Nanoremediation: Information for Decision Makers from NanoRem
FAQ: Where have iron nanoparticles (nZVI) been used in remediation?
The use of iron nano-scale particles (NP) in the remediation of contaminated groundwater is an emerging approach. By the end of 2013 NanoRem identified around 70 documented projects at pilot or full scale since the first reported application in 2000. The technology has been successfully utilised to remediate contaminants within groundwater in a number of countries with their disparate Environmental Regulatory regimes worldwide namely, Germany, Czech Republic, Italy, Taiwan, Canada and USA, with the majority of these projects (36) being undertaken in the USA, where they have been overseen by the US Environmental Protection Agency (US EPA). A full list of these projects can be found in Annex 1 of “A Risk/Benefit Appraisal for the Application of Nano-Scale Zero Valent Iron (nZVI) for the Remediation of Contaminated Sites in the Environment” (See NanoRem nZVI Risk Benefit Appraisal Report). Although nanoremediation has been documented for source treatment, there is a general limitation for in situ NAPL source treatment for groundwater problems which typically have a limited effectiveness. Complete mass removal is rarely possible, and because residual, sparingly soluble NAPL can lead to low concentrations in excess of groundwater threshold values, the residual source is still problematic. Due to these limitations, the use of nanoremediation to date has tended to be restricted to the treatment of contaminated groundwater. In addition, as nanoparticles are rapidly inactivated or inefficient in the presence of air the technology is more suited to the treatment of contaminants within the saturated zone. The vast majority of known in situ applications of nZVI have used direct injection to introduce slurry of nZVI at a specific depth and in a specific amount directly into soil and/or aquifer materials. These are either gravity-fed or under pressure. nZVI is typically supplied in a liquid slurry, both to ensure a stabilised and active iron NP product, and because the introduction of nZVI particles into the subsurface requires their suspension in some form of a slurry.
The first reported field trial to directly inject iron NP into the subsurface to remediate contaminated groundwater was that undertaken at a manufacturing site in Trenton, New Jersey, USA during the summer of 2000. This utilised a modified bi-metallic nanoparticle (BNP), consisting of iron combined with trace amounts of palladium, to address a plume of trichloroethylene (TCE) at a concentration of 445 – 800 mg/l. Approximately 2.5 kg of BNP slurry (approximately 1 g/l by weight) was injected into a trail zone consisting of a 3 m X 4.5 m area over a 6 m saturated aquifer. It should be noted that the particles used during this trial were determined to be generally in the range of 100-200 nm which actually places them outside of the currently accepted size range for nanoparticles.
The majority of the subsequent remediation projects reported have utilised nZVI particles as the reactive agent, although practitioners have used modified iron nanoparticles, including BNP and nano iron oxide particles (FAQ What are nanoparticles and how does nanoremediation work?) with varying degrees of success.
The principal contaminants addressed by the majority of the pilot and field trials have been the chlorinated solvents, in particular chlorinated ethenes, vinyl chloride, chloroform and carbon tetrachloride. Practitioners have successfully extended this range (at either field or pilot scale) to include the contaminants indicated in the table below.
Table 1 Additional Contaminants Successfully Treated at Either Field or Pilot Scale
(See NanoRem nZVI Risk Benefit Appraisal Report)
||Pilot scale |
|Ethyl hexyl phthalate
||BTEX (benzene, toluene, ethylbenzene, xylene)|
|Benzo [a] anthracene
||Polychlorinated biphenols (PCB)|
Due to the vastly different geologies found in the countries where nanoremediation has been utilised, large numbers of different strata have been encountered at the project sites. These have varied from sandy gravels at Bornheim, Germany, to fractured bedrock at Kurivody in the Czech Republic, to glacial tills over fractured bedrock at Rochester, USA, and coarse alluvial silt clay sediments at San Francisco Bay, USA.
When nanoparticles were originally demonstrated to be effective at remediating contaminated groundwater, it was forecast that nanotechnologies would offer a step-change in remediation capabilities and that a rapid take up of the technology would follow. A 2007 report (JRC Ispra 2007) projected that the 2010 world market for applications of environmental nanotechnologies would be approximately $6 billion per annum across four sectors: remediation, protection, maintenance, and enhancement, with remediation identified to be the fastest growing sector. This uptake did not subsequently materialise, though field and pilot scale trials have continued. However, there is very little information in the peer-reviewed literature with respect to cost analyses for nZVI remediation projects. Due to this paucity of information, and the possibility that nZVI effectiveness may be site-specific, it is difficult to extrapolate field-scale remediation costs from bench-scale testing. One of the aims of the NanoRem programme is to increase the uptake of this promising technology by providing fully documented field study reports, combined with data on the relative costs and benefits of using nanoparticles for the remediation of contaminated groundwater.
Further InformationThematic Pages:
These will be available from August 31st 2014
This information is drawn from
the NanoRem report: 'A Risk/Benefit Appraisal for the Application of Nano-Scale Zero Valent Iron (nZVI) for the Remediation of Contaminated Sites'. The full report including additional information, detail and referencing can be downloaded from: www.nanorem.eu/Displaynews.aspx?ID=525.