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

Shuai Yang,Yu Liu,Xinyu You,Xinxin Hu,Wenyan Liang,Wenwen Zhang

doi:10.3390/ijerph19063270

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.

Highlights

The total nitrogen (TN) content of the effluent of most sewage treatment plants can reach as high as 10 mg/L, even after primary and secondary treatment [1]
For samples without PS dosing, the percentage of NO3 − conversion reached 80.5–90.2%, with the percentage conversion increasing in accordance with the applied current
PS activation occurred at the cathodic side of the particle electrode [36], the PS activation process did not interfere with the reduction of NO3 −

Summary

Introduction

The total nitrogen (TN) content of the effluent of most sewage treatment plants can reach as high as 10 mg/L, even after primary and secondary treatment [1]. Advanced treatment methods are required to reduce the TN content of sewage. Electrochemical reduction is a feasible option for the conversion of NO3 − to N2 , with the benefits of simple operational methods, low-environmental impact and economic efficiency [4]. The electro-reduction of NO3 − occurs via a complex process involving multi-electron transfer between the different valence states of nitrogen and its reaction products, such as N2 H4 , NH3 , NH2 OH, N2 , N2 O, NO, NO2 − , and NO2 [5]. During the direct reduction process, NO3 − is first adsorbed onto the electrode and converted to NO3 − (ad). NO3 2− (ad) and NO2 − (ad) are converted (in a stepwise reduction process) to NO(ad) , to N2 and NH4 + , sometimes via the intermediates

Methods

Results

Conclusion