The U.S. Environmental Protection Agency’s (EPA) Water Infrastructure Resiliency and Finance Center, in collaboration with the...
Hollow-fiber ultrafiltration (UF) membranes are an important, innovative addition to the water treatment dealer's toolbox. New UF-based point-of-entry (POE) platforms now make it affordable to combine this unique technology with existing filtration and treatment systems to solve a broad range of water problems.
UF systems provide three fundamental advantages over traditional filtration alternatives:
Many dealers have identified significant market opportunities for UF technology, especially when applied to waters where fine sediment, turbidity and cysts are of primary concern. Most dealer sales opportunities fall into three categories:
Hollow-fiber membranes can be constructed to allow either inside- out or outside-in flow in a dead-end mode (i.e. there is no continuous waste flow).
Like all filtration media, a UF membrane becomes covered with the material it removes from water. Over time, the accumulation of that filtered material reduces membrane flow and increases pressure drop. Similar to the backwash and rapid rinse cycles employed by traditional multimedia filters, many UF systems are designed to flush regularly in order to remove material filtered out of the water.
A flush cycle flow path will be set in either a forward or reverse direction, depending on the configuration of the system. In the case of forward-flush systems, a flush valve is opened so that flow through the bore of the fibers (inside-out) or around the fibers (outside-in) is significantly increased. Retained solids are flushed from the membrane surface due to the velocity of the water flowing around it.
For back-flush systems, a flush valve is opened and feed water is shut off so filtrate is forced to reverse flow through the membrane. This process lifts retained solids from the membrane surface and flushes them to drain. The filtrate used for back flushing can be provided by a storage tank or by other UF membranes that remain in service.
UF systems are used for many applications requiring the removal of suspended solids, including particles, colloids, cysts, bacteria and viruses. Typical residential and commercial applications include:
Surface and well water treatment - UF is used as part of a multibarrier surface water treatment for reduction of:
Pretreatment of RO feedwater - Pretreating RO feedwater with UF increases RO membrane life and lowers operating costs.
Prefiltration of water feeding sensitive equipment - UF can be installed prior to one-time-use specialized filters and other sensitive equipment to lower operating costs:
Postfiltering high purity water in special applications - UF can be installed after an RO/DI system to improve the quality of ultrapure water and lower operating costs in the following ways:
Installed as part of a multibarrier system, UF provides added peace of mind. UF, when used on potable water supplies, acts as an additional barrier against compromises to the water system by reducing cysts, turbidity, bacteria and viruses.
To provide protective redundancy against pathogens when treating nonpotable water supplies, UF should be combined with alternative technologies (such as ultraviolet or chlorination) certified to meet the U.S. Environmental Protection Agency and NSF purifier protocols for cysts, bacteria and virus removal.
Due to the complexity and variability of local regulations, dealers and installers should have a thorough understanding of state and local codes for treating unsafe water supplies. They should provide both certified systems and routine maintenance programs to ensure that the treated water continuously meets those standards.