Kinetics, Mass Transfer and Hydrodynamics in a Packed Bed Aerobic Reactor Fed with Anaerobically Treated Domestic Sewage

Abstract

This study presents an assessment of the kinetic, mass transfer and hydrodynamic parameters of a pilot-scale fixed bed reactor containing immobilized biomass in polyurethane matrices and fed with the effluent of a horizontal-flow fixed bed anaerobic reactor, which was used to treat domestic sewage. It was found that the liquid-solid and intra-particle mass transfer resistances significantly affected the overall oxygen consumption rate and that mechanical agitation could minimize such resistances. The volumetric oxygen transfer coefficient (kLa) values for superficial air velocities between 8.4 cm min&minus1 and 57.0 cm min&minus1 varied from 20.8 h&minus1 to 58.8 h&minus1 for tap water, and 16.8 h&minus1 to 53.0 h&minus1 for the anaerobic pre-treated effluent. The intrinsic oxygen uptake rate was estimated to be 19.9 mgO2 gVSS&minus1 h&minus1. A first-order kinetic model with residual concentration was considered to adequately represent the COD removal rate, whereas nitrogen conversion was considered to be well represented by a model of pseudo-first-order reaction in series. It was also found that the ammonium conversion to nitrite was the limiting step of the overall nitrogen conversion rate. The hydrodynamic behavior of the reactor was represented by three to four completely mixed reactors in series.