Increased biogas production and reduced sludge quantities in Beijing
China is at the moment the world leading country when it comes to investments within environment and renewable energy. There are many discussions about sludge treatment and increased use of biogas instead of coal, to reduce emissions of particulates and air pollution. It is a big challenge to find solutions for use/removal of the sludge in the middle of Beijing, which makes it necessary to search for ways to reduce the amounts as much as possible to optimize the logistics, both from an environmental and cost perspective.
Beijing is a city that is growing rapidly and the existing wastewater treatment plants that were in the city were not enough to handle all the wastewater and sludge that was produced. Therefore space-efficient solutions were required so the customers could have the possibility to increase capacity without using more land. In 2015 Purac got the mission to increase the biogas production and reduce the sludge volumes in five of Beijing’s largest wastewater treatment plants. Purac’s mission included integrated process design and consulting services for system integration and commissioning. Process warranty was also included. Purac did also provide key equipment such as agitators for the digesters and heat exchangers. Two of the plants (Gaobeidian, Xiaohongmen) were existing plants with anaerobic digestion plants that should be upgraded, while three of them (Huaifang, Qinghe, Gaoantun) were completely new plants. Purac had a strong partnership with the Norwegian company Cambi and delivered a solution with the greatest possible gas extraction in as little space as possible to meet customer needs. The process is called THP (Thermal Hydrolysis Process) and changes the capacities of the slurry and thereby increases the gas exchange. At the same time the residues after the biogas reactors can be dewatered to a higher solid content compared to conventional processes. This means that the volume of the final product is lower than for most other digestion and dewatering processes.
The sludge plant consists of the following process steps: thickening, predewatering, THP, digestion, chamber filter pressing and deammonification. The same process is present in all five upgraded/new treatment plants. In total, the five plants treats 6,000 tons of sludge/day, which makes this one of the largest sludge projects with THP technology and digestion in the world.
Biogas production in Beijing
Gaobeidian WWTP: 60 000 m3/day
Xiaohongmen WWTP: 58 000 m3/day
Gaoantun Sludge Disposal Center: 115 000 m3/day
Qinghe WWTP: 53 000 m3/day
Huaifang WWTP: 79 000 m3/day