Modelling of a falling sludge bed reactor using Aquasim

ABSTRACT – The Falling Sludge Bed Reactor is a novel bioreactor design that allows for increased biomass retention due to sludge settling and recycle. A mathematical model was developed to simulate the bioreactions taking place in the bioreactor being fed a mixture of primary settled sewage sludge and neutralised acid mine drainage. The aim of the bioreactor was to hydrolyse the particulate organic matter from the primary settled sewage sludge. The biological reactions taking place inside the bioreactor included the anaerobic digestion of particulate organic matter, as well as biological sulfate reduction. The reaction scheme, rate equations and kinetic constants were selected from the literature. The model was used to predict the performance of the bioreactor in order to propose operating conditions that would increase the amount of particulate organic matter that is hydrolysed. The hydraulic retention time was the most influential of the operating parameters, while the sludge recycle ratio and feed COD: SO42- ratio were also varied to obtain simulated trends