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Abstract
Due to the extensive use as well as improper storage, handling and disposal practices, toxic chlorinated ethanes are frequently found as subsurface and groundwater contaminants all over the World, including Portugal. Because of their high toxicity, physicochemical properties and impact on living organisms, research of effective remediation techniques of these compounds are required.
In this thesis, bioelectrochemical systems (BES) for the anaerobic reductive dechlorination of chlorinated ethanes are examined as a novel, more sustainable and effective remediation technique.
The main studied parameters include the influence of the set cathode potential and the presence of a redox mediator, either in solution or grafted on the cathode surface, on the chloroethanes’ bioelectrochemical dechlorination rate and efficiency.
The dynamics of microbial communities directly and indirectly involved in the dechlorination process were also tracked during each experiment. The newly developed PNA-FISH biomolecular technique was adapted for the detection and monitoring of two strains of a key dehalorespiring microorganism. Additionally, conductive minerals were tested for their role as conduits for the syntrophic dechlorination of 1,2-dichloroethane (1,2-DCA).
Initial tests provided a set of recommended parameters for process optimization in a simplified BES, while other tests with anthraquinone-2,6-disulfonate (AQDS) addition demonstrated an increase in dechlorination rate, for both AQDS in solution and grafted on the cathode, although at varying degrees. Protocols for AQDS grafting are also reported.
In addition, the use of conductive minerals led to a 3-fold increase in dechlorination rate. It is assumed that the tested mineral is used in interspecies extracellular electron transfer, facilitating catalytic electron transport.
This work demonstrates the potential of bioelectrochemical systems for anaerobic biodegradation of chlorinated ethanes and provides a detailed description of relevant optimized parameters as well as several novel protocols for redox mediator immobilization, biomolecular monitoring tools, etc. These protocols can be applicable to a wide variety of different situations and contaminants.
