By micro and ultra filtration mainly macro molecules und small particles as well as suspensions and emulsions are separated. The passages between micro filtration and ultra filtration are fluent: Membranes of a pore size between 0,1µm and a few µm are associated with micro filtration, membranes of a pore size between 0,01µm and 0,1µm are associated with ultra filtration. The working pressure of micro filtration is between 0,5 bar (approx. 7 PSI) and 5 bar (approx. 73 PSI), the working pressure of ultra filtration is between 0,5 bar (approx. 7 PSI) to 10 bar (approx. 145 PSI).
The separation effect of the micro and ultra filtration is based mainly on sieve effects, i.e. particles with a diameter bigger than the average pore size of the membrane are retained. Additionally, also effects of solubility and diffusion are of importance.
Depending on the application, various module designs are suitable. The most common designs are spiral wound modules, tubular modules as polymeric or ceramic element, plate modules, capillary modules and hollow fiber modules. These designs are distinguished from each other by the hydraulic diameter and the related specific package density.
Field of applications of micro filtration:
- Separation of pickling sludge
- Separation of abrasive particles, e.g. hydroxides, CaCO3, grinding particles
- Separation of activated sludge
- Separation of colloidal components out of acids and brines
- Separation of catalysts
- Pre-concentration of suspensions