Separation of Biomass From Moving Bed Biofilm Reactors (MBBRs)

The Moving Bed Biofilm Reactor (MBBR™) process was developed in Norway 20 years ago. It is used in a biofilm process where the biomass is attached to small plastic elements that move freely along with the water in the reactors. The movement is caused by aeration in aerobic reactors, and by mechanical mixers in anoxic reactors. The moving bed is used in pure biofilm systems (without sludge recycle), as well as in IFAS-systems. This paper deals with separation of biomass in the pure biofilm systems. The paper describes experiences in the separation of biomass from a moving bed biofilm reactor using different biomass separation technologies with and without pre-coagulation; such as traditional settling, microsand ballasted lamella settling, flotation, microscreening (with different light openings), media filtration (coarse and fine media) and membrane (UF) filtration. The settling properties of biomass from MBBR's are not the best and in the paper particle size distributions will demonstrate why this is so. Therefore it is quite customary to enhance flocculation – either chemically, by the addition of a coagulant/flocculant - or biologically by letting the MBBR effluent pass a suspended biomass zone.