Water Treatment and Purification
There are a lot of pollutants in water that needs to be dealt with. All sources of water can be treated for suspended solids, colloidal particles, odour, etc through steps designed for specific purposes.

Ultrafiltration

Application

When Suspended solids, bacteria / viruses or macro-molecules need to be separated from the fluid being treated, ultrafiltration membranes are used to clarify, concentrate and purify. Ultrafiltration (UF) membranes are normally used where the Molecular Weight Cut-Off (MWCO) of the particles being separated range from 10,000 to 150,000 Daltons. One of the more common uses of the UF process is prior to a Reverse Osmosis (RO) plant for suspended solids reduction and to reach a Silt Density Index (SDI) level of less than 3.

Operation

During the filtration process, water passed through the membrane and permeate is taken out. Periodic backwashing is carried out to remove the solids which are separated out by the membrane. Typical filtration runs range from 30 minutes to 1 hour with a one minute backwashing operation (with or without air scouring). Periodic chemical clean through a chemically enhanced backwash and / or a Clean-in-Place procedure is required to maintain permeate flow. The UF system can be operated in “dead-end” mode (where all the feed is taken out as permeate) or in “cross-flow” mode where some of the feed comes out of the reject port. Typical UF membrane materials include Polysulfone, PVDF, Polyacrylonitrile and Polyethersulfone. The membranes are also available in “inside-out” filtration configuration, where the fluid flows direction is from inside the hollow fibre, through the fibre to the outside and “outside-in” configuration where the filtration flow direction is from outside the fiber to the inside of the fiber.