Electro-bioremediation of nitrate from saline groundwater and concomitant chlorine production

Groundwater pollution and salinization have increased steadily over the years [1, 2], therefore a sustainable approach to the recovery of such important water resource has become essential. A 3-compartment cell configuration was tested for the simultaneous denitrification and desalination of nitrate contaminated saline groundwater. The reactors were initially operated in potentiostatic mode to promote autotrophic denitrification at the biocathode [3], and then switched to galvanostatic mode to improve the desalination of groundwater in the central compartment. The average nitrate removal rate was 39±1 mgNO3--N L-1d-1 and no intermediates (i.e, nitrite and nitrous oxide) were observed in the effluent. Groundwater salinity was considerably reduced (average chloride removal was 63±5%). Within a circular economy approach, part of the removed chloride was recovered in the anode compartment and converted into chlorine. Production rates of 6.1 mgCl2 L-1d 1 were achieved, corresponding to a concentration of 26.8±3.4 mgCl2 L-1. The accumulated chlorine represents a value-added product, which could also be gently dosed for the disinfection of treated water. This proof-of-concept configuration was able to meet WHO and European legislation for drinking water in terms of nitrate, nitrite, and salinity, with low specific power consumptions (0.13±0.01 kWh g 1NO3- Nremoved). These results pave the ground to develop a sustainable technology which tackles an urgent environmental issue.