Dechlorination of chlorinated hydrocarbons by zero-valent iron nano-particles

Nano-particle zero-valent iron has been used for several years by Golder Associates in the United States to reduce chlorinated hydrocarbons. Its first application (in the form of a pilot test) in Europe was successfully performed at a large industrial facility in the Czech Republic. The test site, located on alluvial terraces of the Elbe River, is among the oldest chemical production facilities in Europe, where a large array of chemicals (from fertilizers and detergents to chlorinated solvents) was manufactured over several decades. Lack of awareness regarding environmental protection and continuous neglect have resulted in the release to the sub-surface of significant quantities of chlorinated solvents, now present both as free product and in the dissolved phase in the aquifer underlying the site, and presently endangering the water quality of the Elbe River. Groundwater chemistry has been changed by this human activity, and is characterised by the presence of about 8mg/l chlorinated solvents and up to 500mg/l sulphates. Preliminary tests involved spike and bench tests as a means to calibrate the field test. Several concentrations of iron were experimented with during preliminary tests. The pilot test consisted of the injection of iron nano-particles into one well, and the monitoring of hydraulic and chemical parameters over several months, both in the injection well and in two monitoring wells located up- and down-gradient of the injection site. The test results showed a rapid decrease in solvent concentrations in the first week after injection, and concentrations remained low thereafter. Iron particles were detected in the down-gradient monitoring well, proving that they can move with groundwater, thus enhancing their spatial effectiveness.