The first nanoremediation pilot-test in Brazil: site selection criteria and nZVI mobility studies

More than two billion people rely on groundwater as their primary water source. Groundwater contamination is a major global problem which can cause significant health issues for communities relying on it. We present the results of the first phase of a collaborative multi-disciplinary and multi-country research project, that aims to perform the first pilot-scale nano-based groundwater remediation (nanoremediation) project in Brazil. Our work is focused on the state of Sao Paulo which has significant groundwater problems due to industrial activities and population growth[1]. Since 2002, the state environmental agency publishes a registry of contaminated areas, annually, to inform the public of the actions carried in those areas[2]. The registry provides a summary of the data from consulting companies reports acquired during site management phases, portraying the site conditions updated at the end of each year for thousands of contaminated areas.

The target of this work is to prepare for and carry out subsurface injections of nanoscale zero valent iron particles (nZVI) within a selected aquifer known to be contaminated with chlorinated solvents, which are among the most persistence groundwater contaminants[3]. To achieve this, we studied 10 major contaminated sites in the State of Sao Paulo. We have used the databases published by the environmental agency to select these areas to consider for this pilot study. A set of criteria was developed based on previous successful pilot/field applications of nZVI remediation to assist with the selection of the site most suitable for using nanoremediation technology, through performing a mapping exercise.

The key criteria considered were: (i) quality of the existing site description, as more robust conceptual site models will result in design of more effective nanoremediation processes; (ii) availability of previous tracer tests to aid defining the hydraulic connections between the injection and the monitoring wells; (iii) type of contamination and concentration levels; (iv) total volume of the contamination; and (v) water salinity, as nanoremediation can be applied where water salinity is in the order of ppm (or mg/L), however, if it reaches thousands of ppm (or g/L), the technology becomes limited as both the life span of the nanoparticles and the particle mobility will be reduced.

The two selected sites are different considering: (i) the amount, type, and distribution of contamination currently present at each site, and (ii) the available data and equipment, given previous remediation activities/studies carried out at each site. The following step was investigating the mobility of nZVI in each site using the MNMs software[4]. Based on site-specific hydrogeological information, the nZVI injection through a screened well (radial geometry) is simulated in each site to estimate the expected radius of influence and final particle distribution within the aquifer. A sensitivity analysis is then performed to determine the best set of operating parameters (e.g. injection flowrate, well size and screened length, particle concentration) to be applied for an effective iron delivery. The comparison of the results in terms of expected particle mobility will allow to finally choose the optimal site for this pilot-scale nanoremediation application.