11. What is the effect of temperature on water production?
The higher the temperature, the higher the water production, and vice versa. When operating at a higher temperature, the operating pressure should be lowered to keep the water production constant, and vice versa. For the temperature correction coefficient TCF for water production changes, please refer to the relevant chapters.
12. What is particle and colloid pollution? How to measure?
Once the particle and colloid fouling occurs in the reverse osmosis or nanofiltration system, it will seriously affect the water production of the membrane and sometimes reduce the salt rejection rate. The early symptom of colloidal fouling is the increase in system pressure difference. The source of particles or colloids in the membrane water source varies from place to place, often including bacteria, sludge, colloidal silicon, iron corrosion products, etc., and the pretreatment part of the medicines such as polymerization Aluminum and ferric chloride or cationic polyelectrolyte, if not effectively removed in the clarifier or media filter, may also cause fouling. In addition, the cationic polyelectrolyte will also react with the anionic scale inhibitor, and its sediment will foul the membrane element. The fouling tendency or pretreatment in water is evaluated by SDI15. Please refer to the detailed introduction in the relevant chapters.
13. Without system flushing, how long is the maximum allowable downtime?
If the system uses post-resistance agent, when the water temperature is between 20～38℃, about 4 hours; when it is below 20℃, about 8 hours;
If the system does not use antiscalant, about 1 day.
14. How can the energy consumption of the membrane system be reduced?
Use low-energy-consumption membrane elements, but it should be noted that their salt rejection rate is slightly lower than that of standard membrane elements.
15. Can the reverse osmosis pure water system start and stop frequently?
The membrane system is designed based on continuous operation, but in actual operation, there will always be a certain frequency of startup and shutdown. When the membrane system is shut down, the produced water or pre-treated qualified water must be used for low-pressure flushing to replace high-concentration but scale inhibitor-containing concentrated water from the membrane elements. Measures should also be taken to prevent water from leaking in the system and introducing air, because if the components lose water and dry out, irreversible water flux loss may occur. If the shutdown is less than 24 hours, there is no need to take measures to prevent the growth of microorganisms. However, if the shutdown time exceeds the above-mentioned regulations, a protective liquid should be used for system preservation or regular flushing of the membrane system.
16. How to determine the direction of the salt water sealing ring installed on the membrane element?
The salt water seal ring on the membrane element is required to be installed on the water inlet end of the element, and the opening faces the direction of water inlet. When water is fed into the pressure vessel, the opening (lip) will further open, completely sealing the inlet water from the membrane element and The side flow between the inner walls of the pressure vessel.
17. What impurities can RO membrane remove?
RO membrane can remove ions and organics very well, reverse osmosis membrane has a higher removal rate than nanofiltration membrane, reverse osmosis can usually remove 99% of the salt in the feed water, and the removal rate of organic matter in the influent water ≥99%.
18. How do you know which cleaning method should be used to clean your membrane system?
In order to obtain the best cleaning effect, it is very important to choose symptomatic cleaning agents and cleaning steps. Wrong cleaning will actually deteriorate the performance of the system. Generally speaking, for inorganic fouling pollutants, it is recommended to use acidic cleaning fluids, microorganisms or organic For pollutants, alkaline cleaning fluid is recommended.
19. How often should the reverse osmosis pure water machine system be cleaned?
Under normal circumstances, when the standardized flux drops by 10-15%, or the system desalination rate drops by 10-15%, or the operating pressure and the pressure difference between sections increase by 10-15%, the RO system should be cleaned. The frequency of cleaning is directly related to the degree of pretreatment of the system.
When SDI15<3, the cleaning frequency may be 4 times a year;
When SDI15 is around 5, the cleaning frequency may be doubled
However, the frequency of cleaning depends on the actual situation of each project site.
20. What is SDI?
At present, the best technology that can effectively evaluate the colloidal pollution in RO/NF system inlet water is to measure the siltation density index (SDI, also known as the fouling index) of the inlet water, which is an important parameter that must be determined before RO design. During RO/NF operation, regular measurements must be made (for surface water 2-3 times a day), ASTM D4189-82 specifies the test standard. The inlet water regulation of the membrane system is that the SDI15 value must be ≤5. Effective technologies to reduce SDI pretreatment include multi-media filters, ultrafiltration, microfiltration and so on. Adding polyelectrolyte before filtration can sometimes enhance the above-mentioned physical filtration and reduce the SDI value.