Effect of Thermal Hydrolysis Pretreatment on Different Sludge Properties and Anaerobic Digestion Performance

Sludge was an important by-product of sewage treatment. With the continuous expansion of number and scale of sewage treatment plants, the amount of sludge generated was increased. In the process of sludge stabilization, harmless and resource treatment, hydrothermal pretreatment and anaerobic digestion technology were widely used. In order to compare and analyze the effects of hydrothermal treatment on sludge properties and anaerobic digestion performance of different sources, the viscosity, ammonia nitrogen, pH value, TS components and anaerobic digestion performance of sludge from four different sources were studied. The results showed that under the same hydrothermal temperature treatment, sludge viscosity, ammonia nitrogen concentration and pH value were greatly affected by the sludge source. Hydrothermal pretreatment had a good modification effect on different sludges. The sludge properties remained basically unchanged after the hydrothermal temperature reached 170℃. There was no significant difference in the gas production rate of sludge from different sources with the increase of OLR, but there were differences in the operation. The gas production performance of anaerobic digestion of sludge from different sources was significantly improved after hydrothermal pretreatment, but there was a significant difference in the proportion of increased gas production rate of VS. Sludge VS gas production rate in Beijing, Shanghai and Shandong was increased by 25.2%~69.8%, as the sludge in Guangxi was pure excess sludge, the gas production rate of VS was increased by 101.6%~133.8% after hydrothermal treatment. However, the increase in gas production per unit VS was not significantly different, and the fluctuation with the change of gas production performance was small, the increase was about 83~218 m3/t (the average was 143 m3/t). After hydrothermal pretreatment, the fluidity of the sludge became better, the high-concentration and high-load feed of anaerobic digestion could be realized, and the capacity reduction rate of the reactor could reach 38%~71%. By analyzing the hydrothermal modification effect and digestion capacity gain of different sewage sources and treatment processes, it was expected to provide reference for the design of sludge hydrothermal and anaerobic digestion processes in different regions. © 2020, Chinese Society of Agricultural Machinery. All right reserved.