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U.S. EPA Contaminated Site Cleanup Information 

(CLU-IN) 

CLU-IN I Technologies I Remediation I About Remediation Technologies I Nanotechnology: Applications for Environmental 

Remediation 

C For more Information on Nanomaterlals, please contact: 

G1911 G81V819 

Technology .Aaeumant Branch _J PH: (703) 60~0690 I Emall: geaals.gregoty@eoa.gov 

Nanotechnology: Applications for Environmental 

Remediation 

Application 

Since the early 1990s, site project managers have taken advantage of the 

properties of metallic substances such as elemental iron to degrade chlorinated 

solvent plumes in groundwater. One example of an in situ treatment technology 

for chlorinated solvent plumes is the installation of a trench filled with 

macroscale zenrvalent iron (ZVI) to form a permeable reactive barrier (PRB) 

(ITRC 2005). Based on the success of using macroscale metallic substances 

for environmental remediation, nanoscale materials are being researched and 

applied as in situ contamination reduction technologies. Following are brief 

descriptions of nanoscale materials for environmental remediation. 

Jump to a Subsection 

Nanoscale Materials I Contaminants Known to be Treated Using Nanoscale 

Materials I Reactive Chemistry of Nanoscale Materials I In Situ Application of 

Nanoscale Materials I Factors AffecUng Performance I Fate, Transport. and 

Toxicity I Field Demons1rations and Case Studies I Cost I Nanotechnology 

Vendors I Nanotechnology Products with Potential Remediation Applications 

Nanoscale Materials 

Overview 

Guidance 

Application 

Training 

Additional Resources 

Technology Focus Home 

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Comments 

Most of the bench-6cale research and field application of nanoscale materials for remediation at full scale has 

focused on nanoscale zenrvalent iron (nZVI) and r91ated products. However, other nanoscale materials, such 

as titanium dioxide (Ti~). are in the research and development stages for use in environmental remediation 

(see Nanotacbnology Produc;ts with Potlntlal RlmtcUatlon AppllcatloQI). 

Nanoscala zero-valent Iron (nZVI): Particles of nZVI may range from 10 to 100 nanometers in diameter or 

slightly larger. Macroscale ZVI has been shown to be effective for treating groundwater contaminants within 

PRBs. Particles of nZVI provide the same environmental remediation benefits as macroscale ZVI but have 

larger surface areas per volume of material; this larger surface area provides more reactive sites allowing for 

more rapid degradation of contaminants when compared to macroscale ZVI (.U.S. EPA 20088). A disadvantage 

of nZVI is the agglomeration or clumping of particles to each other or to the soil surface. Agglomeration may 

be caused by groundwater conditions, surface properties of the particles, the age of the materials, or shipping 

conditions (.U.S. EPA 2007A). Modifications to nanoscale iron particles have been made to enhance their 

mobility, reactivity, or stability. Examples include adding coatings such as polyelectrolyte or triblock polymers 

(Saleb at al. 2007: Hydutskv at al. 2007; He at al. 2007) to improve mobility, or encasing in emulsified 

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vegetable oil droplets (Quinn et al. 2005) to improve stability and to improve reactivity by improving contact 

with the contaminant (see EZVI section below}. Some nanoscale materials are made with catalysts (see 

Bimetallic nanoscale particles section below) that enhance the intrinsic reactivity of the surface sites (!rablyek 

and Johnson 2006). It should be noted that modifications to enhance mobility may result in reduced reactivity 

(Phenrat et al. 2009). 

Bimetallic nanoacale partides (BNP): BNPs have been used to remediate contaminants in soil and 

groundwater. BNPs consist of particles of elemental iron or other metals in conjunction with a metal catalyst, 

such as platinum, gold, nickel, and palladium. The combination of metals increases the kinetics of the 

oxidation-reduction (redox) reaction, thereby catalyzing the reaction. Palladium and iron BNPs are commercially 

available and currently the most common. In bench-scale tests, BNPs of iron combined with palladium 

achieved contaminant degradation two orders of magnitude greater than microscale iron particles alone: these 

particles were 99.9 percent iron and less than 0.1 percent palladium <Zhang and Elllot 20QI). Palladium can 

catalyze the direct reduction of trichloroethane (TCE} to ethane without producing other intermediate byproducts such as vinyl chloride (Nutt at al. 2005), BNPs are generally incaporated into a sluny for injection and 

can be injected by gravity or by pressure feed CGil! 2006). 

