Reverse osmosis is a membrane technique, and colloids, bacteria, impure particles, and insoluble salts will inevitably precipitate, on the surface of the reverse osmosis membrane element. Therefore, after being placed into operation, the reverse osmosis equipment used in diverse industries will eventually need to be cleaned, and the cleaning cycle's duration will vary.
Let’s understand the cleaning of contaminated RO membranes!
Membrane failure in RO Plants
In general, 60% to 80% of all system failures are attributable to organic matter-related, membrane system failures. Adsorption of organic matter from influent water onto membrane components results in flux loss.
The membrane channel is frequently blocked and the membrane system becomes contaminated, by organics in many circumstances because the adsorption layer that forms on the membrane surface, acts as a separation barrier for the dissolved salts in water.
How are RO membranes cleaned?
The cleaning techniques listed below are intended specifically for cleaning RO membrane systems, which have been clogged in the presence of organic materials like humic acids, antiscalants, or oils.
The next cleaning stages should be repeated, one for a high pH cleaning solution and the other for a low pH cleaning solution, to properly clean membrane elements that have been contaminated with organic material.
1: Make the cleaning solution as per requirement.
2: Cleaning agent with low flow input
The cleaning liquid is mixed, heated, and replaced with raw water in the element, by the cleaning liquid pump under low flow and low pressure working circumstances. The required pressure only needs to be high enough to compensate, for the feed to concentrate's pressure loss.
The cleaning fluid can be pumped back to the cleaning fluid tank for 30 minutes, after the raw water has been replenished, and should then emerge in the concentrated water pipeline. Drain the cleaning solution and create a fresh cleaning solution, if the colour of the cleaning solution continues to change.
Allow the RO Membrane Elements to fully submerge in the cleaning solution before turning off the cleaning pump. The soaking period lasts between 1–15 hours (soaking overnight will be better).
A reduced circulating flow rate might be used to maintain the temperature, during the soaking procedure. The amount of time spent soaking depends on how bad the pollution is. A half-hour soak is adequate for minor pollutants.
5: Pump circulation with high flow
Give 30 minutes of high flow cycle. High flow rates wash away impurities that cleaning fluid has removed. The highest permissible pressure drop for a single element is 1 bar (15 psi), and the maximum allowable pressure drop for a multi-element pressure vessel is 3.5 bar. Under high flow circumstances (50psi), excessive pressure drop will cause issues.
Unless, there is a corrosion issue, qualified pretreatment effluent can be used to flush the cleaning fluid. The minimum flushing temperature is 20°C, and the system must be flushed for roughly an hour to avoid precipitation.
The degree of prior contamination determines how long it takes for system performance, to stabilise following cleaning.
Please keep in mind the following:
1-The cleaning solution's temperature must be higher than 25°C to maximise cleaning effectiveness. The cleaning solution is better able to remove organic impurities from the membrane surface, due to the increased temperature.
2-For maximum effectiveness, experiment with different cleaning soak periods to eliminate some organics, such as oils, which are especially tough to clean. Additionally, several commercial cleaners contain surfactants and detergents, which aid in removing oil pollution, as do the most efficient cleaning solutions. The chemical supplier should be consulted.
3-It is more beneficial to employ an acidic cleaning solution initially, followed by an alkaline cleaning solution, if the organic pollution is brought on by the addition of too much flocculants in the pretreatment stage.
4-Try to gather samples of system pollutants in order to identify the ideal cleaning solution sequence, and then qualitatively validate which order is best for the sample. It is typically preferable to first wash the organics with a high pH cleaning solution, if the impact is comparable.
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