What is a membrane bioreactor (MBR)?
A membrane bioreactor (MBR) is a procedure that combines a suspended growth bioreactor, and a microfiltration or ultrafiltration membrane unit. It is now commonly utilized in municipal and industrial wastewater treatment plants (WWTPs).
What types of Components of Membrane Bioreactor?
A bioreactor is a chamber that is specifically designed to support a biologically active environment, where bacteria and protozoa (the so-called biomass) can grow and consume some or all of the substances within the raw wastewater.
Depending on the presence or absence of oxygen and nitrates, they can be aerobic (to remove organic matter and oxidise ammonia to nitrate), anoxic (to remove nitrogen from nitrates to nitrogen gas), or anaerobic (to remove organic matter). Membranes are typically erected following aerobic or anaerobic bioreactors.
Types of MBR bioreactors
Three different kinds of bioreactors exist:
· the biomass grows into flocs in suspended growth bioreactors;
· connected growth (or biofilm) bioreactors, in which carriers support the growth of the biomass;
· hybrid bioreactors that mix connected and suspended growth.
Usually, MBR operations take place in suspended growth bioreactors. The usage of hybrid bioreactors is also possible with suitable design.
Membranes function as a solid-liquid separation mechanism in the MBR process, keeping the biomass inside the bioreactor before releasing the treated effluent to the environment. They essentially replace the clarifiers that are used in the standard activated sludge (CAS) process.
MBR applications can employ both micro (MF) and ultrafiltration (UF) membranes
UF membranes are typically the best option due to their greater separation properties, allowing them to remove certain colloids and viruses as well, and reduced tendency to foul as well as because of the smaller pore sizes, these have a lower risk of pore clogging.
Three different membrane geometries are employed for MBRs
1: Flat sheet (FS),
2: Hollow fibre (HF), and
3: Tubular (or multi-tubular, MT).
Spiral-wound (SW) systems, for example, are inappropriate for MBR applications, due to their sensitivity to suspended solids levels.
How does a membrane bioreactor function in the processes of treating wastewater?
Separating solids from a liquid is a major role of membranes. This is often done in activated sludge facilities employing supplementary clarifiers.
There are two possible process configurations:
· If vacuum-driven membranes are utilized, submerged MBR should be used.
· If pressure-driven membranes are employed, side-stream (or external) MBR should be used.
Submerged membranes are typically utilized for medium-sized and larger installations, while pressure-driven membranes are typically employed for smaller installations, or difficult-to-treat industrial wastewaters.
What benefits do membrane bioreactors (MBR) offer?
1: Less space required for new WWTPs or increased hydraulic throughput (existing WWTPs);
2: No longer requirement for large clarifiers. The secondary clarifier, whose size is determined by hydraulic and solids loading, is replaced by a smaller, frequently rectangular-shaped chamber, outfitted with membrane cassettes;
3: Additionally, because the bioreactors can maintain greater biomass concentrations, the same total mass of solids is held in a smaller tank, resulting in a footprint that is up to 50% smaller;
4: High-quality effluent that is free of germs and bacteria;
5: The effluent has less bacteria and virus content and is free of suspended particles, as compared to the activated sludge (CAS) process. As a result, only minimal disinfection is necessary.
6: As a result, the MBR process makes it simple to discharge treated effluent to sensitive receiving bodies, or to reuse it for uses like urban irrigation, utilities, or toilet flushing.
7: It is also of a high enough standard to be fed directly to a reverse osmosis (RO) procedure.
This is becoming more and more important in light of the severe effluent quality criteria, set by municipal rules that will go into force in the coming years.
8: It has a greater automation potential. As opposed to traditional treatment plants, which often require operator intervention, the MBR system can operate entirely automatically. As a result, decentralised sites can also easily implement the MBR process.
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