Emulslftad zero-valent Iron (EZVI): 

EZVI is commercially available and has 

been used to remediate chlorinated 

solvents. EZVI consists of nano- or 

microscale ZVI sunounded by an 

emulsion membrane that facilitates 

treatment of chlorinated hydrocarbons. 

The exterior emulsion membrane is made 

from food-grade surfactant and 

biodegradable oil and the inside of the 

droplets contain water and the ZVI 

particles. Figure 2 illustrates the structure 

of an EZVI particle. The exterior emulsion 

membranes are hydrophobic, similar to 

the properties of dense nonaqueous 

phase liquid {DNAPL) contaminants such 

as TCE. EZVI particles (or "droplets") 

therefore mix directly with DNAPL. When 

the emulsion droplets come into contact 

with with a TCE DNAPL, the TCE 

partitions into the oil membrane and then 

diffuses into the interior of the emulsion 

droplet, where it comes into contact with 

the ZVI and is degraded. A concentration 

gradient is established by migration of the 

TCE molecules into the interior aqueous 

phase of the emulsion droplet and by 

migration of the by-products out of the 

droplet and into the surrounding water 

phase, further driving the degradation 

reactions CO'Hara at al. 2QQ6l. The 

vegetable oil can also provide "food" 

(electron donors) to microorganisms and 

enhance biological activity, which in tum 

contributes to the destruction of the 

Figure 2. Sb"uc:ture of an EZVI particle (modified from Q'Ham et •I· 2006} 

0 

contaminant (Quinn at al. 2005). In addition, EZVI can be especially effective when DNAPL is present 

because DNAPL tends to be miscible in vegetable oil. When DNAPL contacts EZVI, the DNAPL can mix with 

the EZVI, after which the contaminants are in close proximity with the ZVI and can be effectively degraded. 

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Contaminants Known to be Treated Using Nanoscale Materials 

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INanoscale Iron 

Research indicates that nanoscale mater1als such as nZVI, BNPs, and EZVI may chemically reduce the 

following contaminants effectively: tetrachloroethene (PCE), TCE, cis-1,2-dichloroethylene (c-DCE), vinyl 

chloride (VC), and 1-1-1-tetrachloroethane (TCA), polychlorinated biphenyls (PCBs), halogenated 

aromatics, nitroaromatics, metals such as arsenic and chromium (U.S. EPA. 2008A), and nitrate, 

perchlorate, sulfate, and cyanide (Tratnyek et al .. as cited in Tarr 2003). 

Two of the most important reductive dechlorination reaction mechanisms are hydrogenolysis and beta 

elimination. Beta elimination, which occurs most frequently when the contaminant comes into direct 

contact with elemental iron (Fe0), follows the degradation pathway below: 

TCE + Fe0 - Chlorinated Acetylene - Hydrocarbon Products+ c1- + Fe2+/Fe3+ (U.S. EPA. 2008A). 

The hydrogenolysis pathway for reductive dechlorination of PCE, which occurs under the reducing 

conditions fostered by nZVI in groundwater, follows the following degradation pathway: 

PCE - TCE - DCE - VC - ethene (Tratnyak at al .. as cited in Tarr 2003; U.S. EPA 1999). 

The reactions of Fe0 with contaminants may be especially complicated, involving multiple competing 

pathways. 

lather Nanoscale Materials 

Nanoscale Ti02 has been shown to mineralize a variety of herbicides, insecticides, and pesticides via 

photocatalysis and can convert other contaminants to less toxic compounds (Konstantinou and Albanis 

2003). 

