Hydrogeological investigations in preparation of an in situ bioremediation strategy based on a novel bacterial desulfitobacterium dichloroeliminans strain DCAl

Abstract

Understanding the wide variety of aquifer physical, chemical and microbiological processes is necessary for the effective implementation of in situ bioaugmentation strategies. Therefore, a numerical density dependent 3D solute transport model MOCDENS3D was developed in combination with field experiments to characterise the subsurface control parameters. This also allowed for the study of the effect of aquifer heterogeneity upon the fate and transport of the reactive solutes and the injected bacterial strain.

 These investigations were conducted during the evaluation of an in situ bioremediation strategy intended for the cleanup of a test site. The site lies within a historically 1,2- dichloroethane (l ,2-DCA) contaminated sandy phreatic aquifer in Tessenderlo (Belgium). The halogenated compound has a putative carcinogenic effect and a high recalcitrance towards reductive dechlorination. The isolation of the novel anaerobic Desulfitobacterium dichloroeliminans strain DCAI from the soil matrix of the Tessenderlo site at LabMET (Ghent University, Belgium) offered perspectives for the execution of a bioaugmentation strategy at this site, since this strain selectively degrades 1,2-DCA to ethene under anaerobic conditions without the production of toxic vinyl chloride.

 First, a step-drawdown pumping test followed by a forced gradient multiple-well tracer test was conducted to obtain values for the hydrogeological parameters such as hydraulic conductivity, longitudinal and transverse dispersivity and effective porosity. The solute transport model was used as a predictive field-scale modelling tool in aid of designing the preliminary field tests as well as the bacterial injection. The aim of the latter was the assessment of the transport of the augmented strain DCAI. Prior modelling of these experiments provides an insight in the possible design strategies and hence, it can be concluded that profound preliminary field investigation aided by a solute transport model such as MOCDENS3D, results in a more time- and cost-effective execution of large scale cleanup processes of contaminated sites.