politecnico di torino technion institute of technology fileavailable tools for water resources...

Politecnico di TorinoTechnion Institute of Technology

University of Torino 2015

Managing Water Quality for Public Health

October 14th 2015

In cooperation with:

Under the patronage of:

With the support of:

Associazione Italianadegli Incubatori Universitari

e delle Business Plan Competition

• Promoting interactions between water companies and research institutes to set up reference laboratories on EDs in Italy• Developing and validating analytical methods for the determination of EDs in water, in the framework of D. Lgs. 31/2001 (Italian transposition of Drinking Water Directive 98/83/EC)• Evaluating bioassay tests and comparing them with chemical methods• Analyzing case studies representing different actual situations (especially surface waters with different impacts) to help water companies verify the effectiveness of their treatment plants and evaluate possible weak points• Creating a network of laboratories, with the aim of increasing classes and number of the investigated compounds for the benefit of water companies and other subjects concerned by the same issue.

Lately a collaborative research study on the subject of ECs has been started by a pool of Italian water companies, namely Hera (Bologna), SMAT (Turin) and Iren (Genoa).

Avi OstfeldFaculty of Civil and Environmental Engineering, Technion - Israel Institute of Technology

“Water resources system analysis: tools and challenges”

Water resources system analysis is the science of developing and applying mathematical operations research methodologies to water resources systems problems. The scientific and practical challenge in dealing quantitively with water resources management problems is in taking into consideration from a systems perespective, social, economic, environmental, and technical dimensions, and integrating them into a single framework for trading-off in time and in space competitive objectives. Inherently, such problems involve modeling of water quantity and quality for surface water, groundwater, water distribution systems, reservoirs, rivers, lakes, and other systems as stand alone or integrated components.

This talk will have three parts: (1) a description of conceptual issues which should be overcomed when constructing an integrated water resources management framework, (2) examples of available tools for water resources systems analysis: simulation programs (e.g. WMS, GMS, SWAT, AVGWLF, EPANET), and optimization methodologies (e.g. simulated annealing, genetic algorithms, ant colony, cross entropy, non-linear programming), and (3) a case study for demonstrating an integrated water resources management application.



A. Ferrero et. alDepartment of Agriculture, Forest and Food Sciences, University of Torino

“Best management practices for efficient use of water and for preventing contamination from plant nutrients and pesticides”

Agriculture is the major consumer of freshwater resources, as it uses about 70 % of the water taken from rivers and groundwater. About half of this amount returns back, feeding groundwater and rivers. In this context it is necessary to plan and develop new approaches to optimize the use and ensure the quality of water resources.

The application of drip irrigation systems, for instance, allows to greatly reduce the volume of water as compared with any other system, but above all with surface irrigation.. Best management practices need also to be adopted in order to prevent the risk of contamination of surface and deep water bodies as a result of runoff and infiltration into the ground (due to excess water) of pesticides and nutrients applied for the protection and nutrition of the crops.

In the agricultural settings an important challenge is also that of the appropriate management of livestock wastes to prevent the risk of eutrophication of surface and groundwater, and microbial contamination of agriculture fresh products.



A. Vezio PuggioniAgromarketing Netafim Italy

“Growing rice with less water and arsenic for global food security”

La soluzione irrigua a goccia permette oggi di irrigare e gestire le esigenze irrigue di tutte le colture. Anche l’ultimo baluardo costituito dal riso, fino ad oggi gestito prevalentemente per sommersione, è caduto. Dopo dieci anni di prove di campo condotte da Netafim nei paesi leader mondiali nella produzione di riso e in Italia, la tecnica è solida e i vantaggi numerosi e con forti e virtuose implicazioni. Infatti ha importanti e positive prerogative di rispetto ambientale dato che le emissioni di gas serra, che la risaia condotta in sommersione emette, sono drasticamente ridotte nella conduzione a goccia. Il risparmio idrico è enorme, rende disponibile acqua per la conduzione irrigua di molte altre aree. I vantaggi sulle produzioni sono importanti e riguardano sia la quantità che la qualità del riso prodotto.

