HYDRAULIC AND PROCESS MODELLING OF ANAEROBIC BAFFLED REACTORS

Abstract

The successful application of anaerobic technology to the treatment of industrial and domestic wastewaters critically dependent on the development and the use of high rate anaerobic reactors. The Anaerobic Baffled Reactor (ABR) is a compartmentalized reactor to retain solids, thus separating the hydraulic residence time from the solid residence time, resulting in a high rate anaerobic process. This report describes the development of ABR way back from 1980 and its advantages over the other high rate anaerobic bioreactors. An attempt had been made to develop a mathematical model for ABR, in order to predict the reactor performance in terms of COD removal efficiency, flow patterns inside the reactor and the solids content in the sludge blanket of the reactor. A flow model had been developed- to predict the hydraulic behaviour of the reactor and the results of the model were compared with the experimental values. An RTD (Residence Time Distribution) study on the reactor to investigate the mixing patterns and dead space of the reactor and brief procedure of the RTD is presented in the report, and from the results dead space in the reactor, dispersion number of the reactor and theoretical number of the compartments connected in series were computed. A computer program was developed to solve the model equations and mean and variance of the residence time distribution curve. Solids model had been developed to predict the solids content of the reactor. The model considers each ABR compartment as two sections of constant volume, one with high solids concentration and the other with low solids concentration, with gas and liquid flows influencing the material flow between the two sections. Switch functions were used in the model to represent the influent solids to a compartment and effluent solids concentration from the previous compartments. In COD removal model, the Haldane equation was adapted for predicting performance inhibition by undissociated acids as a function of substrate COD and pH. The Monod and adapted Haldane model were solved simultaneously with substrate mass balance for a ABR. The soluble COD removal efficiency and methane productivity were iv predicted as a function of the dilution rate. The predicted results show good agreement with laboratory data.