Removal of Typical Organic Pollutants in Biologically Treated Coking Wastewater by Ionizing Irradiation

Coking wastewater contains a variety of refractory organic pollutants, and among which phenolic compounds often persist in the effluent even after biological treatment, posing potential environmental risks. In this study, ionizing irradiation was used as an advanced treatment technology for the removal of phenolic pollutants from biologically treated coking wastewater. Based on GC-MS analysis of distilled ammonia wastewater and biologically treated effluent, 2,4-dimethylphenol (2,4-DP) was selected as a representative target compound to evaluate the degradation performance and mechanism. The results confirmed that phenolic compounds remained in the biologically treated effluent, while the abundance of alkanes increased compared to that in distilled ammonia wastewater. Ionizing irradiation effectively removed 2,4-DP, and its mineralization increased with increasing absorbed dose. Quenching experiments revealed that hydroxyl radicals (•OH) played the dominant role in degradation, whereas hydrated electrons and hydrogen radicals contributed less. The addition of H2O2 enhanced mineralization by increasing the •OH concentration, and the highest removal efficiency was observed at pH 6. The effects of inorganic anions were concentration-dependent. Chloride ions promoted degradation at low concentrations but inhibited removal at high concentrations, while sulfate ions had little influence on pollutant removal but suppressed mineralization at 10 g/L. Application to actual biologically treated coking wastewater demonstrated efficient removal of phenolic pollutants (phenol and 2,4-DP). Under optimal conditions (5 kGy with 0.5 mM H2O2), the effluent COD decreased to 78 ± 4 mg/L, meeting the Chinese discharge standard for the coking chemical industry (GB16171-2012). These results demonstrate the potential of ionizing irradiation as an effective advanced treatment technology for coking wastewater.