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Reactive Chemistry of Nanoscale Materials 

INanoscale Iron/Iron 

Zero-valent, or elemental, iron is a reducing reagent that can react with both dissolved oxygen (DO) and 

water (Zhang 20()3). The chemical processes of nZVI are driven by the oxidation of Fe0. However, the 

exact transformation mechanism may involve competing pathways and depends on the nature of the 

contaminant and targeted media (Dickinson 2010). In the presence of an oxidizing agent, Fe0 becomes 

oxidized to ferrous ions (Fe2+), and the two released electrons become available to reduce other 

compounds. In aerobic conditions, Fe0 reacts with dissolved oxygen to form ferrous ions and water. Fe0 

can also reduce water to form ferrous ions, hydrogen, and hydroxide ions. These reactions are shown 

below: 

2Fe0 + 4H+ + 02 -2Fe2+ + 2H20 

(Matheson and Tratnyek 1994) 

2Fe0 + 2H20-2F&.!+ + H2 + 20W 

!Matheson and Tratnyek 1994) 

The reactions of Fe0 with contaminants (such as TCE) may be more complicated and may involve 

multiple competing pathways, including beta elimination, where Fe0 releases electrons and TCE is 

transformed to ethane and releases chloride ions. The equations above and these reactions apply to iron 

particles in general; however, the advantages of using nanoscale iron over macro- or microscale iron is 

that reactions may proceed at a faster rate. 

The reductive capability of Fe0 when it comes into contact with chromium contamination in soil and 

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groundwater can be seen in the follOY1ing equation, where iron is oxidized to its ferrous form and chromium 

is reduced from chromium (VI) to the less toxic chromium (Ill) <Cao and Zhang 200§): 

After groundwater treatment using nanoscale iron particles, post-injection observations of the subsurface 

have indicated an increase in pH (caused by the formation of hydroxide ions) and a decrease in oxidationreduction potential (ORP) (a result of the reducing conditions that are created). A IOY1er ORP favors 

anaerobic bacterial growth, which may promote increased degradation for certain contaminants (for 

example, chlorinated solvents). Other chemicals formed when particles such as nZVI are used may 

include hydrogen gas and Fe2 ions, which also would promote microbial growth. After an nZVI injection, 

the ORP tends to decrease sharply before it becomes stable <Zhang 2003). 

l<>ther Matarlals 

When aqueous Ti~ suspensions are irradiated with light energy greater than 3.2 electronvolts (eV), Ti~ 

is activated and can combine with water or dissolved oxygen {or both) to fonn highly reactive species, 

including the hydroxyl radical and the superoxide radical anion, which can oxidize and degrade a range of 

contaminants ru.s. EPA 2008Al. 

In Situ Appllcatlon of Nanoscale Materlals 

The application of nanoscale materials for in situ application is site specific. The method of injection, and 

spacing and distribution of injection points, will depend on the type of geology found in the treatment zone, 

the type and distribution of contaminants, and the fonn of the nanoscale materials that will be injected. 

Injection of nanoscale iron is typically done via direct injection through gravity feed or under pressure. 

Direct injection can be done via several options including, but not limited to, direct push technology or via 

various types of wells (e.g., temporary or permanent injection wells). Recirculation is another option that 

involves injecting nanoscale materials, while extracting groundwater and reinjecting it in the treatment 

zone, possibly adding more nanoscale materials in the process. This method of in situ application keeps 

the water in the aquifer in contact with the nZVI and also prevents larger agglomerated iron particles from 

settling out, promoting continuous contact with the contaminant. Figure 3 shows an example of the 

recirculation in situ application of nanoscale materials. Another common in situ application method for 

nZVI is the direct push method. This method involves driving direct-push rods, similar in size to small 

drilling augers, progressively deeper into the ground. This method allOY1s materials to be injected without 

the need to install pennanent wells (Butler 2000). 

Additional methods and processes 

to apply nanoscale material for in 

situ treatment include pressure pulse 

technology, liquid atomization 

injection, pneumatic fracturing, and 

hydraulic fracturing. Pressure pulse 

technology uses large-amplitude 

pulses of pressure to insert the nZVI 

slun-y into porous media at the water 

table; the pressure then excites the 

media and increases fluid level and 

flOYI COCETA 2003). Liquid 

atomization injection is a technology 

that is proprietary to ARS 

Technologies, a company that 

specializes in pneumatic fracturing 

and injection field services. It 

introduces an nZVl..fluid mixture into 

the subsurface using a carrier gas. 

