There has been an idea that the aeration tank with suspended culture can be replaced with biofilm reactor from the beginning of MBR technology. In this idea, suspended or fixed biocarriers (or media) are added to aeration tank to grow biofilm on the surface of biocarriers . Strainers are required to prevent suspended biocarriers from being carried over to membrane tank and damage membrane. The biocarriers commonly used in moving bed biofilm reactor (MBBR) or integrated fixed film activated sludge (IFAS) can be used for BF-MBR. Fig. 1 shows a typical configuration of BF-MBR.
Following benefits are typically claimed against conventional MBR with suspended culture, but the second and the third claims below are not fully supported by data.
- Improved membrane performance due to the lower MLSS (a great portion of microorganisms are attached, not suspended).
- Improved oxygen transfer efficiency (OTE) due to the lower MLSS. Increased contact time of bubbles with liquid since biocarriers hinder bubbles from rising.
- Due to the increased effective microorganisms population in aeration tank including suspended and fixed microorganisms, volumetric organic, F/V ratio, can increase while tank size shrinks.
The validity of above claims will be discussed in the following subsections.
Fig. 1. The schematic of biofilm and MBR concept (Leiknes, 2006)