Removal of Ammonia Using Persulfate during the Nitrate Electro-Reduction Process

NH(4)(+) is often produced during the electro-reduction of NO(3)(−), which results in inadequate total nitrogen (TN) removal during advanced sewage treatment. In this study, the electro-reduction byproduct NH(4)(+) was oxidized and removed using sulfate radical (SO(4)(•−))-based advanced oxidation. Persulfate (PS) was activated by electrocatalysis, using Co/AC(0.9)-AB(0.1) particle electrodes to produce SO(4)(•−). Results showed that when the influent concentration of NO(3)(−)-N was 20 mg/L, a PS dosage of 5.0 mM could completely oxidize NH(4)(+) at 0.1 A (nondetectable in effluent) reducing the TN concentration from 9.22 to 0.55 mg/L. The presence of coexisting PO(4)(3−), CO(3)(2−) and humic acid suppressed the oxidation and removal of NH(4)(+). Electron spin resonance (ESR) spectra and quenching experiments revealed SO(4)(•−) as the dominant radical in the process of indirect NH(4)(+) oxidation, while •OH radicals only had an assisting role, and the surface accumulated free radicals were responsible for the indirect oxidation of NH(4)(+). Cyclic voltammetry (CV) curves indicated that NO(3)(−) was primarily reduced via atomic H*-mediated indirect reduction. Therefore, the activation of PS using Co/AC(0.9)-AB(0.1) particle electrodes might be a promising alternative method for oxidizing byproduct NH(4)(+) in the electro-reduction of NO(3)(−) and reduce TN concentration in advanced sewage treatment.