1,720,985 research outputs found
Guar gum improves the stability and the mobility of iron microparticles for groundwater remediation
No full textContaminated sites managements represents in Europe one of the most serious issues. Recent data of the European Environmental Agency (EEA) shows how soil contamination due to industry, garbage warehousing, mining and hydrocarbons tanks leakage represents one of the most important threats to the environment [1]. The large volume of waste and the intense use of chemicals during past decades have resulted in numerous contaminated sites across Europe. Contaminated sites could pose significant environmental hazards for terrestrial and aquatic ecosystems as they are important sources of pollution which may result in eco toxicological effects [2]. Emissions of hazardous substances from local sources could deteriorate soil and groundwater quality. Soil contamination is mainly located close to waste land-fills, industrial/commercial activities diffusing heavy metals, oil industry, military camps, and nuclear power plants. The objective of relevant EU policies is to achieve a quality of the environment applying successful technologies. To this purpose, in the last decade EU have been financed numbers of international, multi-partner EU projects; among them, the large scale research project AQUAREHAB (FP7 ENV 2008.3.1.1.1.) , coordinated by VITO (Belgium) and involving 19 partners, started in May 2009 and lasted 56 months, until 2013. It aimed at developing innovative rehabilitation technologies for soils, groundwater and surface waters contaminated by a wide range of priority contaminants (nitrates, pesticides, chlorinated compounds, aromatic compound, mixed pollutions, ecc.). These technologies have been developed within 5 operative work packages (WP1-5) and the guidelines and approaches developed have been extrapolated and applied, in WP8, to real polluted sites. The work herein presented is included in the context of WP5 and WP8 of the AQUAREHAB EU project, in which the group of Groundwater Engineering of the Polytechnic University of Turin is involved; its goal is to develop and apply at the real scale an effective and costeffective in-situ rehabilitation technology based on the injection of micro-sized (100 nm-100 µm) zerovalent iron (MZVI) particles directly into a contaminated aquifer in order to create a reactive zone which is able to treat both the plumeand the source of contamination. Injectable MZVI particles are selected because they can overcome the major hindering factors of the widely accepted ZVI based permeable reactive barriers (PRB) (impossibility to treat the source of contamination and considerable excavation costs), due their high reactivity against a wide range of contaminants thanks to their high specific surface area and to lower costs, longer lifetime and easier handling in respect with nano-sized ZVI (NZVI) particles. Nevertheless MZVI particles disperse in water are prone to gravitational instability and, as a consequence, the resulting mobility is limited [3, 4]. To solve this problem, the use of a stabilizing agent able to modify suspending fluid properties is required. In the recent year the use of biopolymer demonstrated to be successful [5, 6] although a full comprehension of interaction mechanisms with the porous media and a complete system characterization is still missing. In this work, in order to meet AQUAREHAB project requirements and to overcome technology limitations, the use of MZVI suspended in a thickening polymer solution of guar gum hydrocolloid is considere
Modeling the injection of Non-Newtonian shear-thinning dispersions of iron particles in porous media
No full textIn the context of groundwater remediation, an increasing interest is related to the use of nanoscale and microscale zero-valent iron particles (NZVI and MZVI, respectively). MZVI and NZVI are not stable when dispersed in water, due to fast aggregation and sedimentation. Consequently, the use of shear thinning solutions of green biopolymers have been recently studied as kinetic stabilizers and viscous carrier fluids for the delivery of MZVI and NZVI. Shear thinning fluids exhibit high viscosity in static conditions, improving the colloidal stability, and lower viscosity at high flow rates enabling the injection at limited pressures. In this work, co-funded by European Union project AQUAREHAB (FP7 - Grant Agreement Nr. 226565), a modeling approach is described to simulate the transport in porous media of nanoscale iron slurries, and implemented in E-MNM1D software (www.polito.it/groundwater/software). Colloid transport mechanisms are controlled by particle-collector and particle-particle interactions, usually modeled using a non equilibrium kinetic model accounting for deposition and release processes. The key aspects included in the E-MNM1D are clogging phenomena (i.e. reduction of porosity and permeability due to particles deposition), and the rheological properties of the carrier fluid (in this project, guar gum solution). The influence of colloid transport on porosity, permeability, and fluid viscosity is explicitly lumped into the model and the shear-thinning nature of the iron slurries is described by a modified Darcy law generalized for non Newtonian fluids. Since during the injection in wells the velocity field is not constant over the distance, E-MNM1D was modified in order to account for variable colloidal transport coefficients on flow rate thus allowing the estimation of the radius of influence during a full scale interventio
Nanoscale and Microscale iron for groundwater remediation: experiments, modelling and perspectives
No full textL'uso di particelle nanometriche (NZVI) e micrometriche (MZVI) per la degradazione di contaminanti organici in sistemi acquiferi è oggetto di un crescente interesse. Il presente lavoro descrive prove di laboratorio riguardanti il trasporto di tali particelle ferrose in mezzi porosi saturi: in particolare sono state condotte prove di iniezione in colonna e studi delle proprietà reologiche di sospensioni colloidali di MZVI e NZVI (alla concentrazione di 20 g/l) stabilizzate mediante l'uso di biopolimeri quali guar gum e xanthan gum. Viene, inoltre, presentato un approccio modellistico per la simulazione dei processi di trasporto di NZVI ed MZVI in mezzi porosi saturi, e valutate e le possibili strategie per l'iniezione di tali materiali in campo, per la realizzazione di interventi di bonifica a scala real
Studio di laboratorio e modellistico del trasporto di nano- e micro- particelle di ferro per la bonifica di falde contaminate
No full textIn campo ambientale le potenzialità offerte dalle nanotecnologie sono molteplici e vanno dalla prevenzione dell'inquinamento, grazie allo sviluppo di tecnologie in grado di ridurre i consumi di energia o di reagenti, all'individuazione di particolari contaminanti mediante lo sviluppo di sensori che sfruttano le straordinarie proprietà dei nanomateriali. Nell'ambito della bonifica di matrici ambientali inquinate, ed in particolare dei sistemi acquiferi, l'utilizzo di ferro zerovalente di dimensione nanometrica si è dimostrata essere una delle tecniche più interessanti e promettenti. Sebbene l'utilizzo di ferro zerovalente millimetrico all'interno di barriere reattive permeabili (permeable reactive barriers - PRBs) sia ormai diventato un metodo consolidato per il trattamento di contaminazioni da composti organici ed inorganici, questa tecnica non risulta essere sempre di facile applicazione. Il ferro nanoscopico (nanoscale zerovalent iron - NZVI), caratterizzato da particelle di diametro estremamente piccolo e compreso tra 1 e 100 nm, elevatissime superfici specifiche e reattività fino a 1000 volte superiori rispetto a quelle del ferro millimetrico (Zhang et al. 1998), può essere iniettato direttamente in falda, sotto forma di dispersioni colloidale, per trattare una gamma ancora più ampia di contaminanti e per consentire il superamento dei limiti geometrici imposti dalla realizzazione di barriere reattive permeabili. Il presente lavoro, condotto nell'ambito del progetto europeo FP7 AQUAREHAB, descrive l'attività di sperimentazione riguardante il trasporto di tali particelle ferrose in mezzi porosi saturi. Le prove sono state condotte in geometria unidimensionale iniettando, in colonne simulanti il sistema acquifero, sospensioni colloidali di ferro micro e nanometrico (alla concentrazione di 20 g/l) stabilizzate mediante l'uso di biopolimeri (quali guar gum e xanthan gum). Il software MNM1D (disponibile liberamente al link: www.polito.it/groundwater) è stato sviluppato appositamente per la simulazione dei processi accoppiati di trasporto, filtrazione delle particelle di ferro, intasamento del mezzo poroso al fine di fornire uno strumento utile al dimensionamento di un intervento di iniezione su scala real
Injection of non-Newtonian dispersions of iron particles in porous media: modeling of clogging processes
