Nanofiltration
Nanofiltration, also called membrane softening, is a lower pressure reverse osmosis (RO) technology. The term nanofiltration was coined in 1984 to denote greater removal characteristics than microfiltration, but less than those of brackish or seawater RO processes. The distinction is largely one of application, since nanofiltration is generally used to treat water supplies less than 1,500 mg/L TDS.
The softening application utilizes the membranes’ selective removal of divalent calcium and magnesium ions that cause hardness. It should be remembered that all RO membranes exhibit this selectivity, not just nanofiltration membranes. The nanofiltration membrane is mainly used for softening, but is extremely effective in the removal of color, and some organics (which cause trihalomethanes when chlorinated). Nanofiltration systems generally operate utilizing concentrate staging, designed in two or more arrays, to increase the overall system recovery and minimize concentrate (waste) flow.
RO Rentals supplied the nanofiltration (NF) pilot equipment, procured membranes, completed system connections and setup, and provided training of on-site staff for day-to-day operations. Testing demonstrated that NF was a viable softening and treatment process for West Jefferson.