Ultrafiltration, also referred to as UF, is a membrane filtration technique in which a liquid is forced through a semi-permeable membrane under pressure. In ultrafiltration, this membrane has a pore size that varies roughly from 0.1-0.01 μm (10-100 nm). Ultrafiltration membranes are mainly used for the removal of suspended and colloidal substances, bacteria and viruses. Ultrafiltration membranes are supplied in a range of configurations. Possible configurations include:
Besides the specific membrane configurations, there are also a number of different operating methods. The two most commonly used methods are dead-end (this is the method Logisticon generally uses) and crossflow. The names refer to the way the nutrient is supplied to the membrane. With dead-end UF, the supply is fed into the hollow membrane and stopped at the end. This way, the water passes through the membrane and the dirt accumulates. The dirt is regularly washed away by means of a backwash. The dirt is then released and can be removed. This is called semi-dead-end operation. If the dirt is too compressed or is sticking too much to the membrane, the backwash may no longer be sufficient. In this case, chemical cleaning will be performed. In cross-flow operation, the liquid is directed along the membrane surface. The permeate passes through the membrane and the dirt stays behind. This creates a concentrated current. In this operation, the dirt is continuously removed by the supply current flowing past.
