The Chinese biogas digester has been a major influence in the uptake of the anaerobic digestion process globally. In this article, we look at the background of Government Policy, the benefits, the Biogas Programme of Activities (PoA), recent experience and comments. Finally, we conclude on what still needs to be done to reduce China's burgeoning carbon emissions.
Benefits and Use
Biogas digesters, which are also known as anaerobic digestion plants, are commonly considered to be something brand-new by those in the established nations.
Nevertheless, they have been extensively used for several years in developing countries, specifically India and China, as firewood for food preparation ends up being limited
Besides producing the fuel gas, these Chinese Biogas Digester plants (utilizing the procedure of anaerobic digestion) have the added potential advantage of producing a high nutrient slurry fertilizer and providing much better sanitation on farms.
But although there are already millions of small rural biogas plants there is a huge potential for further development of anaerobic digestion in China.
Why China Originally Chose to Promote the Use of Anaerobic Digestion
Biogas methane provides fuel for cooking, not only saving the forests and the women fetching and carrying heavy loads of fuelwood. Unlike firewood, biogas burns without smoke, thus also saving women and children from respiratory distress and disease. Biogas can be used to generate electricity, prolonging the active hours of the day and enabling the family to engage in social or self-improvement activities or to earn extra income.
The second main reason for anaerobic digestion is that methane is a major greenhouse gas, second to carbon dioxide in amount generated, but with a global warming potential 22 times that of carbon dioxide. The methane flux from the exposed slurry is 3.92 mg per square metre per hour, compared with 10.26 mg per square metre per hour from compost in rice fields.
When was Anaerobic Digestion First Used in China?
According to Kangmin and Ho (2006), the first digestion plant to produce biogas from wastes was built in Bombay, India in 1859. By the end of the 19th century, some simple Chinese Biogas Digesters appeared in the coastal areas of southern China.
Ancient Persians observed that rotting vegetables produce flammable gas. In 1859 Indians built the first sewage plant in Bombay. Marco Polo has mentioned the use of covered sewage tanks in China. This is believed to go back to 2,000-3,000 years ago in ancient China.
The Most Common Chinese Biogas Digester Types and Current Findings
In this article, we discuss continuous and batch digesters, with capacities which are usually below 100 m3. In the case of continuous Chinese Biogas Digesters, we have focused on classical models from India and China, since they are the most suitable types for small and middle-sized rural communities.
Common Digester Types Used Nationally
The batch digester is a system that is very simple and suitable for rural properties in which biomass biowaste availability occurs during long periods.
The nutrients that methane bacteria draw from the raw materials are carbon (in the form of carbohydrates), nitrogen (such as found in protein, nitrite, and ammonium), inorganic salts, etc. Carbon provides energy, and nitrogen is used in the formation of cells. The suitable carbon-nitrogen ratio for rural biogas digesters should be 25~30:1. The carbon-nitrogen ratio changes with different raw materials, and one must bear that fact in mind when choosing a mix of raw materials for the digester.
Findings Reported
Most biogas digesters are in remote rural areas, where farmers lack ready access to improved technologies and management methods.
In rural areas, there are more than enough raw materials for biogas fermentation to constitute the material basis for biogas production.
Problems Which Occur
Sadly, according to current experiences in China, the performance of some digesters is unstable, with varying levels of gas production. This should not be considered a failure of the technology.
This is due to the lack of experience among the individual households, limited resources for biogas service support, and insufficient farmer training. Expertise is required to ensure that the digesters function properly, so maintenance and management of Chinese Biogas Digesters require adequate support services and trained staff, which is not available in rural areas.
Much of the investment in biogas technology in China took place in the 2000s. In February 2005, the National People's Congress adopted the Renewable Energy Law of the People's Republic of China. This set out the duties and obligations of the government, enterprises and users in the development and utilization of renewable energy and a series of policies and measures. It included total volume targets, mandatory grid connection, price management regulation, and differentiated pricing. There was a special fund, favourable taxing, etc.
Emerging Additional Benefits of Anaerobic Digestion in China
Biogas methane can also be used as fuel for vehicles and is the cleanest biofuel available. Cars run on biogas methane were voted the environmental cars of the year in 2005. Thousands of them are already operating in Sweden, which has hundreds of filling stations supplied by community biogas digesters.
