Nitrate reduction via micro-electrolysis on Zn-Ag bimetal combined with photo-assistance

A selective and efficient chemical reduction of nitrate to nitrogen gas using micro-electrolysis on Zn-Ag combined with a photo-assisted reduction in the presence of formic acid was investigated. The 99.58% removal of nitrate, 0.073 min(-1) of rate constant and 94.3% nitrogen selectivity were achieved in Zn-Ag/hv/HCOOH system under the initial pH 2.5, 13.8 mmol/L of formic acid and 60 g/L of Zn-0.06%Ag dose at 60 min. The Zn-Ag/hv/HCOOH system had the highest removal rate and nitrogen selectivity for nitrate reduction compared with the alone or two combinations of Zn-Ag bimetals, formic acid, and UV-A. Furthermore, the co-existence anions of HCO3- and CO32- showed a negative effect on nitrate reduction while SO42- had slightly promoted the reduction process. During the nitrate reduction by Zn-Ag/hv/HCOOH process, rapid reduction of NO3- to NO2- was primarily caused by Zn-Ag bimetal. Subsequently, the conversion of NO2- to N-2 was mainly owing to the produced CO2 center dot(-) by the reaction of formic acid and UV-A. The results suggested a novel strategy of chemical reduction combined with photoreduction for denitrification with high reaction kinetic as well as high nitrogen gas selectivity. (C) 2019 Elsevier B.V. All rights reserved.