Main types and characteristics of membrane bioreactor (MBR) (1)

5.
2.
2 Main types and characteristics of membrane bioreactor (MBR)

Membrane modules are the core part of membrane bioreactors, and different types of membrane modules determine the difference in performance
.
There are many classification methods for membrane bioreactors, which are briefly described as follows:

①The structure of the membrane is different, such as hollow fiber, tube type, roll type, flat type, etc.
;

②The applied membrane can have different types, such as ultrafiltration membrane (UF, 0.
01～0.
04um), microfiltration membrane (MF, 0.
1～0.
2um), extraction membrane (with selectivity);

③The material of the membrane can also be different, such as ceramic, cellulose acetate (CA), polysulfone (PS), polyacrylonitrile, etc.
;

④In the membrane bioreactor, the applied bioreactor can have different types, such as aerobic bioreactor, anaerobic bioreactor, etc.
;

⑤ It can also be divided according to the combination of bioreactor and membrane unit, which can be divided into three types of membrane bioreactors: integrated, separated, and isolated
.

During the development of MBR, its meaning has also been expanded
.
The usually mentioned membrane bioreactor is actually a general term for three types of reactors: solid-liquid separation membrane bioreactor (MBR), aerated membrane bioreactor (MABR) and extractive membrane bioreactor (EMBR)

(1) Membrane bioreactor (MBR) According to the relative position of the membrane module and the bioreactor, MBR can be divided into built-in (integrated) membrane bioreactor, external (separate) membrane bioreactor, and composite type.
Three types of membrane bioreactors
.

① Integrated (built-in) membrane bioreactor, as shown in Figure 5-3
.
Its main feature is that the membrane module is immersed in the bioreactor; the effluent needs to be sucked through the membrane unit through negative pressure and discharged

Figure 5-3 Integrated (built-in) membrane bioreactor

②Separate type (external type) membrane bioreactor
.
In the separated membrane bioreactor, the bioreactor and the membrane unit are relatively independent, and the treated water is discharged out after passing through the membrane module through the mixed liquid circulation pump; the mutual interference between the bioreactor and the membrane separation device is small

Figure 5-4 Split (external) membrane bioreactor

(2) Aerated Membrane Bioreactor (MABR) The membrane used in the aeration system is a gas permeable membrane with low mass transfer resistance and can be operated under high pressure
.
When air or oxygen flows in the membrane cavity, it diffuses to the activated sludge outside the membrane under the action of the driving force of the concentration difference

Figure 5-5 MABR schematic

The bubble-free aeration membrane bioreactor has the following advantages: a.
Since the transferred gas is contained in the membrane system, the contact time is increased, and the oxygen transfer efficiency can reach about 100%; b.
Because the gas-liquid two-phase is separated by the membrane, Therefore, it is beneficial to the control of the aeration process, that is, to effectively separate the aeration and mixing functions; c.

Disadvantages: Compared with the traditional aeration system, the aerated membrane bioreactor system has a higher capital cost.
In addition, due to the resistance of the membrane, the driving force required for oxygen mass transfer is large, and the operating cost of the system is increased
.
In addition, due to the use of high oxygen flow to prevent clogging of the membrane, power consumption increases and operating costs also increase