Two-stage liquefaction of sewage sludge in methanol-water mixed solvents with low-medium temperature

Hydrothermal liquefaction could be a promising technology to convert sewage sludge into bio-oil for energy recovery. In this study, in order to obtain the maximum yield of bio-oil and improve the energy recovery of sludge, the influence of temperature and residence time on the multi-temperature continuously liquefaction of sludge in methanol-water mixed solvents was investigated. The results showed that the two-stage liquefaction significantly affected the yield, elemental composition, higher heating value, energy recovery and chemical composition of bio-oil. By optimizing the reaction conditions of hydrothermal liquefaction, the maximum utilization of sludge resources was realized. The maximum yield (42.2 %) and ester content (41.8 %) of bio-oil were obtained when the reaction conditions were 260 degrees C, 40 min for the first stage and 340 degrees C, 40 min for the second stage. The migration and transformation of nitrogen indicated that nitrogen elements were mainly concentrated in the liquid product and the N-heterocyclic compounds are the main forms of nitrogen in bio-oils. (C) 2020 Published by Elsevier B.V.

Automated summary

Hydrothermal liquefaction technology shows promise in converting sewage sludge into bio-oil for energy recovery. By optimizing the reaction conditions, maximum utilization of sludge resources can be achieved, with two-stage liquefaction significantly affecting the yield and composition of the bio-oil.