The filtration pore size of the reverse osmosis filtration system is only 0.0001 microns. Due to the precise pore size of the reverse osmosis membrane, regular backwashing is required to maintain its filtration efficiency. 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%, physical flushing can no longer restore the performance of the osmosis membrane, and chemical cleaning is required at this time.
Chemical Cleaning Frequency of RO Membrane Element
The cleaning cycle of the membrane depends on the actual pollution situation on site. The normal cleaning cycle is every 3-12 months. If cleaning more than once in 1 month, need to improve pretreatment such as additional investment or redesign of membrane system. If the cleaning cycle of reverse osmosis pure water equipment is once every 1-3 months, it should focus on adjusting and optimizing the operating parameters of the existing system. Even if the system has not been polluted for a long time, in order to better ensure the normal operation of the system, it is generally considered to perform chemical cleaning every 6 months.
Choice of Cleaning Agent
Different pollutants should use different cleaning agents. Usually there is not only one contaminant when contamination occurs, so conventional chemical cleaning needs to include two steps of high pH value cleaning and low pH value cleaning. Generally speaking, high pH cleaning solution should be used to clean oil and microbial contamination first, and then low pH cleaning solution should be used to clean inorganic scale or metal oxide contamination. Sometimes it is also first acid washed and then alkali washed, or only one agent is used for cleaning.
Precautions before Cleaning
1. Calibrate pH meter before use;
2. Estimate the volume of cleaning fluid used;
3. When handling, wear safety glasses, protective gloves and work clothes;
4. The temperature and pH range of the cleaning solution meet the specified values;
5. Ensure that all cleaning chemicals are completely dissolved and mixed before the cleaning fluid enters the system;
6. Before using a medicine, carefully read the Drug Safety Form (MSDS) obtained from the drug company and the instructions on the medicine.
Chemical Cleaning Steps
1. Flush membrane elements: flush with reverse osmosis product water or ion exchange water for a few minutes;
2. Prepare the medicine: ensure that the medicine is completely dissolved;
3. Circulation: replace the water in the membrane element with a low flow, discharge a part of the cleaning solution, and then circulate; The cycle operation starts for 5 minutes, and circulates according to the amount of 1/3 of the set flow. During the cycle of 5-10 minutes, it circulates according to the circulation flow of 2/3 of the set flow. After 10 minutes, it circulates according to the flow requirements. The cycle time is determined on a case-by-case basis. Generally it takes 1 hour. During this period, check whether the pH value changes at any time. Pressure should be kept as low as possible, with as little as permeation as possible. At the same time, monitor whether the pressure difference changes;
4. Immersion and recirculation: slowly close the valve at the inlet of the reverse osmosis membrane element, and when the circulation volume is close to zero, close the circulation pump. In order to prevent the liquid form flowing out of the pressure vessel, the relevant valve can be closed during immersion. Usually in the range of 1~12 hours. After soaking, open the relevant valve and recycle;
5. Flushing: use reverse osmosis product water or ion-exchange water to flush the membrane elements and the chemicals in the cleaning device. At this time the system is replaced from the circulating state to the discharging state. Flush the membrane system with supply water. Rinse time is about 20-60 minutes. Whether the flushing is complete can be judged by measuring the pH value and conductivity of the drainage. The values of pH and conductivity are similar to those of the incoming water, and the flushing can be stopped when there is no change;
6. Test run. When the system is started normally, the initial produced water should be discharged until the water quality of the produced water meets the requirements.