Hexachloro-1,3-butadiene (HCBD) is a toxic aliphatic chlorinated hydrocarbon which is widely used as a fungicide, herbicide and heat transformer fluid. HCBD is resistant to microbial degradation and, therefore, persists in aquatic and soil environments worldwide. In this thesis, the ability of non-specific bacteria from various sources to dechlorinate HCBD in the presence of either acetate or lactate (as an electron donor) and cyanocobalamin (as an electron shuttle) under different conditions was investigated. Cultivating specific populations to reduce cyanocobalamin as a method to increase HCBD dechlorination rate was investigated. Also, the factors responsible for HCBD dechlorination and the stalling of dechlorination were studied. Lastly, redox potential measurement during the microbial reductive dechlorination of HCBD for online detection of ongoing dechlorination was evaluated. Findings from the Project „« Non-specific bacteria from activated sludge, anaerobic digested effluent from municipal waste, piggery waste and sheep rumen content are able to dechlorinate HCBD in the presence of cyanocobalamin to chlorine-free C4 gases in a biochemical reaction. „« Dechlorination was equated to the formation of completely dechlorinated end-products from HCBD dechlorination. „« Methanogens were found to be involved in HCBD dechlorination. „« Mediators rather than specific bacteria were responsible for the fast dechlorination rates. Results suggest that activated sludge may release synthesized mediators into the supernatant to enable enhanced HCBD dechlorination. „« HCBD dechlorination can be monitored using oxidation reduction potential (ORP). ORP has an effect on HCBD dechlorination rate. Scientific Significance/Novelty The most significant finding from this research is that it demonstrates chlorine-free end-products in contrast with other studies in literature (Booker and Pavlosthasis, 2000; Bosma et al., 1994) where dechlorination was equated with disappearance of HCBD into bacterial biomass and the detection of partially dechlorinated gases such as trichlorobutadiene. It also shows that, in contrast to literature where specific bacteria (i.e., pure strains/cultures) were commonly used for the dechlorination of polychlorinated hydrocarbons, results from this thesis show that non-specific bacteria were able to dechlorinate HCBD in the presence of cyanocobalamin at ratesƒx sufficiently high to be considered for bioremediation projects. Moreover, results demonstrate that ORP can be used to monitor HCBD dechlorination.