1. Membrane Bioreactors (MBR) for Secondary
Wastewater Treatment
Submitted by
Sowmiya Santhappan
I – Yr, M.Sc.. Microbiology
Department of Microbiology
Vivekananda Arts and Science College for Women
Sankagiri, Salem
Tamilnadu, India
2. What is a membrane bioreactor?
A MEMBRANE BIOREACTOR (MBR) is a process which combines a
microfiltration or ultrafiltration membrane unit with a suspended
growth bioreactor, and is now widely used in both municipal and
industrial Waste Water Treatment Plants (WWTPs).
3. 1) Bioreactor:
• In a wastewater treatment process, a bioreactor is specifically-designed
chamber to support a biologically active environment, namely where bacteria
and protozoa (the so-called biomass) can grow and consume some (or all) the
substances within the raw wastewater.
• They can be aerobic (to remove organic matter and oxidize ammonia to
nitrate), anoxic (to remove nitrogen from nitrates to nitrogen gas) or
anaerobic (to remove organic matter), depending on the presence of oxygen
and nitrates or their absence.
• Typically, membranes are installed after aerobic or anaerobic bioreactors
(respectively, the MBR and the An MBR processes).
4. There are three types of bioreactors:
• Suspended growth bioreactors, where the biomass grows into flocs;
• Attached growth (or biofilm) bioreactors, where the biomass grows
attached to carriers;
• Hybrid bioreactors, which combines suspended and attached growth.
Typically, suspended growth bioreactors are these ones used for MBR
processes. If properly designed, hybrid bioreactors can be used as well.
5. 2) Membranes:
• In the MBR process, membranes act as a solid-liquid separation device,
keeping the biomass within the bioreactor before discharging the treated
effluent to the nature. Basically, they take the place of clarifiers used in the
conventional activated sludge (CAS) process.
• Both micro- (MF) and ultrafiltration (UF) membranes can be used in
MBR applications. Typically, UF membranes are the preferred choice
because of their superior separation characteristics (thus, being able to
remove some colloids and viruses as well) and lower fouling tendency
(because of the smaller pore size, they have a lower risk of pore clogging).
6. There are three types of membrane geometries used for MBRs:
1.Hollow fibre (HF);
2.Flat sheet (FS);
3.Tubular (or multi-tubular, MT).
Other configurations, such as spiral-wound (SW), are not suitable
to MBR applications because of their sensitivity to suspended
solids contents.
7. How does a membrane bioreactor work in wastewater treatment processes?
The crucial function of membranes is to separate solids from a liquid. In activated
sludge facilities, this is traditionally accomplished using secondary clarifiers.
Two process configurations are possible:
•Submerged MBR, in case vacuum-driven membranes are used (like PCI HF-
Zmbr2 Series);
8. Usually, pressure-driven membranes are used for smaller installations and/or
tough-to-treat industrial wastewaters, while submerged membranes are used for
medium and large installations.
9. Advantages of membrane bioreactors (MBR)
1) Smaller footprint (new WWTPs) or higher hydraulic throughput
(existing WWTPs)
Large clarifiers no longer are needed. A smaller often rectangular
shaped chamber, fitted with the membrane cassettes replaces the
secondary clarifier whose size is governed by hydraulic and solids
loading.
On top, because of the higher biomass concentrations that can be
sustained within the bioreactors, the same total mass of solids is stored
in a smaller tank, resulting in up to 50% smaller footprint.
10. 2) High-quality effluent, free of bacteria and pathogens
• In comparison to the activated sludge (CAS) process, the effluent is free
of suspended solids and reduced bacteria and viral content. Therefore,
minimum disinfection is required.
• Therefore, the MBR process easily allows the treated effluent to be
discharged to sensitive receiving bodies or to be reclaimed for
applications such as urban irrigation, utilities or toilet flushing.
Meanwhile, it is also of high quality for feeding directly to a reverse
osmosis (RO) process.
• This is becoming increasingly crucial in the view of the strict effluent
quality requirements imposed by local regulations taking effect during
the recent years and in the near future.
11. 3) Higher automation capabilities
The operation of the MBR system can be fully automated, minimizing
operators intervention that are typically required for conventional
treatment plants. This means that the MBR process can be easily
implemented also in decentralized sites.