The nZVI liquid gas combination 

aerosolizes, allowing for more 

effective distribution; this method 

Figure 3. Conceptual design af rectcula'llon (Hann 2005) .... ~ •M• ..... 

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can be used in geologic fonnations with lower penneability CNAVFAC 2008). Fracturing injection 

{pneumatic or hydraulic) is a high-pressure injection technique using compressed gas {pneumatic) or a 

water-based, highly viscous slurry containing sand (hydraulic) that fractures rock or other low-penneability 

fonnations and allows liquids and vapors to be transported quickly through the channels created. 

Pneumatic fracturing uses compressed gas to create a fracture network of preferential flow paths in rock 

around the injection point to allow liquids and vapors to be transported quickly through the fractured rock; 

pneumatic fracturing improves access to contaminants and allows liquids to flow freely (Pneumatic 

Fracturing Inc. 2008; Zbana 2003). 

Figure 4 illustrates the basic principles of two methods of remediating contaminated groundwater using 

nZVI. The image at the top shows treatment of DNAPL contamination by injection of nanoscale materials. 

In the second image, a reactive treatment zone is fanned by a series of injections of nZVI. These 

injections create overtapping zones of particles that become lodged within the native aquifer material 

{Tratnyek and Johnson 2006). 

Research is under way into methods 

of injection that will allOYt' nanoscale 

materials to better maintain their 

reactivity and increase their access 

to recalcitrant contaminants by 

achieving wider distribution in the 

subsurface. For example, creating 

nZVI on site could reduce the 

amount of oxidation the iron 

undergoes between production and 

use, thereby reducing potential 

losses in reactivity. Researchers in 

green chemistry have successfully 

created nZVI in soil columns using a 

wide range of plant phenols which, 

according to the researchers, allOYt's 

greater access to the contaminant 

and creates less hazardous waste in 

the manufacturing process <vanna 

211111). 

!Qp of page 

Factors Affecting Performance 

A 

B 

Figure 4. SChematlc of two methods of groundwater remediation using 

nanoscale ~n (CGR 20091 

Conuiminated 

Groundwater 

Groundwater Flow 

ConGmjnatfll 

Groundwattr 

PH~able 

RH<tiw 

Barnet" 

lnjtttlon 

Well 

• • 

--;-

/ !-----

Treated 

Grounclwatet" 

Tr.ated 

Groundw.ter 

A number of factors can affect nanoscale performance for site remediation, including: {1) site specific 

conditions, (2) agglomeration, and (3) passivation. Each of these is discussed below. 

Si11Hpecific conditions such as the site location and layout, geologic conditions, concentration of 

contaminants, and types of contaminants may limit the effectiveness of nanoscale materials. Before nanoscale 

materials are injected, geologic, hydrogeologic, and subsurface conditions should be evaluated to assess 

whether injected particles would offer the perfonnance expected. Factors that affect the subsurface mobility of 

nanoscale materials include the surface features of nanoscale materials and site-specific factors including: 

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composition of the soil matrix, ionic strength of the groundwater, hydraulic properties of the aquifer, depth to the 

water table, and geochemical properties (including pH, DO, ORP, and the concentration of nitrate, nitrite, and 

sulfate), among others. Perfonnance will be site specific and will depend on the presence of competing 

oxidants such as DO and No3- (nitrate ion), contaminant concentration, and the pH of the soil and groundwater 

(Liu and Lowry 2006; Liu et al. 2007). 

Agglomeration - Studies have shown that nanoscale materials may not achieve widespread distribution in the 

subsurface because of agglomeration before they completely disperse within the soil or groundwater matrix, 

limiting the radius of influence. nZVI particles are attracted to one another, which can cause them to 

agglomerate into larger micron-sized particles (greater than 100 nanometers) (Tratnyek and Johnson 2006; 

Phenrat et al. 2007). Because of agglomeration, the effective size might range up to hundreds of nanometers. 

