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

Abstract

NH4+ is often produced during the electro-reduction of NO3−, which results in inadequate total nitrogen (TN) removal during advanced sewage treatment. In this study, the electro-reduction byproduct NH4+ was oxidized and removed using sulfate radical (SO4•−)-based advanced oxidation. Persulfate (PS) was activated by electrocatalysis, using Co/AC0.9-AB0.1 particle electrodes to produce SO4•−. Results showed that when the influent concentration of NO3−-N was 20 mg/L, a PS dosage of 5.0 mM could completely oxidize NH4+ at 0.1 A (nondetectable in effluent) reducing the TN concentration from 9.22 to 0.55 mg/L. The presence of coexisting PO43−, CO32− and humic acid suppressed the oxidation and removal of NH4+. Electron spin resonance (ESR) spectra and quenching experiments revealed SO4•− as the dominant radical in the process of indirect NH4+ oxidation, while •OH radicals only had an assisting role, and the surface accumulated free radicals were responsible for the indirect oxidation of NH4+. Cyclic voltammetry (CV) curves indicated that NO3− was primarily reduced via atomic H*-mediated indirect reduction. Therefore, the activation of PS using Co/AC0.9-AB0.1 particle electrodes might be a promising alternative method for oxidizing byproduct NH4+ in the electro-reduction of NO3− and reduce TN concentration in advanced sewage treatment.