Assessment of remediation strategies for recalcitrant pollutants
Chlorinated aliphatic and aromatic hydrocarbons are major pollutants resulting from their widespread use. In this project, one contaminant from each major group, namely trichloroethene and benzene, were studied in a shallow and deep aquifer, respectively. The shallow aquifer contaminated with trichloroethene and other chlorinated aliphatic hydrocarbons was too toxic for microbial processes. Several remediation technologies were investigated in laboratory studies, which were sparging, charcoal adsorption and the injection of chemical oxidants (Fenton's reagent and potassium permanganate). Each of these technologies on its own was found not to be suitable for the present site. The deep anaerobic aquifer contaminated with benzene was considered for enhanced natural attenuation. Despite the lack of constraints for anaerobic benzene degraders, no clear evidence for their presence was found. This was partly explained by a small biomass and aquifer variation as benzene was degraded under field conditions at low rates. The low degradation rates could not be observed in laboratory experiments so that an aerobic enhancement option in the form of hydrogen peroxide and/or nitrate injection was further investigated. Only the addition of hydrogen peroxide was demonstrated to be successful in reducing benzene concentrations. A direct transfer of the treatment to the field was considered unlikely due to the highly reducing in situ conditions. It was concluded that (enhanced) natural attenuation was unviable for both sites. Alternative remediation technologies considered at the respective sites were also found unsuitable based on laboratory results and aquifer properties. The luminescence-based bacterial biosensors provided a valuable tool for the evaluation of contaminant toxicity/bioavailability and the suitability of possible remediation strategies.