Assessing the microbial potential for aromatic hydrocarbon degradation in groundwater from the Griftpark, Utrecht and in batch experiments

Abstract

The groundwater and subsoil of the Griftpark in Utrecht (The Netherlands), a former industrial site, is contaminated with aromatic hydrocarbons into great depths. Currently, the contamination is constrained by a bentonite slurry wall around the park and by extracting groundwater, which is thereafter cost-intensive purified. biogeochemical analyses of the field samples of eight monitoring wells in and around the Griftpark revealed that sulfate-reducing conditions were dominating. Only in the bulk of the contamination, located in the northern part of the Griftpark, methanogenesis occurred. In order to reduce the extraction costs, the potential of the microorganisms community to degrade aromatic hydrocarbons under different conditions was investigated. In light of that batch experiments were performed to test eight scenarios by adding either: Oxygen, oxygen + nutrients, chlorate, nitrate, sulfate, ferrihydrite, nothing or mercury chloride (sterile). The batches were prepared with heavily polluted source water (B22) and mixed with relatively clean water from wells downstream of the Griftpark (BW205 and 60). The contamination in the BW205 and 60 batches was almost completely removed within 14 days in all scenarios. A high potential for aerobic degradation of the contamination in the Griftpark was determined. Adding nutrients or chlorate did not improve the removal of aromatic hydrocarbons, but led to toxic concentrations of nitrite in the groundwater. In the batches with alternative electron acceptors, hypoxic conditions were present, presumably delaying the reduction of nitrate, sulfate, chlorate and ferrihydrite, respectively. Consequently, the incubation of the batches should continue with recontaminating the BW205 and 60 batches.