Bioaugmentation of chlorinated ethene-contaminated groundwater

The development of environmentally friendly, cost-effective, and reliable cleanup technology is a priority to tackle the worldwide contamination by chlorinated ethenes. Bioaugmentation strategy applies exogenous microbial communities to the subsurface (e.g., dense non-aqueous phase liquid (DNAPL) zone or the contaminated plume) to achieve complete chlorinated ethene removal at higher rates. Depending on the geochemical conditions of the contaminated sites (e.g., aerobic/anaerobic) and the dechlorination mechanisms, bioaugmentation of chlorinated ethene-contaminated groundwater could be classified to aerobic metabolic/co-metabolic dechlorination and anaerobic reductive dechlorination. The mechanisms of each bioaugmentation strategy are summarized in Section 6.13.2. Many microbial species have been reported to be able to reductively dechlorinate PCE and TCE to cis-dichloroethene (cis-DCE) or vinyl chloride (VC), while Dehalococcoides is by far the only species that can reductively dechlorinate PCE/TCE all the way to the benign product ethene. The physiology, morphology and ecology of Dehalococcoides-containing microbial are summarized in Section 6.13.3. Various molecular approaches, experimental systems and field analysis methods have been applied to study the microbial ecology, and different biomarkers have been proposed to evaluate the performance of chlorinated ethene-contaminated groundwater bioaugmentation. The molecular methods, experimental systems and field analysis methods to assess the organochlorine respiration performance will be discussed in Section 6.13.4. The factors that affect the bioaugmentation performance, such as electron donor selection, geochemical conditions, as well as the inhibitory factors, will be described in Section 6.13.5. In addition, the methods for predicting the performance of reductive dechlorination (kinetic models and their applications) during bioaugmentation will be described in Section 6.13.6.