Nitrate occurrence in groundwater is a worldwide issue, due to the high exploitation of the resource for water supply, and the worldwide diffusion of the contamination. The consumption of nitrate-contaminated drinking water may lead to severe health issues. Several technologies have been applied; in the last 15 years, bioelectrochemical systems (BES) have emerged as an alternative to conventional technologies for water and wastewater treatment. BESs can be defined as electrochemical systems in which microorganisms act as catalysts in the anode and/or cathode reactions. In the thesis, the design, and application of BESs for groundwater denitrification was described, analyzed, and discussed. Firstly, the development of a denitrifying biocathode was described and analyzed: the biocathode was obtained by the reversal of the anode of a Microbial Fuel Cell (MFC), following a procedure described in literature on smaller scale reactors. Then, the obtained CBD (Controlled Biocathodic Denitrification system) was operated under different operational conditions (i.e. hydraulic retention times, nitrate loading rate, nitrate concentration in the influent). The performances of the CBD in terms of denitrification and energy consumption were analyzed and discussed, and the limitations of the systems were identified. To overcome the emerged limitations, a sequential system composed by 2 CBDs connected in series was developed, and operated at decreasing hydraulic retention times. The combined system showed to obtain high nitrate and total nitrogen removal rates, and to decrease its specific energy consumption (in terms of mass of nitrate removed, and volume treated) at the decrease of the hydraulic retention times. Then, the operation of a buried biocathode for in situ groundwater denitrification was described and analyzed. The biocathode was immersed in sand or gravel, to simulate its displacement in a saturated aquifer. The lack or recirculation in the reactor due to the presence of the sand/gravel led to a substantial decrease in the total nitrogen removal rate, with consequent accumulation of intermediate N-forms, and to an increase in the specific energy consumption. The operation of the buried biocathode suggested the necessity of the development of specially-designed BES for in situ applications. The
analysis of the energy consumption of CBD and MFC for groundwater denitrification in ex situ, and in situ configurations was calculated using data from literature and assumptions, and highlighted the fact that, even though the operation of the CBD was more energy expensive compared to the MFC due to the necessary use of a power supply or a potentiostat, the CBD was the only option to achieve satisfactory performance in terms of nitrate and total nitrogen removal rates. In the last chapter of the thesis, the application of BES for the removal of other contaminants (arsenic, cadmium, chromium, perchlorate, and vanadium) from groundwater is reviewed.