Degradation of p-aminobenzoic acid by peroxymonosulfate and evolution of effluent organic matter: The effect of chloride ion

Abstract

Effluent organic matter (EfOM) and chloride (Cl−) are coexisting in the effluent of wastewater treatment plant. The degradation of p-aminobenzoic acid (PABA) by peroxymonosulfate (PMS) along with the evolution of EfOM in the presence of Cl− were assessed in this study. In PMS/Cl−/EfOM system, the degradation efficiency of PABA was enhanced with the increase of Cl− concentration. Direct PMS oxidation made a major contribution to the degradation of PABA when Cl− dosage was lower than 50 mM. Hypochlorous acid/hypochlorite (HClO/ClO−) were identified to be the main reactive chlorine species (RCS) by experiments together with modelling results. Additionally, singlet oxygen (1O2) also contributed to the decomposition of PABA. The pseudo-first-order rate constant (k’) of direct PMS oxidation (kPMS′) rose slightly with the increase of pH value (6.0–9.0). The k’ of RCS (kRCS′) improved significantly with increasing Cl− concentration, while kRCS′ reduced upon increasing EfOM concentration due to the scavenging effect by EfOM. Comparatively, the contribution of k’ of 1O2 (k1O2′) witnessed a slight rise from 4.17% to 7.96% with the increase of Cl− concentration. Furthermore, the removal efficiency of EfOM showed a marked increase as the Cl− dosage increased. Humic-like component of EfOM was most liable to decomposition, whereas tryptophan-like aromatic protein in EfOM was not amenable to degradation. This study provides useful insights for PABA degradation by PMS in the coexistence of Cl− and EfOM in the advanced treatment of wastewater.