Moving Bed BioReactors Design Recommendations:

Maximum Feed Loading per MBBR: 125 lbs/day

BioReactor Tank:

Height/diameter ratio: 1 to 1.2

  • It is difficult to achieve good mixing and cleaning conditions in narrow/tall tanks and wide/shallow tanks when using only diffusers to provide agitation and mixing.

Maximum diameter: 2 m (6.5 ft)

  • Diameters greater than 2 m require special engineering to provide for mixing and cleaning.

Depth – 1.5 m (50 to 60 inches):

  • Maximum depth for efficient aeration using regenerative blowers.
  • Depths beyond 2 m may cause nitrogen super saturation conditions.

Aeration for mixing, oxygen transfer, CO2 stripping and cleaning:

  • 4.4 scfm/m3 of reactor (0.125 scfm/ft3 of reactor)
  • Five times the reactor volume per hour, plus 50% spare capacity
  • Use coarse bubble diffusers or perforated pipe manifolds (3mm holes)
  • Create a circular pattern of mixing
  • Provides up to 60% CO2 stripping


  • Use a safety factor of 15 to 50% of media volume
  • Design for 50% fill factor with ability to increase to a maximum of 70%

Screen Inlet/Outlet:

  • Design for a flow rate across the discharge screens of 0.2 to 0.5 ft/sec
  • Screen size to ensure the media cannot escape, but large enough to prevent clogging

Please remember that these are only recommendations for MBBR designs. More specific system designs and recommendations are available from AST’s Engineering Services.