Effective advance treatment of secondary effluent from industrial parks by the Mn-based catalyst ozonation process

Catalytic ozonation is a potential technology to eliminate refractory organic contaminants with the low concentration in secondary effluent from industrial park wastewater treatment plants (IPWWTPs). In this study, the catalytic ozonation over the Mn-based catalyst significantly improved the chemical oxygen demand (COD), total organic carbon (TOC), and UV₂₅₄ removals of secondary effluent from IPWWTPs. The Mn-based catalyst/O₃ system achieved 84.8%, 69.8%, and 86.4% removals of COD, TOC, and UV₂₅₄, which were 3.3, 5.7, and 1.1 times that in ozonation alone, respectively. Moreover, the Mn-based catalytic ozonation process exhibited excellent pH tolerance ranging from pH 4.0 to 9.0. Additionally, the depth analysis based on fluorescence excitation-emission matrix (EEM) confirmed that the catalytic ozonation process preferred to degrade toxic aromatic hydrocarbons. The existence of the Mn-based catalyst/O₃ system enhanced 21.4%–38.3% more fluorescent organic matters removal, compared to that in ozonation alone. Mechanistic studies proved that the abundant Lewis acid sites (Mnⁿ⁺/Mn⁽ⁿ⁺¹⁾⁺ and adsorbed oxygen) on the surface of the Mn-based catalyst effectively promoted O₃ decomposition into reactive oxygen species (ROS), and ·O₂⁻/HO₂· and ¹O₂ were the main ROS for degrading refractory organic contaminants. The contributions of ROS oxidation (91.2%) was much higher than that of direct O₃ oxidation (8.8%). Thus, this work provides an effective advanced treatment process for purifying secondary effluent from IPWWTPs.