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Colloidal Iron Oxide Nanoparticles for the REclamation of Toxic Metal Contaminated GROUNDwater Aquifers, Drinking Water Wells, and River Bank Filtrations

Periodic Reporting for period 1 - REGROUND (Colloidal Iron Oxide Nanoparticles for the REclamation of Toxic Metal Contaminated GROUNDwater Aquifers, Drinking Water Wells, and River Bank Filtrations)

Reporting period: 2015-09-01 to 2017-02-28

The basic concept of our technology is the creation of an adsorptive in situ barrier in order to immobilize toxic metal groundwater contaminations. This barrier is made of iron oxide nanoparticles (NPs), which are injected into sediments as colloidal suspension. After injection, the NPs form stable deposits within the aquifer, like a filter, through which the contaminated groundwater flows. During the passage, the heavy metals are adsorbed and thereby immobilized, cleaning the downstream groundwater (Figure 1). The main objective of Reground is the first field application and near-market replication of this innovation and therefore restoring contaminated groundwater aquifers. To do so, we produce Iron oxide NPs that have high adsorption capacity over long-term exposure times, and then inject these NPs in two contaminated aquifers. We monitor the efficiency of the innovation by measuring contamination levels in groundwater after application. We will then actively commercialize REGROUND via a subsequent Business Plan (BP) and a spin-off company. Thus, we will make the developed technology available to the market. The REGROUND technology, due to its low costs and wide applicability, will be made highly available. This will enable immobilization of toxic metal contaminations at sites which were left untreated so far due to technical or economic reasons.
Reground undertakes four interconnected tasks, named as Particles, Protocols, Field, and Market. Below a brief description of work performed in these tasks is provided.
From beginning of the project, at least 26 different potential NP suspensions have been synthesized, tested, and characterized. These NPs are tested to meet the criteria for a successful application: they should form a stable suspension in liquid, be small enough to pass through the pores in soil, and provide a large surface area to adsorb dissolved heavy metal contaminations. In addition, Reground NPs shall contain no additional toxic elements. Also, we ensure that each NP production process can be performed at industrial-scale and yet meeting the above-mentioned criteria. This up-scaling process is a central focus of Reground technology, because one may produce such NPs with pure, analytical-grade materials in laboratory, but producing several tons of such particles with industrial-grade materials and yet fulfilling the above criteria with low, competitive price is a difficult task. Reground has successfully produced such environmental-friendly particles with industrial-grade materials.
In order to ensure their applicability to each environment, each potential Reground NP suspension is going through a set of laboratory tests. These tests examine the stability, mobility, reactivity, and safety of NPs using materials taken from target aquifers. Briefly, in stability tests, we measure the sedimentation time of NPs in contact with tap water and with groundwater from aquifer. Therefore, one can avoid injection of unstable suspension that may clog the pore space. Mobility tests provide us with profile of NP distribution around the injection point. Therefore, an effective radius of influence (ROI) for each well in barrier is obtained. In reactivity tests, we measure the adsorption of heavy metals to NPs in both batch and column. Therefore, the amount of nanomaterials to be produced and injected to the aquifer according to remediation target is determined. Additionally the effect of Reground NPs on living organisms is tested before application to field. For example, we investigated the ecotoxicity of our NPs to terrestrial and aquatic organisms and found that Reground NPs are of low toxicity in the organisms tested in vivo and in the in vitro assays included in this project
Another key focus on Reground is the first-time application in full field-scale. We tested our technology in two pilot sites in Portugal and Spain. Full field applications are planned in April 2017, plus one application in an overseas site. The Spanish site, with Arsenic as main contaminant, is a sandy aquifer that also contains large stones, which make the structure heterogeneous. Due to higher groundwater velocity, the ROI of the small barrier (pilot test) was not uniform; ca. 4 meter in direction of flow. The Portuguese site is mainly contaminated with Arsenic, Zinc, and Copper. The aquifer is more homogeneous compared to the Spanish one, but it has lower conductivity, which limits the mobility on NPs. A pilot injection was performed in this site too, where, as for the Spanish site, reduction in contaminants were observed in downstream. From pilot tests, we have modified our injection scenarios in order to improve the application of NPs. Well placing has been adjusted in a way that a stable barrier of at least 20 meters wide is built in both sites, without losing NPs with groundwater flow.
Along with application in field, Reground focuses on market implementation of the technology. To this aim, in course of the project we promote Reground using dissemination tools to public boards and other stakeholders. A Life Cycle Assessment (LCA) has been prepared to evaluate the potential environmental impacts and benefits of the technology. The LCA quantifies many indicators such as global warming potential and energy demand. The LCA provides additional material for the promotion of REGROUND, as well as
An important challenge in NP-based technologies for groundwater remediation is the issue of particle mobility. Normally NPs such as nZVI show good mobility in column tests. However, when they are injected into aquifer the resulting ROI is low (sometimes below 1 meter). Thus, many wells are to be drilled to build a reactive barrier. In contrast, Reground NPs showed excellent mobility in both laboratory and field conditions. Indeed, our models predict that the even diluted NPs can travel up to 4 meters in the aquifer. Two pilot test injections confirmed this prediction. Assuming a conservative ROI of 2.5 meters, ca. 6 times less number of wells are required compared to the case where the ROI is 1 meter, which significantly impacts the costs of operation.
Another advantage of Reground is the devising of a set of decision-making protocols for production and application of NPs. Until now, the first drafts of these protocols have been prepared and been calibrated according to the results of pilot tests. These protocols simplify the process to decide what modifications (in NPs and in application scenario) are required based on aquifer properties.
Reground is bringing a novel, green and near-market water eco-innovation into the European markets, and beyond. In order to make this possible, the TRL of our technology will be upgraded in several steps from 4 to 7. As an example, we have started with lab-scale application of NPs and moved to pilot-scale of ca. 20m3 of NP suspension to build a small barrier. The main application with size of ca. 150m3 of NP suspension will fit into TRL 7. Therefore, we have upgraded our laboratory tests to larger scale and demonstrated that it can be applied in relevant environments as a new tool for the immobilization of toxic metal contaminations.