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

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

Metallic Iron for Safe Drinking Water Production

researc

Transport and Retention of High Concentrated Nano-Fe/Cu Particles Through Highly Flow-Rated Packed Sand Column

The design of an efficient field-scale remediation based on the use of nanoscale zero valent iron (NZVI) requires an accurate assessment of the mobility of such particles in saturated porous media, both during injection in the subsurface (short-term mobility) and later (long-term mobility). In this study, the mobility of highly concentrated dispersions of bimetallic Fe/Cu nanoparticles (d50= 70±5 nm) in sand-packed columns (0.5 m length and 0.025 m inner diameter) was studied. In particular, the influence of flow rate (V = 5×10-4, 1×10-3, 2×10-3 m/s) and injected particle concentrations (2, 5, 8, 12 g/l) was addressed. Breakthrough curves and water pressure drop along the column, averaged effective porosity and final distribution of retained particles along the column were measured. Experimental results evidenced a good mobility of the Fe/Cu particles, with significant breakthrough in all explored experimental conditions of flow rate and C0, without requiring the addition of any stabilizing agent. Clogging phenomenon of the column and also the pore pressure variation during injection period are strongly affected by injected concentration. Clogging due to deposition of particles following a ripening dynamics was observed in particular for C0= 8 and 12 g/l. The experimental data were 23 modeled using the E-MNM1D software. The study has implications for field injection of bimetallic nanoparticles, suggesting that particular care is to be devoted when selecting injection concentration, to avoid porous medium clogging and control the radius of influenc

Reductive dechlorination of TCE and cis-DCE by zero-valent iron and iron-based bimetallic reductants

CEs are the most frequently detected pollutants in groundwater. Several studies have been shown iron-based bimetallic reductants as a good method toward to chlorinated ethylenes degradation. However, many fundamental issues surrounding the chemistry of this phenomena remains elusive. In this study, kinetics and compound specific isotope analysis for reductive dechlorination of TCE and cis-DCE by unamended iron and iron-based bimetal reductants was evaluated. Generally, all the bimetals reductants tested revealed to increase the reactivity of the degradation, in which palladium and nickel were the additional metals more reactive. Ethene and ethane were the major products of TCE degradation. It is supported the simultaneous hydrogenolysis and β-elimination reaction hypothesis, however, the first step of TCE degradation by Au/Fe undergoes preferably by β-elimination, while by unamended iron, Pt/Fe and Co/Fe goes preferably by hydrogenolysis. No apparent elucidation was obtained to explain the high reactivity on bimetals systems; Degradação do TCE e cis-DCE por ferro de valência zero e redutores bimetálicos à base de ferro Resumo: Etilenos clorados são os poluentes mais frequentemente detetados na água subterrânea. Vários estudos têm mostrado que redutores bimetálicos à base de ferro são um bom método para a degradação dos etilenos clorados. Porém, muitas questões fundamentais acerca da química deste fenómeno permanecem elusivas. Neste estudo foi avaliada a cinética e a análise isotópica de compostos específicos para a degradação do TCE e cis-DCE por ferro e redutores bimetálicos à base de ferro. Genericamente, os redutores bimetálicos mostraram aumentar a reatividade da degradação, sendo paládio e níquel os metais adicionais mais reativos. Os produtos principais da degradação do TCE foram eteno e etano. É apoiada a hipótese da simultaneidade de hidrogenólise e β-eliminação, porém, o primeiro passo da degradação do TCE por Au/Fe é realizada preferencialmente por β-eliminação, enquanto por ferro, Pt/Fe e Co/Fe é realizada preferencialmente por hidrogenólise. Não houve uma elucidação aparente para explicar a reatividade nos sistemas bimetálicos

Hydraulic and Electrokinetic Delivery of Remediants for In-situ Remediation

Nano-scale zero valent iron (nZVI) has shown promising mobility and in-situ reactivity with chlorinated volatile organic compounds when injected into saturated porous media. The current study evaluated nZVI mobility and subsequent reactivity with in-situ contaminants in a variably saturated porous media. The nZVI particles, synthesized onsite at subzero temperatures, demonstrated complete trichloroethene (TCE) degradation within the target area. Furthermore, a three dimensional finite difference model (CompSim) was utilized to investigate nZVI mobility in variably saturated zones. Model predicted well head data were in very good agreement with field observations. Simulation results showed that the injected slurry migrated radially outward from the injection well and that nZVI travel distance increases were not proportional to the increase in injected nZVI volume. This study suggested that the numerical simulator can be a practical tool for optimal design of nZVI field applications. The second study aimed at alleviating back diffusion from low permeability porous media observed at numerous field studies. Experiments were conducted in a two-dimensional sandbox with alternate vertical layers of coarse sand and silt flooded with TCE at aqueous solubility. Electrokinetics (EK) was used to enhance permanganate delivery through the silt layers. The suite of experiments demonstrated that EK was able to drive more permanganate at a faster rate throughout the silt layers in comparison to no-EK experiments. The combined EK and permanganate application resulted in 4.4 orders of magnitude reduction in TCE concentrations compared to a 3.5 orders of magnitude reduction without EK application. This experiment demonstrated that EK coupled with permanganate application can be used to remediate low permeability strata. The third study investigated a novel approach of EK assisted persulfate delivery followed by electrical resistance heating (ERH) for persulfate activation for low permeability soil remediation. The study showed that EK delivered persulfate throughout the silt. The application of ERH was successfully able to activate the persulfate within the porous matrix leading to complete in-situ tetrachlorothene (PCE) degradation. To the authors’ knowledge, this study was the first to combine EK and ERH for persulfate delivery and activation for low permeability soil remediation

Evaluating the Effectiveness of Nanotechnology in Environmental Remediation of a Highly Metal-Contaminated Area—Minas Gerais, Brazil.

