Cathodic groundwater denitrification with a bioelectrochemical system

Nitrate-contaminated groundwater has become a common issue during the last decades, due to the increased levels of detected contamination, the related potential health hazards caused by this contaminant presence in drinking water, and the applicable regulations on water supply quality. In this work, the design, start-up and operation of a bioelectrochemically-based system (BES) for groundwater autotrophic denitrification is described, with the aim to investigate its removal capacity in terms of nitrogen forms. The dual-chamber BES reactor was operated for 27 days, reaching stabile nitrate reduction in its cathodic chamber. Initially, an acetate oxidizing biofilm was grown in the anode chamber in step-feeding operation mode, at a fixed potential of +0.397 V vs. Standard Hydrogen Electrode (SHE). After a 3-day-long inoculation time, and 7 days operation as a microbial fuel cell (MFC), the anode and cathode electrodes were functionally inverted, originating a newly configurated BES process. The biologically active electrode was then fed with nitrate-enriched solution (NO3- concentration = 100 mg L-1), functioning as a biocathode with fixed negative potential of -0.303 V vs. SHE. Results show that the successfully-induced switch in bacterial metabolism lead to consistent nitrate removal by the BES system with efficiency exceeding 90%. Determination of energy consumption by the process show that these are significantly lower than electrodialysis and other similar reported systems.