Synergistic Closed-Loop System for Oily Sludge Valorization via Biomass-Assisted Pyrolysis: Bridging Waste Management to Sustainable Soil Revitalization

Abstract

Oily sludge (OS) and saline-alkali soil (SAS) are two interconnected environmental challenges that persist in petroleum-producing regions, yet conventional remediation strategies address them in isolation. This study innovatively presents a closed-loop system integrating biomass-assisted pyrolysis (BAP) of OS with SAS revitalization using pyrolysis residues. The addition of biomass to OS reduces its viscosity and enhances porosity, lowering pyrolysis activation energy by 8.3–12.8% and increasing oil recovery by 25–30 wt %. Simultaneously, BAP mitigates environmental risks by reducing heavy metal release (∼50%) and residual total petroleum hydrocarbons to ≤3‰, meeting regulatory thresholds. The resulting biochar-rich residue transforms SAS into arable land, improving water retention, microbial activity, and ion exchange capacity. This enables robust Ryegrass growth with plant height, survival rate, and dry biomass increasing by 2.2–2.4, 5.6–7.0, and 10.0–14.2 times, respectively. BAP achieves a 10 times greater carbon reduction than individual OS pyrolysis. By bridging petroleum waste valorization with soil restoration, this work pioneers a circular economy paradigm that simultaneously advances renewable resource recovery and sustainable agriculture, aligning with the United Nations Sustainable Development Goals.