Develop high-efficiency dechlorination consortia and optimize the bioaugmentation strategy of bioremediation in chlorinated contamination: pilot study

Organic halide compounds such as trichloroethyene are refractory pollutants, which often pollute the groundwater in our country and are difficult to remediate. The decommissioning rate of polluted sites is less than 20%. At present, the biggest bottleneck encountered in remediation is that operators often use chemical agents for biological remediation. Remediation eventually leads to the accumulation of vinyl chloride, which is more toxic and carcinogenic. This factor often makes the remediation of a site fail. Through cooperation with the industry in the past, our team has collected groundwater contaminated by chlorinated organic compounds throughout Taiwan, and further cultivated Taiwan's native dechlorination bacteria. Using our unique Dehalococcoides culture platform, we have successfully found several consortia. These consortia can quickly and less produce secondary pollution such as vinyl chloride, to develop innovative novel bioaugmentation strategies. In the first year of this project, through the laboratory of the anaerobic dechlorination bacteria database established by the on-site model field, we will develop the dechlorination consortia used in the field. We will use the fermentation tank in this project to develop. The production process enables the consortia to reach the standard that can be applied to on-site remediation, and at the same time establishes the degradation efficiency of the dechlorination bacteria agent. In the second year of this project, we continued to monitor the degradation of pollutants and reinforced injection wells with low Dehalococcoides counts by performing gravity injections. After these gravity injections, pollutants were successfully degraded to levels below the monitoring standards. Although a temporary rebound of pollutants occurred during the process, they were effectively degraded again when Dehalococcoides counts were sufficient, indicating that the activity of the bacterial strains could be sustained for up to a year. Ongoing monitoring of groundwater microbial communities revealed that the injected bacterial strains altered the local microbiota, but after the pollutants were completely degraded, the local microbial community gradually returned to its original state. This demonstrates the feasibility and environmental friendliness of using native Dehalococcoides combined with the DPI injection method. Ultimately, this method successfully degraded the target pollutant, 1,1-dichloroethylene, with a degradation rate of 96%, leading to the successful delisting of the Wanbao site. This innovative dechlorination bioaugmentation method provides a new approach to enhance the remediation of chlorethenes pollution in Taiwan.