Some vendors refer to their materials as nanoscale even though they are larger than 100 nanometers and 

therefore do not meet the NNI definition of nanotechnology. 

Agglomeration also reduces the exposed reactive surface area of the particles. The pH of the subsurface may 

also limit the effectiveness of nanoscale materials because the sorption strength, agglomeration, and mobility of 

the particles are all affected by the pH of the groundwater (U.S. EPA 20078). The ionic strength and types of 

cations in the groundwater, as well as the chemical and physical characteristics of the aquifer materials, also 

affect the agglomeration and movement of iron nanoscale materials (Saleh et al. 2008). 

Passivation, or deactivation, may limit the effectiveness of iron nanoscale materials. The high surface energy 

of nanoscale materials makes them highly reactive and susceptible to oxidation in the open air, resulting in the 

fonnation of iron oxide and a decrease in the chemical reactivity of the iron nanoscale materials (Wang et al. 

2010). As a rule, injection mechanisms should limit the volume of water injected along with the iron to limit 

exposure to oxygen and other oxidants that could passivate the iron before and during injection. If larger 

volumes are used, deoxygenated water can minimize the iron passivation, but other oxidants may still be 

present to react with the iron (Gavaskar et al. 2005). 

A challenge in evaluating the perfonnance of nanoscale material injection is monitoring the distribution of 

injected particles in the subsurface. It is therefore important to identify the appropriate parameters to measure 

perfonnance. Typically, geochemical measures such as ORP are monitored as a surrogate. Dissolved iron can 

also be monitored. Reaction kinetics are difficult to monitor; however, post-injection chemical concentrations 

are measured using standard approaches. Additionally, the kinetics and reactivity of nanoscale materials in a 

DNAPL source zone may vary from the kinetics and reactivity in a dissolved plume (U.S. EPA 2008A; Liu et 

al. 2007). 

Fate, Transport, and Toxicity 

Although nanoscale materials that contain iron are the most widely used nanoscale materials in site 

remediation, knowledge is limited on the fate and transport of iron nanoscale materials in the environment. 

Furthennore, research is ongoing regarding the potential toxicological effects of nanoscale materials. There are 

insufficient data on the potential for bioaccumulation of nanoscale materials in environmentally relevant species 

(Krey! i ng et al. 2006), and there have been few studies on the effects of any nanoscale materials on 

environmental microbial communities (Klaine et al. 2008). As described in the "Factors Affecting 

Performance" section, agglomeration often affects transport of nanoscale materials in the subsurface. The 

particles may become associated with the aquifer matrix as oxidized iron particles after they react with 

contaminants. Under standard environmental conditions (aerated water and pH 5 to 9), Fe2+ will readily and 

spontaneously oxidize to Fe3+ and precipitate out of the groundwater as insoluble iron oxides and 

oxyhydroxides. Researchers have developed methods, some of which are in use commercially, to improve the 

mobility of iron nanoscale materials within aquifers and to optimize contact between the nanoscale material and 

contaminant. Ongoing studies are evaluating surface coatings and other modifications that would reduce 

agglomeration of nanoscale materials and maximize subsurface mobility (Phenrat 2008). Preliminary research 

indicates that polymers, surfactants, and organic proteins (such as soy) stabilize nanoscale material 

suspensions in aquifers, inhibiting their agglomeration and allowing greater dispersal without compromising the 

ability of the iron to remediate contaminants (He et al. 2007, Zhana 2009). Based on laboratory research, soils 

high in clay content have been shown to allow greater dispersal of nZVI as well; anionic clay particles appear to 

function as a natural stabilizer, allowing for more effective transport (Schrick et al. 2004; Hydutsky et al. 

2007). Increasing mobility without sacrificing reactivity needs to be tempered with methods to control the 

migration of the nanoscale particles due to lack of toxicological infonnation (Lowry et al. 2007). 