Recenti studi indicano, inoltre, la conduzione tradizionale in sommersione come possibile responsabile dell’accumulo di elementi nocivi, quali l’arsenico, nel chicco di riso. I dati sperimentali ci dicono che, irrigando a goccia, la presenza di tali elementi nel chicco di riso è al di sotto del valore minimo misurabile. La fertirrigazione consente la modulazione dei fertilizzanti distribuiti gradualmente con coltura in atto e senza sprechi o dilavamenti e in sintonia con le esigenze variabili della coltura nelle diverse fasi fenologiche. La tecnica a goccia svincola inoltre l’azienda agricola dalla laboriosa e onerosa preparazione della risaia in sommersione permettendo di produrre riso in suoli marginali o non preparati per la sommersione, perfino in pendenza. Il riso a goccia è realtà e rientra nel progetto Demo Field all’interno delle attività di campo legate ad Expo Milano 2015.

Claudia Lasagna*, Franca Palumbo**, Enrico Raffo*** Iren Acqua Gas S.p.A., ** Laboratori Iren Acqua Gas S.p.A.

“Emerging Compounds in water intended for human consumption: experiences and evolution”

Access to drinking water is important for human health, for the purposes of nutrition, personal hygiene and cleanliness, and is a social and political right required for development opportunities.

Among the various compounds of anthropogenic origin that are found in raw water for human consumption, the scientific community has identified a new class of pollutants, namely Emerging Compounds (ECs).

The US EPA defines “Emerging pollutants” as new chemicals without regulatory status and whose impact on environment and human health are understood.

This group includes products used in large quantity in everyday life, such as human and veterinary pharmaceuticals, surfactants and their residues, personal care products, plasticizers and many different industrial additives.

There are no regulations currently restricting ECs, but with the recent media attention and increasing public awareness of the issue, as well as improving technology to detect these substances, regulations may be on the horizon. The future regulatory scenarios to address these ECs will be of most interest to utility managers.

The identification of these compounds requires the use of advanced scientific instrumentation and a support by specialized structures.

This class of compounds also includes substances called Endocrine Disruptors (EDs) that are environmental pollutants that interfere with the normal function of the endocrine system of living organisms. In recent years several EDs of both natural and synthetic origin have been detected in surface water in various EU and non EU countries. Synthetic EDs in the aquatic environment can be generated during either their production, their use, or the disposal of materials that contain them. Natural EDs (mainly hormones) are present due to their excretion by living organisms (humans and animals) in the urine, and the subsequent passage in the wastewater.

Fondazione AMGA in collaboration with the National Institute of Health in Italy has promoted and financially supported a research project directly involving some Italian Water Companies and research institutes. The aim of the project was:

• Studying the impact of EDs on water used for production and distribution of drinking water in Italy (Alkylphenol,17 α-ethinylestradiol, 17 β-estradiol, Estrone,….)

Access to drinking water is important for human health, for the purposes of nutrition, personal hygiene and cleanliness, and is a social and political right required for development opportunities.

Among the various compounds of anthropogenic origin that are found in raw water for human consumption, the scientific community has identified a new class of pollutants, namely Emerging Compounds (ECs).

The US EPA defines “Emerging pollutants” as new chemicals without regulatory status and whose impact on environment and human health are understood.

This group includes products used in large quantity in everyday life, such as human and veterinary pharmaceuticals, surfactants and their residues, personal care products, plasticizers and many different industrial additives.

There are no regulations currently restricting ECs, but with the recent media attention and increasing public awareness of the issue, as well as improving technology to detect these substances, regulations may be on the horizon. The future regulatory scenarios to address these ECs will be of most interest to utility managers.

The identification of these compounds requires the use of advanced scientific instrumentation and a support by specialized structures.

This class of compounds also includes substances called Endocrine Disruptors (EDs) that are environmental pollutants that interfere with the normal function of the endocrine system of living organisms. In recent years several EDs of both natural and synthetic origin have been detected in surface water in various EU and non EU countries. Synthetic EDs in the aquatic environment can be generated during either their production, their use, or the disposal of materials that contain them. Natural EDs (mainly hormones) are present due to their excretion by living organisms (humans and animals) in the urine, and the subsequent passage in the wastewater.

