Nanotechnology for Site Remediation
Marti Otto, Technology Innovation and Field Services Division, EPA, Washington, D.C. USA
Emerging nanotechnologies are contributing to innovations in semiconductors, memory and storage technologies, display, optical and photonic technologies, energy, biomedical, and health sectors. Nanotechnology also is contributing to the development of new environmental applications for pollution prevention, contaminant treatment, and hazardous waste site cleanup. The presentation presents a snapshot of nanotechnology and its current uses in site remediation.
Hundreds of thousands of sites in the United States (U.S.) have been identified with varied degrees of contamination. More than 80% of hazardous waste sites identified by the U.S. Environmental Protection Agency’s (U.S. EPA’s) Superfund program have contaminated groundwater. This is particularly important considering that over half of the U.S. population relies on groundwater for drinking. Once groundwater is polluted, its remediation is often protracted, costly, and sometimes infeasible.
Early treatment remedies for groundwater contamination were primarily pump-and-treat operations. This method involves extracting contaminated groundwater via wells or trenches and treating the groundwater above ground (ex situ) using processes such as air stripping, carbon adsorption, biological reactors, or chemical precipitation. Some of these processes produce highly contaminated wastes that then have to be disposed.
Because of the relatively high cost and often lengthy operating periods for these remedies, the use of in situ treatment technologies is increasing. One example of an in situ innovative treatment technology for chlorinated solvent plumes is the use of nanoscale zero-valent iron (nZVI). nZVI can be injected directly into a contaminated aquifer. nZVI is in use in full-scale projects, with an encouraging measure of success. This technology holds promise in remediating sites cost-effectively and in addressing challenging site conditions, such as where dense nonaqueous-phase liquids (DNAPLs) are present in contaminated aquifers.
The U.S. Environmental Protection Agency published a fact sheet on the use of nanotechnology for site remediation. (See http://clu-in.org/542F08009.) EPA collected information on over 25 sites where nanotechnology has been tested for site remediation.
The presentation discusses environmental applications of nanotechnology and its current uses in hazardous waste site remediation. The talk includes a discussion of concerns regarding potential effects of engineered nanomaterials on human health and the environment and of the need for additional research on the safe application of the technology for site remediation.
Subhasis Ghoshal, Department of Civil Engineering, McGill University, Montreal, Quebec, Canada
In recent years, there has been significant interest in employing zero-valent iron nanoparticles (nano iron) for remediation of sites contaminated with toxic and hazardous compounds such as chlorinated solvents, arsenic and chromium. Nano iron particles have been found to be very efficient in eliminating pollutants such as chlorinated organic compounds, chromium and arsenic that have been found to contaminate groundwater aquifers. Several field tests and laboratory experiments have suggested that the transport of nano iron on subsurface porous media is severely hindered, and it is attributable in part due to the tendency of the nano iron to agglomerate and thus be retained in soil pores. Recent studies show that modifying the surfaces of nano iron with polymers, polyelectrolytes and surfactants make nano iron more transportable. Surface modifications that provide enhanced transport and yet retain their reactivity will significantly enhance our ability to remediate contaminated sites and aquifers.
The presentation will discuss techniques for bottom-up synthesis of polymer-coated nano iron particles, and the characteristics of the resulting particles. Techniques for measuring the size, surface charge, surface chemistry, chemical composition, chemical and colloidal stability of the particles will be discussed. An example of how bottom-up synthesis can be tuned to produce particles of various sizes will be presented. Particle size has significant effect on the transport and longevity of particles. Results from laboratory experiments to evaluate the transport of the surface modified particles in packed columns of granular porous media under selected environmental conditions will be presented. A pilot-scale field study in Canada, where iron nanoparticles and a polymeric dispersing agent was used for remediation of a chlorinated solvent-contaminated site, will be discussed. The potential improvements needed to implement effective nano iron remediation will be discussed.
Gregory V. Lowry, Civil & Environmental Engineering Center for Environmental Implications of NanoTechnology, Carnegie Mellon University, USA
Novel reactive nanomaterials, such as Fe0 nanoparticles (NZVI), offer the potential for highly efficient targeted delivery of remedial agents to subsurface contaminants. The primary challenge to application is selecting appropriate surface modifiers that enable emplacement in the contamination zone, but do not adversely impact the particle’s reactivity with the contaminant. Surface coatings can also decrease the potential toxicity of the particles. Concomitant optimization of mobility, reactivity, while minimizing toxicity requires a fundamental molecular level understanding of the surface modifiers properties and how they affect nanoparticle deposition. Further, optimizing the surface coating to enhance interaction with the contaminant of interest is possible. Dynamic light scattering and electrophoretic mobility measurements, along with Ohshimas’s analysis are used to characterize the layer conformation and properties of different types of common synthetic and natural polyelectrolytes adsorbed onto NZVI. Batch reactivity studies and column and 2-D flow cell studies under a variety of hydrogeochemical conditions and heterogeneities were then conducted on polyelectrolyte-modified NZVI to determine the effect of the adsorbed layer properties and injection conditions on reactivity and mobility. Surface coatings decreased particle reactivity with TCE by up to a factor of 20, and eliminated the particles bactericidal properties. The magnitude of the effect depended on the adsorbed layer conformation of the polyelectrolyte as explained using the Scheutjens and Fleer train-loop-tail conceptual model for homopolymer sorption. More polydisperse samples containing larger particles (several hundred nanometers) are less mobile than monodisperse samples containing only small particles (<100nm) due to a greater tendency to agglomerate during transport. The concentration of the injected Fe0 nanoparticle suspensions also impact mobility. This study emphasizes the important role of aggregation on nanoparticle transport, and the role of organic macromolecules on the transport and toxicity of NZVI used for groundwater remediation.
