A membrane bioreactor is best distinguished from a conventional activated sludge process by the fact that
- Abiomass separation is achieved by membrane retention rather than gravity clarificationCorrect
- Bbiomass oxidation is achieved without the need for aeration
- Cbiological treatment is replaced by pressure-driven membrane desalination
- Dsludge age becomes independent of biomass concentration in the reactor
Solution
Concept
Membrane Bioreactor (MBR) vs Conventional Activated Sludge
Formula
NONE
Step-by-step solution
1. Conventional activated sludge relies on a secondary settling tank (clarifier) for solid-liquid separation by gravity. 2. An MBR replaces the secondary clarifier with membrane filtration modules (MF/UF). 3. The membrane pore size physically blocks suspended solids and bacteria from passing. 4. Therefore, biomass separation by membrane filtration instead of gravity sedimentation is the key distinction. Answer: A
Explanation
A Membrane Bioreactor (MBR) combines biological degradation by activated sludge with physical membrane filtration (microfiltration or ultrafiltration). Unlike conventional activated sludge which relies on gravity sedimentation in a secondary clarifier, MBR uses membranes to physically retain biomass, producing crystal-clear effluent and allowing much higher MLSS levels (8,000–12,000 mg/L).
Why the other options are wrong
B) MBRs are aerobic biological systems that require vigorous aeration for microbial respiration and membrane scouring. C) Biological treatment is preserved, not replaced by desalination. D) Sludge age (SRT) in MBR is controlled by sludge wastage, not made independent of concentration.
Shortcut
MBR = Activated Sludge + Membrane Filtration (replaces gravity clarifier).
Common mistake
Confusing MBR with reverse osmosis desalination or assuming MBR does not require aeration.
Correct answer: A) biomass separation is achieved by membrane retention rather than gravity clarification