Developing Slow-Release Reductant for Treating Herbicide-Contaminated Groundwater

摘要

Herbicide use in agriculture is impor-tant to increase crop yield;however,it has caused groundwater contamination in some countries.Our objective was to develop a slow-release reductant to treat herbicide-contaminated groundwater.The tested herbicides were alachlor(ALC),metolachlor(MTC),2,4-dichlorophenoxyacetic acid(2,4-D),and atrazine(ATZ).Among these,ALC degraded the best,reach-ing a degradation plateau with a small level of Fe~0(2.5％,w/v).Under aerobic conditions,both reduc-tive reactions for electron transfer and oxidative reac-tions for generating active radicals are complex reac-tions responsible for herbicide degradation.By usingslow-release Fe~0(SRZ),we found that the degrada-tion was prolonged and the plateau disappeared,indi-cating the greatest slow-release benefit.Fe~0 and SRZ removed ALC at 15％and 28％faster rates,respec-tively,under anaerobic conditions.At pH 3,the oxide layers on Fe~0 were removed facilitating better elec-tron transfer for ALC degradation.Several reductants were tested in this study,but we mainly used Fe~0 as the main slow-release ingredient that was prepared by mixing Fe~0 with heated paraffin in a 4.7∶1 ratio(w/w)and molding it into a 0.6 cm O×2.5 cm length cylin-drical shape.We stacked slow-release Fe~0 in a 2D ALC-saturated sand tank(70×30×3 cm),spatially collected samples along with the tank sampling array,and quantified the changes in ALC concentration.The results showed that the ALC concentration decreased 20-35％faster compared to DI flushing.These results supported the use of SRZ as an alternative approach for treating herbicide-contaminated groundwater.