In ultrafiltration, water and low-molecular-weight substances are passed through an ultrafine membrane by the application of pressure to the system; flow through the membrane is achieved by applying a pressure gradient between the outer and inner walls of the membrane structure. Feed pressure is from 4 to 100 psig (typically < 30) and transmembrane pressure is generally <14 psig.
- High and consistent product quality measured by turbidity (NTU) or silt density index (SDI).
- Tolerance to feedwater quality upsets.
- No use of pretreatment chemicals (polymer, coagulant, pH adjustment) and associated costs for sludge disposal.
- Small footprint and less weight than media filters.
When used as a pretreatment for reverse osmosis (RO), UF also helps reduce fouling of the RO membranes, which can lead to:
- Reduced chemical cleaning frequency and consequently, lower operating costs and downtime.
- The potential to operate RO at higher flux, with fewer membranes and vessels — leading to lower capital cost for the RO system.