Formation of Brominated By-products in Electrochemically Activated Persulfate Oxidation Processes

The electrochemically activated persulfate (PDS) system was constructed with boron-doped diamond (BDD) anode and Ti cathode to study the transformation of bromide in the presence of humic acid (HA). The mechanism of the electroactive system and the generation path of brominated by-products were analyzed through scanning cyclic voltammetry and free radical quenching experiments. The effects of initial PDS dosage, current density, and initial pH on the formation of brominated by-products in the electroactive PDS system were investigated. The results show that bromate and brominated organic by-products (Br-DBPs) were detected in the system when HA concentration in the reaction solution was 3.0 mg/L (in TOC), bromine ion concentration was 1.0 mg/L, PDS concentration was 5.0 mmol/L, current density was 20 mA/cm2, and pH was 7.0 in the reaction solution, and the highest concentration was 4.11 and 1.02 μmol/L, respectively, within 120 min. The transformation of bromine was mainly caused by the complex radical oxidants (OH· and SO4·-) produced in the system. With the increase of PDS dosage and activation current density, the production of active substances in the solution was increased within a certain range, and the oxidizability of the electrical activation system was improved. Thus, the reaction process of Br-DBPs generation and synchronous mineralization was accelerated. The optimmum pH range for controlling the total production of brominated byproducts was acidic; however, Br-DBPs (especially bromoacetic acid) also showed a higher generation trend in acidic reaction environment. Therefore, in actual use, the operating conditions should be reasonably determined by considering the factors such as degradation efficiency, operating cost, and health risks of produced water.