Field application of hydrogenotrophic denitrification with two-stage injection of electrolytic hydrogen

Long-term continuous treatments of actual nitrate-contaminated groundwater were conducted using a pilot-scale reactor incorporating autotrophic denitrification with electrolytic hydrogen injected in two stages. We modified the hydrogen delivery scheme of a lab-scale reactor and evaluated the feasibility of the proposed reactor. Without adding any nutrients, denitrification and hydrogen utilization efficiencies were observed in the ranges of 21.8–81.6% and 29.5–89.4%, respectively, depending on the applied electric currents and cover materials of the reactor. Except for a condition without electric current, effluent groundwater met the drinking water standards for all nitrogen species, turbidity, chromaticity, and total organic carbon. For a given cover material, the adjustment of applied current was the only requirement for the process control and the reactor never experienced clogging during the operation. The mathematical model with the incorporation of the effect of cover materials fitted the experimental data satisfactorily, responded well to changes in operational conditions, and demonstrated long-term stable treatments. Further improvement could be achieved by preventing the dissolution of oxygen from the atmosphere as well as the dissipation of hydrogen to the atmosphere.