In situ bioremediation of 1,2-dichloroethane under anaerobic conditions MARK DYER 1 , ERWIN VAN HEININGEN 2 and JAN GERRITSE 2 1 University of Durham 2 TNO Netherlands Institute of Environmental Biotechnology (Received 17 February 2000; accepted 9 October 2000) Abstract. Historic spillages of chlorinated hydrocarbons at a vinyl chloride plant in the Rotterdam^Botlek area in The Netherlands has lead to deep-seated pollution of the underlying aquifer. The principal pollutant is 1,2-dichloroethane (1,2-DCA). As a temporary measure, the contamination is being contained using a pump and treat system. In the long term, in-situ bioremediation has been proposed using a biologically active zone where pollutants would be dechlorinated by microorganisms that simultaneously degrade other carbon sources. In order to investigate the suitability of this new technology, a programme of laboratory tests was carried out. The laboratory programme involved a series of anaerobic soil column tests, where the selection and delivery of different carbon substrates that stimulated1,2-DCA dechlorination were investigated.The soil columns were prepared using soil and groundwater samples from boreholes. Groundwater was £ushed through the columns under anaerobic conditions. A comparison was made between the transformation of 1,2-DCA without a carbon substrate and in the presence of sugars (molasses) and alcohol (methanol) respectively. In addition, different modes of delivery were investigated. In the case of molasses, the material was injected into the column as a plug to simulate grout injection in the ¢eld, whereas methanol was delivered as a constant £ow dissolved in the in£uent. Both carbon substrates resulted in the biotransformation of1,2-DCA. However, fermentation of molasses produced secondary effects that led to a drop in pH and an excessive production of carbon dioxide, which temporarily blocked the £ow of groundwater. Key words: bioremediation, carbon substrate, 1,2-dichloroethane, methanol, molasses, soil columns. 1. Introduction Soils and shallow sediments contain a large variety of microorganisms, ranging from simple prokaryotic bacteria and cyanobacteria to the more complex eukaryotic algae, fungi and protozoa (Brady and Weil, 1999; Madigan et al., 1997). Over the past two decades numerous laboratory and ¢eld studies have shown that micro- organisms can degrade a variety of organic compounds in the subsurface environment, including components of hydrocarbon fuel, chlorinated ethanes and ethanes (Weidemeier et al., 1996; Chapelle, 1993; Bouwer, 1994; Bosma et al., 1998). Although the signi¢cance of indigenous bacteria is recognised for the treat- ment of contaminated land, the study of microbial ecology and physiology below the rhizosphere is still in its infancy. Likewise the use of indigenous microorganisms Geotechnical and Geological Engineering 18: 313^334, 2000. 313 # 2000 Kluwer Academic Publishers. Printed in the Netherlands.