Plasma-electrolytic liquefaction of human waste for biofuels production and recovery of ammonium, chlorine and metals

Sustainable production of value-added fuels and chemicals from biomass faces enormous challenges for integration in zero-carbon-emissions technologies and circular economy. In this work, green and renewable solvents, polyethylene glycol 200 and glycerol, were used in a plasma-electrolytic liquefaction (PEL) system to electrically liquefy human feces in the absence of a catalyst. It is demonstrated that the plasma ignition during the liquefaction accelerated the conversion of feces (85.67% liquefaction yield within 12 min), and the intrinsic heating features of the PEL greatly reduced the energy consumption. The obtained biocrude oil at the optimized conditions contained 10.53% aldehydes, 5.39% ketones, 18.48% cyclic oxygen-containing compounds and others, with a high heating value of 28.10 MJ/kg. Further analysis of the PEL-converted products reveals that most of the chlorine in the feces was gasified, the metals were extracted into the solid residue, while ammonia was released. An evaluation of the developed plasma electrolytic feces liquefaction process was carried out and favorably compared with common liquefaction methods. Overall, the proposed approach may provide a new avenue for clean chemical production and sustainable resource recovery from human waste under benign process conditions.