Fondazione AMGA in collaboration with the National Institute of Health in Italy has promoted and financially supported a research project directly involving some Italian Water Companies and research institutes. The aim of the project was:

• Studying the impact of EDs on water used for production and distribution of drinking water in Italy (Alkylphenol,17 α-ethinylestradiol, 17 β-estradiol, Estrone,….)



differentiated into three types of monitoring activities that distinguish between long-term, short-term and continuous monitoring programs as follows:

• Monitoring is the long-term, standardized measurement and observation of the aquatic environment in order to define status and trends.• Surveys are finite duration, intensive programs to measure and observe the quality of the aquatic environment for a specific purpose.• Surveillance is continuous, specific measurement and observation for the purpose of water quality management and operational activities.

The design and implementation of an autonomous system, for monitoring of metals in water, herein will be shown and some preliminary results coming from different test on field will be presented and discussed.

L. Scaltrito, et al.Department of Applied Science and Technology, Politecnico di Torino

“Autonomous system Design for continuous Monitoring of Metals in Water”

Increasing industrialization and the growth of large urban centers have been accompanied by increases in the pollution stress on the aquatic environment. Since ancient times, water in rivers, lakes and oceans has also been considered as a convenient receiver of wastes. This use (or abuse) conflicts with almost all other uses of water and most seriously with the use of freshwater for drinking, personal hygiene and food processing.

All water uses have impacts on the quality of the aquatic environment, including hydrological changes such as storing water in reservoirs or transferring water from one drainage area to another. Human use of water for almost all purposes results in the deterioration of water quality and generally limits the further potential use of the water. As highlighted in several guidelines edited by the World Health Organization, three-point strategy can be developed to resolve the conflicts between quality deterioration and water use as follows:

• The quality of water and of the aquatic environment is determined and water-use procedures that prevent deterioration are adopted. • Wastes are treated before discharge to a water body in order to control pollution. • Unsatisfactory water is treated before use in order to meet specific water quality requirements.

Direct contamination of surface waters with metals in discharges from mining, smelting and industrial manufacturing is a long-standing phenomenon. However, the emission of airborne metallic pollutants has now reached such proportions that long-range atmospheric transport causes contamination, not only in the vicinity of industrialized regions, but also in more remote areas. The extent of the human activities that influence the environment has increased dramatically during the past few decades; terrestrial ecosystems, freshwater and marine environments and the atmosphere are all affected. The scale of socio-economic activities, urbanization, industrial operations and agricultural production, has reached the point where, in addition to interfering with natural processes within the same watershed, they also have a world-wide impact on water resources.

A pressing need has emerged for comprehensive and accurate assessments of trends in water quality, in order to raise awareness of the urgent need to address the consequences of present and future threats of contamination and to provide a basis for action at all levels. Reliable monitoring data are the indispensable basis for such assessments. Monitoring is defined by the International Organization for Standardization (ISO) as: “the programmed process of sampling, measurement and subsequent recording or signaling, or both, of various water characteristics, often with the aim of assessing conformity to specified objectives”. This general definition can be






Increasing industrialization and the growth of large urban centers have been accompanied by increases in the pollution stress on the aquatic environment. Since ancient times, water in rivers, lakes and oceans has also been considered as a convenient receiver of wastes. This use (or abuse) conflicts with almost all other uses of water and most seriously with the use of freshwater for drinking, personal hygiene and food processing.

All water uses have impacts on the quality of the aquatic environment, including hydrological changes such as storing water in reservoirs or transferring water from one drainage area to another. Human use of water for almost all purposes results in the deterioration of water quality and generally limits the further potential use of the water. As highlighted in several guidelines edited by the World Health Organization, three-point strategy can be developed to resolve the conflicts between quality deterioration and water use as follows:

• The quality of water and of the aquatic environment is determined and water-use procedures that prevent deterioration are adopted. • Wastes are treated before discharge to a water body in order to control pollution. • Unsatisfactory water is treated before use in order to meet specific water quality requirements.

Direct contamination of surface waters with metals in discharges from mining, smelting and industrial manufacturing is a long-standing phenomenon. However, the emission of airborne metallic pollutants has now reached such proportions that long-range atmospheric transport causes contamination, not only in the vicinity of industrialized regions, but also in more remote areas. The extent of the human activities that influence the environment has increased dramatically during the past few decades; terrestrial ecosystems, freshwater and marine environments and the atmosphere are all affected. The scale of socio-economic activities, urbanization, industrial operations and agricultural production, has reached the point where, in addition to interfering with natural processes within the same watershed, they also have a world-wide impact on water resources.

