Bioremediation of Tetrachloroethene Contaminated Groundwater by Dechlorinating Microbial Communities

Author: Sayali Surendra Patil

Patil, Sayali Surendra, 2014 Bioremediation of Tetrachloroethene Contaminated Groundwater by Dechlorinating Microbial Communities, Flinders University, School of Biological Sciences

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Improper disposal of chlorinated compounds widely used as industrial solvents, intermediates in chemical industries, pesticides and pharmaceuticals has led to severe subsurface contamination. Common chlorinated compounds include tetrachloroethene or perchloroethylene (PCE), trichloroethene (TCE), dichloroethenes (DCE) and vinyl chloride (VC). Enhanced reductive dechlorination (ERD) represents a promising approach for the complete degradation of these compounds. Successful microbial-mediated remediation has to date been associated with major dechlorinating species such as Dehalococcoides (Dhc), Desulfitobacterium, Desulfuromonas, Dehaloginomonas, Geobacteriaceae and Sulfurospirillum. This research explored the degradation potential of microbial communities other than these well studied groups within groundwater collected from a PCE-contaminated site in Australia. Laboratory based enrichment cultures using groundwater samples with high PCE levels (146 µg/L) showed the dominance of Proteobacteria, Spirochaetes, Firmicutes, Bacteroidetes, Methanomicrobiaceae, Methanosaetaceae and Methanosarcinaceaegroups. The indigenous groundwater community was found capable of the complete dechlorination of PCE to the environmentally safe end product ethene over 24 weeks, with the sequential degradation of PCE via intermediate products. The molecular culture-independent microbial profiling techniques like polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) along with novel statistical Pareto-Lorenz and moving windows analyses were used to assess changes in the indigenous microbial community during PCE removal. A comparison of the effects of using either biostimulation only (BS) with biostimulation plus bioaugmentation (BS-BA) for PCE remediation in a laboratory based system showed that both remediation regimes were successful, with complete PCE degradation occurring over 17 and 21 weeks for BS only and BS-BA, respectively compared to controls which had only 30% PCE degradation. Furthermore, quantitative real time PCR and live-dead cell count (LDCC) analyses showed a 2-3 fold increase in microbial cell abundance with approximately 70-80% viability in both treatments indicating active growth of PCE dechlorinators. We further employed BS, BS-BA and monitored natural attenuation (MNA) strategies for commercial bioremediation at TCE contaminated site in Victoria, Australia. Over the period of nine months of BS, MNA and BS-BA treatments TCE concentration was reduced from 40, 79 and 150 µg/L to below maximum concentration level of 5µg L-1,respectively. Although, this work highlighted ERD as an effective way of PCE remediation, this technology has a few disadvantages. Hence, an alternative microbial electric system (MES) was established where bioenergy was generated through the catalytic actions of microorganisms during PCE dechlorination. Multiple lab-scale MESs fed with acetate and carbon electrode/PCE as electron donors and acceptors, respectively under BS only and BS-BA regimes further highlighted the bio-electrochemical potential of indigenous non-Dhc community against previously well studied Dhc and Geobacteriaceae species. The indigenous non-Dhc community was found to contribute significantly to electron transfer with ~61% of the current generated. Microbial colonization and biostimulation resulted in 100% dechlorination in both treatments with complete dechlorination occurring 4 weeks earlier in BS-BA samples and up to 11.5 µA of current being generated than BS only MES. Overall, this study contributes to better understanding of the dechlorinating potential of indigenous non-Dhc microorganisms; their structure, dynamics and functional organization in response to PCE dechlorination that will assist to advance the bioremediation field in a rational manner. In addition, evidence of advances in the current bioremediation practices in terms of methodology (LDCC) and techniques (MES) are presented.

Keywords: Reductive dechlorination,Chloroethene,Bioremediation,Groundwater,Microbial community

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2014
School: School of Biological Sciences
Supervisor: Associate Professor Ian Menz