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Studies are being conducted on the potential toxicity of various types of manufactured nanoscale material. The 

increased surface area and larger number of reactive sites of nanoscale materials may equate to greater 

biological activity per unit mass than with micro- or macroscale particles of the same composition. Substances 

considered nontoxic at the macroscale may have negative impacts on human health when nanoscale particles 

are inhaled, absorbed through the skin, or ingested (Kreyling et al. 2006). Because of the small size of 

nanoscale materials, the particles have the potential to migrate to, or accumulate in, places that larger particles 

cannot, such as the alveoli in the lungs (Grassian et al. 2007), thereby potentially increasing toxicity. Some 

nanoscale materials have demonstrated an ability to increase the bioavailability of certain hydrophobic 

contaminants, for example, by increasing the mobility of contaminants bound to soil and sediment surfaces 

CTungittiplakom et al. 2005). Potential health effects of nanoscale materials have been reviewed in 

Nanoparticles: Health Effects--Pros and Cons, written by Maureen Gwinn and Val Vallyathan. Issues of 

toxicity and safety have limited the use of nanoscale materials for remediation by some private-sector 

companies. For example, DuPont has ruled out the use of nZVI for remediation at its sites until issues 

concerning fate and transport have been more thoroughly researched. The company has cited questions of 

post-remediation persistence and potential human exposure to the particles as areas of particular concern 

(DuPont 2007). As another example of a cautionary approach, the Continental Western Group of insurance 

companies announc:ecm;i that it will no longer cover injury or damage arising from nanotubes or 

nanotechnology, as used in products or processes. 

U.S. Environmental Protection Agency's (EPA) Office of Research and Development (ORD) published a 

Nanomaterial Research Strateav <NRS>m in June 2009 to act as a guide for nanotechnology research 

within ORD. The NRS centers around progressing EPA's understanding of nanomaterials for decision support 

and focuses on four research themes: 

• Identifying sources, fate, transport, and exposure 

• Understanding human health and ecological research to inform risk assessment and test methods 

• Developing risk assessment approaches 

• Preventing and mitigating risks (U.S. EPA 2009). 

In addition, EPA ORD has prepared a document, Nanomaterial CSH Studies: Nanoscale Titanium Dioxide 

in Water Treabnent and in Topical Sunscreen. The document discusses two case studies on the use of 

nanoscale Ti~: 1) to remove arsenic from drinking water, and 2) as an active ingredient in topical sunscreen. 

The document was designed to define the information required to perform a comprehensive environmental 

assessment of the potential risks associated with nanoscale Ti02. 

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Field Demonstrations and Case Studies 

As of November 2011, data that exhibit varying degrees of comprehensiveness were obtained for 36 sites using 

or testing nanoscale materials for remediation or in the planning stages. Details on these selected sites are 

available at http://clu-in.om/products/nanozvi and will be updated periodically as new information is received. 

Performance data are limited because many of the remediation projects using nanoscale materials are just 

beginning or are ongoing. However, as the technology is applied at an increasing number of sites with varying 

geologies, more data will become available on performance, providing site managers and other stakeholders 

with additional information to evaluate whether the technology might be applicable for their sites. 

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Cost 

In 2001, when field demonstrations of nZVI technology first took place, the cost of nZVI was considered high 

(nearty $500/kilogram [kg]) due to a limited number of commercial suppliers. In addition, the effectiveness and 

quality of commercially-available nanoscale material products were highly variable when compared to 

laboratory-prepared nanoscale material due to insufficient characterization and quality assurance/quality control 

procedures (Li 2006). By 2006, nZVI costs had reduced to about $50 to $100 per kg. Decreasing nZVI costs 

and improved quality control procedures that provide better homogeneity are making this technology more viable 

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in today's remediation market. While costs may remain high in some applications, the total costs of deploying 

the technology at a site compared to the life cycle cost of an ex situ technology can be quite competitive. 

