Co-reduction of nitrate and perchlorate in a pressurized hydrogenotrophic reactor with complete H₂ utilization

A novel pressurized hydrogenotrophic reactor operating at high rates was recently developed specifically for the removal of nitrate (NO₃⁻) from drinking water. The reactor is characterized by safe and economical operation since hydrogen (H₂) purging intrinsic to conventional H₂-based denitrifying systems is not required and H₂ loss occurs only through the effluent, resulting in H₂ utilization efficiency above 90%. In this research, a new treatment scheme to remove NO₃⁻ and perchlorate (ClO₄⁻) combining the pressurized reactor with a following open-to-atmosphere polishing unit is presented. In the pressurized reactor, NO₃⁻ and ClO₄⁻ are simultaneously removed. In the polishing unit, the residual dissolved H₂ from the pressurized reactor serves to further reduce ClO₄⁻ to trace concentrations below recommended levels. First, ClO₄⁻ reduction together with denitrification was demonstrated in the pressurized reactor without special inoculation and a maximal ClO₄⁻ volumetric removal rate of 1.83 g/(L_reactor·d) was achieved. Microbial population analyses before and after the addition of ClO₄⁻ were similar with a large fraction of the genus Dechloromonas. Results show that the combined treatment scheme consisting of the pressurized reactor and the polishing unit allowed for the reduction of ClO₄⁻ concentration down to a minimal value of 2 µg/L with a simultaneous increase of the H₂ utilization efficiency from 95% up to almost 100%.