Kinetic and Mechanism Studies on the Photodegradation of Cold-Rolling Emulsion Wastewater by the UV/H₂O₂Process

The UV/H2O2 process was employed to purify cold-rolling emulsion wastewater (CREW). The degradation of CREW was mainly attributed to the combined UV/H2O2 process and exhibited pseudo-first-order reaction kinetics. The reaction parameters, including the H2O2 dosage, initial pollutant concentration, initial pH, UV intensity, and inorganic anions, were found to influence the removal efficiency of chemical oxygen demand (COD) and reaction rates. In addition, the optimal experimental conditions were determined: H2O2 dosage of 0.2 mol/L, initial pH of 9.13, and UV intensity of 4.0 mW/cm2. The final residual COD concentration decreased from 3573 mg O2/L to 67 mg O2/L, and the treated wastewater complies with the wastewater discharge standards in China (COD concentration of 80 mg O2/L) and can be discharged. Meanwhile, •OH was identified as the primary reactive radical in the process. Sodium dodecyl sulfonate (SDS) and hexahydro-1,3,5-tris(hydroxyethyl)-s-triazine (BK) were selected as representative pollutants in CREW to explore the degradation mechanism. The products generated were identified by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS). Potential degradation pathways were proposed and discussed. The operational cost is 0.115 USD/L, which was calculated for the best conditions.