Wheat straw biochar-supported nanoscale zerovalent iron for removal of trichloroethylene from groundwater.

Hui Li,Yun Jiang Yu,Yong Di Liu,Xiao Li Wang,Yue Feng Qiu,Shuai Chen,Xiao Li Duan,Ya Qin Chen,Shu Guo,Jorge Paz-Ferreiro

doi:10.1371/journal.pone.0172337

Abstract

This study synthesized the wheat straw biochar-supported nanoscale zerovalent iron (BC-nZVI) via in-situ reduction with NaBH4 and biochar pyrolyzed at 600°C. Wheat straw biochar, as a carrier, significantly enhanced the removal of trichloroethylene (TCE) by nZVI. The pseudo-first-order rate constant of TCE removal by BC-nZVI (1.079 h−1) within 260 min was 1.4 times higher and 539.5 times higher than that of biochar and nZVI, respectively. TCE was 79% dechlorinated by BC-nZVI within 15 h, but only 11% dechlorinated by unsupported nZVI, and no TCE dechlorination occurred with unmodified biochar. Weakly acidic solution (pH 5.7–6.8) significantly enhanced the dechlorination of TCE. Chloride enhanced the removal of TCE, while SO42−, HCO3− and NO3− all inhibited it. Humic acid (HA) inhibited BC-nZVI reactivity, but the inhibition decreased slightly as the concentration of HA increased from 40 mg∙L-1 to 80 mg∙L-1, which was due to the electron shutting by HA aggregates. Results suggest that BC-nZVI was promising for remediation of TCE contaminated groundwater.

Highlights

Trichloroethylene is a widespread and persistent contaminant of groundwater which poses a serious threat to groundwater environmental safety and human health[1]
It showed that the wheat straw biochar had a rough and porous surface (Figure A1 in S1 File), which provided the suitable sites to support nanoscale zerovalent iron (nZVI)
The nZVI particles dispersed on the biochar were hard to distinguish after reacting with TCE (Figure A3 in S1 File), because nZVI particles were oxidized during the reaction

Summary

Introduction

Trichloroethylene is a widespread and persistent contaminant of groundwater which poses a serious threat to groundwater environmental safety and human health[1]. Removal of TCE from groundwater is a challenging task considering the complex subsurface environment. Zerovalent iron (ZVI) has been effectively used to degrade halogenated organic compounds since 1994[2]. ZVI research has shifted to the nanoscale material[3], because ZVI is passivated and has a relatively slow reaction rate due to its large size[4]. Nanoscale zerovalent iron (nZVI) has high dechlorination rates and transform chlorinated solvents completely without accumulation of chlorinated byproducts[5,6].

Methods

Results

Conclusion