Temperature Control
Temperature can be controlled in a few different ways. Chinese Biogas Digesters are typically buried underground and built much larger than they need to be. This way they can be overloaded in the winter months to maintain consistent gas production. Other designs employ a greenhouse or coop house over them. More advanced systems integrate a heat exchanger, which can be heated with solar collectors.
Do Biogas Plants Really Work?
I can guarantee the reader on my life biogas works, and it works great. The ancient Assyrians used biogas to heat their baths in 3,000 BC, the famous gas lamps of Victorian England were fuelled with biogas, Sweden runs all its city buses with biogas and today there are an estimated 50 million households in China using biogas. There are no technical reasons every home in the world is not already using biogas for cooking energy and some light electricity. The failure of any biogas project big or small is a result of violating one or more of these five easy-to-remember steps.
Perhaps the record of uptake is the best answer to this question. We understand that the situation is that It costs $260 to build a small Chinese Biogas Digester. Their government pays half. And, they are going up like wildfire in rural China.
Up to the end of 2005, China has 17 million digesters with an annual production of 6.5 billion m3.
the Biogas Programme of Activities (PoA)
biogas, mostly in rural areas, with 50 million people enjoying the benefits of biogas technology. The annual production of biogas is projected to reach 25 billion m
The Biogas Programme of Activities (PoA)
by 2020. Biogas could provide energy to one-quarter of households in rural areas.
All households using new biogas-fuelled cookstoves have described a notable reduction in indoor air pollution. Biogas mitigates eye inflammations and respiratory diseases such as asthma, tuberculosis and lung cancer, among rural women and children. These diseases have been a serious health issue and, so, women's and children's health are benefitting the most.
Recent AD Plant Developments
BioGTS Completes a Biogas plant in central China – The operation of a BioGTS biogas plant was initiated in the summer of 2018. The annual feedstock capacity of the plant is about 31,000 tons of agricultural biomass, including corn and straw. The produced biogas is utilized as a substitute for natural gas in traffic use and injected to the natural gas grid.
Comments on the Biogas Programme of Activities (PoA)
In the beginning, it was hard to find international partners and investors to share the project risks and to help us implement our household biogas programme.
Most of them just smiled at us, when they saw our initial project concept and walked away because they deemed it too ambitious and unattainable. So finally, we did it alone together with our Chinese supporters, Chengdu Oasis and the SREO. And now, against all odds, our Sichuan Household Biogas PoA is one of the leading carbon offset programmes around the globe.
Climate Change Factors
Due to limitations in knowledge and analysis methods, there exist large uncertainties in the present assessment of climate change impacts carried out by various countries.
Studies indicate that climate change has caused some impacts on China, such as sea-level rise in the coastal areas, glacial retreat in the northwest area, and the earlier arrival of spring phenophase. It will also bring about significant impacts on China's natural ecosystems and social-economic system in the future.
Meanwhile, as a developing country at a low development stage, with a huge population, a coal-dominant energy mix and a relatively low capacity to tackle climate change, China will surely face more severe challenges when coping with climate change along with the acceleration of urbanization, industrialization and the increase of residential energy consumption.
The Role of Biogas Engines in China
Of course, the biogas produced can simply be used for cooking, lighting and space heating for homes, farms, factories and barns. However, there are many advantages to extending biogas use to electricity production and transport by using biogas engines.
Biogas engines are generally suitable for powering vehicles like tractors and light-duty trucks as has been successfully demonstrated in China. From an energy utilization point of view. Biogas can be used to operate four-stroke spark ignition engines.
Electricity Generation is much more efficient for lighting than mantle lamps. Electricity from a biogas plant can illuminate many homes. whereas the same volume of biogas can serve only seven lamps for one hour.
Sanitary Benefits
The most obvious sanitary benefit of installing an anaerobic digester system is the improvements to toilet facilities in households. Throughout China and other developing countries, where no sewer system is in place, toilet facilities are in simple shacks.
The toilet is generally a slot in the floor with either a pit underneath or alternatively a trough running to a storage pit behind the building.
