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MBR Components

An image of yellow lego bricks scattered on the right hand side of a bright blue background.

MBR building blocks

As with a conventional biological wastewater treatment process, an MBR is a combination of tanks, pipework, pumps and blowers, with the addition of the membrane differentiating it from classical processes.

A simple design of a small MBR has been provided by Lo et al (2015). This is a general design for a municipal wastewater treatment based on an immersed membrane and an MLE (modified LudzackEttinger) process. The specifications of the individual pieces of equipment (power, flow and/or pressure ratings) then depend on the application and assumptions made.

Most MBR installations must also include a control system for regulating flows and pressures.

Fig. 1. Components of an MBR plant
Fig. 1. Components of an MBR plant
A graphic of the components of an MBR, including (not in sequence) raw water tank, primary sedimentation tank, equalisation tank, rotary fine screen, sludge holding tank, membrane tank, aeration tank, anoxic tank, treated water tank.
Table 1. MBR plant components and design basis
Category Component(s) ID Description/purpose
TanksRaw waterT1Storage tank for inlet wastewater
Primary sedimentationT2Removal of gross, settleable solids
Equalisation (EQ)T3Equalisation of flow
Anoxic (Ax)T4Denitrification
Aeration (Ae)T5Nitrification and biological oxidation
MembraneT6Membrane separation
Treated waterT7Storage of permeate water
SludgeT8Storage of wasted sludge
Chemicals storageT9, T10
PumpsSettled sludge transferP1Submerged, settled sludge to sludge storage tank
FeedP2EQ tank through rotary screen
PermeateP3Self-priming, membrane suction filtration
Sludge return/dischargeP4Submerged, sludge recirculation and excess
Sludge transferP5WAS to dewatering
ChemicalsP6, P7Cleaning chemicals transfer to membrane, x2
BlowerProcessB1Biological process aeration
MembraneB2Membrane scouring
MixerEQ tank mixerX1High speed, equalisation tank
Ax tank mixerX2Low speed, anoxic tank
ScreenRotary screenS1Fine screening of feed
MembraneMembrane moduleM1FS membrane plus frame with built-in aerator
DiffusersFine bubble diffuserD1Process aeration
Coarse bubble diffuserD2Membrane aeration

Membrane modules terminology

Terms for the individual components of a membrane technology are used inconsistently for membrane bioreactors.

  • An ‘element’ can be considered to be the smallest replaceable component of the membrane technology.
  • The term ‘module’ normally applies to a single element for a rectangular hollow fibre technology, but usually to a collection of elements in the case of flat sheets.
  • The term ‘stack’ can be considered to apply generally to a collection of elements, with the terms ‘rack’, ‘unit’, ‘cassette’ and ‘skid’ (for an externally-mounted array of modules) also being used.
  • A line of immersed stacks is usually called a ‘train’, and the train may include an aeration lane of the biological tank if one aeration lane is associated with a discrete row of immersed membrane modules.
Table 1. Terminology for MBR membrane products and technologies
Component Flat sheet (FS) Hollow Fibre (HF) rectangular panel Hollow Fibre (HF) cylindrical bundle; Multitube (MT)
ElementPanel, element, sheet, cartridgeModule, sub-unitModule
Collection of elements IModule, cassette, unitRack, cassette, cartridge, moduleSkid
Collection of elements IIStack, frameStack, frame

Other key terms and abbreviations

A number of abbreviations are used for the different polymeric membrane materials, the first letter invariably being 'P' (for 'polymeric'). For ceramic membranes the chemical formula is used to identify the membrane material.

The configuration of the MBR process defines how the membrane is integrated into the overall MBR process. It can be either immersed (or 'submerged') in a tank (hence the term 'iMBR') or placed outside of the tank as a sidestream (i.e. 'sMBR').

The MBR process configuration is to be distinguished from the membrane configuration which defines the membrane geometry and permeate flow direction. The main three geometries used for MBR technologies (Table 1) are flat sheet or flat plate (FS), hollow fibre (HF) and multitube (MT).


Lo, C.-H., McAdam, E., and Judd, S. (2015). The cost of a small membrane bioreactor, Water Sci Technol 72(10) 17391746.

About this page

'MBR Components' was written by Simon Judd

This page was last updated on 05 February 2024


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