Reverse osmosis is the process of pushing a solution through a filler that traps the solute on one side and allows the pure solvent to be obtained from the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.
This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semi permeable, meaning it allows the passage of solvent but not of solute.
The membranes used for reverse osmosis have no pores; rather, the separation takes place in a dense polymer layer of only microscopic thickness. In most cases the membrane is designed to allow only water to pass through. The water goes into solution in the polymer of which the membrane is manufactured, and crosses if by diffusion.
This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2-14 bar (30-200 pounds per square inch) for fresh and brackish water, and 40-70 bar [(600-1000 psig)] for sea water, which has around 24 Bar (350 psi) natural osmotic pressure which must be overcome.
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It is observed that the lowering of water table has reduced the availability of ground water and deteriorated its quality. In some areas it is simply not available. Because of such and other reasons today industries are actively considering a recycle of wastewater.
There are already some effluent recycle installations in India and abroad working in various industries. There is enough data on operation and maintenance of such system. This paper is intended to share the practical technical aspect of Effluent Recycle System.
The Effluent Recycle usually makes an in- house, reliable, good quality additional water source available for the industry. Hence, even if today it is not required, the Effluent Recycle plant can be planned for future. It is obvious that with time all the industries will be asked to go for. “Zero Liquid Discharge”.
With present practices of Effluent Recycle, the cost of Recycle water is higher than the fresh water available. (It ranges from Rs. 20-30 per M3). But the recycled water quality is usually much better for common applications like boiler feed, cooling lower make up, some parts of process.
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Reject disposal is one of the most important deterrents in the Feasibility study of recycle system with Reverse Osmosis.