The filtration elements are installed externally to the reactor. The biomass can be pumped directly through a number of membrane modules and back to the bioreactor. Alternatively, the biomass can be pumped to a bank of modules, from which a second pump circulates the biomass through the modules in series. Cleaning and soaking of the membranes can be undertaken in place with the use of an installed cleaning tank, pump, and pipework. Despite the more favorable energy usage of submerged membranes, there continues to be a market for the sidestream configuration, particularly in industrial applications. For ease of maintenance, the side-stream configuration can be installed on a lower level in a plant building and membrane replacement can be undertaken without specialized lifting equipment.