Hydrothermal liquefaction of wet waste biomass: a practical assessment to achieve an integral valorization of municipal sludge

Hydrothermal liquefaction of municipal sludge was conducted to perform a practical assessment to achieve an integral valorization of this wet waste biomass. Experiments were done to investigate the effects of sub- and supercritical water and of the fluid dynamic regime on the energy recovery of the process and on the quality of the products. Experimental runs were performed at two different temperatures (350°C and 400°C) changing reaction time in order to work at the same kinetic severity of the process (LogR0=8.9, calculated as in ref. [3]). An improvement of the C % in the solid residues and of the ration of H/C of the biocrude was obtained when stirred reactor was used both in sub- and supercritical water. An hydrocarbon fraction was separated from biocrude. The maximum value of the hydrocarbon yield was 25% and it was achieved in supercritical conditions. Moreover results showed that the cumulative energy recovery of the products was significantly higher than 100% suggesting that hydrothermal liquefaction of municipal sludge could be fed by renewable source of thermal energy.