UPSC Prelims 2024 Q39: Membrane Bioreactors — Explained
"Membrane Bioreactors" are often discussed in the context of:
- Assisted reproductive technologies
- Drug delivery nanotechnologies
- Vaccine production technologies
- Wastewater treatment technologies
Answer: (d) Wastewater treatment technologies
Statement-wise explanation
- a: incorrect — Assisted reproductive technologies such as IVF and ICSI handle eggs, sperm and embryos in culture dishes and incubators. They do not filter large volumes of water through a membrane. Membrane bioreactors play no part in ART.
- b: incorrect — Drug-delivery nanotechnology uses carriers such as liposomes, dendrimers and polymeric nanoparticles. 'Membrane' in that field means a lipid layer around a carrier, not a filtration unit attached to a reactor. The term 'membrane bioreactor' does not refer to a drug-delivery system.
- c: incorrect — Vaccine production does use bioreactors to grow cells or microbes, and it uses membranes for purification steps. That overlap makes this the most tempting distractor. But 'Membrane Bioreactor' (MBR) is the standard name for a process engineering technology, and that technology is used to treat wastewater, not to make vaccines.
- d: correct — A membrane bioreactor combines activated-sludge biological treatment with micro- or ultrafiltration membranes. The membrane replaces the secondary settling tank (clarifier) of a conventional sewage treatment plant. Ultrafiltration membranes with pore sizes around 0.04 µm hold back solids and most pathogens. In one published municipal plant study, the treated water had BOD below 5 mg/L and suspended solids below 1 mg/L, which is good enough for reuse.
How to eliminate
You cannot reliably eliminate options here without knowing the term. 'Bioreactor' fits vaccine production, and 'membrane' sounds like nanomedicine, so word association misleads you. The fact to remember is that MBR = activated sludge + membrane filtration, used in sewage and industrial effluent treatment. It also appears with its sister terms SBR (Sequencing Batch Reactor) and MBBR (Moving Bed Biofilm Reactor) in STP tenders under Namami Gange and AMRUT. A weaker clue: UPSC puts the phrase in quotes and asks where it is 'often discussed'. That usually points to a technology with a fixed name in one field, and 'MBR plant' is a common phrase in water and sanitation news.
Know more
What an MBR does. Sewage first goes to an aerated tank. There, microbes (the 'activated sludge') eat the dissolved organic matter. In a conventional plant, the sludge then settles by gravity in a clarifier. In an MBR, the clarifier is replaced by membranes (microfiltration or ultrafiltration) that are submerged in the tank or placed beside it. Clean water (the permeate) is drawn through the membranes, and the biomass stays behind.
Why it matters. The treated water is low in BOD, suspended solids and turbidity, so it suits reuse in industry, flushing or gardening. The plant also needs much less land, which helps in crowded cities. Drawbacks: the membranes clog over time (membrane fouling). They are cleaned by heavy aeration, which uses a lot of energy, and the membranes themselves cost more.
Common STP technologies in India
| Technology | Core idea | Typical strength |
|---|---|---|
| Conventional Activated Sludge (CAS) | Aeration tank + gravity clarifier | Simple, proven |
| SBR (Sequencing Batch Reactor) | Fill, aerate, settle and draw in one tank, in cycles | Compact; widely used in Namami Gange STPs |
| MBBR (Moving Bed Biofilm Reactor) | Plastic carriers with a biofilm on them float in the aerated tank | Easy to upgrade an existing plant |
| MBR (Membrane Bioreactor) | Activated sludge + membrane filtration | Water good enough for reuse, smallest footprint |
| Constructed wetlands / phytorid | Plants and soil media treat the water | Cheap and nature-based, but need more land |
Related terms: Anaerobic MBR works without oxygen and produces biogas. Reverse osmosis is a separate, finer membrane step often added after an MBR to remove dissolved salts. BOD (biochemical oxygen demand) is the main measure of how polluted the water is before and after treatment.
NCERT Concepts to Revise
- Water pollution: Defines the organic and suspended pollutants in sewage that any treatment technology in the options would have to remove.
- Polluted river stretches: Uses BOD, the standard measure for judging how well a sewage treatment process cleans water.