1. Storage method of reverse osmosis membrane elements
In order to prevent the growth of membrane surface organisms during storage and the degradation of performance during subsequent operations, the membrane elements must be kept in a special solution.
1.1 New membrane element
(1) The membrane elements have been tested by water before leaving the factory, and the use of 1% sodium sulfite solution for storage treatment, and then vacuum packaging with oxygen isolation bags;
(2) The membrane element must always be kept in a wet state. Even if it is necessary to temporarily open in order to confirm the quantity of the same package, it must be done in a state that does not damage the plastic bag, and this state should be saved until the time of use;
(3) The membrane element is best stored at a low temperature of 5~10 ° C. When stored in an environment where the temperature exceeds 10 °C, a well-ventilated place should be selected, and direct sunlight should be avoided, and the storage temperature should not exceed 35 °C;
(4) If the membrane element freezes, physical damage will occur, so insulation measures should be taken to avoid freezing;
(5) When stacking membrane elements, the packing box should not exceed 5 layers, and ensure that the carton is kept dry.
1.2 Used membrane elements
(1) The membrane element must always be kept in a dark place, the storage temperature should not exceed 35 °C, and to avoid direct sunlight;
(2) There is a risk of freezing when the temperature is below 0 °C, so anti-freezing measures should be taken;
(3) In order to prevent the growth of microorganisms during short-term storage, transportation and system standby, it is necessary to prepare sodium sulfite (food grade) protection solution with a concentration of 500~1,000ppm and pH3~6 with pure water or reverse osmosis production water. Typically, Na2S2O5 is used, which reacts with water to form a bisulfite: Na2S2O5 + H2O - 2NaHSO3.
(4) After soaking the membrane element in the preservation solution for about 1 hour, remove the membrane element from the solution and package it in an oxygen isolation bag, seal the bag and label it, indicating the packaging date;
(5) After the membrane element to be stored is repackaged, the storage conditions are consistent with those of the new membrane element.
(6) The concentration and pH of the preservation solution should be kept in the above range, which should be checked regularly. If deviation from the above range is possible, the preservation solution should be modulated again;
(7) No matter under what circumstances, the membrane should not be kept in a dry state.
(8) In addition, formaldehyde solution with concentration (mass percentage concentration) of 0.2-0.3% can also be used as a preservation solution. Formaldehyde is a stronger microbial killer than sodium bisulfite and does not contain oxygen.
2 Stop the reverse osmosis system for maintenance
2.1 The following items need to be considered when storage
(1) After shutdown, use treated reverse osmosis supply water, softened water or product water to flush the system;
(2) In order to maintain the performance of the system, the membrane element must always be kept moist;
(3) In order to prevent the growth of bacteria in the pressure vessel, disinfection should be carried out;
(4) If the membrane element is contaminated, there may be a system failure, so chemical cleaning should be carried out before storage, so that dirt can be removed from the membrane element, limiting the growth of bacteria to the minimum possibility;
(5) The allowable temperature and pH range when stored in the pressure vessel is as follows:
Temperature range: 0~35℃, pH range: 3-7
(6) The preservation solution is acidic sodium bisulfite (SBS) solution. The water in which the preservation solution is prepared must not contain residual free chlorine or other oxidizing agents.
2.2 Short-term storage (less than 48 hours)
If the reverse osmosis system downtime is longer than one day but less than two days, take the following measures to save the system:
(1) Flush the system with RO water, while draining the air in the system;
(2) When the pressure vessel is filled with water, close the inlet and concentrated water valves.
Repeat the steps every twelve hours.
2.3 Long-term storage (more than 48 hours)
If the downtime of reverse osmosis equipment is greater than 48 hours, the following procedures can be adopted for system preservation:
(1) Prior to all preservation, the system needs to be cleaned to remove all contaminants and dirt deposited on the membrane surface (this operation is only used if the membrane element is contaminated or expected to be contaminated). Use recommended standard cleaning procedures or consult us for individual cleaning and disinfection procedures prior to prolonged system outages. After successful cleaning and disinfection, store as soon as possible, with a maximum interval of 12 hours from the most recent cleaning/disinfection.
(2) Preservation is accomplished by circulating 500-1,000ppm sodium bisulfite solution using a cleaning system. In this way, the membrane element will be thoroughly wetted in the preservation solution. By circulating the solution throughout the system in this way, the amount of remaining air can be minimized after the completion of the secondary cycle (about 1 hour). Ensure that no air is contained in the system during storage to seal and that the air tightness is good.
(3) Close all valves at the supply end and brine end. Any contact of the sodium bisulfite solution with the outside air (oxygen) will cause the sodium bisulfite to be oxidized to sulfate, and the pH will continue to drop. After all the bisulfite has been consumed, the remaining oxygen will not be absorbed, and the state of living things will become unstable.
(4) The pH value of the stored reverse osmosis system needs to be adjusted regularly (at least once a month) to ensure that the pH value of the solution will not be lower than 3. If the pH of the preservation solution is found to be below 3, then the preservation solution must be replaced. The preservation solution must be replaced once a month.
(5) During the shutdown, the storage temperature should not exceed 35 °C, but not lower than 0 °C to prevent freezing.
(6) Formaldehyde solution with a mass percentage concentration of 0.2-0.3% can also be used instead of sodium bisulfite as a preservation solution. Formaldehyde is a stronger microbial killer than sodium bisulfite and does not contain oxygen in its composition.
Note: Because formaldehyde has certain toxicity, when using formaldehyde, we must pay attention to the safety regulations of formaldehyde use; Membrane elements must be used under normal conditions for at least 24 hours before being stored with formaldehyde solution, otherwise it may lead to a significant reduction in water production flow.
