Energy-Efficient Membrane Bio-Reactors

Membrane bio-reactors (MBR) are modified activated sludge systems, whereby secondary clarifiers are replaced by membrane filters.

• MBR systems combine biological wastewater treatment with membrane filtration and disinfection.
• Mixed-liquor solids concentration is increased by a factor of 3 - 5 and tank volume reduced to 20 – 35 %.
• Ultra-filtration membranes retain all solids and bacteria; effluents are of excellent quality.
• Power consumption of MBR-systems is 40 – 80 kWh/(PE•a), whereof about 50 % is consumed by membrane filter operation.
• Membrane scouring air introduces some oxygen into the wastewater so that oxygen supply by fine bubble aeration can be reduced.
• Increased mixed-liquor concentration lowers aeration alpha-factors (e.g. from 0.7 to 0.5) and thus aeration efficiency.
• These two effects approximately cancel each other out.
• MBR-systems increase power consumption by around 10 % in comparison with conventional biological treatment + sand filtration + disinfection.
• MBR-systems should be used where plant footprint is limited and/or where excellent effluent quality is required.

Since membrane filters are major power consumers, installation of energy-efficient units is very important.

The table shows power consumption of a HUBER Vacuum Rotation Membrane VRM® Bioreactor for a 20,000 PT plant in comparison with those of competitors.