The storage method of reverse osmosis membrane elements is to prevent the growth of surface organisms during storage and the decrease in performance during subsequent operations. The membrane elements must be stored in a specially formulated solution.
1.1 New membrane components
(1) Membrane components undergo water testing before leaving the factory and are stored in a 1% sodium sulfite solution before being vacuum packed in oxygen isolation bags;
(2) Membrane components must be kept in a moist state at all times. Even when temporarily opening to confirm the quantity of the same packaging, it must be done in a state that does not damage the plastic bag, and this state should be saved until use;
(3) Membrane components are best stored at a low temperature of 5-10 ℃. When storing in an environment with a temperature exceeding 10 ℃, choose a well ventilated place and avoid direct sunlight. The storage temperature should not exceed 35 ℃;
(4) If the membrane element freezes, it will suffer physical damage, so insulation measures should be taken to prevent it from freezing; (5) When stacking membrane components, the packaging box should not exceed 5 layers and ensure that the cardboard box remains dry.
1.2 Used membrane components
(1) Membrane components must be kept in a dark place at all times, with a storage temperature not exceeding 35 ℃, and should be protected from direct sunlight;
(2) There is a risk of freezing when the temperature is below 0 ℃, so anti freezing measures should be taken;
(3) In order to prevent the growth of microorganisms in membrane components during short-term storage, transportation, and system standby, it is necessary to soak the components in a protective solution of sodium sulfite (food grade) with a concentration of 500-1000ppm and a pH of 3-6 prepared from pure water or reverse osmosis water. Usually, Na2S2O5 is used, which reacts with water to form bisulfite: Na2S2O5+H2O-2NaHSO3
(4) Soak the membrane element in the storage solution for about 1 hour, remove it from the solution, and package it in an oxygen isolation bag. Seal the bag and label it with the packaging date;
(5) After repackaging the membrane components that need to be stored, the storage conditions should be consistent with those of the new membrane components.
(6) The concentration and pH of the preservation solution should be maintained within the above range and checked regularly. If there is a possibility of deviation from the above range, the preservation solution should be prepared again;
(7) Under no circumstances should the film be kept in a dry state during storage. (8) Additionally, a formaldehyde solution with a 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 bisulfate and does not contain oxygen in its composition.
2. Shutdown and maintenance of reverse osmosis system
2.1 The following considerations need to be taken into account when saving:
(1) After shutting down, rinse the system with treated reverse osmosis supply water, softened water, or product water;
(2) In order to maintain the performance of the system, membrane components must be kept moist at all times;
(3) To prevent the growth of bacteria in pressure vessels, disinfection treatment should be carried out;
(4) If the membrane element is contaminated, system failure may occur, so chemical cleaning should be carried out before storage to remove dirt from the membrane element and limit bacterial growth to the minimum possibility;
(5) The allowable temperature and pH range for storage in pressure vessels are as follows:
Temperature range: 0~35 ℃, pH range: 3-7
(6) The preservation solution is an acidic sodium bisulfite (SBS) solution. The water used to prepare the preservation solution must ensure that it does not contain residual free chlorine or other oxidants.
2.2 Short term storage (less than 48 hours) If the reverse osmosis system is shut down for more than one day but less than two days, the following measures should be taken to store the system:
(1) Rinse the system with RO water and simultaneously remove the air inside the system;
(2) When the pressure vessel is filled with water, close the inlet and concentrate valves. Repeat the above steps every twelve hours.
2.3 Long term storage (greater than 48 hours) If the shutdown time of the reverse osmosis equipment is greater than 48 hours, the following procedures can be adopted for system storage:
(1) Before all storage, the system needs to be cleaned to remove all contaminants and dirt deposited on the membrane surface (this operation is only used when the membrane element is contaminated or expected to be contaminated). Before long-term system shutdown, use the recommended standard cleaning procedures or consult with Dongli Company for individual cleaning and disinfection procedures. After successfully completing cleaning and disinfection, it is important to store as quickly as possible, with a maximum interval of 12 hours between the most recent cleaning/disinfection.
(2) Save by circulating 500-1000ppm 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 entire system in this way, the remaining air volume can be minimized after the second cycle is completed (approximately 1 hour). Ensure that the system is sealed without air during storage and has good airtightness.
(3) Close all valves on the supply and saltwater ends. Any contact of sodium bisulfite solution with external air (oxygen) will cause sodium bisulfite to be oxidized into sulfate, and the pH value will continue to decrease. After all bisulfite salts are consumed, the remaining oxygen will not be absorbed, and the state of the organism 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 does not fall below 3. If the pH value of the preservation solution is found to be below 3, the preservation solution must be replaced. The preservation solution must be replaced once a month.
(5) During the shutdown period, the storage temperature should not exceed 35 ℃, but should not be lower than 0 ℃ to prevent freezing.
(6) Formaldehyde solution with a mass percentage concentration of 0.2-0.3% can also be used as a storage solution instead of sodium bisulfite. Formaldehyde is a stronger microbial killer than sodium bisulfate and does not contain oxygen in its composition.
Attention: Due to the toxicity of formaldehyde, it is important to pay attention to the safety regulations when using formaldehyde; Membrane components must be used under normal conditions for at least 24 hours before being stored in formaldehyde solution, otherwise it may significantly reduce the water production flow rate
