About adding MBBR media to expand capacity of wastewater plants

MBBR media with biofilm. Photo from AAEES.ORG.

Moving Bed Biofilm Reactor (MBBR) media has potential to expand wastewater treatment plant capacity, but as with any technology there are some tradeoffs compared to conventional suspended growth systems. Usually constructed of HDPE (polyethylene) with a density near that of water - 0.95 g/cm3. The HDPE is extruded into high surface area shapes which provide a surface for bacterial biofilm development. Biofilm treatment systems go back as far as trickling filters - it is just plastic gives us more options for supporting the biofilm. The MBBR media is kept in the aeration basin by screens with excess biosolids soughing off during movement.

MBBR Benefits

• Allows higher levels of biological solids than suspended growth activated sludge systems. Meaning that you can run high MCRT & lower F/M for a given aeration basin/secondary clarifier.
• Lower F/M means less solids production - older biomass but this does require sufficient D.O. to prevent filamentous bacteria development.
• Helps if your clarifiers are not able to support high MLSS due to hydraulic constraints.

So why don't we see every system converted to MBBR technology? There are a few challenges:

• Media can be expensive
• Heavy FOG (grease) loadings can foul the media
• Running further into the growth curve - lower F/M - requires oxygen normally seen in aerobic digesters. Do you have the aeration capacity for more biomass?