Rural Biogas in China
Author: Wenyue Ji, revised by Yeray López
The biogas systems in China contain an aerobic digester (see figure 4), where the feedstock is a combination of plant and animal waste plus water. In this digester the fermentation is produced, creating biogas which contains 70% methane. The energy content is 22 gigajoules/m3. The process occurs with the help of bacteria (temperature between 8-60ºC). 
Biogas development in rural China has gone through three main stages since 1949, including types of energy demand, ecological demand, and ecological home development . The large -scale development of household biogas in rural China began in the 1970s and small rural biogas digesters have dominated in China. The digesters were designed to use biomass from household sizes from four to eight persons and a farm production of two to ten pigs or cattle. Moreover the sediments from the bottom part of the tank can be used as a fertilizer . From 1973 to 1983, rural biogas development fluctuated dramatically . The number of household biogas digesters built in the early 1970s was 6 × 106, which increased to more than 7 × 106 in the mid-1970s but fell to less than 4 × 106, in the early 1980s  (see Fig. 3). During this early stage, the challenges in household biogas production included poor management and lack of secure and mature technologies to support the industry. From 1984 to 1994, the rural biogas construction remained in an adjustment period, with 8.27× 105 new households using biogas , focusing on the scientific research of technological systems and repair of pathological digesters. Thus, the pace of biogas development steadily increased annually since 1994. By the end of 2009, there were over 30.5 million household biogas digesters in China (that convert wastes into clean-burning fuel) and the total biogas yield was 12.4 billion m3 in 2009  (see Fig.1.), which is equivalent to 19.0 million of standard coal . The number of built household biogas digesters and its annual output in 2010 was more than the double that in 2005  (see Fig.2.). Around the 1.2% of the total energy used in China comes from biogas .
Fig.1.The development in the number of rural household biogas digesters from 1991-2009
Fig.2. Number of household biogas digesters built and annual output of biogas in China.
Fig. 3. Number of household biogas digesters in China, 1973-2002. 
Fig.4. Basic biogas digester 
According to the survey, the People’s Republic uses less than eight percent of its total biogas potential for energy generation. Hence, the improvement plans are ambitious: the Chinese National Energy Administration plans a rise of the biogas capacity from 19bn dry standard cubic meter (Nm³) in 2015 to 48bn Nm³ in 2020. It is above all centralized medium-sized and large projects that are being promoted. According to the AHK analysis, China still lacks the technologies required to safeguard the efficient operation of complex large-scale plants; as such, they see some potential in the supply of components, such as pumps and agitators, but also in the fields of measurement engineering and high technology systems for, e.g., the processing of biogas .
Fig. 5 Biogas production of different sectors from 1989 to 2014 
The Policy Measures
Biomass is widely available energy resource in China and the central government strongly supports the development and application of biomass energy, including biogas, bioethanol, biodiesel and so on. To the end, it has formulated a series of policies and programmes to promote the development of energy from biomass.
- In 1986, the China National Economic Committee issued the "Circular on Improving Rural Energy Development", which was the first policy paper on renewable energy development that promulgated the importance of bioenergy. 
- In 1995, China's government approved the "1996-2010 New Energy and Renewable Energy Development Programme", which provided a strong impetus for the development of renewable energy .
- In 2005, China's government issued the "Renewable Energy Law", which came into force on 1 January 2006. 
- In 2007, China's government published the "Medium and Long-term Development Program for Renewable Energy". 
- On 1 April 2010, the revised "Renewable Energy Law" became effective, which stipulated that the State would implement a fully supported system for power generated by renewable energy. 
Evaluation of the effect of these measures.
More active financial policies for bioenergy are gradually being implemented in China. The central government has decided to use some of their financial incentives to the sector to support the provision of monitoring and consultancy by local authorities and commercial enterprises.
Local governments focus on improving the rural biogas service systems, continuously introducing incentive policies to encourage the setup of various service systems for biogas production. These must be tailored to a market economy and meet the needs of users. Many local service and consultancy organizations have been created, which will contribute to the efficient operation of biogas projects.
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