Integrating NZVI and carbon substrates in a non-pumping reactive wells array for the remediation of a nitrate contaminated aquifer

Abstract

The work explores the efficacy of a biochemical remediation of a nitrate-contaminated aquifer by a combination of nanoscale zero-valent iron (NZVI) and bacteria supported by carbon substrates. Nitrate removal was first assessed in batch tests, and then in a laboratory bench-scale aquifer model (60cm length×40cm width×50cm height), in which a background flow was maintained. Water and natural sandy material of a stratified aquifer were used in the tests to enhance the reliability of the results. An array of non-pumping-reactive wells (NPRWs) filled with NZVI (d50=50nm, and SSA=22.5m(2)/g) mixed with carbon substrates (beech sawdust and maize cobs) was installed in the bench-scale aquifer model to intercept the flow and remove nitrate (NO3(-) conc.=105mg/l). The NPRW array was preferred to a continuous permeable reactive barrier (PRB) since wells can be drilled at greater depths compared to PRBs. The optimal well diameter, spacing among the NPRWs and number of wells in the bench-scale model were designed based on flow simulations using the semi-analytical particle tracking (advection) model, PMPATH. An optimal configuration of four wells, 35mm diameter, and capture width of 1.8 times the well diameter was obtained for a hydraulic conductivity contrast between reactive materials in the wells and aquifer media (KPM/Kaq=16.5). To avoid excessive proximity between wells, the system was designed so that the capture of the contaminated water was not complete, and several sequential arrays of wells were preferred. To simulate the performance of the array, the water that passed through the bench-scale NPRW system was re-circulated to the aquifer inlet, and a nitrate degradation below the limit target concentration (10mg/l) was obtained after 13days (corresponding to 13 arrays of wells in the field). The results of this study demonstrated that using the NZVI-mixed-carbon substrates in the NPRW system has a great potential for in-situ nitrate reduction in contaminated groundwater. This NPRW system can be considered a promising and viable technology in deep aquifers.

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

“…The combined use of ZVI and a carbon substrate for in situ biochemical denitrification has been considered in recent years and has been shown to be effective at the laboratory scale in improving denitrification rates (Della Rocca et al, 2006;Della Rocca et al, 2007). Huang et al (2015) and Hosseini and Tosco (2015) demonstrated the efficacy of nitrate removal from contaminated groundwater by a combination of ZVI and carbon substrates (pine bark, beech sawdust and maize cobs) in laboratory tests. Liu et al (2013) demonstrated that the main role of ZVI in two-layer permeable reactive barriers consisting of ZVI and activated carbon immobilizing denitrifying microbial consortia was as an oxygen capturing reagent and not for direct nitrate reduction.…”

Complex-conductivity monitoring to delineate aquifer pore clogging during nanoparticles injection

“…A particular case refers to the so-called daylighting, the incident in which renegade particles emerge to the surface along preferential flow paths, for instance through fractures developed by non-intended fracking. Fracking results from pressure building up during the NP injections due to continuous injections performed at high pressure (Hosseini & Tosco 2015;Luna et al 2015), as well as from clogging of the pore space following aggregation and sedimentation of the injected particles (e.g. Tosco & Sethi 2010) enhanced by slow injections (e.g.…”

A Study on the Mechanism and Kinetic of Nitrate Reduction by the nZVI-g-C3N4/TiO2  Composite Under the Simulated Sunlight

“…Pu et al [13] also report that the efficiency of nitrate removal by promoting electron migration from nZVI surface to rGO surface is enhanced. Up to now, supported nZVI materials such as goethite [14], diatomite [15], chelating resin [16,17], C [4,18], active carbon [19], biochar [20], silicon [21], graphene [22] have been studied. But these carriers still exist the disadvantages of tedious preparation and high cost.…”