The reverse osmosis filtration system's filtering pore size is 0.0001 microns. The reverse osmosis membrane's exact pore size necessitates routine backwashing, to maintain its filtration effectiveness.
Physical flushing can no longer restore the performance of the osmosis membrane. When the permeate volume of the reverse osmosis system drops by 10-15%, the system pressure difference between the influent and concentrated water increases to 1.5 times the initial value, or the quality of the permeate water drops by 10-15%. At this point, chemical cleaning of RO System is necessary.
Frequency of RO Membrane Chemical Cleaning
The membrane's cleaning cycle is determined by the level of pollution present at the time. The typical cleaning cycle lasts three to twelve months. If cleaning is required more than once per month, pretreatment needs to be improved by either more expenditure or modification of the membrane system.
When cleaning reverse osmosis plant, which should be done every one to three months, the emphasis should be on correcting and improving the system's operational parameters. Even if the system hasn't been contaminated in a while, it is typically recommended to execute chemical cleaning every six months, in order to better ensure the system's regular performance.
Selecting a cleaning agent in RO Plants
Different cleaning chemicals should be used for various contaminants. When contamination occurs, there are typically multiple contaminants, thus standard chemical cleaning requires two steps: high pH value cleaning and low pH value cleaning.
In general, cleaning solutions with high pH should be used to remove oil and microbiological contamination, before using cleaning solutions with low pH to remove inorganic scale or metal oxide pollution. Additionally, sometimes only one cleaning agent is utilized, or it is first cleaned in acid and then in alkali.
Safety measures before cleaning RO membranes
1. Before usage, calibrate the pH metre;
2. Calculate the amount of cleaning agent utilized;
3. Put on work clothes, gloves, and safety glasses when handling;
4. The cleaning solution's temperature and pH range must be within the acceptable ranges;
5. Before the cleaning fluid enters the system, make sure that all cleaning agents are thoroughly dissolved and blended;
6. Carefully read the instructions you obtained from the manufacturer before using it.
How to chemically clean a reverse osmosis (RO) system?
1. Rinsing: Rinse the membrane elements for a few minutes with reverse osmosis product water or ion exchange water.
2. Preparation: Prepare the chemicals by making sure it is fully dissolved.
3. Circulation: Discharge a portion of the cleaning solution before replacing the water, in the membrane element with a low flow. The cycle action starts after 5 minutes and circulates 1/3 of the predetermined flow. It circulates at a rate of 2/3 of the programmed flow for the duration of the cycle of 5–10 minutes.
It circulates in accordance with the necessary flow after ten minutes. Case-by-case analysis is used to determine the cycle time. In most cases, it takes an hour. Check to see whether the pH value changes at any point during this time. With the least amount of permeability, pressure should be kept as low as feasible. Watch to see if the pressure difference changes concurrently.
4. Immersion and recirculation: When the circulation volume is nearly nil, turn off the circulation pump and gradually close the valve at the reverse osmosis membrane element's inlet.
The relevant valve can be closed during immersion to stop the liquid form from leaking out, of the pressure vessel. It is usually between one and twelve hours. Open the appropriate valve after soaking and then recycle.
5. Flushing: To flush the chemicals and membrane components in the cleaning equipment, use reverse osmosis product water or ion-exchange water. The transition from the circulating state to the discharging state takes place at this point. Apply supply water to the membrane system to flush it.
It takes 20 to 60 minutes to rinse. The pH and conductivity of the drainage can be used to determine, whether the flushing is complete. When there are no changes and the pH and conductivity levels are similar to those of the entering water, flushing can be halted.
6. Run a test: The initial produced water should be discharged after a regular system start-up, until the produced water's water quality satisfies the standards.
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