In addition to the costs associated with the nanoscale material, other factors contribute to the cost of site 

remediation such as site type, contaminant type, contaminant concentration, extent of the contaminant plume, 

and any challenges that may occur during remediation. Additional factors that may increase the total cost of 

nanoscale material application may include operational requirements connected with any contamination found 

underneath a building, or the need to treat or dispose extracted fluids (Wilson 2004). Currently, project-specific 

financial information is limited because many of the remediation projects using iron nanoscale materials are just 

beginning or are ongoing. Proprietary concerns may also preclude cost data from being made publicly available. 

However, as the use of the technology increases at sites with varying geologies, more cost data will become 

available, providing site managers and other stakeholders with additional information to evaluate the 

applicability and cost-effectiveness of the technology for their sites. 

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Nanotechnology Vendors 

The properties of particles such as reactivity, mobility, and shelf life can vary depending on the manufacturing 

process or the vendor that provides the particle (Miehr et al. 2004). Several vendors supply nanoscale 

materials for site remediation. See http://clu-in.om/products/nanozvi for information about vendors 

associated with site-specific applications. More information about vendors and other types of nanoscale 

materials can be found on the Internet at sites such as htm://www.nanovip.com or http://www.nanotechnow.com/business.htrn. The inclusion of these websites should not be considered to be an endorsement by 

EPA. 

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Nanotechnology Products with Potential Remediation Applications 

Researchers are developing a variety of other nanoscale materials for potential use to adsorb or destroy 

contaminants as part of either in situ or ex situ.p,rocesses. The stage of development ranges from bench to pilot 

scale. These particles include Ti02, SAMMS M, nanotubes, ferritin, dendrimers, metalloporphyrinogens, and 

swellable organically modified silica (SOMS). 

Nanoscale Ti02 is being pilot tested for ex situ treatment of contaminated groundwater as part of a pump and 

treat system. Additional information on nanoscale Ti02 is available within Contaminants Known to be Treated 

Using Nanoscale Materials and Reactive Chemistry of Nanoscale Materials. 

Some materials can be made with surface functional groups to serve as adsorbents to scavenge specific 

contaminants from waste streams. SAMMSTM materials consist of a nanoporous ceramic substrate coated 

with a monolayer of functional groups tailored to preferentially bind to the target contaminant. The functional 

molecules covalently bond to the silica surface, leaving the other end group available to bind to a variety of 

contaminants. Though SAMMSTM materials are larger than the nanoscale range, the~ are considered a 

nanotechnology because of their nanoscale pores. According to researchers, SAMMS M maintains good 

chemical and thermal stability and can be readily reused or restored (Frvxell et al. 2007). SAMMSTM has a 

large surface area to allow for quick sorption kinetics. Contaminants successfully sorted to SAMMSTM include 

radionuclides, mercury, chromate, arsenate+ pertechnetate, and selenite (M@Miaod 2003; Tratnyek and 

Johnson 2006). According to the SAMMsi.M Adsorbents website, SAMMSM materials have produced 

positive results in pilot-scale tests for remediation of mercury in well water with a high concentration of 

dissolved solids, aqueous mercurr in low concentrations, highly radioactive mercuric waste, and gaseous 

elemental mercury. Since SAMMS M materials adsorb the contaminants, these materials are used primarily as 

an ex situ treatment technology (!ratnyek and Johnson 200§). 

Nanotubes are engineered molecules most frequently made from carbon. They are electrically insulating, highly 

electronegative, and easily polymerized. Nanotubes have also been made from Ti02 and have demonstrated 

the potential for use as a photocatalytic degrader of chlorinated compounds (Chen et al. 2005). Bench-scale 

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research has shown Ti02 nanotubes are particularty effective at high temperatures and are capable of reducing 

contaminant chemical concentrations by more than 50 percent in 3 hours (Xu et al. 2005). Ti02 is considered 

an ex situ strategy because effective illumination usually requires that treatment occur in a reactor that is 

designed for this purpose (!ratnvek and Johnson 200§). 

