In situ chemical reduction of chlorinated organic compounds from lindane production wastes by zero valent iron microparticles

In situ chemical reduction using commercial zero valent iron microparticles (ZVIm) resulted to be an efficient technique for the removal of recalcitrant and toxic chlorinated organic compounds (COCs) dissolved in groundwater. Groundwater was obtained from Bailin's landfill (Sabinanigo, Spain), where liquid and solid wastes of an old lindane factory were uncontrollably dumped during decades. 28 COCs were identified and quantified by gas chromatographic analysis: five isomers of hexachlorocyclohexane (alpha, beta, epsilon, gamma, delta-HCH), benzene, 10 chlorobenzenes and 12 cyclic non-aromatic organochlorine compounds (Sigma COCs= 93 mg L-1). Batch-wise and column experiments were carried out using soil and groundwater from the polluted landfill. It was found that the dechlorination rate increases with the chlorine content of the organic molecule. Non-aromatic COCs with high chlorine content (from 5 to 7 atoms), as well as HCHs, were very rapidly eliminated in the presence of ZVIm via dechloroelimination, while conversions from 60% to 80% were obtained for chlorobenzenes at the end of the treatment, the last ones, dechlorinated via hydrogenolysis. It has been proved that ZVIm appears as an efficient, stable and cost-effective treatment for COCs reduction and the results obtained in the laboratory can be used at full scale. Therefore it was concluded that ZVIm can be used for the on site treatment of the pumped groundwater and also, for the in situ treatment ( as permeable reactive barriers (PRBs)) of the groundwater, leading to the complete degradation of the most toxic COCs, those with higher chlorine content, less aromaticity and lower vapor pressure.