Pyrite-Catalyzed Persulfate Oxidation Optimization with Biological Treatment for Pulp and Paper Industry Wastewater Remediation

The pulp and paper industries are highly energy-intensive and generate effluents rich in persistent and recalcitrant organic compounds, limiting the effectiveness of conventional biological treatment. This study presents an integrated approach to wastewater treatment in the pulp and paper industry by combining sulfate radical-based advanced oxidation process with biological treatment. The collected effluent exhibited a high chemical oxygen demand (COD) of 1,008 mg/L, a biochemical oxygen demand (BOD5,20) of 300 mg/L, and a low biodegradability (BOD5,20/COD) ratio of 0.29. Persulfate was activated using a pyrite (FeS2) catalyst, synthesized using a wet-chemical method, and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy-energy-dispersive X-ray (EDX) analysis/spectroscopy. Process optimization using a Box–Behnken design was performed, and the optimal conditions determined were pH 3, catalyst dosage of 0.48 g/L, oxidant dosage of 0.13 g/L, and a reaction time of 2 h. The measured COD and BOD values under these conditions were 190 and 90 mg/L, respectively, representing 81.15% COD removal efficiency, and the BOD/COD ratio increased to 0.47. Post-treatment processes, including iron removal and pH neutralization, enabled further reductions in COD and BOD to 144 and 45 mg/L, respectively, through biological treatment. Phytotoxicity tests using Vigna radiata confirmed reduced toxicity, supporting the sustainability and effectiveness of this combined treatment for recalcitrant industrial wastewater.