No full textIn the context of groundwater remediation, an increasing interest was found towards nanoscale and microscale zero-valent iron particles (NZVI and MZVI, respectively). However, MZVI and NZVI are not stable when dispersed in water, due to fast aggregation and sedimentation. Consequently, the use of shear thinning solutions of green biopolymers have been recently studied as viscous carrier fluids for the delivery of MZVI and NZVI. In this work, co-funded by European Union project AQUAREHAB (FP7 - Grant Agreement Nr. 226565), a modeling approach is described to simulate the transport in porous media of nanoscale iron slurries, implemented in the E-MNM1D software, previously developed by the authors (www.polito.it/groundwater/software). The key aspects included in the E--MNM1D are clogging phenomena (i.e. reduction of porosity and permeability due to particles deposition), and the rheological properties of the carrier fluid (in this project, guar gum solution) for a correct estimate of pressure drops. Colloid transport is modeled with a dual-site (physico-chemical interactions plus straining) advection-dispersion-deposition equation. A general formulation for attachment/detachment dynamics is adopted. The influence of colloid transport on porosity, permeability, and fluid viscosity is explicitly embedded into the model through correlations from the literature, or derived on purpose. The shear-thinning behavior of the iron slurries is described with a modified Darcy law generalized to non Newtonian fluids. ions of MZVI and NZVI -based remediation, for the estimate of the radius of influence of the slurry injectio
Pilot Injection of Microscale Zerovalent Iron for Aquifer Remediation
Get PDFBackground/Objectives. Concentrated suspensions of microscale and nanoscale zerovalent iron particles (MZVI and NZVI) have been studied in recent years for the remediation of contaminated aquifers. In the framework of the research project AQUAREHAB (FP7 - G. A. Nr. 226565), a pilot injection test of guar gum stabilized microsized zerovalent iron has been designed and performed under low pressure in a CAHs contaminated site in Belgium and the resulting radius of influence was determined. Approach/Activities. A shear thinning guar gum solution (2 g/l) was selected as an environmentally friendly stabilizer of the iron particles. The relevant properties of the iron slurry (iron particles size and concentration, polymeric stabilizer type and concentration, slurry viscosity) were designed in the laboratory based on several tests (namely iron reactivity tests towards contaminants, sedimentation tests and rheological measurements). Since the injection regime of iron slurries depends on subsurface geotechnical parameters, aquifer hydraulic conductivity, and fluid properties, a specific injection well and monitoring strategy have been developed in order to achieve high discharge rates and radii of influence, and a more homogeneous distribution of the iron particles through low pressure injection. The injection well has been designed and sealed in order to sustain average to high discharge rates, preventing the daylighting of the product. Moreover the well has been hydraulically tested by means of innovative water and guar gum step rate tests in order to determine the most suitable injection rate for the iron slurry. The injection of 50 kg of microsized iron particles (BASF, Germany), dispersed in 5 m3 of a 2 g/l guar gum suspension, was performed at a discharge rate of 1.5 m3/h. The monitoring of the process has been conducted measuring injection rate and pressure as well as iron concentration by means of a magnetic susceptometer. After the injection, the iron distribution in the subsurface was determined through liners extraction and the iron concentration measured both via non-invasive magnetic susceptibility measurements and chemical analysis. Results/Lessons Learned. Even if the field test was specifically designed to inject in a permeation regime, or on the threshold between permeation and fracturing, the results of monitoring injection pressure and iron distribution proved that particles migration in the porous medium occurred via preferential flow. Nevertheless significant radius of influence was achieved during the pilot tes
Green stabilization of microscale iron particles using guar gum: bulk rheology, sedimentation rate and enzymatic degradation
