Highly effective membrane filtration process as an alternative to the conventional activated sludge process

operational area | usage

  • High cleaning capacity equipment used in municipal and industrial wastewater treatment to save space
  • Phase separation through use of membranes instead of settling process – leading to high total solids in the activated sludge
  • A compact design solution without  the need for a secondary settlement tank is therefore possible

Technology | Process

In the MBR process the membrane module replaces secondary settlement. Construction volume can be reduced due to increased mixed liquor suspended solids in the aeration tank.

The aeration tank is combined with a membrane filter to separate the water from the activated sludge. The biologically treated wastewater is drawn in through the membrane. The biomass remains in the aeration tank or in the filter chamber and must be removed separately.

The process engineering design of the MBR plant is carried optimised with the design of the aeration tank (tank volume, mixed liquor suspended solids, sludge age, air requirement, etc.) and design of the membrane filtration (membrane area, number of filtration units, filtration volume, permeate flux, etc.).

Various process steps are necessary for membrane cleaning: Backwashing with filtrate, creation of turbulences at the membrane surface through air flow (cross flow), chemical intermediate and intensive cleaning with substances such as sodium hypochlorite, citric acid or similar.

Mixed liquor suspended solids in the activated sludge: 8–15 kg/m³
Membrane pore size: 0.1–0.4 µm

Process Engineering Components

  • Extremely fine screens for mechanical pre-cleaning
  • Aeration tank, if applicable with filtration units (integrated MBR system)
  • Membrane filtration tank (for separate MBR system)
  • Permeate / backwashing pumps, return activated sludge pumps (with downstream filtration tanks), surplus sludge removal
  • Cross-flow blower
  • Chemical dosing for membrane cleaning


  • Compact solution with high biomass content in the activated sludge stage making secondary settlement tank unnecessary
  • Easily extendable
  • Outstanding treatment capacity with regard to carbons and nutrients as membranes are partially permeable structures, which retain organic and inorganic solids, bacteria and substances attached to solids (solids 0 mg/l, COD < 30 mg/l)
  • Extensive disinfection of the treated wastewater (bathing water quality, water reuse as non-potable water, key water reuse technology)
  • High degree of operating reliability due to the formation of parallel lines, no sludge output through bulking or floating sludge; independent of the settling properties of sludge
  • Effective for upgrade/extension of existing wastewater treatment plants
  • Membrane filtration plants fully automated, no operator required for normal operation