Simultaneous production of biocrude oil and recovery of nutrients and metals from human feces via hydrothermal liquefaction

Hydrothermal liquefaction (HTL) is a thermochemical process specifically suitable for treating wet wastes. This study investigated its potential for the production of biocrude oil and the recovery of nutrients and metals from human feces via HTL. Specifically, the effects of temperature (260 °C, 300 °C, 340 °C), retention time (10 min, 30 min, 50 min) and total solid (TS) content (5%, 15%, 25%) were studied. The maximum liquefied fraction was 87.89% and the highest biocrude yield reached 34.44% with a higher heating value of 40.29 MJ/kg. Experimental results showed that 54% of carbon in the human feces was migrated to the biocrude oil while 72% of nitrogen was released to the aqueous phase. In addition, most of heavy and alkaline-earth metal elements in the human feces, including Ca (89%), Mg (81%), Al (88%), Fe (72%) and Zn (94%) were distributed in the solid residue, whereas K (89%) and Na (73%) were mainly dissolved into the aqueous phase. This study demonstrated that the efficient degradation of human waste via HTL without any pretreatment and its potential for the valorization in biocrude oil as well as separated nutrients and metals.