Hydrothermal liquefaction of sewage sludge under isothermal and fast conditions.

We investigated the effects of water loading, sludge moisture content, recovery solvent, and additives on the product yields and compositions from isothermal (673K, 60min) and fast (773K, 1min) hydrothermal liquefaction (HTL) of sewage sludge. The water loading (which affects pressure within the reactor) plays a small role in product yields. The sludge moisture content had a larger effect with the highest biocrude yields (26.8wt% from isothermal HTL and 27.5wt% from fast HTL) being produced from sludge that was 85wt% moisture. The HTL biocrude from sludge mainly contains long-chain aliphatic hydrocarbon moieties and aliphatic acids. Dichloromethane recovered more biocrude and energy content (∼50%) than did the other solvents tested. Added K2CO3, Na2CO3, HCOOH, CH3COOH, MoO3-CoO/γ-Al2O3 and Ru/C significantly decrease the biocrude yield when their loadings are 50wt% of the dried sludge. The additives, excepting carbonates, enhance gasification of sludge.