4.7 Article

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

Journal

SUSTAINABLE MATERIALS AND TECHNOLOGIES
Volume 35, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.susmat.2022.e00533

Keywords

Biorefinery; Sewage sludge; Waste valorization; Clean oil; Metal oxides

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Due to limited processing techniques, much sewage sludge is not treated effectively, leading to pollution and resource waste. This study successfully converted sewage sludge into biocrude and fly ash-like residue using plasma-electrolytic technology. The resulting crude oil had low N and S content and high heating value, while the residue showed similar properties to fly ash and met the national standard for preparation of paving blocks. This plasma-enabled approach provides a viable option for biomass and waste utilization, with significant socioeconomic and environmental benefits.
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 biocrude and fly ash-resembling residue. Reactive plasma species with strong oxidation capacity (center dot O and center dot 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.

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