Membrane Bioreactor

Membrane Bioreactor (MBR)

The Membrane Bioreactor (MBR) process (membrane activated sludge process) is an advanced wastewater treatment technology and constitutes a suspended growth activated sludge system, which instead of secondary clarifiers utilises low-pressure membranes for solid/liquid separation. As opposed to secondary clarification, the quality of solids separation is not dependent upon the mixed liquor suspended solids concentration, or the settling characteristic. Hence, the fact that MBRs can operate with much higher mixed liquor suspended solid concentrations, which provides an intensified biological process. Accordingly, the two major benefits of the MBR process are substantially reduced land and space requirements, and the reclamation of water (permeate) of excellent quality, which is a valuable source for higher demand reuse applications (LAHNSTEINER et al. 2007). 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 and Tubular. 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. Pollutants removal efficiency: BOD₅: 99%, COD: 95%, TSS: 99%, Pathogen: 99.99% (FITZGERALD 2008).

Most MBRs employ chemical maintenance cleaning on a weekly basis and recovery cleaning when filtration is no longer durable (once or twice per 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 lifetime (RADJENOVIC et al. 2008). All O&M tasks have to be done by skilled workers. Modern systems are maintained with chemicals, i.e. it is not necessary to remove the membranes from the membrane tank (KUBOTA 2010).

Although MBR capital and operational costs (membranes, oxygen utilisation, expert design, etc.) exceed the costs of conventional process, it seems that the upgrade of conventional process occurs even in cases when conventional treatment works well. This can be related to increase of water prices and the need for water reuse as well as with more stringent regulations on the effluent quality.

At present, approximately 800 MBRs with a total capacity of nearly 1.2 million m³/day are treating municipal wastewater worldwide. Indeed, since 2000, the number of plants has tripled and total capacity has increased by a factor of 20 (PINNEKAMP 2007). Most of the plants have been built in Asia (303 MBRs) followed by North America (295 MBRs), while in Europe only 169 MBRs have been realised. However, if the total capacities are considered, the picture is quite different, i.e. North America: 492,000 m³/day, Europe: 423,000 m³/day, Asia: 268,000 m³/day (LAHNSTEINER et al. 2007).

In Europe, the first full-scale MBR plant for treatment of municipal wastewater was constructed in Porlock (UK, commissioned in 1998, 3,800 PE), soon followed by Buechel and Roedingen WWTPs (Germany, 1999, resp. 1,000 and 3,000 PE), and Perthes-en-Gatinais WWTP (France, 1999, 4,500 PE). Only a few years later, in 2004, the largest MBR plant worldwide so far was commissioned to serve a population of 80,000 PE in Kaarst, Germany. The installations have thus grown from “small-size WWTPs” to “very large-size WWTPs” within only a few years (LESJEAN & HUISJES 2007).

The Manual on Sewerage and Sewage Treatment published by the Indian Ministry of Urban Development in 1993 (last update on 2012) emphasised conventional sewage treatment technologies such as Activated Sludge Process (ASP), Waste Stabilisation Pond (WSP), Upflow Anaerobic Sludge Blanket (UASB) Reactor, etc. Over the last two decades, many new technologies for sewerage and sewage treatment have emerged like membrane bioreactors. This technology, which is being used in other parts of the world, has not been deployed in India on a large scale until recently. Because of the advantages of the technology, the Jawaharlal Nehru National Urban Renewal Mission (JNNURM) has recently adopted the MBR technology as a suitable technology for the Indian conditions.

Some examples of MBR plants in India are:

• Delhi Games Village - Water treatment plant. Capacity: 4,545 m³/d.
• India’s first wastewater recycling plant for IOCL Panipat. Capacity: 21,600 m³/d.
• India’s largest lamella wastewater treatment plant for the Brihan Mumbai Municipal Corp. (BMC).
• India’s first wastewater treatment plant based on a (Build-Own-Operate-Transfer) BOOT model for Alandur. Capacity: 24,000 m³/d.

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