A pressing need has emerged for comprehensive and accurate assessments of trends in water quality, in order to raise awareness of the urgent need to address the consequences of present and future threats of contamination and to provide a basis for action at all levels. Reliable monitoring data are the indispensable basis for such assessments. Monitoring is defined by the International Organization for Standardization (ISO) as: “the programmed process of sampling, measurement and subsequent recording or signaling, or both, of various water characteristics, often with the aim of assessing conformity to specified objectives”. This general definition can be






T. Schilirò et al.Department of Public Health and Pediatrics, University of Torino

“Aquatic effect-based monitoring tools”

The monitoring and the assessment of water quality require an integrated approach. Chemical analysis generally requires a priori knowledge about the type of substances to be monitored as, for technical and economic reasons, it is not possible to analyse, detect and quantify all substances that are present in the aquatic environment. Furthermore, to estimate the risk of effects related to the large number of substances that are present and detected in the environment (including pollutants of emerging concern, metabolites and transformation products), it would be necessary to develop a very large number of assessment criteria.

Considering these points, the most appropriate way of detecting and studying the effects of contaminants and their mixtures may be through the use of effect-based tools (e.g. bioassays, biomarkers and ecological indicators) that could be used in the context of the different monitoring programmes (surveillance, operational and investigative). This can be achieved through, preferably, in vitro bioassays, which, although they cannot assess behavioral effects, have the benefit of closely related natural systems without the use of animal testing. Such bioassays can detect compounds based on their effects, enable the detection of the effects caused by currently unidentified compounds, and integrate the effect of complex chemical mixtures.

The in vitro bioassays measure effects at the subcellular level, such as receptor activation and DNA damage, rather than investigate cells or tissues of organisms exposed in the field (as it is the case with biomarkers), the effects are studied in cells after exposure to environmental samples. An advantage of this approach is that in vitro bioassays can often be performed on many different matrixes (such as concentrated extracts of surface water, sediment or pore water samples, biological tissues, passive samplers and effluents).

robots.

Membrane technology has been extensively applied for clean water production since several decades ago. It has been recently predicted by means of molecular dynamics simulations that nanoporous graphene could separate ions from water based on size exclusion and act as a highly effective reverse osmosis (RO) membrane. This nanoporous graphene provides a robust base material that allows for exceptionally high permeability – more than two orders of magnitude larger than current RO membranes. The researchers of the group “Materials and Processes for Micro and Nanotechnologies” at PoliTO, are exploring a highly manufacturable form of ultra-thin nanoporous membranes for desalination. In particular, with a combined computational and experimental investigation, they propose reduced graphene oxide (rGO) membranes for water filtration technologies as a potential low-cost alternative to nanoporous graphene. The first obtained results concern the formation of nanopores (i.e., defects) in rGO and in graphene films under different processing conditions, and the possibility of obtaining a controllable pore size distribution.

pore-water ionic strength. These parameters can substantially vary according to the field of application and the involved subsurface formations (e.g. nZVI injected in contaminated aquifers, nanoparticles released leachate from a landfill, nanoparticles injected in a reservoir for enhanced oil recovery, etc.). Therefore, it is essential that mathematical models take into account the effects of ionic strength and pore water velocity transient conditions on particles mobility.

A modelling approach was developed at Politecnico di Torino by the Groundwater Engineering Group (DIATI) to simulate the transport in porous media of nZVI and mZVI slurries, and implemented in MNMs (www.polito.it/groundwater/software). The key aspects included in MNMs are the influence of salt concentration on attachment and detachment kinetics (both under constant and transients in I.S), clogging phenomena (i.e. reduction of porosity and permeability due to particles deposition), and the rheological properties of the carrier fluid. 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, the model was then extended to a radial geometry, simulating theinjection of the particle slurries through a screened well at the field scale. The transport equations were modified in order to account for variable colloidal transport coefficients on flow. The governing equations and model implementation are presented and discussed, along with examples of injection simulations.