A column experiment at a laboratory level was carried out to assess the effect of the application of nanotechnology in the decontamination of soils and alluvial deposits with high levels of poten-tially toxic elements (PTEs). A suspension of zero-valent iron nanoparticles (nZVI) was injected at three different concentrations in selected samples (two sediments, one soil). For most of the el-ements, the retention by nZVI was proportional to the concentration of the suspension and the trend was similar. Metals were immobilized by adsorption on the surface layer of the nanoparti-cles and/or by complexation, co-precipitation, and chemical reduction. By day 60 following injec-tion, the nZVI lost reactivity and the retained species were desorbed and back into the soluble phase. The definition of spatial patterns for PTEs’ distribution allowed for the construction of contamination risk maps using a geostatistical simulation approach. The analysis obtained from the extractable contents of five target elements (Zn, Cu, Cd, Pb, As) was cross-checked with the estimated map network to assess their retention efficiency. Data from the analysis of these ele-ments, in the extractable phase and in the porewater of the sediments/soils, indicate the nZVI injection as a suitable technique for reducing the risk level of PTEs in contaminated Fe-rich tropical environments

Evaluating the Effectiveness of Nanotechnology in Environmental Remediation of a Highly Metal-Contaminated Area—Minas Gerais, Brazil

A column experiment at a laboratory level was carried out to assess the effect of the application of nanotechnology in the decontamination of soils and alluvial deposits with high levels of potentially toxic elements (PTEs). A suspension of zero-valent iron nanoparticles (nZVI) was injected at three different concentrations in selected samples (two sediments, one soil). For most of the elements, the retention by nZVI was proportional to the concentration of the suspension and the trend was similar. Metals were immobilized by adsorption on the surface layer of the nanoparticles and/or by complexation, co-precipitation, and chemical reduction. By day 60 following injection, the nZVI lost reactivity and the retained species were desorbed and back into the soluble phase. The definition of spatial patterns for PTEs’ distribution allowed for the construction of contamination risk maps using a geostatistical simulation approach. The analysis obtained from the extractable contents of five target elements (Zn, Cu, Cd, Pb, As) was cross-checked with the estimated map network to assess their retention efficiency. Data from the analysis of these elements, in the extractable phase and in the porewater of the sediments/soils, indicate the nZVI injection as a suitable technique for reducing the risk level of PTEs in contaminated Fe-rich tropical environments.info:eu-repo/semantics/publishedVersio

BIMETALLIC NANOPARTICLES INTEGRATED MEMBRANES FOR GROUNDWATER REMEDIATION: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS

