Water Treatment Methods and Principles: Ultrafiltration

Ultrafiltration, similar to reverse osmosis, also uses a semi-permeable membrane, but it cannot control ion removal because the membrane's pore size is relatively large, approximately 10-200 Å. It can only remove bacteria, viruses, pyrogens, and particulate matter, but cannot filter water-soluble ions. The main function of ultrafiltration is to act as a pretreatment step in reverse osmosis to prevent bacterial contamination of the reverse osmosis membrane. It can also be used as the final step in water treatment to prevent upstream water from being contaminated by bacteria in the pipeline. The effectiveness of the ultrafiltration membrane is generally determined by the pressure difference between the inlet and outlet water. Similar to activated carbon, it is usually removed by backflushing to remove impurities adhering to it.