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

•A two-stage hydrogenotrophic process to remove NO3− and ClO4− is presented.•NO3− is removed in a first unsaturated-flow pressurized reactor stage.•The residual H2 is coupled to ClO4− reduction in a second polishing stage.•Large presence of Dechloromonas was detected before and after ClO4− addition.•Effluent ClO4− concentration of 2 μg/L and ∼100% H2 utilization were achieved.

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/(Lreactor·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%.