Isotopic evidence of nitrate degradation by a zero-valent iron permeable reactive barrier: Batch experiments and a field scale study

Abstract

Permeable reactive barriers (PRBs) filled with zero-valent iron (ZVI) are a well-known remediation approach to treat groundwater plumes of chlorinated volatile organic compounds as well as other contaminants. In field implementations of ZVI-PRBs designed to treat these contaminants, nitrate consumption has been reported and has been attributed to direct abiotic nitrate reduction by ZVI or to denitrification by autochthonous microorganisms using the dissolved hydrogen produced from ZVI corrosion. Isotope tools have proven to be useful for monitoring the performance of nitrate remediation actions. In this study, we evaluate the use of isotope tools to assess the effect of ZVI-PRBs on the nitrate fate for the further optimization of full-scale applications. Laboratory batch experiments were performed using granular cast ZVI and synthetic nitrate solutions at pH 4-5.5 or nitrate-containing groundwater (pH=7.0) from a field site where a ZVI-PRB was installed. The experimental results revealed nitrate attenuation and ammonium production for both types of experiments. In the field site, the chemical and isotopic data demonstrated the occurrence of ZVIinduced abiotic nitrate reduction and denitrification in wells located close to the ZVI-PRB. The isotopic characterization of the laboratory experiments allowed us to monitor the efficiency of the ZVI-PRB at removing nitrate. The results show the limited effect of the barrier (nitrate reduction of less than 15-20%), probably related to its non-optimal design. Isotope tools were therefore proven to be useful tools for determining the efficacy of nitrate removal by ZVI-PRBs at the field scale.

A Novel Method for Treating Heavy Metal-Contaminated Soil: The Combined Electrokinetics and Permeable Reactive Barrier Technique

“…Using various barrier materials, PRB can remove a variety of pollutants. Commonly used materials include zero-valentiron (Fe(0)), activated carbon (AC), zeolite, lime, apatite, transformed red mud (TRM), and biologically reactive materials (Zijlstra et al, 2010;Vermeul et al, 2014;Ranjbar et al, 2017;Vukojević Medvidović et al, 2018;Gibert et al, 2019;Grau-Martí nez et al, 2019;Huang et al, 2019). Pollutants that can be removed with the PRB technique include organic pollutants such as chlorinated hydrocarbons, polychlorinated biphenyls, polyaromatic hydrocarbons, and the benzene series (Chang and Cheng, 2006;Chen et al, 2011;Du et al, 2013; heavy metal and metalloid pollutants including nickel (Ni), copper (Cu), zinc (Zn), lead (Pb), Cd, selenium (Se), arsenic (As), chromium (Cr), and mercury (Hg) (Huang et al, 2015;Robles et al, 2015;Han et al, 2016;Ranjbar et al, 2017;Medvidović et al, 2018;Huang et al, 2019;Xu et al, 2019); radioactive materials such as caesium-137 and strontium-90 (Vermeul et al, 2014;Torres et al, 2017); and inorganic salt pollutants such as nitrate (Li et al, 2017;Gibert et al, 2019).…”

Abiotic Reduction of Nitrate and Chlorate by Green Rust

“…On Mars, Fe-rich minerals have been discovered in high abundance including nontronite found in Martian Ancient Terrains, jarosite in Gale Crater, and hematite detected in Sinus Meridiani, Aram Chaos, and Valles Marineris. − ClO 3 – and NO 3 – reduction were reported during the extraction of an H-type chondrite, potentially as a result of the presence of native metallic iron (Fe 0 ) and/or other reactive iron oxides present. Due to their ability to degrade NO 3 – , Fe 0 and iron minerals have been applied as packed media in filter columns for water treatment. − In soil and groundwater, green rust (GR) is a reactive reductant arising in iron-rich anoxic environments or produced from Fe 0 corrosion. , Structurally, GR comprises alternating trioctahedral Fe II and Fe III hydroxide layers with interlayer anions including sulfate, chloride, and carbonate. , Since the early reports of NO 3 – reduction, GR has received continuous attention as a reactive iron mineral for redox transformation of organic and inorganic solutes in water and as an important intermediate phase between Fe II and Fe III (hydro)­xides. ,,, GR reduces NO 3 – to ammonium (NH 4 + ) forming magnetite as a stable product, and GR-mediated NO 3 – reduction is considered to play an important role in nitrogen cycling in environments where microbial activity is low. Other than NO 3 – and nitrite (NO 2 – ), GRs or GR-like substances have been reported to reduce chlorinated aliphatics and reducible metal contaminants. − …”

Configuration of Non-Pumping Reactive Wells Considering Minimum Well Spacing

“…Groundwater containing soluble contaminants encounters the reactive material in the PRB and passes through it, resulting in the removal of the contaminants. PRB technology has been applied to treat groundwater contaminated with heavy metals [6][7][8], nutrients [9][10][11], radionuclide [12], petroleum hydrocarbons [13][14][15], and chlorinated solvents [16][17][18].…”