Retrofitting of MBR membrane technology on existing wastewater treatment plants

Most of the conventional wastewater treatment plants apply the activated sludge treatment. Inside the aerated activated sludge tank a multitude of microorganisms (above all bacteria) eliminate different contaminants by means of metabolic and cell growth processes. With the downstream unaerated secondary clarifier the bacterial sludge and the clear phase of the treated water a separated from each other by means of gravity settling / sedimentation. A certain portion of the sludge is returned to the activated sludge tank and the excess sludge unergoes dewatering and elimination.

By applying membrane techlology one can convert a traditional activated sludge system into a membrane bioreactor (MBR). Those differ from conventional systems mainly in two things:

  1. In MBR applications the activated sludge tanks can be operated with a far higher concentration of bacteria. This leads to a higher treatment capacity at the same tank volume.
  2. In MBR applications the treated clear water is not separated by means of gravity settling but by means of membrane filtration. Therefore there no secondary clarifier necessary and the outlet quality is imroved.

Ceramic flat sheet membranes in MBR applications

In the field of MBR Atec focusses on ceramic flat sheet membranes made from silicon carbide (SiC). The membrane racks are installed in a submerged way inside a filtration tank. By applying a slight negative pressure, the filtrate is sucked through the membrane and leaves the plant as clean and germ-free water or can be reused directly. On the dirt water side of the membrane bacteria and suspended solids are held back.

Scaling and fouling of the membrane with organic and inorganic compounds is counteracted by means of coarse bubble air scouring, backwash and chemical cleaning and chemically enhanced backwash. The high chemical resistance and inert characteristics of ceramics (especially of silicon carbide) are very useful for the process and the possibilities of membrane cleaning.

Advantages of membrane bioreactors (MBR)

  • Increased treatment capacity with the same tank volume
  • High quality of the outlet / treated water
  • Germ-free treated water which is suitable for direct reuse
  • Less space required that with traditional secondary clarifier