Turning Urban Manure Into Organic Fertilizer

During the three week biogas training workshop, we visited Kunming Dongran Technology Company, a business that specializes in treating human manure through anaerobic digestion and turning the bio-slurry into an organic fertilizer.  Dongran Technology was founded in 2003 with a capital investment of 10 million RMB.  With the advancement of its scientific capabilities, the Yunnan National Reform and Development Commission approved Dongran as a suitable BOT (Build-Operate-Transfer) project for Kunming City’s Wu Hua District.  BOT is a form of project financing, where the private enterprise receives funding from the government to finance, design, construct, and operate a facility.  The financing from the government allows proponents to recover its investment, operation, and maintenance expense in the project.   Usually, the project is transferred to the government at the end of the concession term, and in the case of Dongran, the company will be transferred to the government in twenty years.  Fortunately for Dongran, the return in investment is only 2-3 years, so the company can make a quick return.  BOTs are quite common in China.  When I went to Beijing to visit Beijing Sound Environmental Group, a municipal solid waste company, I learned the company was also a BOT.

Dongran is the first company in China to design an urban manure treatment facility and use the manure to generate power.  Every day, Dongran treats 300 tons of human manure from the Western districts of Kunming, and in the coming years, it will treat all of the human manure of Kunming, a city with approximately 5-6 million residents.

In most urban areas, human manure is often treated with wastewater, but Dongran specifically treats manure as a separate entity from wastewater, and reduces the likelihood of disease transmission by proper manure management.   Additionally, through Dongran’s separation of manure from the wastewater treatment process, the Environmental Protection and Sanitation Bureau’s waste management burden is reduced.  While Dongran receives money from Kunming’s Wu Hua District to treat the waste, Dongran’s main source of income is from producing organic fertilizer through the fermentation of manure.  The solid organic fertilizer is used on tobacco farms, a major industry and source of income for Yunnan Province, and also on vegetables, flowers, fruits, and tea.  The liquid organic fertilizer is often used as a nutrient for seeds. Not only does organic fertilizer improve food quality, but also improves soil quality as well.

The biogas technology designed by Dongran not only treats urban manure, but can also treat municipal organic waste and the water algae that cause water pollution in the nearby Dianchi Lake.  The multiple layers of fermentation guarantee the organic fertilizer produced is poison free and odorless.   Through the whole process of manure treatment and fertilizer production, no pollution is emitted since the biogas produced from anaerobic digestion supplies sufficient energy to power the facility.

The manure and organic material undergoes anaerobic fermentation in the biogas digester where the bacteria are removed, and the bio-slurry produced is similar to an odorless sludge.  Since the bio-slurry is only 10% solid and 90% liquid, it must undergo solid liquid separation before it can be produced as a solid fertilizer.  Through a centrifugal wall, the liquid is sieved and the solid is sent to a machine to undergo compression and dehydration. Dongran has the capacity to produce 45 tons of solid organic fertilizer a day.

For the production of liquid organic fertilizer, the fermented liquid is biologically treated and then undergoes filtration.  Two thirds of the fermentation liquid will be recycled as medium quality water (such as toilet water);  the other one third of the fermentation liquid is rich in organic material and can be used as liquid fertilizer after undergoing additional filtration to remove harmful substances.  70 tons of liquid fertilizer can be produced daily along with 200 tons of medium quality water per day.

During the process of anaerobic digestion, 100-140 cubic meters of biogas are produced.  Through the use of a biogas electricity generator, every cubic meter of biogas produced can generate 1.6 kWh of electricity.  Therefore 100 cubic meters of biogas produced can generate 160 kWh, which is used to provide power on-site, but can be also sold to the electric grid.

Beijing’s Haidian District government (where China’s elite universities are located along with Beijing’s Silicon Valley, ZhongGuanCun) has visited Dongran’s facility and is planning to use the company’s technology to build a biogas waste management system.  The large scale biogas digester is an excellent technology to not only solve the problem of proper waste treatment, but create a marketable product as well.

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