Reverse osmosis membranes will reject dissolved and suspended materials including monovalent salts. Close to 99% of all dissolved and nearly all suspended material is rejected by the membrane.
Reverse osmosis is a moderate to high pressure (80-1200 psig) driven process for separating larger size solutes from aqueous solutions by means of a semi-permeable membrane. This process is carried out by flowing a process solution along a membrane surface under pressure. Retained solutes (such as particulate matter and dissolved salts) leave with the flowing process stream and do not accumulate on the membrane surface. The amount of salt and other impurities is often referred to as TDS, or total dissolved solids. The higher the TDS, the more feed pressure required.
Membranes
Membranes are made with various rejection rates for different applications. Membrane polymers to cover the full spectrum of reverse osmosis pressure ranges. One of these membrane types is a thin-film-composite family, (TFC) ideal for low TDS or softening type applications. For higher purity permeate, an ultra-low pressure (ULP) membrane line offers high water flux and salt rejection in a 125 psi class membrane.
When salt rejection is paramount, the high rejection (HR) elements offer 99.5% in standard form, or 99.7% in a premium model. Typically used in brackish water applications with up to 2000-5000 mg/l TDS, they operate around 200 psi. When the water is higher in TDS, the extreme rejection (XR) element comes into its own with 99.7% salt rejection and excellent silica and TOC (total organic carbon) removal too.
For seawater desalination, the single stage (SS) membrane in various sizes and configurations allow optimum system design. In the Premium line, salt rejection is at least 99.75%! Many of the SS products are designed to run up to 1200 psi for high salinity/high recovery installations.
Reverse Osmosis General Atomic, (ROGA) elements are made with a CA (cellulose acetate) blend membrane, which is resistant to organic fouling due to its smooth surface and neutral charge. The CA membrane operates well on chlorinated feeds, making it ideal for wastewater plants or other applications where chlorine is present or desired to minimize bacterial activity.