The Moving Bed Biofilm Reactor (MBBR) technology was developed in Norway at the Norwegian University of Science and Technology in cooperation with a Norwegian company Kaldnes Miljǿteknologi (now AnoxKaldnes AS). The MBBR is a complete mix, continuous flow through process which combines the benefits of fixed film and suspended growth processes. Benefits include increased treatment capacity, improved settling characteristics, enhanced process stability, and reduced sludge production (Metcalf & Eddy, 2003). The process can either be used as a
1. pre-treatment system ahead of an existing activated sludge system for increased organic matter removal
2. stand alone biological treatment process for BOD removal, nitrification and/or denitrification
3. a retrofit of an existing activated sludge processes to help increase overall nitrification capacity of the existing system.
The MBBR process uses small plastic carrier elements to provide sites for bacteria attachment in a suspended growth medium. The carrier elements allow a higher biomass concentration to be maintained in the reactor compared to a suspended growth process, such as activated sludge. This increases the biological treatment capacity for a given reactor volume. The carrier elements are continuously kept in suspension by either a mixer or an aeration system. The agitation pattern in the reactor is designed to provide an upward movement of the carriers across the surface of the retention screen which creates a scrubbing effect to prevent clogging. Coarse bubble and jet aeration are typically used to provide oxygen for an aerobic reactor. Reports using fine bubble aeration in an MBBR system indicate the media cause the bubbles to coalesce, thereby reducing oxygen transfer efficiency (Zimmerman, et al., 2005).
A stainless steel coarse bubble aeration system is employed to mix the suspended media evenly throughout the reactor while providing the mixing energy required to slough old biofilm from the internal surface area of the media and maintain the dissolved oxygen required to support the biological treatment process.
Stainless steel wedge wire screens retain the cultivated biofilm / media in a process-designated reactor while allowing the treated wastewater and sloughed biofilm to flow through to the next treatment phase.