RO (reverse osmosis) water treatment and water treatment technology has taken the place of complete ion exchange desalination plants in the last 10 years. With this modern filtration technology, water quality of up to 10µs can be produced. The reverse osmosis (RO) device is a water filter with an opening of 0.0001 microns, ie with this water purification we can remove organic impurities, heavy metals and bacteria from the water.
Areas of application:
boiler feedwater treatment, pharmaceutical industry, cosmetics industry, flat glass and semiconductor manufacturing, auto parts manufacturing.
The RO equipment is nothing more than a high-efficiency filter equipment, the main component is the RO membrane. It is a special membrane that consists of a laser “perforated” plastic “quilt” that is then carefully wound around a perforated tube. The membrane or membranes thus produced are placed in a membrane housing, where they are pressurized under high-pressure raw water pressure of 10-25 bar during operation. Because the “gap size” of the membranes is so small that “almost” only elementary water can pass through it, while on one side of the membrane the ultrapure water leaves, on the other the water condensed with impurities and mineral salts leaves. Purified water is called permeate, while wastewater concentrate is called. An RO system is as reliable as the pretreatment of the RO equipment is solved, so serious emphasis should be placed on this in the design. A very important and expensive element is the membranes of the RO equipment. These can work for many years with a good pretreatment, but if the RO pretreatment is not good or incomplete, the membrane can break down in as little as a few months. Effective membranes give almost completely pure water, but they cannot provide distilled water either, so this purification is max. It can be 99.9%. If even better water quality is required, other combined technologies such as mixed bed ion exchange or EDI should be used.
In an RO unit, the quality of the water produced depends to a large extent on the quality of the incoming water, the well-selected pre-treatment, the classification of the membranes, the sizing of the booster pump, and the post-treatment. There is also a difference in the type of membranes, but this is not as significant as the former. What is also important for an RO unit is the amount of water produced, i.e. the amount of permeate (purified water) produced from the raw water. In general, all types of membranes are manufactured by the manufacturer in 50-50% yield. This yield would be an unacceptable and wasteful cleaning efficiency for larger systems, so a “trick” should be applied here. To achieve this normal 50-50% yield efficiency, a concentrate backmix should be used, which can increase the yield up to 80%. But if even better yields are to be achieved, this is only possible if the concentrate is further purified with another RO equipment.
The highest operating costs for RO equipment are the water loss already mentioned, the periodic maintenance cost (dry cleaning of the membranes) and the energy consumption of the booster pump. The maintenance interval of the RO equipment is also greatly influenced by the quality of the pretreatment and raw water. The energy consumption of the booster pump is decided at the design stage. You can save a lot here too. For example, by using the pressure of the mains water or the well water pump, since this pressure can be added to the pump of the RO equipment, so much less and less consuming equipment is needed.
– pre-treatment: as already mentioned, this is one of the most important elements in the RO equipment system, so contaminants must be removed from the water in advance or their harmful effects must be eliminated. A pre-treatment definitely consists of a pre-filter, as there is no water in which there is no floating dirt. If the dirt is too much and too large, it can quickly clog the membranes, so a pre-filter of up to 5µ is used. Depending on the composition of the raw water, a water softener may be required, antifouling chemical dosing for larger systems, an iron removal device, or, in the case of mains water, dechlorination, an activated carbon filter.
– RO equipment: industrial RO equipment is usually always made up of similar elements:
These elements are usually found on all RO equipment, but can be simpler or even more complex versions.
– after-treatment: we talk about after-treatment when the water quality produced by the RO equipment is not sufficient for the given task or application. For example, when producing feed water for a steam boiler, because the RO equipment usually cannot produce water softer than 0.2-0.3 Nk °, but even softer water is required for these applications. A sodium ion exchange plasticizer or a mixed bed ion exchange equipment can then be used for post-treatment. Aftercare can be another chemical addition, such as e.g. a conditioning chemical, or e.g. also an EDI (electrolytic desalination plant).
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