Potential and drawbacks of microbiology-membrane interaction in membrane bioreactors

In membrane bioreactors (MBRs), biomass and membranes interact in a number of ways, making it difficult to extrapolate phenomena and models known from conventional activated sludge processes. Originally, MBRs were thought to enable immense process intensifications through very high MLSS (mixed liquor suspended solid) concentrations and resulting low footprint. Economic considerations, however, currently lead to lower concentrations because high biomass content impedes oxygen transfer and increases sludge viscosity. On the other band, the interactions can lead to a number of new potentials, which as yet were unknown in each unit operation individually such as efficiencies through a change in the increased removal microbial community or sludge age. Here, both potentials and limits of biomass- membrane interactions are reviewed with a focus on recent results from Europe, especially from Germany. (c) 2005 American Institute of Chemical Engineers.