A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources & Development

Thesis (M.Eng.) - Asian Institute of Technology, 1994

The use of microbial cells, artificially immobilized inside the porous support matrix in Biological Fluidized Bed Reactors (BFBR) has long been practiced for fermentation processes; only recently, this technique has been applied for wastewater treatment (nitrification etc.). At present, none of the existing models adequately explain the effect of temperature on BFBRs used for nitrification. Temperature dependence of the biological reaction rates is very important in assessing the overall efficiency of the process, since it influences the biological reaction rates, mass-transfer rates and so on. In this study, an integrated approach of describing the effect of temperature on the substrate removal by the biomass, immobilized inside the porous matrix in a BFBR was attempted. Mathematical models, at steady state were developed for four different combinations, considering the distribution (Uniform and Linear) of biomass inside the support matrix and the order (Zero and First) of biological reaction rates. Steady state biofilm and a single rate limiting substrate were assumed. The developed models were tested with the reported data obtained from a lab-scale BFBR for various temperatures. It was found that the effluent water quality predicted by the models using first order rate kinetics fitted well with the observed data, showing positive correlation of 0.8891and0.8940 for Uniform and Linear first models respectively. Among them Linear-First model predicts better. The predicted removal efficiencies at various temperatures by these models were compared with those in suspended growth, activated sludge process, computed under similar environmental conditions using existing models/ process equations. It was found that the rate of nitrification or the effluent quality was less affected by the temperature change in immobilized process (BFBR) than in suspended growth, activated sludge process. It was also found that the external resistance to diffusion by the stagnant liquid layer is not significant in BFBR.