High-rate hydrogenotrophic denitrification in a pressurized reactor

Abstract Most conventional hydrogenotrophic denitrification reactors based on packed- or fluidized-bed present a similar H 2 delivery scheme of continuous gas purging to the atmosphere in order to improve H 2 transfer rates and enable discharge of N 2 gas produced during denitrification. This operation results in a significant release of H 2 gas to atmosphere with its related economic and safety concerns. The current research proposes a novel pressurized high-rate hydrogenotrophic reactor for denitrification without gas purging. The investigation performed refutes a prevalent notion that N 2 gas accumulates in the headspace of a closed reactor during denitrification. Instead, this research shows that during continuous operation a gas–liquid equilibrium is established in the reactor according to Henry’s law and excess N 2 gas is carried out by the effluent in dissolved form. Therefore, no gas purging is required and H 2 loss is limited only to the dissolved H 2 in the effluent. As a consequence, a simple low-cost and high-rate reactor with closed headspace can be designed for denitrification. The proposed reactor is operated as a trickling filter where water is recirculated over biofilm carriers with high surface area. The feasibility of the proposed reactor was shown for two effluent concentrations of 10 and 1 mg NO 3 − -N/L. Average denitrification rates of 2.1 ± 0.2 and 1.06 ± 0.06 g NO 3 − -N/(L reactor  d) with H 2 utilization efficiencies of 92.8% and 96.9% were measured for the two effluent concentrations, respectively. Higher denitrification rates of up to 5 g NO 3 − -N/(L reactor  d) were observed at higher recirculation flow rates and higher partial pressures of H 2 .