With the improvement of urbanization level, the sewage treatment volume of China has risen to the first place in the world, and the urban sewage treatment rate has exceeded 90%. As a by-product of sewage treatment, the annual production of sewage sludge has exceeded 60 million tons (based on a moisture content of 80%).
For a long time, sewage treatment has been paid more attention to than sludge treatment in the treatment policy, 80% of sludge in China has not been disposed safely, which caused severe water, air and soil pollution, and also wasted the resources and energy in sludge. The safe disposal of sludge, which is directly related to the benefit of sewage treatment project, is an important task for China to win the tough battle of water pollution prevention and control.
Sewage sludge is perishable, which enriched 30%-50% organic matter and pathogens in sewage. Sludge stabilization is an indispensable stage to achieve the safe treatment and disposal of sludge. Anaerobic digestion has been taken as the mainstream technology of sludge stabilization treatment all over the world for its excellent performance to achieve stabilization, reduction, harmlessness and resources of sludge, as it can degrade perishable organic matter, reduce pathogenic bacteria, reduce sludge volume and recover energy. Sewage sludge produced in China has the low-quality, including a high content of micron-sized inorganic particles and a low content of organic matter. As a consequence, there are three bottleneck problems in the anaerobic digestion process of the low-quality sludge in China: 1) the poor biodegradability of the sludge organic matter (the low bioconversion potential), 2) the low organic load rate and biogas production (the low process efficiency), and 3) the poor running benefit and stability effect (the low beneficial result), which hinder the promotion and application of anaerobic digestion technology of sewage sludge in China. Therefore, it is urgent to develop high-efficiency anaerobic biological stabilization treatment technology and the corresponding equipment suitable for China's low-quality sludge.
Prof. Xiao-hu DAI, Dean of College of Environment Science and Engineering(CESE) and Director of NERC, Tongji University