Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - METAL-AID (Metal oxide Aided Subsurface Remediation: From Invention to Injection)

Teaser

Thousands of sites across Europe are polluted with toxic metals and organic solvents; many more exist worldwide. As EU population grows, clean water will determine quality of life and economic stability. Most sites remain contaminated because existing technologies are costly...

Summary

Thousands of sites across Europe are polluted with toxic metals and organic solvents; many more exist worldwide. As EU population grows, clean water will determine quality of life and economic stability. Most sites remain contaminated because existing technologies are costly and disruptive. Society needs an innovative way to decontaminate soil and groundwater directly underground. To respond to this challenge, the Metal-Aid network was created with the aim to train 14 Early Stage Researchers (ESRs) for interdisciplinary leadership roles in the EU contamination remediation community through integrated, intersectoral research, using advanced technology, ranging from nanometre to field scale. Specifically, in Metal-Aid, 4 science work packages (WP) have been set up, to investigate all aspects of a new reactant, from initial development in the lab to rigorous testing and its application in the field:
WP1 (4 ESRs) – Developing novel metal oxide reactants
WP2 (4 ESRs) - Reaction kinetics and mobility of novel metal oxide reactants
WP3 (3 ESRs) - Reactivity and long term fate of spent reactants and contaminants
WP4 (3 ESRs) – Field contaminant remediation by novel metal oxide reactants

Work performed

All 14 Metal-Aid ESRs have made excellent progress in their projects in these first 24 months and these are summarised below:
WP1 aims at reactant development, where we focus on 1) redox inactive layered double hydroxides (LDH) and engineer them to have enhanced sorption properties (surface area, hydrophobicity) and 2) on redox active LDHs that contain reduced Fe(II), usually called green rust (GR), to enhance reduction capacity towards a range of pollutants to reduce their mobility and toxicity. Experimental results have shown that the reduction kinetics and mechanisms vary greatly as a function of GR structure and chlorinated solvents. Known GR compounds showed little if any reactivity towards chlorinated ethylenes (PCE, TCE, cis-DCE), while they were effective towards carbon tetrachloride. Moreover, substitution of cations in GR hydroxide layers leads to drastic changes in GR particle properties and greatly affects its reactivity with chlorinated solvents and toxic metals. In terms of the inactive LDHs, we have shown that intercalation of organic anions in the interlayer of Mg,Al-LDH substantially enhances sorption affinity towards chlorinated solvents and they are stable in contaminated groundwater.

In WP2, the reactants developed in WP1 are tested in batch and flow through reactors, to gain deeper understanding of the reaction kinetics and mechanisms controlling interactions between contaminants and reactants. In addition, reactant transport and reactivity is also tested in columns, to derive injection protocols for field scale application. A better understanding of the reaction kinetics and mechanisms has been obtained for refined GR compounds (obtained from WP1) with chlorinated solvents and metals. For example, data has shown that arsenic species have a high sorption affinity towards GR materials and they can be oxidised in this process, depending on GR formation pathways. We are currently testing the stability and reactivity of our refined GR compounds in waters collected from the two contaminated field sites in Denmark. Moreover, kinetic dissolution and precipitation analyses have been performed with other redox active Fe minerals, that form dominantly in reduced Icelandic peats (observed in WP3) for comparison. Lastly, column experiments are in full swing and first results have shown that GR reactivity is substantially lower in porous matrices compared to batch systems, but this is also dependent on column settings, GR types and pollutants.

In WP3, focus is on the reactivity and long term fate of reactants and contaminants after sorption and/or reduction has occurred in the soil and groundwater. Through experimental and modelling work, along with studying natural analogues, this WP aims to determine reactant and contaminant residual reactivity and stability to assess remediation effectiveness over the long term. In this first period, we have assessed the fate and long-term stability of Cr following reduction by GR materials and we have developed new GR particle modifications to further maximise reactivity and long-term stability in the environment. The main Fe minerals that sequester toxic metals in Icelandic peat areas have been identified and these match well with geochemical modelling results of the investigated systems. These Fe minerals are currently being tested in WP2. In terms of modelling, a multiphase fluid flow model in porous and fractured media has been established and amended with the geological and hydrogeological data from the Danish contaminated site to simulate DNAPL dispersion in the subsurface, and evolution of the plume over time. These models are presently combined with particle injection models to simulate the process of contaminant capture through reactant injection.

WP4 is focussed on processes at the field scale, including characterisation of the contaminant site (geology, microbiology, hydrogeology and contaminant plume), development of injection technology, injection of reactants an

Final results

Over this first reporting period, Metal-Aid has already achieved many of its intended impacts, with 14 young scientists being trained to meet the challenges of ensuring clean water for drinking, agriculture and industry, which will be of benefit to European society, the environment, the water industry and other sectors. Metal-Aid outputs also have commercial potential and we are currently working with a refined reactant and new injection techniques that have potential for exploitation. Moreover, Metal-Aid ESRs have been extremely active in public outreach activities, talking to people of all ages and all backgrounds, in schools, at university open days, at companies, and through social media (facebook, twitter, blog sphere). They have presented their results at international conferences and have begun publishing in peer-reviewed journals. In conclusion, the Metal-Aid network is functioning well and set to not only reach but exceed its anticipated objectives.

Website & more info

More info: http://nanogeoscience.dk/metalaid/.