Simultaneous bioelectrochemical denitrification and desalination of groundwater with integrated chlorine recovery: Toward drinking water compliance

Groundwater contamination by nitrate and salinity poses serious health concerns, compromising access to safe drinking water. This study overcomes a major limitation of prior electro-bioremediation studies by achieving simultaneous nitrate and salinity removal to satisfy drinking water compliance while co-producing chlorine as an on-site disinfectant. Systematic evaluation of multiple key operating parameters such as current density (j), anode/cathode area ratio (A/C), and anodic hydraulic configuration, on the performance of a three-chamber bioelectrochemical system (BES) identified the conditions that maximize both contaminant removal and chlorine recovery. Under optimal conditions (j = 2.4 A m⁻², A/C = 0.6:1, and batch-operated anode), the system achieved complete nitrate removal and reduced electrical conductivity below drinking water standards, with a low specific energy consumption (SEC_v = 1.42 ± 0.02 kWh m⁻³_{treated water}). Successful validation of the results with real contaminated groundwater confirmed the system’s applicability and robustness, addressing a key gap in previous proof-of-concept studies. Further process intensification based on reduction of the hydraulic retention time (from 7 to 5 h) led to a 44 % increase in nitrate removal rate (from 100.2 ± 1.9 to 144.6 ± 0.5 mgNO₃^–-N L⁻¹ d⁻¹), alongside reduction in SEC_V (from 1.53 ± 0.05 to 1.17 ± 0.04 kWh m⁻³_{treated water}), with only a decrease in chlorine recovery (from 30.7 ± 2.3 to 20.1 ± 2.3 g m⁻³_{treated water}). Microbial community analysis revealed the dominance of Achromobacter in the biocathodic biofilm with both synthetic and real groundwater, highlighting its contribution to cathodic denitrification under different influents. These findings represent a significant advancement toward sustainable groundwater remediation, supporting practical feasibility for cost-effective scale-up and integration with resource recovery.