Bromide significantly promoted the abatement of micropollutants by peroxymonosulfate: Roles of HOBr and Br2

Abstract

Peroxymonosulfate (PMS) is extensively investigated for water treatment, which can inevitably interact with bromide (Br−) in water to form bromine species. This study differentiated specific roles of bromine species for carbamazepine degradation during PMS treatment with Br− (PMS/Br−) via experiments and modeling. The second-order rate constants of HOBr, OBr−, Br2, Br2O, BrCl, and BrOCl with carbamazepine were first determined to be 59.5 M−1 s−1, 14.3 M−1 s−1, 1.1 × 104 M−1 s−1, 2.2 × 105 M−1 s−1, 1.4 × 107 M−1 s−1, and 2.7 × 106 M−1 s−1, respectively. By modeling, HOBr and Br2 substantially contributed to carbamazepine degradation. The contribution of Br2 was enhanced at higher Br− level and lower pH, and reached 99% at pH 3. Interestingly, Cl− significantly enhanced while HCO3− slightly enhanced the removal of carbamazepine. NOM was a sink for bromine, thereby retarding carbamazepine degradation in PMS/Br−. The maximum of total organic carbon (TOC) removal rate reached 43%, and the conversion ratio from the consumed bromine to total organic bromine (TOBr) formation was only 9% at 10 min in PMS/Br−. The primary transformation pathways of carbamazepine were hydroxylation and deacetylation, whereas bromination happened as the minor pathway. The acute toxicity was significantly reduced, and the total yields of known brominated disinfection by-products including tribromomethane and dibromoacetonitrile only accounted for 0.6% of TOBr at 10 min in PMS/Br−. This study firstly quantified specific roles of bromine species for micropollutant degradation under environmentally relevant conditions during PMS treatment of Br−-containing water.