Recovery of water for ground crop irrigation from municipal waste water in North Africa using MBRs: Process performance, modelling & water quality

Three pilot-scale membrane bioreactor systems were operated alongside a full sized activated sludge plant treating domestic waste water 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, e.g. pumps, blowers, etc. Specific energy demand was measured for the membrane bioreactor systems and compared with the full sized activated sludge plant. A model was developed for each of the membrane bioreactors based on dynamic mass and energy balances combined with microbial kinetics and stoichiometry. Energy consumption was evaluated as a function of various operating parameters such as the mixed-liquor suspended solids concentration, membrane permeate fluxes, and the resultant treated water quality (including COD, nitrogen, phosphate, suspended solids, pathogens, trace metals etc). The model demonstrated that modifying one of the membrane bioreactors would provide treated water suitable for unrestricted irrigation, with energy consumption lower than the activated sludge plant. This work demonstrates the potential for using MBRs in decentralised domestic water treatment in the North African region, at energy consumption levels similar or lower than a conventional activated sludge system, with the added benefit of producing treated water suitable for unrestricted human ground crop irrigation.