Microfiltration defines a physical filtration process that removes suspended solids from water due to the small pore size of the filtering medium, typically a membrane. Unlike reverse osmosis and nanofiltration, microfiltration utilizes only physical filtration to remove particles in the 0.1 to 10 micron range, including bacteria but unlike nano and RO, microfiltration does not remove dissolved contaminants.
Typically, similar to reverse osmosis and nanofiltration, water microfiltration is carried out by cross-flow separation, where a feed stream is introduced into the membrane element under pressure and passed over the membrane surface in a controlled flow path. A portion of the feed passes through the membrane and is called permeate.
The rejected materials are flushed away in a stream called the concentrate. Cross-flow membrane filtration uses high cross flow rates to enhance permeate passage and reduce membrane fouling. It also operates at a lower pressure (less than 100 psig) than nanofiltration and reverse osmosis.
Microfiltration systems are typically used for:
- Cold sterilization of beverages and pharmaceuticals.
- Clarification of fruit juices, wines and beer.
- Pretreatment upstream of RO to remove suspended solids which can foul membranes.
- Separation of bacteria from water (water microfiltration has become the method of choice for many municipal and community water treatment systems due to its ability to consistently remove spores such as Cryptosporidium and Giardia).
- Some types of effluent treatment.
- Some oil / water separation applications.
Microfiltration, like other membrane processes, must be correctly applied with adequate pretreatment to prevent frequent and / or irreversible membrane fouling. The WaterProfessionals® have extensive experience applying this and other water treatment technologies to assure economical, effective long-term operation.