A partly permeable membrane is used in the reverse osmosis (RO) method of water purification, to get rid of bigger particles, undesirable compounds, and ions from drinking water. When feedwater with its load of dissolved salt and other impurities is forced through a semi-permeable membrane in a RO system, pressure is employed to overcome natural osmotic pressure, and a high proportion of the contaminants are removed. Water that has undergone this procedure is extremely pure.
Why is pre-treatment needed in RO Plants?
Pre-filtration is a typical method of pretreatment for membrane filtration systems, which is intended to remove large particles and debris, which involves screening or coarse filtration. Pre-filtration can be used on the entire membrane filtration system or on individual membrane units. Depending on the kind of membrane filtration system used and the calibre of the feed water, different pore sizes are linked with the pre-filtration process.
Typically, RO, MF and UF systems are made to remove suspended solids, a type of big particle debris that can clog or harm the fibres of the membrane.
Before the water passes through the main filtering system, a pre-filter, often referred to as a sediment filter, works to remove dirt, sand, rust, silt, and other substantial suspended particles and sediments.
Importance of pre-treatment in RO Plants
The reverse osmosis membrane has a high need for the incoming water, since it is a semi-permeable polymer membrane, with highly precise pore sizes. Additionally, the incoming water particles must be less than 5 microns otherwise the reverse osmosis membrane will become contaminated, reducing the service life and raising the filtration cost as a result.
Therefore, if the inlet water particle size is less than 5 microns, it satisfies the reverse osmosis inlet water quality criteria. Installing a pre-filtration system is not necessary in this situation. Installing a pre-filtration equipment is necessary if the incoming water particle size is greater than 5 microns. In general, a pre-filtration device made up of one or more security filters is utilized, before the reverse osmosis equipment.
Additionally, reverse osmosis pre-filtration filters are typically installed with 1 micron or 5 micron filter elements or filter bags, in order to guarantee that the incoming water particles of the process are within 5 microns.
Use of ultrafiltration as pretreatment for reverse osmosis
Ultrafiltration is frequently employed in the pre-filtration of reverse osmosis in addition to microfiltration. The steady water quality of ultrafiltration can essentially remove particles larger than 0.1 microns, limit impurity pollution on reverse osmosis, and reduce clogging of reverse osmosis membranes, extending the useful life of the latter and lowering filtration costs.
Conclusion
The goal of pretreatment is to increase the service life of the reverse osmosis membrane, and decrease the filtration cost, regardless of whether microfiltration or ultrafiltration is chosen, as the pre-filtration of reverse osmosis. When selecting the reverse osmosis pre-filter solution, we should take into account both the filtration cost and the degree of water quality pollution.
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