Thesis - faculty.ait.ac.th - Asian Institute of Technology

Air Compressor
Influent
Air Diffuser
Air Outlet
Bio-Reactor
Return Sludge
Membrane Unit
(a) (b)
Figure 2.10 Schematic Diagrams of (a) External Recirculation MBR and (b) Submerged
MBR System
2.11.1 Membrane Configuration
Effluent
Influent
Membrane bioreactor configurations include: extractive membrane bioreactors
(EMBR), bubble-less aeration membrane bioreactors (MABR), recycle membrane
bioreactors and membrane separation bioreactors.
Treatment by aerobic processes is often limited by insufficient oxygen while using
air as an oxygen source. The implementation of oxygen as opposed to air as an aeration
medium would increase the degradation rate of the system. However, since conventional
aeration devices have high power requirements and a high rate of mixing, these devices
cannot be used with biofilm processes. MABR process uses gas permeable membranes to
directly supply high purity oxygen without bubble formation in a biofilm (Stephenson, et
al., 2000). The membranes are generally configured in either a plate-and-frame or hollow
fibre module. However, research has focussed on the hollow fibre arrangement with gas on
the lumen-side and wastewater on the shell-side. The hollow fibre modules are preferred
since the membrane provides a high surface area for oxygen transfer while occupying a
small volume within the reactor.
The membrane recycle bioreactor consists of a reaction vessel operated as a stirred
tank reactor and a membrane module containing the membrane. The substrate and
biocatalyst are added to the reaction vessel in pre-determined concentrations. Thereafter,
the mixture is continuously pumped through the membrane. While the biocatalyst adheres
to the membrane surface, the medium permeates through the membrane and is recycled to
the reactor vessel.
A summary of the advantages and disadvantages of each bioreactor configuration is
presented in Table 2.18.
The versatility and treatment capability of membrane bioreactors has catapulted the
technology as a viable alternative in water and wastewater treatment over a short period.
Initial design configurations of external loop systems were prone to fouling which
prevented stable operation and hence was confined to small-scale operations with limited
value and applicability.
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Feed Tank
Compressed Air Effluent
Level Control
Tank
Membrane
Air Diffuser