References

Tiraferri A.; Chen K.L; Sethi R; Elimelech M, 2008. Reduced aggregation and sedimentation of zero-valent iron nanoparticles in the presence of guar gum. In: J Colloid Interf Sci, vol. 324, pp. 71-79. - ISSN 0021-9797Gastone, F., Tosco, T., Sethi, R., 2014. Green stabilization of microscale iron particles using guar gum: bulk rheology, sedimentation rate and enzymatic degradation. J Colloid Interf Sci 421, 33-43, DOI:http://dx.doi.org/10.1016/j.jcis.2014.01.021.Tosco, T., Gastone, F., Sethi, R., 2014a. Guar gum solutions for improved delivery of iron particles in porous media (Part 2): Iron transport tests and modeling in radial geometry. Journal of Contaminant Hydrology166(0), 34-51, DOI: http://dx.doi.org/10.1016/j.jconhyd.2014.06.014.Tosco, T., Petrangeli Papini, M., Cruz Viggi, C., Sethi, R., 2014b. Nanoscale iron particles for groundwater remediation: a review. Journal of Cleaner Production 77, 10-21, DOI: 10.1016/j.jclepro.2013.12.026.Tosco, T., Sethi, R., 2010. Transport of non-newtonian suspensions of highly concentrated micro- andnanoscale iron particles in porous media: A modeling approach. Environmental Science and Technology44(23), 9062-9068, DOI: 10.1021/es100868n.Xue, D., Sethi, R., 2012. Viscoelastic gels of guar and xanthan gum mixtures provide long-term stabilization of iron micro- and nanoparticles. J Nanopart Res 14(11), Art. No.: 1239.

D. Vione et al.Department of Analytical Chemistry, University of Torino

“Photochemical self-depuration processes in surface waters”

Sunlight-induced reactions play an important role in the attenuation of biorefractory pollutants (including many emerging contaminants) in surface water bodies. Without these processes, the current problems of water pollution would be much more serious. The ability of surface waters to photochemically get rid of contaminants depends on several parameters including water chemistry and depth. These parameters may undergo important variations due to climate change and human disturbance, with unavoidable consequences on the self-depuration capacity of sunlit surface waters. In particular, a good environmental management (or, on the contrary, the lack of management) has key effects on the ability of sunlit waters to induce the degradation of pollutants.

Marzia QuaglioCenter for Space Human Robotics IIT@PoliTo

“How nanotechnologies can contribute to water treatments? From nanostructured electrodes for water splitting to bio-inspired microbial electrochemical cells and graphene-based desalination membranes”

The photo-electrochemical splitting of water is a promising route for clean, low-cost, environmentally friendly and virtually inexhaustible fuel production from solar energy. The intriguing idea is to use light from the sun, in presence of well-designed semiconducting and catalytic materials, to obtain water dissociation into hydrogen and oxygen, and eventually the production of fuels if the generated hydrogen is employed to reduce CO2. Since the development of this concept using a TiO2 photoelectrode by Fujishima and Honda, research is focused on materials and devices able to grant the stability, cost and efficiency required to foresee large-scale applications. On one hand efforts are needed to improve photocatalysts, especially investigating nanostructured materials, that must be easy to prepare, and highly stable in water based solutions and oxygen evolving conditions. On the other hand, low-cost integrated devices are required, especially designing photo-electrochemical cells with high solar power to fuel conversion efficiencies. IIT@PoliTO and the Department of Applied Science and Technology of the Politecnico di Torino recently proposed a new design of transparent, conductive and porous electrodes to be employed as support for photo-active materials. These new electrodes offer all the advantages of the TCO/glass substrates in term of high transparency, low electric resistance and easy adhesion of photocatalysts, moreover permitting the passage of water and gases and being possible to use them in a MEA assembly for PEM photo-electrolyzers.

Another fascinating and promising technology for water treatment and management is represented by Bio-Electrochemical Systems (BES). BES are devices in which microbial electrosynthetic processes can be driven. The involvement of biological catalysis in BES differentiates them from electrochemical cells. BESs can be operated as Microbial Fuel Cells (MFC) with the aim of producing power, or as Microbial Electrolysis Cell (MEC), using energy to increase the kinetics of reactions and/or to drive thermodynamically unfavorable reactions. Optimization of Bio-Electrochemical Systems can be pursued only performing a joint research on materials, device architectures and biofilm activity. New, high surface area nanostructured materials must be designed, in order to boost inorganic catalysis and favor exoelectrogenic biofilm growth on the electrodes. The “Bio-Inspired Energy” team of IIT@PoliTO is working on the optimization of microbial electrochemical fuel cells able to directly and efficiently harvest chemical energy of organic substrates (fuels) from environmental and waste waters, coupling this energy production with water treatment. The long term vision is to obtain a new class of energy devices sensitive to the operative environment, and able to contribute to the design of energetically self-sustainable

robots.




