Treatment of simulated textile sludge using the Fenton/Cl− system: The roles of chlorine radicals and superoxide anions on PAHs removal

The main content of this work is to investigate the removal of polycyclic aromatic hydrocarbons (PAHs: phenanthrene, anthracene, and fluoranthene) from simulated sludge solid phase employing an Fenton/Cl− system under various Cl− contents and pH values. The steady-state concentrations of the hydroxyl, chlorine, and dichloride anion radicals ([·OH]ss, [·Cl]ss, and [Cl2·-]ss) in heterogeneous system were first measured using tert-butanol, nitrobenzene, and benzoic acid. The outcomes exhibited that increasing the Cl− content from 50 to 2000 mg/L (pH = 3.0) or raising the pH from 3.0 to 5.0 (1000 mg/L Cl−) caused [·OH]ss to continuously decrease and [Cl2·-]ss and the concentration of superoxide anions (HO2·/O2·-) to continuously increase. When the pH was 3.0 and the Cl− concentration was 1000 mg/L, [·Cl]ss had a maximum value of 9.27 × 10−14 M. Combining the results of PAH removal, radical quenching, and product analysis, it was found that ·Cl in the Fenton/Cl− system promoted the oxidative degradation of phenanthrene without forming chlorination byproducts. Furthermore, HO2·/O2·- was helpful in removing anthracene and fluoranthene. Under the environment of high Cl− content (≥1000 mg/L), PAHs could be removed more effectively by using HO2·/O2·-. This investigation underpins further study on the regulation of reactive species and the efficient degradation of target organic matter in Fenton/Cl− system, and provides a basis for studying the formation of chlorinated or toxic byproducts in the process of treating textile dyeing sludge by Fenton.