The expenses for the disposal of industrial and municipal wastewater are increasing strongly due to more stringent governmental legislation ordering lower discharge limits and higher discharge taxes. Moreover, the intake of ground water is being limited to prevent a dehydration of the soil having a destructive influence on nature's flora and fauna. The call for a closed water cycle is becoming louder and more efficient wastewater treatment techniques have been developed, such as the membrane bio-reactor (MBR).
 

An MBR is a compact-built purification system combining the biological degradation step with a membrane separation step. The influent is fed to the aerated bio-reactor where the organic components are oxidised by the activated sludge. Next, the aqueous activated sludge solution passes through a membrane filtration unit separating the water from the sludge. The latter returns to the bio-reactor, while the permeate is discharged or re-used as particle-free effluent.

The combination of biological treatment with membrane filtration offers several significant advantages over a conventional activated sludge system as presently being  used for municipal wastewater treatment, such as a higher biomass concentration and less sludge carry-over.

The higher biomass concentration results in a more compact system being an advantage for both highly populated (space requirement) as remote areas (flexibility). The decrease in sludge carry-over in the effluent reduces the need of post-treatment of the effluent protecting ecologically sensitive areas.
 

Norit Airlift MBR systems are used for:

• high mixed liquor suspended solids (MLSS) streams, up to 15,000 mg/l.

Main references are found in:

• municipal waste water treatment.
  
  

The Norit AirLift MBR system uses uses X-Flow modules:

• 3 m long 8” modules with COMPACT 5.2 mm ultrafiltration  membranes;
• permanent hydrophilic low-fouling ultrafiltration membranes.
  
  
  
  
   

The Airlift system provides a low power consuming technique in which sludge is recycled of verticaly installed membranes. An air injection below these membranes supports the recyling flow and enhances turbulance inside the tubular membranes. Due to this turbulence high flux rates can be achieved. This at a very low Trans Membrane Pressure (TMP). A controlled permeate withdrawal and back pulsing allows to run this plant in optimal circumstances.
The airlift system is a cost-effective solution, with an energy consumption of less than 0.2 kWh/m3.

 

Norit Airlift MBR systems are available as standardised, modular skids. The modules are placed vertically resulting in very reliable and compact installations.

If desired customer-built systems can be supplied.