References


The photo-electrochemical splitting of water is a promising route for clean, low-cost, environmentally friendly and virtually inexhaustible fuel production from solar energy. The intriguing idea is to use light from the sun, in presence of well-designed semiconducting and catalytic materials, to obtain water dissociation into hydrogen and oxygen, and eventually the production of fuels if the generated hydrogen is employed to reduce CO2. Since the development of this concept using a TiO2 photoelectrode by Fujishima and Honda, research is focused on materials and devices able to grant the stability, cost and efficiency required to foresee large-scale applications. On one hand efforts are needed to improve photocatalysts, especially investigating nanostructured materials, that must be easy to prepare, and highly stable in water based solutions and oxygen evolving conditions. On the other hand, low-cost integrated devices are required, especially designing photo-electrochemical cells with high solar power to fuel conversion efficiencies. IIT@PoliTO and the Department of Applied Science and Technology of the Politecnico di Torino recently proposed a new design of transparent, conductive and porous electrodes to be employed as support for photo-active materials. These new electrodes offer all the advantages of the TCO/glass substrates in term of high transparency, low electric resistance and easy adhesion of photocatalysts, moreover permitting the passage of water and gases and being possible to use them in a MEA assembly for PEM photo-electrolyzers.

Another fascinating and promising technology for water treatment and management is represented by Bio-Electrochemical Systems (BES). BES are devices in which microbial electrosynthetic processes can be driven. The involvement of biological catalysis in BES differentiates them from electrochemical cells. BESs can be operated as Microbial Fuel Cells (MFC) with the aim of producing power, or as Microbial Electrolysis Cell (MEC), using energy to increase the kinetics of reactions and/or to drive thermodynamically unfavorable reactions. Optimization of Bio-Electrochemical Systems can be pursued only performing a joint research on materials, device architectures and biofilm activity. New, high surface area nanostructured materials must be designed, in order to boost inorganic catalysis and favor exoelectrogenic biofilm growth on the electrodes. The “Bio-Inspired Energy” team of IIT@PoliTO is working on the optimization of microbial electrochemical fuel cells able to directly and efficiently harvest chemical energy of organic substrates (fuels) from environmental and waste waters, coupling this energy production with water treatment. The long term vision is to obtain a new class of energy devices sensitive to the operative environment, and able to contribute to the design of energetically self-sustainable

robots.




References


Rajandrea Sethi, Tiziana ToscoDIATI, Department of Environment, Land and Infrastructure Engineering, Politecnico di Torino

“Nanoscale iron particles for groundwater remediation”

Nanoscale zero-valent iron particles (nZVI) have been studied in recent years as a promising technology for the remediation of contaminated aquifers (Tiraferri et al. 2008, Tosco et al., 2014b). NZVI particles, thanks to their reduced size, much smaller than pores of aquifers, can be dispersed in aqueous slurries, and directly injected in the subsoil, thus allowing to directly target the contaminant close to the source of contamination. The reduced size of nZVI results in a very high surface to volume ratio of nZVI particles, with a positive impact on degradation kinetics. More recently, the use of larger particles, micrometric in size (microscale iron particles, mZVI) has also been proposed and investigated. Both mZVI and nZVI were found effective in degrading most of the organic contaminants found in aquifer systems, and in particular chlorinated aliphatic hydrocarbons.The mobility in porous media of nZVI and mZVI, and consequently their successful application for groundwater remediation, is negatively affected by the poor colloidal stability of particles dispersed in water.

To be effective for in situ aquifer remediation, iron particles should remain in suspension for a time sufficient to allow slurry preparation, handling and injection in the subsurface. Also, they should have a sufficient mobility in the subsurface to be transported for some extent around the injection point. However, several studies have shown nZVI to be scarcely mobile and stable, mainly due to the strong tendency of nZVI particles to aggregate when dispersed in water, following magnetic attractive forces. On the other hand, mZVI, due to its large particle size, undergoes very fast sedimentation. To improve colloidal stability and mobility in the subsurface, the use of biopolymers is usually required (Gastone et al., 2014).