In the case of a pit toilet, the slurry in the pit is often literally moving with insect larvae, and in all cases the toilets are smelly and fly infested. For these reasons, toilets are generally located as far away from the other household buildings as practical.
When a Chinese Biogas Digester is installed in a pit the detritus is immediately drained away into the digester. This takes it away from flies, and the high temperature of the digester kills most of the organisms harmful to human health.
How Pig Rearing is Synergistic with Biogas Plant Operation
Northern China has cold winters but enough sunshine. Digesters do not operate below 10ºC, and pigs raised in winter eat but do not fatten. People also lack fresh vegetables in winter.
All these problems are solved with a four-in-one eco-model that provides a greenhouse to plant vegetables, a shed to raise pigs, a Chinese Biogas Digester underneath the pig shed and a toilet in the big greenhouse adjoining the pig shed.
The pigs grow well with manure flowing into the digester together with human excreta.
However, for most of China, low temperatures are not a problem for biogas production. More than half of China's rural population are in areas where mean ambient temperatures exceed 10ºC, for 8 to 12 months of the year.
Gas production is temperature-dependent, but Chinese sources say production is only inhibited at mean ambient temperatures less than 10ºC.
Sichuan Province Support for Advanced Biogas Digesters
A POA for the province aims to support up to one million low-income rural households in China's Sichuan province with advanced biogas digesters and smoke-free biogas cookstoves. The small and reliable Chinese Biogas Digester design supported avoids methane emissions from pig manure and carbon dioxide emissions from coal and firewood. In addition, these plants provide the participating farmer households with clean, renewable and free biogas used for cooking, heating, or lighting.
For example, the participating households produce their own renewable biogas energy and organic fertilizer. As a result, they have reported about a 30% increase in disposable annual income.
Therefore, these households save on the expenditures for coal and synthetic fertilizer. In addition, the manure-rich digestate increases agricultural output and revenue. Biogas also reduces the time spent on gathering wood and feeding kitchen fires.
National Plans Which Supported Anaerobic Digestion
During the 10th Five Year Plan, the government invested 35 billion Yuan to promote an ecological model based on biogas. It devoted great effort to developing 2,200 biogas engineering projects for wastes from intensive animal husbandry and poultry treating more than 60 million tonnes of manure a year. In addition, it installed 137 000 digesters to treat sewage.
Since the 1970s, China has been promoting the use of underground, individual household scale, anaerobic digesters to process rural organic wastes. There are approximately 5,000,000 households using anaerobic digesters in China. The Chinese Biogas Digester produces biogas that is used as an energy source by the households and produces fertilizer that is used in agricultural production.
Conclusion to the Chinese Biogas Digester
The country which has made by far the most use of biogas production in agriculture is China, where, particularly in Sichuan province, there are several million working biogas units. This development took place almost entirely within the last 10-15 years. The value of the fertilizer output usually surpasses the value of the energy produced by the process in China. The waste disposal and sanitation aspects of the process are also important justifications for its use.
Despite this action rural China is currently experiencing significant growth in fossil fuel energy consumption, particularly coal and liquefied petroleum gas (LPG). Their per capita fossil fuel consumption has increased from 54.44 kg standard coal in 2001 to 92.51 kg standard coal in 2008, with an annual average growth rate of 9.42%. Per capita carbon emission from the burning of fossil fuels for domestic energy use in China's rural areas increased 63.5% between 1996 and 2007.
China clearly needs to do much more to achieve global climate change limitation commitments. China is the second largest energy consumer of the world and is responsible for good part of the greenhouse-effect gases that are thrown into the atmosphere, and thus has invested heavily in environmental protection projects and in the generation of renewable energy. With the adoption of this policy, the Chinese government has substantially stimulated research toward the construction, operation and efficiency of digesters (Sinton et al., 1998; Chen, 1997; Sinton et al., 2000; Martinot, 2001).
In rural China, anaerobic digesters can be important tools in reducing carbon emissions, providing energy for households as well as producing agricultural fertilizer. As mentioned earlier, their benefits of the systems include improved sanitation and conservation of alternative fuels. China must be encouraged to do much more to improve the national uptake, wherever possible, of biogas digestion.
