Nanofiltration
(NF) & Reverse Osmosis (RO) - Design Criteria
NF and RO modules may be arranged in parallel or series configurations. Each element has a diameter of approximately 12-inches and a length of up to 60-inches. Two to six elements are assembled in a single cylindrical module. The size and the operating pressure vary depending on the installation. For example, brackish water treatment is operated at approximately 1,000 to 1,200 psi while landfill leachate treatment process can reach pressures up to 1,800 psi.
In contrast to UF, a more defined pretreatment is required for nanofiltration (NF) and reverse osmosis (RO). In general, the water/wastewater should have a low Silt Density Index (SDI) to avoid membrane clogging. RO membranes may also clog via calcium and magnesium precipitation (ions are retained by RO membrane), which can be avoided by water softening. A microfiltration or ultrafiltration stage upstream of RO membranes can remove organics, algae and fine particles to avoid fouling during desalination.
Illustrated below is a conventional RO/NF membrane process diagram.
NF and RO modules may be arranged in parallel or series configurations. Each element has a diameter of approximately 12-inches and a length of up to 60-inches. Two to six elements are assembled in a single cylindrical module. The size and the operating pressure vary depending on the installation. For example, brackish water treatment is operated at approximately 1,000 to 1,200 psi while landfill leachate treatment process can reach pressures up to 1,800 psi.
In contrast to UF, a more defined pretreatment is required for nanofiltration (NF) and reverse osmosis (RO). In general, the water/wastewater should have a low Silt Density Index (SDI) to avoid membrane clogging. RO membranes may also clog via calcium and magnesium precipitation (ions are retained by RO membrane), which can be avoided by water softening. A microfiltration or ultrafiltration stage upstream of RO membranes can remove organics, algae and fine particles to avoid fouling during desalination.
Illustrated below is a conventional RO/NF membrane process diagram.
