Reverse osmosis and Reverse osmosis Units – Silt Density Index (SDI)
There are many different types of filtration but they all have the same purpose – to remove particles and pathogens from the water. Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane. In reverse osmosis, an applied pressure is used to overcome osmotic pressure. Reverse osmosis can remove many types of molecules and ions from solutions, and is used in both industrial processes and the production of potable water. The result is that the solute is retained on the pressurized side of the membrane and the pure solvent is allowed to pass to the other side. To be “selective”, this membrane should not allow large molecules or ions through the pores, but should allow smaller components of the solution to pass freely. SILT DENSITY INDEX (SDI) Membrane fouling is the main cause of permeate flux decline and loss of product quality in reverse osmosis (RO) Systems, so fouling control dominates RO system design and operation. SDI is a measurement of the fouling potential of suspended solids. It measures the time required to filter a fixed volume of water through a standard 0.45µm pore size microfiltration membrane with a constant given pressure of 30 psi (2,07 bar). An SDI of less than 5 is considered acceptable for the reverse osmosis systems and no pre-filtration is necessary. A media (sand-type) filter is required if the value of SDI ranges from 5-10. If the SDI is greater than 10, a 2-stage media filtration is necessary, possibly with the aid of coagulants or settling tanks .
Reverse osmosis purified water is used in homes, Crop and Livestock farms, hospitals, Boilers, Chillers, Cooling towers, Food processing, Dairy and Cheese industry and general industrial processes.