J.P. Davit1 & M. Pupeza, Golder Associates – Europe
F. Gheorghiu, and M. Borda, Golder Associates – United States
With nearly 10 years of experience, Golder Associates Inc. (Golder) is a leader in the manufacture and implementation of nano-scale zero-valent iron (nZVI) for environmental remediation applications. Golder has designed and implemented nZVI injections in the United States, Canada, Europe and Australia including, ten (10) pilot-scale studies, ten (10) bench-scale studies and one (1) full-scale implementation. Golder’s global experience has led to several significant advancements in the technology including, verifying the need to include palladium (Pd) as a catalyst for in situ treatment using mechanically crushed material, verifying the need to include a surface modifier (e.g., soy powder) to enhance the mobility of nZVI in the subsurface, and establishing the enhanced treatment potential of combined nZVI/enhanced bioremediation alternatives. In addition to these advances in implementation, Golder is also advancing the types of nZVI used in the field including the manufacture of mechanically crushed nZVI through licensing with Lehigh University and in-well precipitated nZVI. Golder continues to stay involved in the research and development efforts taking place in the academic sector with several key industry-academic partnerships and is actively exploring advanced injection technologies for the more efficient delivery of the material to the sub-surface. Findings from Golder’s most recent applications will be discussed.
Deployment of nZVI to soil for polychlorinated biphenyl remediation: impacts on soil microbial communities
Emma L. Tilston, Laurence Cullen, Chris D. Collins & Liz J. Shaw: Department of Soil Science, University of Reading
Geoff R. Mitchell: Centre for Advanced Microscopy, J.J. Thomson Physical Laboratory, University of Reading
Zerovalent iron (ZVI) is a reducing agent that can reductively dehalogenate a broad range of chloro-organic compounds and has therefore successfully been used in environmental remediation, particularly in the subsurface. ZVI particles at the nanoscale (nZVI) are characterized by high surface area-to-volume ratios and studies to date have concluded that nZVI particles are more effective in contaminant breakdown than their micro-scale equivalent. With the development of particle stabilisation methods (e.g. water-soluble polyelectrolytes) to minimise aggregation and adhesion, nZVI technology could potentially be extended from the cleanup of the saturated subsurface to the remediation of contaminated unsaturated soils. For example, soil contaminated with polychlorinated biphenyls (PCBs), an important class of toxic, bioaccumulative and recalcitrant soil contaminants could be a useful target for nZVI remediation. For the remediation of PCB-contaminated soil, the following two-step strategy can be envisaged: (1) Deployment of nZVI to dehalogenate the most recalcitrant higher chlorinated PCB congeners; (2) Use of microbial remediation to remove the resulting lower chlorinated PCBs that are much more amenable to aerobic microbial catabolism and cometabolism.
A significant constraint to the success of the above strategy and the wider application of nanoremediation technologies is that we do not know whether, in the short term, nanoparticles impact upon the diversity and activity of soil microbial communities responsible for bioremediation of chlorinated and non-chlorinated aromatics. Further, adverse impacts to microbes will not only undermine soil natural attenuation functions, but, could also have implications for microbial plant symbiotic and plant nutrient mineralization functions important for the long-term revegetation and stabilisation of the site.
This talk will outline experiments funded by the Natural Environment Research Council (UK) Environmental Nanoscience Initiative to investigate nZVI impacts on microbial communities using the above PCB remediation scenario. The experimental aims were to characterize the effects of nZVI and the stabilizer polyacrylic acid (PAA) on general soil microbial activities (ammonia oxidation potential, dehydrogenase activity) and numbers and activities of chloroaromatic-degrading microorganisms. An additional aim was to evaluate post-treatment effects on plant-microbe interactions with plant species commonly used for site revegetation (Trifolium repens and Lolium perenne).
Young Haeng Lee, Center for Environmental Technology Research, Korea Institute of Science and Technology, Seoul, South Korea
This presentation reviews the researches on the nano-based water treatment technologies currently conducted by researchers in center for environmental technology research at Korea Institute of Science and Technology (KIST). Environmental conditions as well as environmental laws in South Korea are first introduced. Furthermore, the improvement of water quality over past decade is reviewed in detail. Current researches on the application of nano-based technologies (i.e., zirconium mesostructures, gold nanoparticles supported on titania, nanoscale zero-valent iron particles, and etc.) to the water and wastewater treatments system are covered. Brief highlights are made on the membrane-based technologies and membrane-coupled biotechnologies for the water treatment. Therefore, this presentation provides an overview of the chronologically developed environmental policies corresponding to the change of environmental issues, and outlines the researches on the nano-based water treatment technologies successfully applied to solve the current environmental problems in South Korea.