MBBR

A REPORT ON MBBR (MOVING BED BIOFILM REACTOR)

WHAT IS MBBR (MOVING BED BIOFILM REACTORS) ? .MBBR are a hybrid of activated sludge and biofilter processes (Odegaard, 2004). Unlike most fixed film bioreactors, MBBR utilize whole tank volume for biomass. However, contrary to activated sludge reactor, MBBR does not need return activated sludge (RAS). MBBR achieve its treatment strategy by having a biomass grow on plastic high surface area carriers that move freely in the water volume of the reactor kept within the reactor  volume by a sieve arrangement at the reactor outlet. At the bottom of the tank, large bubble aeration system assures mixing and floating of plastic carriers with attached biomass. WHAT IS BIOFILM CARRIER LIKE ? The biofilm carrier is made of high density PP (0.92 g/cm3) and shaped as small cylinders with a cross on the inside of  the cylinder and “fins” on the outside. Various shapes and sizes are introduced by numerous manufacturers. One of the important advantages of the moving bed biofilm reactor is that the filling fraction of carrier in the reactor may be subject to needs. That means that by increasing the filling fraction one can increase surface area and capacity of the reactor to reduce BOD’s without additional tanks (it shall be noted that Oxygen demands also increases simultaneously). Microorganisms growing on such media are also much more resistant to pH and toxic shock as well as fluctuations in BOD’s. Produced biosolids are also easy to separate and dewater. The bactera’s/activated sludge grow on the internal surface of the carriers. The bacteria’s break down the organic matter  from the waste water. The aeration system keeps the carriers with activated sludge in motion. Only the extra amount of   bacteria’s growth, the excess sludge will come separate from the carriers and will flow with the treated water towards the final separator.

For this option, Kaldnes provided the design concept criteria. Media would be added to the existing aeration tanks, where nitrification would occur. Data below summarizes design criteria for the MBBR nitrification system and denitrification system. Because the MBBRs would be treating primary effluent, the analysis for MBBR accounted for  nitrogen removed via assimilation into the biomass produced during BOD removal. The biomass for biological treatment would grow on the media, thus eliminating the need for recycling solids from the secondary clarifiers. Stainless steel sieves would be installed at the outlets of the aeration basins to retain the media.

Additional facilities for producing oxygen would also be required in comparison to

the conventional aeration systems. Effluent from the aeration basins would be deaerated  before flowing to additional MBBRs for  denitrification. De -aeration can  be accomplished by nitrogen stripping, which drives dissolved oxygen from the wastewater. Nitrogen gas is a by-product of the cryogenic pure-oxygen generation system. Carrier media movement is provided by coarse bubble aeration/ fine bubble aeration in the portion of the reactor containing the media. DESIGN CRITERIA FOR MBBR  Moving Bed Bio-film Reactor for Nitrification With Specific surface area m2/m3 500 % fill of carrier element 65 Moving Bed Biofilm Reactor for Denitrification Loading rate g/m2.d 2.45 With Specific surface area m2/m3 500 % fill of carrier element 40 Table 1. Showing design specifications for MBBR  MBBR Design Specifications Design influent BOD (average, mg/l) 1,200 Design influent TSS (average, mg/l) 400 Design average FOG (mg/l) 60 Design maximum temperature ( oC) 35  Number of tanks 2 Reactor Empty Bed Volume (m3) 67.96 Bulk volumetric filling of carriers% 50 Hydraulic Retention Time at Design Flows (Hours) 8 Specific biofilm surface area (m2/m3) 250