Get PDFGuar gum can be used to effectively improve stability and mobility of microscale zerovalent iron particles (MZVI) used in groundwater remediation. Guar gum is a food-grade, environment friendly natural polysaccharide, which is often used as thickening agent in a broad range of food, pharmaceutical and industrial applications. Guar gum solutions are non-Newtonian, shear thinning fluids, characterized by high viscosity in static conditions and low viscosity in dynamic conditions. In particular, the high zero shear viscosity guarantees the MZVI dispersion stability, reducing the sedimentation rate of the particles thus enabling its storage and field operations. In this work, a comprehensive rheological characterization of guar gum-based slurries of MZVI particles is provided. First, we derived a model to link the bulk shear viscosity to the concentration of guar gum and then we applied it for the derivation of a modified Stokes law for the prediction of the sedimentation rate of the iron particles. The influence of the preparation procedure (cold or hot dissolution and high shear processing) on the viscosity and on the stability of the suspensions was then assessed. Finally, the dosage and concentration of enzymes - an environment friendly breaker - were studied for enhancing and controlling the degradation kinetics of the suspensions. The derived empirical relationships can be used for the implementation of an iron slurry flow and transport model and for the design of full scale injection intervention
Shear thinning fluids to optimize the injection of engineered microparticles for groundwater remediation
Get PDFNanoscale and microscale zerovalent iron particles (NZVI and MZVI) are promising materials for the remediation of contaminated aquifers. These particles are dispersed in water-based slurries and injected in the subsoil to generate a reactive zone. However, the successful injection of MZVI and NZVI may be significantly hindered by the reduced colloidal stability, and therefore mobility in the porous medium, due to the fast sedimentation (MZVI) and aggregation (NZVI) of the particles when dispersed in water. To overcome this issue the use of stabilizing agents wax proposed: shear thinning solutions of green biopolymers have been recently studied as kinetic stabilizers and viscous carrier fluids for the delivery of MZVI and NZVI. Shear thinning fluids exhibit high viscosity in static conditions, improving the colloidal stability, and lower viscosity at high flow rates enabling the injection at limited pressures. In this work the use of guar gum is presented. Polymeric solutions (1.5 to 7 g/l) were prepared following different procedures, and their efficacy in stabilizing highly concentrated dispersions of MZVI (20 g/l, average size 1.2 um) was evaluated. Ideally, the optimal guar gum suspension should (i) keep the MZVI suspended for a time sufficient for its injection; (ii) be easily degradable, to avoid possible negative effects on MZVI reactivity; (iii) do not clog the porous medium due to residual undissolved guar gum. With these targets in mind, a detailed rheological characterization of the guar gum, both in the bulk and when injected in a porous medium, was carried out. A modified Cross model, linking guar gum concentration and bulk shear viscosity, was derived based on bulk rheological measurements. Column filtration tests were then performed, and a modified Darcy law was derived to predict pressure gradients arising during guar gum injection. The kinetics of guar gum degradation was studied to investigate the correct enzymes dosage required to achieve a complete breakdown of the suspensions, and a modified Stokes law for the prediction of the sedimentation rate of the MZVI was proposed and validated. All derived empirical relationships (namely, rheological model, modified Stokes law and Darcy law) were finally included in MNMs (www.polito.it/groundwater/software/MNMs.php), a software for particle transport simulation in 1D (column) and radial domain. MNMs can be used as a tool for a preliminary design of the field injection of MZVI/NZVI - guar gum mixtures, providing an estimate of particle transport and pressure build up associated to the injection at the pilot scale. Funded by: EU FP7 Aquarehab Grant Agreement No. 22656
Zerovalent iron micro and nanoparticles for groundwater remediation: from laboratory to field scale
Get PDFThe poster presents an overview of laboratory tests, field applications and modelling approaches for the development of an innovative groundwater remediation technique based on the injection of zerovalent iron micro and nanoparticles dispersed in shear thinning fluid
Guar gum solutions for improved delivery of iron particles in porous media (Part 2): Iron transport tests and modeling in radial geometry
Get PDFIn 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 path
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