One-stage unit with the membrane module (UF, NF or RO) for purification and concentration of the suspension and solutions

In variouos technological processes it is necessary to remove all or some dissolved substances from the solution and to concentrate them in solvent small volume - most often water. Simultaneously proceeds the solvent purification and this way a large volume of it (water) is recovered. Such process can be carried out by means of the semipermeable membrane used for pressure-driven filtration: ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). The pressure vessel and the membrane inserted within create the module (separlator) - the separating element of the membrane unit shown on Fig. 1.
The solution circulates through the module parallel to the membrane surface - only the solvent and small part of dissolved substances penetrate across the membrane and create a partially purified solution, the permeate. The solution retained by the membrane - the retentate - has then a higher concentration of dissolved substances than the feed solution; this concentration increases in course of time, and the retentate volume decreases. The membrane retains ions and molecules and then the membrane method can be applied to the treatment of various very dilute hazardous waste, particularly liquid radioactive waste. The decrease of specific activity after one-stage membrane separation is often inadequate, then the multistage cascade (UF + NF + n · RO) must be constructed. This way the waste volume can be reduced more than one order of magnitude and more than 90% of the water (specific activity: some Bq/dm³) is recovered.
Studies and research works on the application of membrane methods in nuclear technology are carried out in the INCT since 1985.

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