Treatment of Coking Wastewater by α-MnO₂/Peroxymonosulfate Process via Direct Electron Transfer Mechanism

Side reactions between free radicals and impurities decelerate the catalytic degradation of organic contaminants from coking wastewater by Advanced Oxidation Processes (AOPs). Herein, we report the disposal of coking wastewater by α-MnO₂/PMS process via a direct electron transfer mechanism in this study. By the removal assays of the target compound of phenol, the PMS mediated electron transfer mechanism was identified as the dominated one. Water quality parameters including initial pH, common anions and natural organic matters demonstrated limited influences on phenol degradation. Afterwards, α-MnO₂/PMS process was applied on the disposal of coking wastewater. The treatment not only eliminated organic contaminants with COD removal of 73.8% but also enhanced BOD₅/COD from 0.172 to 0.419, within 180 min of reaction under conditions of 50 g/L α-MnO₂, 50 mM PMS and pH₀ 7.0. COD removal decreased only 1.1% after five-time cycle application, suggesting a good reuse performance. A quadratic polynomial regression model was further built to optimize the reaction conditions. By the model, the dosage of α-MnO₂ was identified as the most important parameters to enhance the performance. The optimal reaction conditions were calculated as 50 g/L α-MnO₂, 50 mM PMS and pH₀ 6.5, under which COD removal of 74.6% was predicted. All aforementioned results suggested that the α-MnO₂/PMS process is a promising catalytic oxidation technology for the disposal of coking wastewater with good practical potentials.