Plasma-electrolytic biorefinery of sewage sludge for clean oil and bio-derived metal oxide production

Due to the lack of performance- and cost-effective processing techniques, a large proportion of sewage sludge is not effectively treated or utilized, resulting in environmental pollution and a waste of resources. In this study, plasma-electrolytic technology was successfully employed for the electrified refinery of sewage sludge into bio-crude and fly ash-resembling residue. Reactive plasma species with strong oxidation capacity (·O and ·OH), were beneficial to the precipitation of metal ions in the raw sludge. With the addition of NaOH, the thus-obtained crude oil contained only 0.11% N and 0.02% S under the optimized conditions and featured a high heating value (HHV) of 28.04 MJ/kg. Analysis of the residue confirmed that the metal oxides and their contents were similar to fly ash, which is widely used as a performance-enhancing admixture for cement and concrete. Using the residue as the admixture for paving block preparation, with the residue addition of 15%, the compressive strength of the blocks exceeded 35 MPa (C35), and the water absorption was <6.5%, thus meeting the China's national standard (GB 28635–2012). This plasma-enabled power-to-X approach may provide a viable option for biomass or waste valorization and comprehensive utilization leading to substantial socioeconomic and environmental benefits.