Modelling energy consumption in membrane bioreactors for waste water treatment in North Africa

Two pilot-scale membrane bioreactors were operated alongside a full-sized activated sludge plant in Tunisia, in order to compare specific energy demand and treated water quality. Energy consumption rates were measured for the complete membrane bioreactor systems and for their different components. Specific energy demand was measured for the systems and compared with the activated sludge plant, which operated around 3 kWh m^-3 . A model was developed for each membrane bioreactor based on both dynamic and steady-state mass balances, the microbial kinetics and stoichiometry, and the energy balance. Energy consumption was evaluated as a function of mixed-liquor suspended solids concentration, net permeate fluxes, and the resultant treated water quality. This work demonstrates the potential for using membrane bioreactors in decentralised domestic water treatment in North Africa, at energy consumption levels similar or lower than conventional activated sludge systems, with the added benefit of producing treated water suitable for unrestricted crop irrigation.