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In order to provide a clear guidance for biogas development in rural China, the progress and current status of rural biogas, critical factors influencing biogas development in rural areas, and probable biogas transformations are discussed in this paper. Rural biogas in China experiences rapid development in the past fifteen years and subsidies and policies from Chinese government are two main driving forces for promoting this development. For the recent days, the growth rate of household biogas decreased and that of Medium-to-large biogas projects (MLBPs) obviously increased. Several surveys showed that the utilization rate of household biogas greatly decreased and more and more digesters were discontinued. The underlying reasons for these changes come from the development of large-scale livestock farms, agricultural modernization and urbanization, which deeply affect the agricultural and social environment in rural China. The development of these agricultural and social factors all create positive conditions for MLBPs, but they negatively affect household biogas projects in terms of biomass supply and their participation in modern agricultural processes. Ongoing transformations and developments in local agriculture and rural society significantly influence the patterns of biogas projects. For future biogas development, MLBPs should be encouraged and the reduction of household biogas projects should be allowed to continue. However, recommendations on probable biogas development transformations suggest that the decision for expanding or abandoning the household projects in certain regions should be consistent with the developments and trends of local agriculture and society. For MLBPs, suitable developing models and reasonable operating mechanisms should be fully considered for assuring their benefits and continuous operation. [ABSTRACT FROM AUTHOR]

With the rising demand for renewable energy and environmental protection, anaerobic digestion of biogas technology has attracted considerable attention within the scientific community. This paper presents a comprehensive review of research achievements on anaerobic digestion developments for biogas production. The review includes a discussion of factors affecting efficiency (temperature, pH, C/N ratio, OLR and retention time), accelerants (greenery biomass, biological pure culture and inorganic additives), reactors (conventional anaerobic reactors, sludge retention reactors and anaerobic membrane reactors) and biogas AD processes (lignocellulose waste, municipal solid waste, food waste, livestock manure and waste activated sludge) based on substrate characteristics and discusses the application of each forementioned aspect. The factors affecting efficiency are crucial to anaerobic digestion, because they play a major role in biogas production and determine the metabolic conditions for microorganism growth. As an additive, an accelerant is not only regarded as a nutrient resource, but can also improve biodegradability. The focus of reactor design is the sufficient utilization of a substrate by changing the feeding method and enhancing the attachment to biomass. The optimal digestion process balances the optimal digest conditions with the cost-optimal input/output ratio. Additionally, establishment of theoretical and technological studies should emphasize practicality based on laboratory-scale experiments because further development of biogas plants would allow for a transition from household to medium- and large-scale projects; therefore, improving stability and efficiency are recommended for advancing AD research. [ABSTRACT FROM AUTHOR]

Abstract: As a renewable energy source, biogas not only alleviates energy shortage in rural areas but also effectively reduces the environmental risk associated with agricultural waste management. This study presents a comprehensive overview of development of household bio-digesters and medium and large-scale biogas plants (MLBPs) in China, and discusses the advantages and disadvantages of both biogas systems in terms of environmental performance, role in agriculture, economic benefit, government support, energy efficiency, societal influence, and resident living mode. Both systems have their relative strengths and weaknesses. The operation and maintenance of household bio-digesters are easier, and their environmental and economic performances are superior compared to those of MLBPs. However, MLBPs have higher energy efficiency and better social effect. Thus, the choice of a biogas generation system depends on the local circumstances. Household bio-digesters are suitable for undeveloped regions where the rural residents live far apart from each other, whereas MLBPs are suitable for developed regions where people live close together. The government can play a positive role in preventing the negative impacts of rural social structural change, such as those of urban migration of adults, on household biogas development. Additionally, establishment of scientific and technological support and service systems is recommended for further development of biogas in rural China. [Copyright &y& Elsevier]