MBR (Membrane Bio Reactor)
Compared to other biological processes such as fixed bed, the MBR process is extremely sensitive, is unable to deal with overloading and has very high operation and maintenance costs. Chemicals are also required for membrane cleaning. An MBR (Membrane Bio Reactor) plant uses biological breakdown and physical separation.
A screen for the removal of grit and grease forms part of the upstream equipment, to prevent the membrane from clogging.
A MBR system (Membrane Bio Reactor) is a filtration facility with a high concentration of bacteria (held within the membrane), that is 4-5 times higher than FBBR and MBBR systems. Depending on the size of the pore diameter of the membrane, even germs can be separated from the water. Negative pressure is required to support the wastewater flow through the membrane, which is an energy-intensive process and can be expensive. It is furthermore necessary to backwash the membrane in set intervals and the membrane needs to be replaced occasionally. This system requires regular professional maintenance and servicing.
The MBR system has an upstream activated sludge buffer. The sludge production is thus less than that of FBBR (Fixed Bed Bio Reactor) and MBBR (Mixed Bed Bio Reactor) and no sludge settlement is required, which is space saving.
MBR flow chart:
MBBR (Moving Bed Bio Reactor)
The upstream screening for the removal of grit and grease is also required, but particles smaller than 3mm are allowed to pass and even a manual screening is acceptable. In contrast to the MBR (Membrane Bio Reactor) the MBBR (Mixed Bed Bio Reactor) only uses bacteria for the breakdown of impurities.
MBBR plants contain particles (eg. produced from UV-stabilised polyethylene), on which bacteria grow, developing a biofilm on the free moving particles, which reduce the impurities and, therefore, the sludge mass (but not as effectively as an MBR plant). Sludge settlement is required after the bio-reactor in the form of lamella technology. The advantage is that spare parts are cheaper and long lasting, so operational expenses are lower than with MBR (Membrane Bio Reactor).
MBBR flow chart:
The FBR system functions like the MBBR (Mixed Bed Bio Reactor), the only difference being, that where the MBBR uses small particles which are free moving within the reactor, while the FBR system has fixed bed material (substrate is produced from UV-stabilised polyethylene) on which the biofilm grows. The FBR system has lower O&M costs than any other wastewater treatment process.
This biological layer (micro-organic colonisation) transforms the organic contaminants contained in the wastewater into sedimentary and mineral substances. This is mainly the work of aerobic organisms, which require oxygen. An aeration system installed underneath the fixed-bed material in the reactor, supplies the organisms with sufficient air. In addition, the rising air causes a current that, owing to the geometry of the fixed-bed material used, results in the contents of the tank being completely (horizontally and vertically) mixed (characteristic of an intermixed cylinder). The advantage of this system is it is self regulatory, very effective, with cheaper, uncomplicated and long lasting spare parts, ensuring that operational expenses are lower than MBR systems (Membrane Bio Reactor) .
FBR flow chart:
The table below shows the pros and cons of all three systems:
|Effluent water quality||Superior||Acceptable for irrigation||Acceptable for irrigation|
|Sensitivity to shifting of complex or toxic substances||Good||Medium||Medium|
|Handling of an electrical shutdown||Up to 24 hours without problems||Up to 10 hours. Afterwards bacteria will form bio-cakes*||Good handling|
|Susceptibility to a grease leak||Very sensitive. Membrane needs to be cleaned well/replaced||Very sensitive*||Leaked oil will float upwards and is easy to remove.|
* Material has to be changed, the plant will need a ten day restarting-time (green = advantage, white/grey = normal, red = disadvantage)