Offline cleaning precautions for reverse osmosis membranes
As a deep filtration method, reverse osmosis membranes inevitably retain colloids, microorganisms, impurity particles, and the precipitation of sparingly soluble salts on their surface. Therefore, once a reverse osmosis device is put into use, it will eventually require cleaning, only the cleaning cycle varies in length.
Reverse osmosis membrane element cleaning is divided into two methods: online cleaning and offline cleaning.
Online cleaning is a routine cleaning method, mainly for the maintenance of the reverse osmosis system. The biggest problem with online cleaning is that the concentration of the cleaning solution at the end of the cleaning direction gradually decreases. When the reverse osmosis system has been running for a certain period or the reverse osmosis membrane is severely polluted, online cleaning becomes ineffective, at which point offline cleaning of the reverse osmosis membrane elements is required.
Conditions for offline cleaning of reverse osmosis membranes:
1. When the single-stage pressure difference of the reverse osmosis system is more than twice the initial single-stage pressure difference of the system.
2. The water production of the reverse osmosis system decreases by more than 30%.
3. The weight of a single reverse osmosis membrane element exceeds the normal value by more than 3 kg.
4. The performance of the reverse osmosis system cannot be restored through online cleaning.
During online cleaning, the targeting of membranes at different locations is poor. Since a membrane shell usually does not contain only one membrane element, the pollution conditions of these membrane elements also vary. When using cleaning solutions of the same concentration to clean membranes with different pollution conditions, it will inevitably cause some membranes to be over-cleaned, while others are insufficiently cleaned, resulting in poor cleaning effect and easy cross-contamination.
Based on the above reasons, offline cleaning is proposed. Its main characteristics are: using spare membranes to replace the reverse osmosis membranes used on site without affecting the normal production of the user. Using a special cleaning device for single reverse osmosis membrane cleaning, this device can specifically handle membranes with different pollution conditions, and can easily achieve positive and negative washing of the reverse osmosis membrane, with sufficient cleaning flow for a single membrane. During the cleaning process, the cleaning status of the RO membrane can be monitored at any time, and the cleaning degree can be determined according to the actual situation. By analyzing the main components of pollutants in the cleaning solution, the pollutants in the system are determined, and corresponding system adjustment suggestions are put forward to extend the service life of the customer's system.
Offline cleaning steps for reverse osmosis membranes:
1. First, replace the membrane elements to be cleaned on the reverse osmosis system with high-performance spare membrane elements to ensure that the reverse osmosis system does not stop running and ensure the continuous stability of the entire production process.
2. Test the performance of the reverse osmosis membrane elements:
3. Understand the current operating status of the system before cleaning; collect the various parameter indicators of the running reverse osmosis system and make original records.
4. Determine the cleaning process based on the user's raw water full analysis report, performance test results, and the understood system information.
5. Identification of pollutants. First, make a preliminary judgment based on the analysis results in 3.4, and then further verify it through special equipment and instruments to determine the specific type of pollutant.
6. Determine the required cleaning formula and concentration based on the analysis results.
7. On the reverse osmosis dedicated cleaning equipment, use the above cleaning agent combined with the cleaning method for experimental cleaning to select the appropriate cleaning formula and cleaning procedure.
8. Determine the cleaning method and process all the above membrane elements.
9. Test the cleaned membrane elements on the test platform and record the results. Those that do not meet the requirements will be sent back to the cleaning equipment for processing.
