1. State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment,Tsinghua University, Beijing 100084, China 2. Department of Civil Engineering, College of Engineering and Informatics, National University of Ireland, Galway, Ireland
With low organic matter content, sludge in China has low reaction rates and low biogas production rates. Thermal hydrolysis at about 60 ℃ will enhance the digestion. Thermal hydrolysis of excess sludge at low temperatures was conducted in thermal tanks with a heat pump as a heat source. The effects of hydraulic retention time (HRT), temperature (T), solid content and organic matter ratio (CVSS/CSS) of the sludge on thermal hydrolysis were analyzed. The results showed that the optimal operating conditions for thermal hydrolysis was HRT=1 d, T=54-60℃, and a solid content=3%. Adding alkalis enhanced the hydrolysis, with a solid content of 5%, NaOH was added to increase the pH to 10 to increase the VSS removal rate by 46.8% and the solution rate of organic substances by 100%. Orthogonal experiments indicated that the temperature, solid content and CVSS/CSS were all crucial to the VSS removal rate and the solution rate of the organic matter. The solid content had the largest effect followed by the temperature and CVSS/CSS. The biogas production rate of the sludge hydrolyzed with optimal conditions during 10 days anaerobic digestion at 35℃ was 44% higher than that of sludge without hydrolysis.
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