An apparatus and method for treatment of water borne oxidized contaminants, using hydrogen as an electron donor for denitrification and reduction of other oxidized contaminants. Preliminary results reported here show that a biofilm of autotrophic denitrifiers accumulates rapidly in the wastewater setting, the MBfR can drive NO3− concentrations below 1 mgN/L, and the H2 pressure controls the NO3− flux.