Effects of co-existing nitrate on TCE removal by mZVI under different pollution load scenarios: Kinetics, electron efficiency and mechanisms

Jia Xin; Shufen Fan; Mengjiao Yuan; Xiaohui Wang; Xuejiao Zhang; Xilai Zheng

doi:10.1016/j.scitotenv.2020.137111

Effects of co-existing nitrate on TCE removal by mZVI under different pollution load scenarios: Kinetics, electron efficiency and mechanisms

Sci Total Environ. 2020 May 10:716:137111. doi: 10.1016/j.scitotenv.2020.137111. Epub 2020 Feb 4.

Authors

Jia Xin¹, Shufen Fan², Mengjiao Yuan², Xiaohui Wang², Xuejiao Zhang², Xilai Zheng²

Affiliations

¹ Key Lab of Marine Environmental Science and Ecology, Ministry of Education, Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China. Electronic address: xinj15@ouc.edu.cn.
² Key Lab of Marine Environmental Science and Ecology, Ministry of Education, Shandong Provincial Key Laboratory of Marine Environment and Geological Engineering, College of Environmental Science and Engineering, Ocean University of China, Qingdao 266100, China.

PMID: 32059314
DOI: 10.1016/j.scitotenv.2020.137111

Abstract

Microscale zero-valent iron in situ reaction zone (mZVI-IRZ) has proved to be effective and efficient for the removal of chlorinated aliphatic hydrocarbons (CAHs) from groundwater. However, nitrate (NO₃^-), which is ubiquitous in groundwater, affects the mZVI-based attenuation of CAHs in a complicated manner. Both the reaction rate constant (k) and electron efficiency (EE) of mZVI must be considered to comprehensively reflect the effects of NO₃^- on the short and long-term remediation performances of mZVI. Therefore, the influence of NO₃^- on trichloroethylene (TCE) removal under high-pollution-load (iron limited) and low-pollution-load (iron excess) conditions was investigated. Low concentrations of NO₃^- (10 and 50 mg N L^-1) were found to enhance the TCE removal rate and efficiency, whereas high concentrations of NO₃^- (100 mg N L^-1) inhibited the reaction. Although TCE removal was increased at low concentrations of NO₃^-, the EE of mZVI was dramatically decreased in the presence of NO₃^- at all concentration levels. Therefore, both the short-term TCE removal characteristics and the EE of mZVI should be considered when evaluating the long-term remediation effectiveness of mZVI-IRZ technology. The effects of NO₃^- on the TCE removal trends under high- and low-pollution-load scenarios were similar, but had different magnitudes. NO₃^- affected the TCE removal mainly by promoting mZVI corrosion, competing for electrons and affecting passivation product evolution. Our results provide guidance for the practical application of mZVI-IRZ technology.

Keywords: Electron efficiency; Microscale zero-valent iron; Nitrate; Pollution load; Trichloroethylene.