Reverse Osmosis, often abbreviated to RO is a technology that is used to remove a large majority of contaminants from water by pushing the water under pressure through a semi-permeable membrane. Such semi permeable membranes are common in nature; the skin is a good example and this phenomenon, osmosis, explains why you get thirsty as you swim in the sea or “plump-up” in a long fresh water bath. In RO, an applied pressure is used to overcome osmotic pressure, a colligative property that is driven by chemical potential, a thermodynamic parameter. RO can remove many types of molecules and ions from solutions and is used in both industrial processes and in producing 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 (holes), but should allow smaller components of the solution (such as the solvent) to pass freely.
In the normal osmosis process, the solvent naturally moves from an area of low solute concentration (High Water Potential), through a membrane, to an area of high solute concentration (Low Water Potential). The movement of a pure solvent is driven to reduce the free energy of the system by equalizing solute concentrations on each side of a membrane, generating osmotic pressure. Applying an external pressure to reverse the natural flow of pure
Solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, there are key differences between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration. Moreover, reverse osmosis involves a diffusive mechanism so that separation efficiency is dependent on solute concentration, pressure, and water flux rate.
Reverse osmosis membranes
Reverse osmosis membranes do not have definable pores in the way that the films used in ultra filtration do; there are only spaces between the fibers making up the film which can take up water because of the acetyl or similar groupings which form the surface. The dense layer of active surface is about 0.25 microns thick supported by a thicker porous layer. Membranes are cast in thin sheets or extruded as hollow fibres 80 or 250 um in diameter.
Typical RO membrane types and characteristics
||Medium water flow
||pH range 4-8
||Max. temp.95 F
|Composite(thin film composite,TFC)
||High water flow
||pH range 2-11
||Max. temp. 113 F
||Vulnerable to oxidizers (chlorine)
||Low water flow
||pH range 4-11
||Max. temp, 95 F
Industrial waste water Reverse Osmosis
An industrial reverse osmosis system is the best way to ensure the purest water on hand at all times. This equipment is specially designed to filter out the tiny ions that salt and other compounds create when they are dissolved in water. Reverse osmosis is a process that industry uses to clean water, whether for industrial process applications or to convert brackish water, to clean up wastewater or to recover salts from industrial processes. Reverse osmosis will not remove all contaminants from water as dissolved gases such as dissolved oxygen and carbon dioxide not being removed. But reverse osmosis can be very effective at removing other products such as trihalomethanes (THM's), some pesticides, solvents and other volatile organic compounds (VOC's).
The effluent discharged to the sewer typically contains between 200 to 10,000 parts per million (ppm) total dissolved solids (TDS). With the proper pretreatment technology followed by RO, this water can be recycled.
How does Reverse Osmosis work?
The objective of secondary treatment is the further treatment of the effluent from primary treatment to remove the residual organics and suspended solids. Secondary treatment typically removes the smaller solids and particles remaining in the wastewater through fine filtration aided by the use of membranes or through the use of microbes, which utilize organics as an energy source. In most cases, secondary treatment follows primary treatment and involves the removal of biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes. Aerobic biological treatment is performed in the presence of oxygen by aerobic microorganisms (principally bacteria) that metabolize the organic matter in the wastewater, thereby producing more microorganisms and inorganic end-products (principally CO2, NH3, and H2O). Several aerobic biological processes are used for secondary treatment differing primarily in the manner in which oxygen is supplied to the microorganisms and in the rate at which organisms metabolize the organic matter.
Most RO technology uses a cross flow process to allow the membrane to continually clean itself. As some of the fluid passes through the membrane the rest continues downstream, sweeping the rejected species away from the membrane.
RO systems used in industrial and commercial applications, where large volumes of treated water are required at a high level of purity, typically operate at pressures between 100 and 1,000 psig, depending on the membranes chosen and the quality of the water being treated. Most commercial and industrial systems use multiple membranes in series. The processed water from the first stage of treatment can be passed through additional membrane modules to achieve greater levels of treatment for the finished water. The reject water also can be directed into successive membrane modules for greater efficiency, though flushing will still be required when concentrations reach a level where fouling is likely to occur
Reverse osmosis systems can be used to treat boiler feed water, industrial wastewater, process
water and more. A few of the major uses are:
Boiler Feed Water Treatment:
RO is used to reduce the solids content of waters prior to feeding into boilers for the power generation and other industries.
Reverse osmosis is an approved treatment process for the production of United States Pharmacopeia (USP) grade water for pharmaceutical applications.
Food & Beverage:
Water used to process food products and to produce beverages is often treated by a reverse osmosis system.
Reverse osmosis is an accepted component of a treatment process to produce ultrapure water in the semiconductor industry.
RO systems have been successfully applied to a variety of metal finishing operations including several types of copper, nickel and zinc electroplating; nickel acetate seal; and black dye.
Electro plating industry
Iron and Steel (involving processing from ore/ integrated steel plants and or Sponge Iron Unit
Fermentation Industry (Distilleries, Maltries and Breweries)
Milk processing and dairy products (integrated project)
Automobiles industries (Integrated facilities)/ Automobiles servicing, repairing and painting (excluding only fuel dispencing)
Pulp and Paper industry
Slaughter House, Meat & Sea Food Industry
Food and Fruit Processing Industry
Textile Industries/ Man-made fiber (synthetic)/ Woolen Mills/Cotton/Yarn/ textile processing involving any effluent/ emission- generating process ,bleaching, dyeing, printing and scouring
Rice Mills with boiler/furnance and dry rice mills
Pesticide Manufacturing and Formulation Industry
Hotel Industry (Hotels (10 rooms and above) /Restaurants having 30 chairs & above)
Inorganic Chemical Industry
Edible Oil & Vanaspati Industry
Soda Ash Industry (Solvay process)
Lead acid battery manufacturing (excluding assembling & charging of acid lead batteries.
Ferrous and Non ferrous metal extraction involving different furnaces through melting, refining, reprocessing, casting and alloy making
Synthetic fibers including rayon, tyre cord, polyster filament yarn
Health care establishment (20 Beds & Above)
Manufacturing of Paints, Varnishes, pigments and intermediate (excluding blending/ mixing) etc.