The detoxification of chlorinated organics from groundwater, such as trichloroethylene (TCE), tetrachloroethylene (PCE), polychlorinated biphenyl (PCB) and carbon tetrachloride (CTC), is a challenging area. Reductive dechlorination has been investigated using iron and iron-based nanoparticles, such as bare Fe, sulfidized Fe (S-Fe) and palladized Fe (Pd-Fe). However, issues including particle agglomeration, difficulties in recycling and particle leaching have been reported to hinder the application and wide usage of these techniques. The integration of nanoparticles and membranes can address these issues because of the large surface area, stability, and the potential for versatile functionalities. In this study, commercial polyvinylidene difluoride (PVDF) microfiltration membranes were functionalized with poly (acrylic acid) (PAA) or poly (methacrylic acid) (PMAA). The functionalization allows the in-situ generation of iron-based nanoparticles through ion-exchange and reduction processes. These membranes were then tested for the removal of chlorinated organics from synthetic and site groundwater. Both the PAA and PMAA functionalization showed a responsive behavior in water flux through membranes. The deprotonation of carboxyl groups (-COOH → -COO-) makes PAA or PMAA become hydrophilic when pH \u3e pKa. Membrane permeability was decreased by 5-30 folds when pH increases from 2.3 to 10.5. PAA and PMAA are anionic polymers in the water at neutral and basic pH, which can capture metal cations for the in-situ synthesis of metallic nanoparticles through a reduction reaction. Uniform Pd-Fe particles with a size of 17.1 ± 4.9 nm were quantified throughout the pores of membranes using a developed focused ion beam cross-sectioning method. The reactive particles incorporated membranes presented over 96% degradation of 3,3\u27,4,4\u27,5-pentachlorobiphenyl (PCB-126) in less than 15 s residence time in passing through the membrane domains. Roles of Pd fractions, particle compositions and water parameters (pH and temperature) in degradation were evaluated using 2-chlorobiphenyl (PCB-1) as a model compound. The H2 evolution (Fe corrosion in water) was quantified with various Pd coverages on the Fe surface. H2 can be activated by catalytic Pd for the hydrodechlorination reaction. However, insufficient H2 production was observed under the higher Pd coverage (\u3e10.4%, corresponding to 5.5 wt%), resulting in the hindrance of dechlorination. Pd fractions from 0.5 wt% to 5.5 wt% (1.0% to 10.4% Pd coverage) yielded higher dechlorination performance. In addition, Pd-Fe bimetallic nanoparticles showed an18-fold mass normalized reaction rate (kmass) than that of isolated Pd and Fe nanoparticles. The investigation of nanoparticles’ intrinsic properties and PCB degradation guided the application of the Pd-Fe nanoparticles incorporated membranes in the treatment of contaminated groundwater. Cooperating with Arcadis Us Inc. (a global environmental consulting firm), the contaminant groundwater was obtained from a hazardous waste site in Louisville, KY. In a single pass of Pd-Fe-PMAA-PVDF membranes (0.5 wt% Pd), chlorinated organics in groundwater sample, such as TCE (177 ppb) and CTC(35 ppb), were degraded to 16 and 0.3 ppb, respectively, at 2.2 seconds of residence time. The surface area normalized reaction rate (ksa) in the treatment of the groundwater followed the order of CTC (0.101 Lm-2min-1)\u3e TCE (0.034 Lm-2min-1)\u3e PCE (0.017 Lm-2min-1)\u3e chloroform (0.002 Lm-2min-1). A long-term study showed less than 5% CTC and 20% PCE remained in a continuous flow through the membranes within the first 5 h (equivalent of 42 L/m2 treatment of water). A significant decrease in degradation performance was found after 36 h continuous flow (equivalent of 299 L/m2 treatment of water), which the reactivity of incorporated nanoparticles was recovered through regeneration using NaBH4. As expected, the on-site technology evaluation also showed effective remediation of the groundwater samples at the similar residence time of the degradation tests in the lab: less than 0.1% CTC, 12% TCE and 18% TCE remained at a residence time of 2.4 seconds. Successful regeneration and reuse of the reactive membranes were also achieved on-site. Analysis of typical samples was also validated by an environmental testing lab (Eurofins TestAmerica, Inc). The on-site remediation evaluation and the studies of regeneration/reuse enhance the optimization of the reactive membrane systems for the potential to scale up. Alternatives of Pd-Fe were studied in the solution phase to understand the fundamentals. S-Fe were prepared, after the synthesis of precursor Fe0 nanoparticles (spherical, ~35 nm radius), for the long-term study of CTC. Pd-Fe (0.3 mol% Pd) increased the degradation rate by 20-fold (ksa = 0.580 Lm-2min-1) compared to that of Fe while S-Fe presented a greater lifetime (deactivated after 17 days of aging). During the aging process, Fe core was converted to FeOOH and Fe3O4/γ-Fe2O3 which deactivated the particles. The restoration of Fe0 was achieved using NaBH4 (400 mol%), which regenerated Fe and Pd-Fe nanoparticles. Even though the Fe core was also restored for S-Fe, the formed FeSx layers (FeS, FeS2) disappeared. The results suggest that S-Fe extends the longevity of Fe, but the loss of FeSx makes S-Fe eventually perform like Fe in terms of CTC degradation

Guar gum solutions for improved delivery of iron particles in porous media (Part 2): Iron transport tests and modeling in radial geometry

In the present work column transport tests were performed in order to study the mobility of guar-gum suspensions of microscale zero-valent iron particles (MZVI) in porous media. The results were analyzed with the purpose of implementing a radial model for the design of full scale interventions. The transport tests were performed using several concentrations of shear thinning guar gum solutions as stabilizer (1.5, 3 and 4 g/l) and applying different flow rates (Darcy velocity in the range 1 · 10− 4 to 2 · 10− 3 m/s), representative of different distances from the injection point in the radial domain. Empirical relationships, expressing the dependence of the deposition and release parameters on the flow velocity, were derived by inverse fitting of the column transport tests using a modified version of E-MNM1D (Tosco and Sethi, 2010) and the user interface MNMs (www.polito.it/groundwater/software). They were used to develop a comprehensive transport model of MZVI suspensions in radial coordinates, called E-MNM1R, which takes into account the non Newtonian (shear thinning) rheological properties of the dispersant fluid and the porous medium clogging associated with filtration and sedimentation in the porous medium of both MZVI and guar gum residual undissolved particles. The radial model was run in forward mode to simulate the injection of MZVI dispersed in guar gum in conditions similar to those applied in the column transport tests. In a second stage, we demonstrated how the model can be used as a valid tool for the design and the optimization of a full scale intervention. The simulation results indicated that several concurrent aspects are to be taken into account for the design of a successful delivery of MZVI/guar gum slurries via permeation injection, and a compromise is necessary between maximizing the radius of influence of the injection and minimizing the injection pressure, to guarantee a sufficiently homogeneous distribution of the particles around the injection point and to prevent preferential flow paths