Reverse osmosis plant maintenance steps
What is reverse osmosis and its relationship to water desalination:
- Osmosis is the natural physical force of water with a high concentration of certain dissolved atoms as it moves through a semi-permeable membrane to a region of water with a low concentration of dissolved atoms, where waterworks to find a balance on both sides of the membrane, in other words, the water on both ends of the membrane will become of one concentration of atoms dissolved.
- The process of reverse osmosis means pushing water with a high pressure that allows it to cross the membrane in a direction opposite to what is happening in normal life, which leads to the penetration of pure water through the membrane and thus confines the salt atoms in a high salinity area.
- As for desalination, it is a separation process used to reduce the percentage of dissolved salts in saline water to a level at which this water becomes usable and drinkable.
Conditions for using reverse osmosis in water treatment:
The necessary treatment of water before initiating the reverse osmosis process depends on:
- Experience and technical capabilities of the staff: The feed water should contain small amounts of solid impurities and silt in order to preserve the membranes from clogging, and this can be accomplished by removing these impurities or suspending them and capturing them during their passing through one of the initial treatment stages.
- When water passes through reverse osmosis membranes, the percentage of ions increases, and this inevitably leads to a rise in the percentage of dissolved salts (TDS), especially calcium and magnesium, and the deposition of part of it inside the membranes. Despite the possibility of removing calcium and magnesium or adding a chemical to keep them liquefied, many water treatment experts recommend the use of a Softener unit in the water line before entering the membranes and replacing its ions with sodium ions.
- Also, chlorine must be completely removed when using Thin Films or reducing its percentage with CTA membranes, and this is done using a carbon filtration unit, and this is what water treatment experts encourage. As for injecting sodium metabisulphite, it is effective, but it contributes to the growth of bacteria that clog the membranes as well. and reduce its performance.
- Large plants must be compulsorily equipped with PH adjusting fittings between 5.5 and 6.55 This helps to keep the membranes clean and prevent clogging.
Stages of reverse osmosis water treatment:
1 – Pre-treatment stage:
The feedwater flow is treated to make it compatible with the working conditions of the membranes and to be free of solid particles through:
- Sand Filter Multimedia Filter
- Ph Adjustment
- Adding Chemicals Dosing to curb any subsequent calcification of different materials such as calcium sulfite.
2 – pressure stage:
At this stage, the pressure of the treated effluent is initially raised to a pressure level suitable for the membranes and according to the percentage of salts in the raw water.
3 – The stage of separation by membranes:
At this stage, the permeable membranes allow only freshwater to pass through, but the dissolved salts are not able to do so and are transferred to the drainage line with a high salt concentration, knowing that a very small percentage remains in the freshwater flow and this is due to the incompleteness of the membranes that allow the passage of These are few percentages.
4 – The stage of installation or post-treatment:
Freshwater produced from membranes requires PH adjustment, and this is done by raising it from about 55 to 7.5.
It is also provided with a certain percentage of chlorine to immunize it during storage and pumping into the network from any bacteria that may enter it.
Reverse osmosis system maintenance
1- Membranes age: It plays a role in the increase of produced water salts, and thus washing the membranes leads to clear changes in the specifications of the membranes, and the percentage of rejection drops to 90%.
2- Preventing membrane clogging: This can be applied through water purification and filtering to remove fine impurities and colloidal substances, and then there are two ways to reduce the possibility of membrane clogging.
The first method is by adding an anti-calc chemical and precipitating salts in the high pressure pump feed line before the reverse osmosis unit.
The second method is to remove the hardness of the water in the primary treatment.
3- Membrane washing: The principle of the process is very easy, although it requires some supplies such as a pump, tank, and water hoses, in addition to certain chemicals or replacing them with acid to wash the low PH.
The process takes place by circulating the required liquid into the membranes tube and from there to the tank for a period of no less than an hour, after which the membranes are washed with clean water, the connections are made, and the station is started again.
In general, membranes last for several years, and it is rare for all of them to fail at the same time, but they begin to fail gradually until they reach a stage where they must be completely replaced, knowing that there are membranes in use for more than twenty years.
4 – Preventing the growth of bacteria: Bacteria can grow in the stored water, and here it appears the importance of pumping chlorine into the water produced to immunize it and prevent the growth of any germs in it.
It is also recommended to paint the walls of the tanks in opaque colors such as black and others, in order to prevent the appearance of algae on them.
Maintenance of reverse osmosis plants:
The basic maintenance works of desalination plants consist of the following:
Periodic maintenance and follow-up to the status of Booster pumps, in addition to cleaning them and preventing leakage.
Lubrication and lubrication of pumps and motors, if necessary, according to the program approved by the manufacturers.
Washing and rinsing the Media, sand & carbon filters on a daily or weekly basis, according to the quality of the raw feeding water.
Replace micron filters (cartridge filters) every eight weeks.
Ensure that measuring devices are read and adjusted, if necessary, either mechanically or with special solutions.
Maintaining the presence of sufficient quantities of chemicals in the tanks for the pre-and post-treatment phases.
Conducting a periodic Probing Inspection of the membranes.
Record readings and results of water tests on a daily basis and present them to specialists to understand changes, address weaknesses, and anticipate any emergency problems.
Inventory of chemicals, consumables, and spare parts and order what is missing from them.
At Water Care, we have a specialized team to carry out the maintenance work of reverse osmosis plants.