Kinetic model of autotrophic denitrification in sulphur packed-bed reactors

Autotrophic denitrification of synthetic wastewater by Thiobacillus denitri ficans in upflow sulphur packed-bed reactors was studied in order to establ ish the process kinetics for prediction of effluent concentration. Elementa l sulphur particles of different size served as energy substrate as well as the physical support for the microbial biofilm. Experiments were performed under operating conditions of (i) different flow rates at constant influen t nitrate concentration; and (ii) different influent nitrate concentrations at constant flow rate. The experimental results show that autotrophic deni trification rates in upflow sulphur packed-bed reactors can be described by a half-order kinetic model for biofilms. IL was found that the half-order kinetic constants of upflow packed-bed reactors are 2.94-3.60, 1.47-2.04, a nd 1.12-1.29 mg(1/2)/L-1/2 h for sulphur particle sizes of 2.8-5.6, 5.6-11. 2, and 11.2-16 mm, respectively. The half-order kinetic constants could be related to the specific surface area of the reactor media by a simple equat ion, Successful application of the half-order reaction rate model was demon strated for an actual wastewater (nitrified leachate). A comparison with th e literature showed that the half-order reaction rate constants for autotro phic denitrification using elemental sulphur are approximately one order of magnitude lower than those of heterotrophic denitrification. An improved s toichiometric equation for autotrophic denitrification using elemental sulp hur as electronic donor is also proposed. (C) 2001 Elsevier Science Ltd. Al l rights reserved.