low energy production efficiency of fermentative hydrogen production (FHP) and fermentative methane production (FMP), the two types of fermentation were effectively combined in this study. Using sucrose as feedstock, both successive fermentative production of hydrogen followed by methane (SFPHM) and successive fermentative production of methane followed by hydrogen (SFPMH) were performed to improve the energy production efficiency of the overall anaerobic process. The results showed that the energy conversion efficiency of SFPHM was 79.85% whereas that of SFPMH was only 43.12%. Therefore, SFPHM can significantly improve the energy production efficiency of traditional anaerobic biological treatment.

DNA as an intriguing organic ligand has been widely employed for synthesizing metal nanoclusters and engineering their properties. This review aims to present recent progress on DNA-encoded metal (Ag, Cu, Au, Ag/Pt, Cu/Ag, etc.) nanoclusters (DNA-MNCs), focusing on their applications in the fields of analysis, logic operation, and therapy based on properties including fluorescence, electrochemiluminescence (ECL), and antibacterial and catalytic activity, and summarizes the attractive features of the latest research. The key points are briefly described as follows. (1) Analytical systems have been constructed based on fluorescence regulation, and nuclease-assisted and enzyme-free amplification strategies have been extensively adopted with fluorescent DNA-MNCs for amplified analysis. (2) DNA-MNCs may play more than one role (emitter, quencher, or catalyst) in ECL-based analytical systems. (3) Apart from antibacterial activity, DNA-MNCs also possess apparent catalytic capability, such as enzyme-like activity (i.e., nanozymes), which has been applied in colorimetric systems. (4) Reversibly regulating the catalytic activity of DNA-MNCs has been attained with DNA systems. It is believed that through in-depth investigation of the relationship between atomic structure and property, more novel DNA-MNCs will be explored and applied in the future.

The catalytic deoxygenation experiments of stearic acid and hydrogen were performed for 6 hours in the presence of a solvent, dodecane, in a temperature range of 295-305°C and the rotational speed of 100rpm, under a certain hydrogen partial pressure (in argon), using palladium supported on active and mesoporous carbon as a catalyst. The results showed, the main liquid-phase product was n-heptadecane, while the main gaseous products were CO₂ and CO. When the partial pressure of hydrogen is 3.0MPa, the acid value of primary product is the lowest and the reaction tends to be gentle, conversion rate of stearic acid and selectivity to n-heptadecane is the highest.