Electro-bioremediation of nitrate contaminated saline groundwater

Sustainable exploitation of coastal aquifers is often hindered by the presence of contaminants and high salinity levels. This study proves for the first time the electro-bioremediation of nitrate contaminated saline groundwater. Two 3-chamber bioelectrochemical systems (BES) were operated in potentiostatic mode for the treatment of a synthetic medium mimicking saline groundwater from the Nitrate Vulnerable Zone of Arborea (Sardinia, Italy). This groundwater is characterised by high nitrate concentrations (>33 mgNO3--N/L) and conductivity (>3.5 mS/cm). The electrochemically active microbial community grown on the surface of the biocathode was able to achieve nitrate removal rates and efficiencies of 6.8±0.4 mg/L·d and 87±2%, respectively. Conductivity significantly decreased (from 4.11±0.2 to 0.17±0.2 mS/cm) by enhancing the electromigration of ions from the middle chamber to the peripheral anodic and bio-cathodic chambers. Under the applied conditions, WHO (World Health Organization) drinking water threshold limits for nitrate (11.3 mgNO3--N/L) and conductivity (2.5 mS/cm) were satisfied. Moreover, high chloride migration was observed (63±7 mg/L·d), suggesting its possible recovery as chlorine in the anodic chamber using a specific electrode (Ti-MMO), within a circular economy-based approach. The results pave the way to the potential development of a new electro-bioremediation technology for water recovery (i.e., simultaneous denitrification and desalination) and sustainable chemicals production (i.e., chlorine).