We are the leading reverse osmosis treatment plant manufacturer in coimbatore, chennai, Madurai, Tirupur, Kerala, Karnataka
Reverse osmosis is a water purification technology that uses a semipermeable membrane to remove ions, molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential differences of the solvent, a thermodynamic parameter.
Reverse osmosis can remove many types of dissolved and suspended species from water, including bacteria, 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 (holes), but should allow smaller components of the solution (such as solvent molecules) to pass freely
In one word: analysis. Every source of water is different, and you never know what's in your water until you have it analyzed. The water analysis, LSI, SDI, or CFI values are used to determine the precise pretreatment requirements for a particular RO System. Since water supplies vary considerably from one location to another, each pretreatment requirement will be different. On average, most Reverse Osmosis Systems need an antiscalant injector or water softener to prevent damage to the membrane.
A detailed chemical analysis of the RO feed water is an absolute necessity for identifying potential foulants. This should include a measurement of the hardness (calcium and magnesium), barium, strontium, alkalinity, pH, and chlorine. The data from the chemical analysis can be used by the RO equipment designers to determine the optimum membrane array that will both minimize the tendency of scale and deposit formation and maximize the recovery and flux rate.
For example, the Langelier Stability Index (LSI), a measure of the calcium carbonate scaling tendency of the water, is computed from the water analysis to determine the maximum permissible concentration of dissolved minerals in the reject stream before scale deposition becomes a problem. Because of the number of variables that must be considered, these calculations are difficult to do with pencil and paper. Fortunately, the membranes manufacturers have developed computer programs that make these computations fast and easy to perform where the user can project the performance of membranes at actual feed conditions.
Although a water analysis is helpful in predicting the tendency of dissolved minerals to cause problems in the RO System, it does not always forecast the fouling tendency of colloids and other finely dispersed suspended solids. The Silt Density Index (SDI) is a useful tool for quantifying the fouling tendency of the feed water. This test is conducted by filtering a sample through a 0.45 micron (µm) filter and measuring the time required to collect a unit volume of filtrate. An index number is calculated from this data. Traditionally, a SDI value of less than 3.0 is desirable for RO feed waters. The SDI measurement has certain limitations in that it does not model the cross flow design of an RO membrane.
Just as acidic solutiosn aren't good for membranes, caustic solutions are equally damaging to membrane elements. Acid injection may be incorporated into the RO pretreatment system to control pH and minimize the scale-forming tendency of the feed water. Acid injection is indicated if the scale-forming tendency of the brine stream is above +0.3 as measured by the LSI. Either sulfuric or hydrochloric acid can be used for this purpose. However, sulfuric acid is less costly, and is more commonly used.