Chapter 3 - Design, Operation and Maintenance

Abstract

This chapter summarizes the various governing principles of membrane bioreactor (MBR) membrane filtration, key membrane design, and operating parameters. Existing established biochemical/biokinetic expressions can be used to design the biological component of an MBR, aided by available tools for this purpose. The key interrelationships between flux, permeability, and scouring (by aeration or liquid crossflow) for the membrane component can be arrived at through heuristic data or empirical study. The frequency of maintenance, which incurs downtime and thus decreases the overall flux, can be determined in the same way. An MBR plant is more complicated, both in design and operation, than a conventional activated sludge plant and is exposed to a greater risk of process failure. There is a greater onus to engage in the maintenance of all the constituent parts, including both the membranes and peripheral equipment such as the screens, blowers, motorized valve drives, and process instrumentation. It is also the case that more conservative operation---less variable and lower applied fluxes and loads coupled with higher and/or uniformly applied membrane aeration rates---alleviates the primary causes of process performance deterioration, these being fouling and clogging, and that rigorous screening retards the latter. Upon analysis, it is suggested that the plants operating under such conditions are subject to significantly less unscheduled manual intervention. Given the energy penalty incurred by higher membrane aeration rates, the industry may have to contend with higher capital costs associated with both larger membrane area and flow equalization to allow operation at lower fluxes and more regulated loads.