MODELING OF UASB REACTOR USING BIOFILM THEORY

Abstract

Anaerobic treatment is widely used around the world as a biological stage in both domestic and industrial wastewater-treatment plants. The two principal advantages of anaerobic treatment over aerobic treatment are the production of biogas, which can be used as fuel, and the lower rate of biomass production, which results in lower maintenance costs for the plant. In the last few decades, the Upflow Anaerobic Sludge Blanket (UASB) reactor has been recognized as an efficient anaerobic wastewater treatment system with considerable amount of energy recovery. Though it was invented in early seventies, yet it is still sized based on empirical designs. There is practically no method available to predict the reactor performance except resorting to studies on laboratory, pilot or full scale plants. A model has been proposed for the performance evaluation of UASB reactor using biofilm theory in this study. The developed model is based on mass balances for the substrate and biomass in the reactor, and substrate transport 'and utilization kinetics. The substrate has been assumed to diffuse into the biofilm via Fick's law. Its degradation is described by a Monod type equation. The kinetic coefficients and diffusion coefficients for anaerobic biofilm collected from literature have been used as constant input parameters to the model. The model developed predicts the effluent concentration of substrate from the reactor, considering reactor operating characteristics and hence calculates the treatment efficiency. The model was solved using MATLAB software. It has been validated with the experimental data of UASB reactor treating domestic sewage reported by Uemura and Harada, (2000). The results show that the extremities of the percentage error between the observed and the predicted efficiencies of the reactor were -6.6 % and 6.3 %. The average and standard deviations of the % error were found to be 1.116 and 3.226 respectively. Thus, it has been concluded that the biofilm model -predictability is good in the. estimation of the performance of UASB reactors.