Peter J. M. Middeldorp

Anaerobic microbial reductive dehalogenation of chlorinated ethenes

The current knowledge on microbial reductive dechlorination of chlorinated ethenes (CEs) and its application are discussed. Physiological studies on CEs dechlorinating microorganisms indicate that a distinction can be made between cometabolic dechlorination and halorespiration. Whereas cometabolic dechlorination is a coincidental and nonspecific side reaction, catalyzed by several methanogenic and acetogenic bacteria, halorespiration is a specific enzymatic reaction from which metabolic energy can be gained. In contrast to the well-studied biological dechlorination of PCE to cis-DCE, little is known about the biology of the further dechlorination from cis-DCE to ethene. Bacteria performing the latter reaction have not yet been isolated. Microbial reductive dechlorination can be applied to the in situ bioremediation of CEs contaminated sites. From laboratory and field studies, it has become clear that the dechlorination of tetrachloroethene (PCE) to cis-clichloroethene (cis-DCE) occurs rapidly and can be s...

Stimulation of reductive dechlorination for in situ bioremediation of a soil contaminated with chlorinated ethenes

A soil from a former chemical redistribution company, contaminated with mainly chlorinated aliphatics, was studied for bioremediation purposes. Groundwater analyses revealed that the original pollutants, i.e. tetrachloroethene (PCE) and trichloroethene (TCE), were present at levels ranging from 2.3 to 122 mg/L. Dichloroethene (DCE), vinylchloride (VC), ethene and ethane were also detected at significant concentrations although they had never been introduced to the soil. Relatively high concentrations of cis -DCE as compared to trans -DCE and 1,1-DCE indicated that a slow in situ biodegradation had taken place by reductive dechlorination. Laboratory experiments with flow-through soil columns were performed to determine the optimal conditions for the enhancement of reductive dechlorination by the indigenous dechlorinating population. The addition of single electron donors to artificial groundwater resulted in the dechlorination of PCE to TCE and cis -DCE, whereas complete dechlorination to ethene was solely achieved with compost extract added to native groundwater.

Reductive dechlorination of hexachlorocyclohexane (HCH) isomers in soil under anaerobic conditions

The biological anaerobic reductive dechlorination of β-hexachlorocyclohexane under methanogenic conditions was tested in a number of contaminated soil samples from two locations in the Netherlands. Soils from a heavily polluted location showed rapid dechlorination of β-hexachlorocyclohexane to benzene and chlorobenzene with lactate as electron donor. Soils from an adjacent slightly polluted location did not show substantial dechlorination of β-hexachlorocyclohexane within 4months. A heavily polluted sample was selected to optimise the dechlorination. All tested hexachlorocyclohexane isomers (α-, β-, γ-, and δ-), either added separately or simultaneously, were dechlorinated in this soil sample. The most rapid dechlorination was observed at a temperature of 30°C. Dechlorination of β -hexachlorocyclohexane was observed with acetate, propionate, lactate, methanol, H2, yeast extract and landfill leachate as electron donors. In a soil percolation column, packed with a selected heavily polluted soil sample, the presence of 10mM sulphate in the influent led to simultaneous dechlorination of β-hexachlorocyclohexane and sulphate reduction. When the column was fed with 10mM nitrate instead of sulphate, dechlorination ceased immediately. After omitting nitrate from the influent, dechlorination activity recovered in about 1month. Also in a separate column, the addition of nitrate from the start of the experiment did not result in dechlorination of β-HCH. The significance of these experiments for in situ bioremediation of polluted soils is discussed.