Guar gum improves the stability and the mobility of iron microparticles for groundwater remediation

Contaminated sites managements represents in Europe one of the most serious issues. Recent data of the European Environmental Agency (EEA) shows how soil contamination due to industry, garbage warehousing, mining and hydrocarbons tanks leakage represents one of the most important threats to the environment [1]. The large volume of waste and the intense use of chemicals during past decades have resulted in numerous contaminated sites across Europe. Contaminated sites could pose significant environmental hazards for terrestrial and aquatic ecosystems as they are important sources of pollution which may result in eco toxicological effects [2]. Emissions of hazardous substances from local sources could deteriorate soil and groundwater quality. Soil contamination is mainly located close to waste land-fills, industrial/commercial activities diffusing heavy metals, oil industry, military camps, and nuclear power plants. The objective of relevant EU policies is to achieve a quality of the environment applying successful technologies. To this purpose, in the last decade EU have been financed numbers of international, multi-partner EU projects; among them, the large scale research project AQUAREHAB (FP7 ENV 2008.3.1.1.1.) , coordinated by VITO (Belgium) and involving 19 partners, started in May 2009 and lasted 56 months, until 2013. It aimed at developing innovative rehabilitation technologies for soils, groundwater and surface waters contaminated by a wide range of priority contaminants (nitrates, pesticides, chlorinated compounds, aromatic compound, mixed pollutions, ecc.). These technologies have been developed within 5 operative work packages (WP1-5) and the guidelines and approaches developed have been extrapolated and applied, in WP8, to real polluted sites. The work herein presented is included in the context of WP5 and WP8 of the AQUAREHAB EU project, in which the group of Groundwater Engineering of the Polytechnic University of Turin is involved; its goal is to develop and apply at the real scale an effective and costeffective in-situ rehabilitation technology based on the injection of micro-sized (100 nm-100 µm) zerovalent iron (MZVI) particles directly into a contaminated aquifer in order to create a reactive zone which is able to treat both the plumeand the source of contamination. Injectable MZVI particles are selected because they can overcome the major hindering factors of the widely accepted ZVI based permeable reactive barriers (PRB) (impossibility to treat the source of contamination and considerable excavation costs), due their high reactivity against a wide range of contaminants thanks to their high specific surface area and to lower costs, longer lifetime and easier handling in respect with nano-sized ZVI (NZVI) particles. Nevertheless MZVI particles disperse in water are prone to gravitational instability and, as a consequence, the resulting mobility is limited [3, 4]. To solve this problem, the use of a stabilizing agent able to modify suspending fluid properties is required. In the recent year the use of biopolymer demonstrated to be successful [5, 6] although a full comprehension of interaction mechanisms with the porous media and a complete system characterization is still missing. In this work, in order to meet AQUAREHAB project requirements and to overcome technology limitations, the use of MZVI suspended in a thickening polymer solution of guar gum hydrocolloid is considered.