WP 4 Mobility and Fate of Nanoparticles
|WP 4 Objectives
• Develop standardised experimental protocols in order to facilitate inter‐laboratory comparison of nanoparticle mobility and fate studies, enabling regulators and/or consultants to decide on the most suitable particles for a certain application and for certain field conditions.
• Optimise nanoparticle delivery based on the understanding of particle-particle, particle-aquifer, and particle-biofilm interactions, and deliver the effective nanoparticle transport parameters for computational modelling. Provide field-relevant information on nanoparticle reactivity and deliver reaction kinetic parameters for computational modelling.
• Provide field relevant information on chemical and size transformations, decomposition, performance, and long-term fate of nanoparticles.
The effectiveness of in-situ groundwater remediation by nanoparticles depends to a great extent on their mobility in the subsurface. Nanoparticle mobility is limited to decimetres or at most a few metres, owing to their aggregation (due to particle-particle interactions) and their deposition onto the surface of the aquifer matrix (due to particle-collector interactions). Nanoparticle aggregation and deposition are influenced by in-situ hydrogeological factors. The interactions between the nanoparticles and the aquifer materials used in within the NanoRem project need to be well understood and quantified in order to promote the use of nanoparticles in remediation. This should include in-situ hydrochemical conditions, such as groundwater composition, ionic strength, and pH also influence particle stability, mobility, and reactivity. Finally, the composition of nanoparticles, their density, size, and surface properties (e.g. surface charge) play a major role in the extent of both mobility and reactivity.
In the case of nano scale zerovalent iron (nZVI), mobility is additionally reduced by magnetic interactions. Modifications of nanoparticle surfaces by surface coating with polymers, polyelectrolytes, or surfactants (see WP2) is an approach to improve mobility of nanoparticles, which might at the same time reduce particle reactivity. Nanoparticle reactivity in natural porous media has rarely been investigated, but is essential for designing field applications. Therefore, reactivity and fate of nanoparticles during their transport through natural saturated porous media has to be evaluated. NanoRem is investigating mobility, reactivity, and long-term fate of nanoparticles in standardised and natural saturated porous media at the bench scale. The outcomes provide:
- Improved understanding of particle-particle and particle-solid matrix interactions related to composition and surface properties of particles produced and optimised within NanoRem, to hydrochemical and hydrogeological conditions, including aquifer surface heterogeneities and potential for their modifications, the latter tested for the first time by NanoRem. This knowledge will enable selection of the most applicable nanoparticles and site protocols for in-situ remediation under given hydrogeological settings.
- Harmonized experimental protocols to facilitate inter-laboratory comparison of transport and reactivity studies and their outcomes, including aquifer material from the selected sites for pilot applications, thus enabling regulators or consultants to decide which particles are the most suitable for a certain application. An experimental protocol has now been developed for mobility, fate and ecotoxicology testing of nanoparticles for in-situ remediation of groundwater. The protocol also provides experimental procedures to investigate and test particle mobility in the presence of the non-aqueous phase liquids and particle reactivity in the contaminant source zone.
- Input parameters for the computational modelling of particle transport and reactivity under near-nature conditions. These parameters will enable modellers (WP7) to validate the models and to design in-situ remediation strategies at pilot sites. This leads to best practice and field-site specific application of nanoparticles for groundwater remediation and reduces the risk of inappropriate use. Characterisation and transport studies have also been performed in column experiments and mobility parameters were determined for the selected nanoparticles (NANOFER 25S, NANOFER STAR, optimised Iron Oxide, Milled Iron, Carbo-Iron® and Biomagnetite). Modifications of nanoparticles were also tested (e.g. inorganic and organic shells). Results indicated that important parameters impacting the mobility of the NPs are: 1) porosity of the porous media, 2) type and concentration of the stabilizer (e.g. carboxymethyl cellulose for Carbo-Iron® NPs), 3) injection flow rate, 4) particle characteristics, and 5) particle concentration. Optimised particles developed by NanoRem have resulted in a significant improvements, for example optimised iron oxide particles had improved stability and mobility; biomagnetite mobility was indicated to be significantly increased in the presence of stabilisers such as starch.
- Information on transformation, decomposition, and long-term fate of nanoparticles in saturated porous media under well-defined and near-natural conditions. This information will assist decision making and dissemination processes (WP9). The reactivity and the long term behaviour of milled nZVI particles, Carbo-Iron® and NANOFER 25S has been tested in the presence of PCE phase as a DNAPL according to experimental protocols. The three materials exhibited different reactivity: NANOFER 25S was most effective at degrading PCE but was also subject to highest corrosion; Carbo-Iron® resulted in complete removal of PCE; Milled Iron was least reactive in terms of PCE degradation and but exhibited less corrosion than NANOFER 25S. Combinations of milled nZVI with Al or Mg particles resulted in an increase in reactivity. Composite materials (metal alloy) containing nZVI and Al or Mg are currently being tested for reactivity and mobility. The preliminary results of ongoing work on interactions between bacteria and nZVI indicated an increase in the oxidation of NANOFER 25S in the presence of certain bacteria.