High-rate hydrogenotrophic denitrification in a pressurized reactor

Abstract

Most conventional hydrogenotrophic denitrification reactors based on packed- or fluidized-bed present a similar H2 delivery scheme of continuous gas purging to the atmosphere in order to improve H2 transfer rates and enable discharge of N2 gas produced during denitrification. This operation results in a significant release of H2 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 N2 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 N2 gas is carried out by the effluent in dissolved form. Therefore, no gas purging is required and H2 loss is limited only to the dissolved H2 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 1mgNO3−-N/L. Average denitrification rates of 2.1±0.2 and 1.06±0.06gNO3−-N/(Lreactord) with H2 utilization efficiencies of 92.8% and 96.9% were measured for the two effluent concentrations, respectively. Higher denitrification rates of up to 5gNO3−-N/(Lreactord) were observed at higher recirculation flow rates and higher partial pressures of H2.