Bench-scale tests using ferritin, an iron storage protein, have indicated that it can reduce the toxicity of 

contaminants such as chromium and technetium in surface water and groundwater to facilitate remediation 

(Temple University 2004). Like Ti02, ferritin is photocatalytic; in one bench-scale project, the addition of 

visible light caused ferritin to reduce toxic, water-soluble hexavalent chromium to the less toxic trivalent 

chromium, which is not water soluble and precipitates out of solution (U.S. EPA 2008A). Ferritin is being 

researched for in situ use ITemple Universitv 200fl. 

Dendrimers are hyper-branched, well-organized polymer molecules with three components: core, branches, 

and end groups. Dendrimer surfaces terminate in several functional groups that can be modified to enhance 

specific chemical activity. Fe0/FeS nanocomposites, synthesized using dendrimers as templates, could be 

used to construct permeable reactive barriers for remediation of contaminated groundwater. Bench-scale 

research has indicated that delivery options for dendrimers are flexible (Diallo et al. 2006). Dendrimers can be 

used in situ or ex situ (Xu 200§). 

Metalloporphyrinogens are complexes of metals with naturally occurring, organic porphyrin molecules. 

Examples of biological metalloporphyrinogens are hemoglobin and vitamin B12. Batch-reactor experiments have 

shown that metalloporphyrins are capable of reducing chlorinated hydrocarbons such as TCE, PCE, and carton 

tetrachloride under anoxic conditions to remediate contaminated soil and groundwater. Laboratory research 

using metalloporphyrinogens is being performed for the potential in situ remediation of groundwater (Dror et al. 

21m). 

SOMS (commercial name Osort) is organically modified silica that swells and captures small molecule organic 

compounds such as gasoline, natural gas, acetone, ethanol, pharmaceuticals, and solvents. When organic 

compounds are introduced to SOMS, the powder swells, capturing the organic compounds. SOMS may be able 

to capture up to eight-times its volume in organic compounds that are present either as neat liquids, vapors, or 

dissolved in water. The SOMS material is hydrophobic and does not absorb water (Edmiston 2009). 

• lron-Osorb incorporates nZVI into Osorb, forming a material that can dechlorinate captured organics. The glass 

matrix concentrates the chlorinated solvents and protects the embedded metal particles from deactivation by 

dissolved ions. After the lron-Osorb has captured the organic compounds, it can be put through a thermal or 

rinsing process to release the compounds allowing for the capture of the organic compound and the reuse of the 

lron-Osorb. lron-Osort can go through this regeneration process over 100 times (ABS Materials 20108). The 

manufacturer reports that lron-Osort material is designed to last over 10 years in the subsurface. For long-term 

remediation, it can be injected as a soft curtain barrier to protect groundwater areas from incoming plumes. In situ 

pilot scale testing was performed at several sites in Ohio in 2009 for groundwater remediation of TCE1 l 

• Palladium-Osorb is a similar metal-glass hybrid material used in ex situ treatment systems for remediation of 

chlorinated volatile organic compounds (VOCs) (Edmiston 2010). Palladium nanoparticles are incorporated into 

the Osort to remove halogenated VOCs from groundwater pumped through the system. A hydrogen gas source 

supplies a proton that completes the reductive dehalogenation of contaminants inside the Palladium-Osort, and 

reduces contaminants to benign products of ethane gas and salts (in the reduction of TCE) (ABS Materials 

2010A). Pilot scale testing at an Ohio site has shown the continuous reduction of TCE from 5800 parts per 

million to no detect by the ex situ system. The manufacturer reports that Palladium-Osorb is a catalytic 

material that does not break down or need replacement. An above ground unit has been designed to treat 1 O 

gallons per minute of produced water (ABS Materials 2010A) and the unit has been modified to be able to treat 

the oil sheens and mousses that result from oil spills. The unit is being field-tested for possible use in the Gulf of 

Mexico (Boccieri 2010). 

Researchers are also using nanotechnology to develop membranes for water treatment, desalination, and water 

reclamation. These membranes incorporate a wide variety of nanoscale materials, including those composed of 

alumina, zero-valent iron, and gold (Theron et al. 2008). Carbon nanotubes can be aligned to form membranes 

with nanoscale pores to filter organic contaminants from groundwater (Mauter et al. 2008; Meridian Institute 

2006). 

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