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(1) New Membrane Elements
① Before leaving the factory, all membrane elements undergo a water flow test and are stored using a 1% sodium sulfite solution, then vacuum-packed in oxygen-barrier bags;
② Membrane elements must always be kept moist. Even when temporarily opening the package to confirm the quantity of the same item, this must be done without damaging the plastic bag, and this condition should be maintained until use;
③ Membrane elements are best stored at a low temperature of 5-10℃. When storing in environments exceeding 10℃, choose a well-ventilated location and avoid direct sunlight; the storage temperature should not exceed 35℃;
④ Membrane elements will physically break if they freeze, so insulation measures must be taken to prevent freezing;
⑤ When stacking membrane elements, the packaging boxes should not exceed 5 layers, and the boxes must be kept dry. (2) Used Membrane Elements
① Membrane elements must be kept in a dark place at all times, with a storage temperature not exceeding 35℃, and direct sunlight should be avoided;
② There is a risk of freezing at temperatures below 0℃, so anti-freezing measures must be taken;
③ To prevent microbial growth during short-term storage, transportation, and system standby, the elements need to be soaked in a sodium sulfite (food grade) protective solution with a concentration of 500~1,000ppm and a pH of 3~6, prepared with pure water or reverse osmosis permeate. Typically, Na₂S₂O₅ is used, which reacts with water to form bisulfite: Na₂S₂O₅ + H₂O → 2NaHSO₃.
④ After immersing the membrane element in the preservation solution for approximately 1 hour, remove the membrane element from the solution, package it in an oxygen-barrier bag, seal the bag, and label it with the packaging date.
⑤ After repackaging the membrane element to be preserved, the storage conditions should be the same as for new membrane elements.
⑥ The concentration and pH of the preservation solution must be maintained within the above-mentioned ranges. Regular checks are necessary; if deviations from these ranges occur, the preservation solution should be prepared again.
⑦ Under no circumstances should the membrane be allowed to dry out during preservation.
⑧ Alternatively, a 0.2–0.3% formaldehyde solution (mass percentage concentration) can be used as the preservation solution. Formaldehyde is a stronger microbial agent than sodium bisulfite and does not contain oxygen.
(I) Considerations for Storage
① After shutdown, flush the system with treated reverse osmosis feed water, softened water, or product water;
② To maintain system performance, the membrane elements must be kept constantly moist;
③ To prevent bacterial growth in the pressure vessel, disinfection is necessary;
④ If the membrane elements are contaminated, system malfunctions may occur. Therefore, chemical cleaning should be performed before storage to remove fouling and minimize the possibility of bacterial growth;
⑤ The permissible temperature and pH ranges for storage in the pressure vessel are as follows: Temperature range: 0~35℃, pH range: 3-7
⑥ The storage solution should be an acidic sodium bisulfite (SBS) solution. The water used to prepare the storage solution must be free of residual free chlorine or other oxidizing agents.
(II) Short-Term Storage (Less than 48 Hours)
If the reverse osmosis system shutdown time is longer than one day but less than two days, take the following measures to preserve the system:
① Flush the system with RO feed water, simultaneously removing air from the system;
② When the pressure vessel is filled with water, close the feed water and concentrate valves.
Repeat the above steps every twelve hours.
(III) Long-Term Storage (More than 48 Hours)
If the reverse osmosis equipment shutdown time is longer than 48 hours, the following procedure can be used to preserve the system:
① Before any storage, the system needs to be cleaned to remove all contaminants and fouling deposited on the membrane surface (this operation is only used when the membrane elements are fouled or expected to be fouled). Before a long-term system shutdown, use the recommended standard cleaning procedure or consult Toray Industries for individual cleaning and disinfection procedures. After successful cleaning and disinfection, store the system as soon as possible, with a maximum interval of 12 hours between the last cleaning/disinfection.
② Preservation is accomplished by circulating a 500-1000 ppm sodium bisulfite solution through the cleaning system. This thoroughly wets the membrane elements in the preservation solution. Circulating the solution throughout the system in this manner minimizes residual air after a second circulation (approximately 1 hour). Ensure the system is airtight and airtight during preservation.
③ Close all valves at the supply and brine ends. Any contact between the sodium bisulfite solution and outside air (oxygen) will cause the sodium bisulfite to oxidize into sulfate, resulting in a continuous decrease in pH. After all the bisulfite has been consumed, the remaining oxygen will not be absorbed, making the biological state unstable.
④ The pH of the preserved reverse osmosis system needs to be adjusted regularly (at least once a month) to ensure the solution pH does not fall below 3. If the pH of the preservation solution is found to be below 3, the preservation solution must be replaced. The preservation solution must be replaced monthly.
⑤ During shutdown, the storage temperature should not exceed 35°C but should not fall below 0°C to prevent freezing. ⑥ A 0.2-0.3% (w/w) formaldehyde solution can also be used instead of sodium bisulfite as the preservation solution. Formaldehyde is a stronger microbial agent than sodium bisulfite and does not contain oxygen.
Note: Because formaldehyde has a certain degree of toxicity, safety regulations for its use must be strictly observed. Membrane elements must be used under normal conditions for at least 24 hours before being preserved with formaldehyde solution; otherwise, the permeate flow rate may be significantly reduced.
