Composting in china
ALTHOUGH the statistical data of organic solid wastes generated in China is incomplete, we can still make a rough estimate based on the available information which includes municipal solid waste (MSW), sewage sludge, crop residues and animal manure. Annual generation of crop residuals is estimated as 0.6 to 0.7 billion tons. About 36.6 percent was returned to farmland; 23.7 percent was used as household fuel; 22.6 percent as feedstuff, and other amounts for field burning, paper pulping or discarded.
China is the largest producer of various animal products. Total generation of animal manure has reached 2.4 billion tons in 2005 and will grow at a rate of four to five percent. The State Environmental Protection Administration of China (SEPA) reports that most of the animal manure in the countryside was untreated. Only 20 percent was applied on farmland, and just three percent of the 20 percent figure was treated by composting.
China has started to build many wastewater treatment plants since the 1990s, and the amount of sewage sludge increased from 3.45 million tons in 1995 to 13.6 million tons in 2005. Thirty-one percent of the sludge was landfilled, and 44.8 percent was used on land. Further, 60 percent of land-used sludge was discharged directly without any treatment.
In 2005, China’s MSW production reached 156 million tons, and the organic solid wastes contribute around 50 percent. Separation of MSW was not adopted extensively, so 89.5 percent of MSW was landfilled in Beijing, where the organic solid waste was about 3.8 million tons in 2005. The percent of composting and incineration were only 4.8 percent and 1.6 percent respectively.
MAIN COMPOSTING PROCESSES AND RESEARCH
Maximizing the flow of organic solid wastes, both urban and rural sources, to organic fertilizer/soil amendments is one of the big targets for a country like China where the farmland is limited and the land is intensely used. Currently, the main composting processes used in China include traditional, windrow, “tank” and tunnel.
The traditional composting method was recorded by Chen Fu in his early book “Chenfu Agricultural Book” as early as the year of 1149, when he first described the composting method by using oilcake amended with crop residues. Traditional composting was basically a kind of anaerobic composting taking as long as 3-6 months and still was practiced by farmers, particularly in areas of vegetable growing.
Since then, farmers in China applied compost extensively and helped the nation sustain agriculture for centuries and the application of organic fertilizer ratio was over 80 percent until 1970.
Windrow composting is one of the common processes in China. The main differences are the use of turning machines. Some plants use the domestic turner, some import them, like a Backhus turner, and few are turned by human power. Windrow composting is mainly used to process MSW and animal manure.
“TANK” AND TUNNEL COMPOSTING
“Tank” composting – a most popular process in China – is a kind of near-closed composting system. The tank size can be adjusted, with a width of 2m to 6m and depth between 1m and 1.5m. The length depends on the actual length is variable.
Tracks are fixed on the top of the tank wall, and the turning machine can move along the track and finish the turning with a rate around 1 m/minute. Most of these turners are made in China.
The tank composting system can be operated in a greenhouse, which is better for maintaining temperature, but needs to be provided with a ventilation system for the control of odor. The system is mainly used for the treatment of sewage sludge and animal manure.
The tunnel composting system is one of the few reactor systems, which was mostly imported and used in the MSW treatment plants. The Beijing Nangong composting plant was one of the earliest plants equipped with 30 tunnels, and the waste treatment capacity is about 400 tons per day.
The composting industry in China is still at the beginning stages. Most of the composting processes have not been well established, which is mostly correlated with the lack of research on composting technology and engineering.
In the last decades, the Chinese government has launched some research programs on composting and beneficial use of solid wastes. For example, the Ministry of Science and Technology supported two research projects on the treatment of hazardous wastes and MSW, and research on the resource use of solid waste between 1990 and 1995. Then between 2000 and 2005, some work had been done in a project on the technology development and demonstration of ecological agriculture, including research on organic fertilizer.
In the five year plan (2006-2010), the research grants include: research and demonstration on the integrated treatment and beneficial use of municipal solid wastes; development of new and high efficiency fertilizers; research and demonstration of organic fertilizer production in animal farms and research and demonstration of the integrated control of farmland pollution. The China Agricultural University also sponsors the annual national workshop on composting technology and engineering. These activities will contribute to development of the composting industry in the future.
REGULATIONS ON COMPOST AND ORGANIC FERTILIZER
In recent years, China’s commercial organic fertilizer industry has developed very fast including both organic and bioorganic fertilizers. The corresponding standards are already established.
Organic fertilizer is generally classified as two types – granular or powder – which are regulated by the national standard for organic fertilizer (Table 1). The main criteria are the organic matter concentration, which should be above 30 percent and moisture content, which should be below 20 percent.
Bioorganic fertilizer is produced by introducing some functional microbes as nitrogen-fixing bacteria, phosphorus-dissolving bacteria and other multiple-functional compound microbes. The bioorganic fertilizer is regulated by the standards of NY 884-2004 (Table 2), and the major criteria are the quantity of beneficial microbes and those health indicators.
Organic-inorganic fertilizer is made from organic fertilizer blended with inorganic fertilizer at different ratios, which can be set according to the specific demands of certain crops. Farmers are becoming interested in such fertilizers because they have both short-term and long-term effects and are good for soil quality and efficient use of nutrients. The organic-inorganic fertilizer manufacturer is actually a terminal supplier of various fertilizers that are better adapted for local conditions, as crop nutrients requirement, weather and soil conditions. The main criteria of organic-inorganic fertilizer were regulated by the standard of NY 481-2002) (Table 3).
The regulation of MSW and sewage sludge for agricultural use was established early in the 1980s. The major criteria are sanitation and the concentration of heavy metals. Table 4 shows standards for MSW used in agriculture (GB8172-87). Table 5 covers standards for sewage sludge used in agriculture. The heavy metals concentration, mortality of lumbricoid eggs and the number of E. coli in organic fertilizer should be consistent with the requirements of GB 8172.
The MSW in urban China has not been separated effectively, so the compost from MSW was often not accepted by farmers because of the low quality. Meanwhile, sewage sludge is welcomed by composting factories as long as the concentration of heavy metals in sludge is decreased, basically because of control of those polluting industries and the higher percentage of municipal waste-water in the treatment plants.
PROSPECTS OF COMPOSTING IN CHINA
China, as one of the biggest producers of solid waste in the world, will become a huge market (over 35 billion tons) for the treatment and disposal of organic solid waste, and will be boosted by the determination of the central government and the tremendous demands from individual clients. The composting industry, as a beneficial and circular pathway, will surely be promoted in the future.
Statistical data from Ministry Of Agriculture showed that the number of organic fertilizer factories and production has risen to 1,580 and 9.87 million tons respectively in 2006 with an annual growth rate of 20 percent since 2000. The share of organic fertilizer in the whole fertilizer market will be 40 to 50 percent and targeted at 50 million tons in the late century.
Development of Chinese organic fertilizer is fundamentally market-oriented, including the use of microbial agents, the development of rapid composting technology, and building of many organic-inorganic fertilizer production lines. These will be good for the world and for cooperation between China and other countries.
