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.