Biological treatment: membrane bioreactor (MBR)

Purpose

• Removal of organic substances (TOC, COD, BOD, ...)

• Breakdown of biodegradable detergents, oils and fats, ... 

• Nitrogen removal (ammonification, nitrification, denitrification)

• Phosphate removal

• Removal of suspended solids

Principle

A membrane bioreactor (MBR) is a biological wastewater treatment system that uses microfiltration or ultrafiltration membranes to separate treated water and biomass. These membranes have a pore size of 0,1 µm or smaller and separate all the bacteria and suspended solids from the purified water. The membrane module can be submerged in the aeration basin or placed in a separate tank outside the aeration basin.

Scheme

Applications

MBR installations are in most cases more expensive and more energy consuming than classical biological wastewater treatment systems. Their advantage is the excellent effluent quality which makes the effluent directly fit for re-use. The footprint of a MBR installation is also significantly smaller since no clarifier is required and in a lot of cases the activated sludge concentration can be higher, which means smaller aeration basins.

Configuration

Several membrane choices are possible depending on the scale and type of wastewater. In submerged MBR reactors the choice falls most often for flat sheets or hollow fibers, which are cleaned by aeration and optionally chemical enhanced backwashing. Externally disposed membrane modules are typically hollow-fiber or multi-tubular system, in this case the cleaning is done by means of a high flow rate of the sludge along the membranes and backwashing of the membranes.

Approach Trevi

The type of waste water determines the nature and filterability of the sludge in a MBR reactor. Trevi always performs pilot tests during the dimensioning of a new MBR wastewater treatment plant. This way a realistic flux is selected, with a maximum service life for the membranes and a minimal cleaning frequency.