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Trichloromethane is often used as a chemical inhibitor to pretreat the inoculum to improve hydrogen yield in dark fermentation. In this study, five different doses of trichloromethane were used for methanogenic inhibition of methanogenic microbial community operating in stable (inoculum A) and anaerobic microbial community in natural environment (inoculum B). High concentrations of trichloromethane inhibited the activity of microbial community in the system and hindered the production of hydrogen and methane. At the same time, it would greatly reduce the pH, causing it to fall below the threshold of suitable hydrogen yield. In turn, ethanol-type fermentation was triggered, and the ethanol content of the system increased with increasing concentration of trichloromethane addition. The comprehensive assessment concluded that a 0.10% (v/v) trichloromethane concentration gave the best hydrogen yield performance in both inoculums. However, anaerobic microbial community in natural environment was able to produce hydrogen more efficiently than the operationally stable methanogenic microbial community. The highest cumulative hydrogen yield was 111.16, 34.36, and 72.76 mL/g VS in phase Ⅰ, phase Ⅱ, and the whole stage, respectively. In addition, the butyrate production in the reactor at this concentration was considerable, with an average yield of 21.3 g/L.

The anaerobic co-digestion (AcoD) of FWs produces variable methane yields, mainly due to variable carbon/nitrogen (C/N) ratio and proportions of lipids (L), carbohydrates (C), and proteins (P) in different FW samples. In this study, a significant interaction between C/N ratio and LCP composition was found and contributed to the differing trends between special (SMP) and theoretical methane production. The highest SMP of 595 mL CH4 gVS-1 occurred at C/N of 25 and LCP of 63.25:22.62:14.13, followed by 592 mL CH4 gVS-1 at C/N of 30 and LCP of 48.94:39.74:11.32, which also reflected their interaction. Attributing to their interactive effect on obtaining optimal process parameters and microbial community, the inhibition threshold of lipid as well as the methane yield was increased. Understanding the interaction between C/N ratio and LCP composition is an effective and promising way to obtain suitable mixture ratios of organic wastes under AcoD.

Promoting the biomass industry in China would provide significant ecological, economic, and societal benefits by ameliorating soil and groundwater pollution and providing a sustainable energy source. However, although there is great potential for expanding the biomass industry in China, it currently faces large obstacles, with respect to its utilization, low economic performance, and other limitations. This study conducts a comprehensive literature review on biomass utilization methods, and establishes a new recycling model that couples the use of anaerobic digestion (AD) and its byproducts with biochar. In the model, biomass waste is used for biogas and biochar production, and biogas residues are further cracked into biochar. Biochar is also used as an additive to modify the AD process and promote methane production. In addition to its single application, biochar is further used in combination with biogas slurry or residue as a soil conditioner to repair soil and promote the growth of crops. This circulation model differs from models in which biomass alone is used in biogas or biochar production, and it combines all processes to promote the use of biomass, increase its conversion efficiency and strength the applications of such processes in the agricultural sector. Previous reports have shown that each part of the model can play a positive role in improving overall efficiency. Therefore, the application of the combined circulation model would be beneficial in biomass utilization and as such is a promising method for promoting the sustainable development of energy and agriculture in China, while protecting the environment.

Few studies have addressed how to blend wastes for anaerobic co-digestion. This study investigated the effects of waste sources on anaerobic co-digestion (AcoD) performance, by varying the quality of food wastes (FWs) from six sources in Xi’an region, China that were individually co-digested with pre-treated corn straw and cattle manure. These effects were analysed in terms of their volatile solid (VS) ratios, C/N ratios, and the chemical composition of the FWs. The results indicated that the VS ratios were not suitable as a common mixture method because the VS ratios at which the best methane potentials occurred differed significantly among the six FW groups. The C/N ratios within a 17–24 range resulted in better methane potentials when the FWs were co-digested with other wastes. Synergistic effects were found among the carbohydrates, proteins, and lipids of the FWs; however, the optimum ratios of these components could not be determined. Thus, the C/N ratio is recommended as a mixture method when co-digesting FWs with other organic wastes in selected region.

The effects of chemical composition (carbohydrates, lipids, and protein) on the anaerobic co-digestion performance of food wastes (FW) were investigated from the viewpoints of methane production, dynamic parameters, and microbial community structure. The results of this study showed that a notable gasification rate was positively correlated with the proportion of the composition. A T2 reactor, which consisted of 60% carbohydrates, 20% lipids, and 20% protein, held a higher gasification rate of 65.09% compared to other groups, while its process parameters showed some deficiency regarding the stability of digestion, especially for low biochemical methane potential (BMP), which was not beneficial for the actual practice. A T4 reactor, with a highest gasification rate of 70.68%, held the maximum BMP (497.44 mL/g VS). The stable chemical parameters achieved the optimal proportion, consisting of 40% carbohydrates, 40% lipids, and 20% protein. Furthermore, its microbial populations were rich and achieved a balance of the two main dominant communities of acetoclastic methanogens and hydrogenotrophic methanogens, whose relative abundance was close. It was obvious that interactive effects were caused by different proportional composition, which led to constantly changing chemical parameters and microbial community.

In order to promote China's biogas industry development, this paper comprehensively compared the biogas status and related policies between China and Europe and tried to find the shortage and potential implications. China has access to abundant biomass resources, with considerable biogas potential and an annual theoretical output of 73.6 billion m3. Household-based biogas digesters coexist with medium and large-scale biogas plants (MLBPs) in China. Although the number of MLBPs in China was almost two times higher than Europe, the annul biogas production yield was only half of those in Europe. In China, biogas is mainly used for heating and cooking, and its power generation capacity is far lower than that in Europe. Overall, biogas industry is more commercialized in Europe than China. In terms of biogas related policies, China has an advantage in quantity, but is weak in their implementation. Biogas related policies in China mainly focus on agricultural and rural development, while in Europe, they are aimed at increasing the utilization of renewable energy and reducing greenhouse gas emissions. In addition, policies in China are mostly filled with encouragement, lacking detailed subsidy schemes and modes, whereas in European countries are more targeted and scientific. Based on the dissimilarity of current status and the disparity in policies, a series of countermeasures and suggestions for the development of the Chinese biogas industry are presented.