Membrane separation process configurations

MBR membranes can be set up in two process configurations: immersed (iMBRs) and sidestream (sMBRs).

Immersed membrane bioreactors

The immersed configuration is also sometimes referred to as ‘submerged’, which obviously leads to confusion when abbreviated, or ‘internal’ – as opposed to external – for a sidestream membrane.

Further process configurations using immersed membranes, based on the way in which the membrane is used, include ‘diffusive’ and ‘extractive’. However, neither of these have reached the stage of commercialisation; all current commercial MBRs employ a membrane solely for retaining the sludge in the bioreactor whilst producing a high-quality permeate product.

Sidestream membrane bioreactors

The first membrane bioreactors developed in the late 1960s were based on the sidestream configuration. For this configuration the membrane system is placed outside the biological treatment process tank. The sludge is then pumped through the membranes in ‘crossflow’ mode, normally at an elevated pressure (2-3 bar), and the permeate forced through the membrane under the combined action of the pressure and the crossflow. The unpermeated stream is then returned to the biotank.

For the more recent immersed configuration, introduced in the early 1990s, the membrane is placed in the biotank and scoured with air introduced by an aerator placed beneath or within the membrane module.

As with almost all membrane separation processes, key to sustaining the flow of water through the membrane is the generation of ‘shear’. This relates to the flow of fluid over the membrane surface, which for sidestream configurations is sustained by the flow of sludge and for immersed systems by the action of the air bubbles.

‘The MBR Site’ is a trading division of Judd and Judd Ltd, a company registered in England and Wales, registered number 8082403.

Registered office: Suite 2, Douglas House, 32-34 Simpson Road, Fenny Stratford, Buckinghamshire, MK1 1BA, United Kingdom. Email:

Banner image: full treatment plant for pharmaceutical wastewater in Taizhou, Linhai Park, Zhejiang Province, China, including Shanghai MEGAVISION  flat sheet UF membrane modules in two MBR units. Image courtesy of VALORSABIO, Lda.

Image credits:

– Image for our Chinese largest plants 全球最大的MBR项目 homepage link: Image supplied by Apex Environmental
– Image for our Consultants and Contractors homepage link: Image supplied by Ovivo USA, LLC.

Disclaimer: The information given on this website is reproduced in good faith. No liability is accepted for errors or omissions. The MBR Site does not endorse any products, services, organisations, events or any other listing included in this site. You are strongly advised to check all information, including specifications and installation details, before acting on any information given in this website. The MBR Site links to third-party websites – note that we are not responsible for the content of third-party websites and third-party websites are visited at your own risk. Please read our terms and conditions and privacy policy. Use of this website indicates acceptance of these conditions.

This website is designed for modern browsers – if you have problems viewing our website, you may wish to upgrade your browser.