About Membrane Bioreactor (MBR)

MBR in Bangladesh is very popular in Waste Water Treatment System. Membrane Bioreactors (MBR) are treatment processes in a modern technology in waste water treatment, which integrate a perm-selective or semi-permeable membrane with a biological process. Membrane Bioreactors (MBR) is the combination of a membrane process like microfiltration or ultrafiltration with a suspended growth bioreactor, and is now widely used for municipal and industrial wastewater treatment with plant sizes up to 80’000 population equivalents (BEDDOW 2010). Due to it being a very technical solution; it needs expert design and skilled workers. Furthermore it is a costly but efficient treatment possibility. With the MBR technology, it is possible to upgrade old wastewater plants. So the demand of MBR in Bangladesh is growing up.

The Treatment Process and Basic Design Principles of MRB

The treatment process of MBR is quite excellent. MBR combine conventional biological treatment (e.g. activated sludge) processes with membrane filtration to provide a progressive level of organic and suspended solids removal. When designed accordingly, these systems can also provide an advanced level of nutrient removal. In an MBR system, the membranes are submerged in an aerated biological reactor. The membranes have porosities ranging from 0.035 microns to 0.4 microns (depending on the manufacturer), which is considered between micro and ultra-filtration.

This level of filtration allows for high quality effluent to be drawn through the membranes and eliminates the sedimentation and filtration processes typically used for waste water treatment. Because the need for sedimentation is eliminated, the biological process can operate at a much higher mixed liquor concentration. This dramatically reduces the process tank-age required and allows many existing plants to be upgraded without adding new tanks. To provide optimal aeration and scour around the membranes, the mixed liquor is typically kept in the 1.0-1.2% solids range, which is 4 times that of a conventional plant.

Type of Membrane Configuration

During MBR wastewater treatment, solid–liquid separation is achieved by Microfiltration (MF) or Ultrafiltration (UF) membranes. A membrane is simply a two-dimensional material used to separate components of fluids usually on the basis of their relative size or electrical charge. The capability of a membrane to allow transport of only specific compounds is called semi-permeability (sometimes also permselective). This is a physical process, where separated components remain chemically unchanged. Components that pass through membrane pores are called permeate, while rejected ones form concentrate or retentate.

There are five types of membrane configuration which are currently in operation:

• Hollow fibre (HF)
• Spiral-wound
• Plate-and-frame (i.e. flat sheet (FS))
• Pleated filter cartridge
• Tubular

(Adapted from RADJENOVIC et al. 2008)

Operation and Maintenance

Most MBRs employ chemical maintenance cleaning on a weekly basis, which lasts 30–60 min, and recovery cleaning when filtration is no longer durable, which occurs once or twice a year. A deposit that cannot be removed by available methods of cleaning is called “irrecoverable fouling”. This fouling builds up over the years of operation and eventually determines the membrane life-time (RADJENOVIC et al. 2008). All O&M tasks have to be done by skilled workers. Applicability of MBR

Membrane Bioreactor systems are widely used in municipal and industrial wastewater treatment plants. Furthermore, MBRs are also suitable for landfill leachate treatment. It is a high-tech system that needs expert design and professional operators.