Efficiency and Mechanisms of Sunlight-Driven Photocatalytic Degradation of Total Petroleum Hydrocarbons Using Pyrolyzed Drilling Waste Residue

This study addresses the challenges associated with deep-well drilling mud cuttings, including large waste volumes, high transportation costs, and complex organic pollutants. A low-cost synergistic technology was developed for the resource utilization of pyrolyzed drilling waste residue (PDWR) and the in situ remediation of oil-contaminated drill cuttings. A ternary photocatalytic system consisting of PDWR, H2O2, and oxalic acid was proposed and demonstrated to effectively degrade total petroleum hydrocarbons (TPH) in drill cuttings under solar irradiation. Systematic optimization identified optimal dosages of PDWR, H2O2, and oxalic acid as 250 mg, 280 mg, and 90 mg, respectively. The addition of oxalic acid significantly enhanced photocatalytic oxidation performance, increasing H2O2 utilization by 63.8% and improving the TPH degradation rate by a factor of 3.03. Under optimal conditions and 7 days of solar irradiation, TPH degradation efficiencies of 65.19–88.66% were achieved for initial TPH concentrations ranging from 5000 to 12,000 mg kg−1. Mechanistic analysis revealed that a Fenton-like reaction between transition metals in PDWR and H2O2 dominated the photocatalytic process, while oxalic acid facilitated metal redox cycling through coordination and electron transfer, promoting sustained generation of reactive oxygen species (·OH). This study demonstrates a feasible and sustainable approach for high-value utilization of drilling waste residue and solar-driven in situ remediation of oil-contaminated drill cuttings, highlighting its strong potential for practical application.