Reverse osmosis technology is becoming more widely adopted due to its numerous advantages, such as high efficiency and excellent water purification performance. However, improper maintenance of reverse osmosis systems can lead to significant issues, especially for users with limited technical expertise. Proper management of the equipment is essential to prevent serious problems and ensure long-term performance.
One important maintenance practice is low-pressure flushing. Regularly flushing the system with high flow, low pressure, and slightly acidic water helps remove contaminants that accumulate on the membrane surface, preserving its efficiency. If the SDI (Silt Density Index) of the feedwater suddenly rises above 5.5, it's crucial to perform a low-pressure flush until the SDI returns to acceptable levels before restarting the system.
Another key aspect is protection during system downtime. Frequent shutdowns are common in many applications, and proper measures must be taken when the system is not in use for short or long periods. Inadequate protection can lead to irreversible membrane damage.
For short-term shutdowns (up to 15 days), a low-pressure flush every 1–3 days is recommended. At temperatures above 20°C, stagnant water in the system can quickly become contaminated, leading to bacterial growth. Therefore, it's advised to flush the system daily if the temperature is over 20°C, and every three days if it’s below 20°C. After each flush, all inlet and outlet valves should be closed to prevent contamination.
For long-term shutdowns (over 15 days), a protective solution should be used. A typical formula includes 10% formaldehyde, 20 mg/L isothiazolone, and 1% sodium bisulfite. This helps prevent microbial growth and maintains the integrity of the membrane.
Chemical cleaning is also an essential part of maintenance. Over time, membranes can become fouled by inorganic deposits, colloids, microorganisms, or metal oxides. These contaminants can reduce water production, lower desalination efficiency, and increase pressure differences. In severe cases, the membrane may be irreversibly damaged. To restore performance, chemical cleaning is necessary.
It is generally recommended to clean the membranes every 3 to 12 months. If cleaning is required more frequently—such as once a month—it indicates that the pretreatment system needs improvement. If cleaning is needed every one to three months, it suggests that operational procedures should be optimized. Determining whether to enhance the pretreatment system depends on the frequency and severity of fouling.
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