Autotrophic Denitrification Of Groundwater In A Granular Sulfur-packed Up-flow Reactor

Abstract

Autotrophic denitrification is an effective treatment technique for nitrate removal from groundwater. Six basic elements are required for the growth of autotrophic denitrifiers: (1) electron donor, (2) electron acceptor, (3) active bacteria, (4) anoxic/anaerobic environment, (5) micronutrients, and (6) optimum pH and temperature. In this research, granular sulfur is an electron donor; nitrate is an electron acceptor; anoxic and anaerobic environment was maintained in the reactor, and micronutrients were added; pH was controlled between 6 and 9, and temperature was maintained at the room temperature (20 + 2 oC). Batch reactor and continuous up-flow reactor experiments were carried out to investigate the denitrification rate, and reaction rate kinetic constants. The observed nitrate removal corresponded to the first order reaction kinetic. The data correlation between alkalinity destruction and nitrate nitrogen reduction was linear with a slope of 3.09 mg-CaCO3 alkalinity destroyed per mg-NO3 N removed. The data correlation between sulfate production and nitrate nitrogen reduction was linear with a slope of 6.91 mg- produced per mg- removed. Based on the biologically mediated half-reaction equations, the overall reaction equations were developed. Based on the experimental data, the energy coefficients and the stoichiometry of autotrophic denitrification were developed. Finally, an analytical model based on conjugate reaction kinetic was utilized. The reaction rate constants k1 and k2 were determined from the experimental data. The model provides an analytical tool to predict the nitrate and nitrite concentrations in the effluent from the up-flow column. An example is presented to illustrate the design procedure of a sulfur-packed up-flow column. In this example a sulfur-packed up-flow column is designed to treat a given flow rate and influent concentration of nitrate nitrogen to achieve a desired degree of treatment.