Process improvement by application of membrane bioreactors

Membrane bioreactors (MBR) - combinations of common bioreactors and membrane separation units for biomass retention - offer new possibilities for bioprocesses and wastewater treatment according to the particular goal and demands of the process. MBRs combine the benefits of high biomass concentrations to increase removal rates or volumetric productivity with the possibility to run a continuous process at controlled biomass retention e.g., by individual control of hydraulic and biomass residence times, production or degradation kinetics as well as biocoenosis composition can be optimized beyond chemostat or common activated sludge process performance. Although several practical experiences and data are already available for design and operation of MBR processes there is still considerable optimization potential. In MBRs, bioreactor and membrane filtration cannot be regarded as individual unit operations as they interact in a number of ways. Therefore, MBRs need to be considered as hybrid reactors. In this paper, some of the biology-membrane interactions are exemplarily discussed and data from different research and technical aspects including maintenance kinetics, membrane fouling, and rheology are presented.