The presence of high concentrations of nitrates (NO3-) in groundwater is a worldwide concern. In some geographical areas like Catalonia, nitrates exceeds the healthy standards for drinking-water consumption (above 50 mgNO3-·L-1 (11.29 mgN·L-1)) recommended by the World Health Organization (WHO). Technologies currently available in the market (reverse osmosis, reverse electrodialysis and ion exchange) allow reducing the nitrate content below the standard for drinking-water, but their high energy demand and environmental impact (nitrate is separated and concentrated in waste brine of difficult disposal) limits their usage. For this reason, new technologies need to be investigated in order to reach a nitrate treatment at an affordable economic and environmental cost.
The thesis entitled “Bioremediation of nitrate-polluted groundwater using bioelectrochemical systems” by Narcís Pous Rodríguez is focused on the application of bioelectrochemical systems (BES) to the treatment of nitrate-polluted groundwater. Bioelectrochemical systems are based on using microorganisms able to carry out oxidation/reduction processes by delivering/obtaining electrons from an electrode. Narcís Pous investigated the use of microorganisms able to use the electrode as an electron donot (biocathode) to reduce nitrates into dinitrogen gas (inert). Thus, his research was focused on optimizing BES for treating nitrate-polluted groundwater. As a result, a process was developed and patented by LEQUIA research group, in which BES are able to treat nitrates at high denitrification rates (up to 700 gN·m-3NCC·d-1), with a competitive energy demand (0.68·10-2 – 1.27·10-2 kWh·gN-1treated), without sludge generation and without requirement of chemicals. Moreover, the microorganisms were electrochemically characterized, and the key subcommunities of the process were elucidated.
In summary, this thesis – that was supervised by Dr Sebastià Puig Broch, Dr Maria Dolors Balaguer Condom and Dr Jesús Colprim Galceran – demonstrates that bioelectrochemical systems have the potential of becoming a competitive alternative for the treatment of nitrate-polluted groundwater.