Polymers can be dosed in low concentrations to modify surface properties and increase particle-particle repulsion (mainly for nZVI) or in high concentration to form shear-thinning fluids preventing particle sedimentation and improve delivery (mainly for mZVI) (Tosco et al., 2014a). Several biopolymers, like guar gum, xanthan gum, and mixtures of guar gum and xanthan gum, are particularly suitable for this use, thanks to their shear- thinning behaviour. Aqueous solutions of such polymers, at low shear rate, exhibit a high viscosity, thus hindering particle aggregation and sedimentation. Conversely, at higher shear rate, which is the condition during slurry injection in the subsurface, the viscosity is significantly reduced, thus facilitating the delivery in the subsurface. In particular, the use of guar gum and xanthan gum have been studied at Politecnico di Torino (Xue and Sethi, 2012; Gastone et al., 2014).

Nanoparticles transport in porous media is usually described by a modified advection-dispersion equation that takes into account the mass exchanges between liquid and solid phase due to physical and physico-chemical interactions (Tosco and Sethi, 2010). The interaction kinetics, resulting in particles deposition onto and release from the solid matrix, have been proven to be strongly influenced by both operative, e.g. injection flow-rate, and natural conditions, e.g.

Nanoscale zero-valent iron particles (nZVI) have been studied in recent years as a promising technology for the remediation of contaminated aquifers (Tiraferri et al. 2008, Tosco et al., 2014b). NZVI particles, thanks to their reduced size, much smaller than pores of aquifers, can be dispersed in aqueous slurries, and directly injected in the subsoil, thus allowing to directly target the contaminant close to the source of contamination. The reduced size of nZVI results in a very high surface to volume ratio of nZVI particles, with a positive impact on degradation kinetics. More recently, the use of larger particles, micrometric in size (microscale iron particles, mZVI) has also been proposed and investigated. Both mZVI and nZVI were found effective in degrading most of the organic contaminants found in aquifer systems, and in particular chlorinated aliphatic hydrocarbons.The mobility in porous media of nZVI and mZVI, and consequently their successful application for groundwater remediation, is negatively affected by the poor colloidal stability of particles dispersed in water.

To be effective for in situ aquifer remediation, iron particles should remain in suspension for a time sufficient to allow slurry preparation, handling and injection in the subsurface. Also, they should have a sufficient mobility in the subsurface to be transported for some extent around the injection point. However, several studies have shown nZVI to be scarcely mobile and stable, mainly due to the strong tendency of nZVI particles to aggregate when dispersed in water, following magnetic attractive forces. On the other hand, mZVI, due to its large particle size, undergoes very fast sedimentation. To improve colloidal stability and mobility in the subsurface, the use of biopolymers is usually required (Gastone et al., 2014).

Polymers can be dosed in low concentrations to modify surface properties and increase particle-particle repulsion (mainly for nZVI) or in high concentration to form shear-thinning fluids preventing particle sedimentation and improve delivery (mainly for mZVI) (Tosco et al., 2014a). Several biopolymers, like guar gum, xanthan gum, and mixtures of guar gum and xanthan gum, are particularly suitable for this use, thanks to their shear- thinning behaviour. Aqueous solutions of such polymers, at low shear rate, exhibit a high viscosity, thus hindering particle aggregation and sedimentation. Conversely, at higher shear rate, which is the condition during slurry injection in the subsurface, the viscosity is significantly reduced, thus facilitating the delivery in the subsurface. In particular, the use of guar gum and xanthan gum have been studied at Politecnico di Torino (Xue and Sethi, 2012; Gastone et al., 2014).

Nanoparticles transport in porous media is usually described by a modified advection-dispersion equation that takes into account the mass exchanges between liquid and solid phase due to physical and physico-chemical interactions (Tosco and Sethi, 2010). The interaction kinetics, resulting in particles deposition onto and release from the solid matrix, have been proven to be strongly influenced by both operative, e.g. injection flow-rate, and natural conditions, e.g.



References




References


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