ENHANCING BIOREMEDIATION OF TCE-CONTAMINATED GROUNDWATER AT THE BEAVERDAM ROAD LANDFILL

Abstract

Trichloroethene (TCE) is one of the most frequently found groundwater contaminants, thus remediating TCE-contaminated groundwater bodies is crucial in providing safe drinking water to people around the world. However, due to the resistance of its intermediates to degradation and their toxicity, TCE bioremediation is still challenging. Years after the installation of a permeable reactive barrier (PRB), the levels of toxic TCE dechlorination intermediates had increased downgradient from the PRB, indicating the need for actions to prevent the contaminated water from reaching a stream nearby. A review of the reports and monitoring results showed that low groundwater residence time and low pH levels were contributing to the inefficiency of the PRB. A trench was purposed to be installed upgradient from this PRB to increase the groundwater contact time with the microorganisms and organic carbon content of the soil using wastewater biosolids, limestone, and biochar to increase the buffer capacity of the soil and the sorption of TCE to the soil. Bench-scale studies were conducted with biosolids and limestone to observe the effect of the biosolids microbial population on a TCE-dechlorinating mixed microbial community. Both dechlorinating bacteria and methanogens use hydrogen in their metabolism and potentially can compete with each other. While biosolids-limestone reactors produced significantly higher concentrations of methane, the activity of methane-producing microorganisms did not adversely affect TCE dechlorination. Furthermore, the characterization of the microbial community of the reactors indicated the positive effect of biosolids. Based on the results from this study, the trench was installed in January 2020 at the site. The sampling and monitoring results nine months after its installation indicated that the trench filling material had positively affected the soil microbial community and decreased the TCE levels downgradient from the trench. To further characterize the microbial community of the site, passive samplers using biochar were installed upgradient and inside the PRB to compare the activity of the dechlorinating bacteria. It was shown that the PRB microbial population was capable of complete dechlorination of TCE, while dechlorinating bacteria detected in the upgradient samples were not active, resulting in the different TCE concentrations observed in these locations. Overall, the study showed that biosolids can be used as an amendment in the TCE bioremediation purposes. Future work should focus on further monitoring the effect of the treatments, applied in this site.