Summary of common problems of reverse osmosis in t

2022-07-27
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Summary of common reverse osmosis problems in sewage treatment

generally, when the standardized flux decreases by 10-15%, or the desalination rate of the system decreases by 10-15%, or the operating pressure and the pressure difference between sections increase by 10-15%, the RO system should be cleaned. The cleaning frequency is directly related to the degree of system pretreatment. When sdi153, the cleaning frequency may be 4 times a year; When SDI15 is around 5, the cleaning frequency may be doubled, but the cleaning frequency depends on the actual situation of each project site

2. What is SDI

at present, the best effective technology to evaluate the possible colloidal pollution in the ro/nf system inlet water is to measure the sedimentation density index (SDI), which is an important parameter that must be determined before the RO design. During the ro/nf operation, it must be measured regularly (2-3 times a day for surface water). ASTM D specifies the standard for this test. The SDI15 value must be ≤ 5 for the water inlet of membrane system. Effective technologies to reduce SDI pretreatment include multi-media filter, ultrafiltration, microfiltration, etc. Adding Poly dielectrics before filtration can sometimes enhance the above physical filtration and reduce the SDI value

3 should reverse osmosis process or ion exchange process be used for general influent

under many influent conditions, it is technically feasible to use ion exchange resin or reverse osmosis, and the selection of process should be determined by economic comparison. Generally, the higher the salt content, the more economical the reverse osmosis is, and the lower the salt content, the more economical the ion exchange is. Due to the popularity of reverse osmosis technology, the combined process of reverse osmosis + ion exchange process or multi-stage reverse osmosis or reverse osmosis + other deep desalting technologies has become a recognized technical and economic more reasonable water treatment scheme. For further understanding, please consult the representative of the water treatment engineering company. 4. how many years can the reverse osmosis membrane element normally be used? The service life of membrane depends on the chemical stability of membrane, physical stability of components, cleanability, water source, pretreatment, cleaning frequency, operation and management level, etc. According to economic analysis, it is usually more than 5 years

4. How many years can the reverse osmosis membrane element normally be used

the service life of the membrane depends on the chemical stability of the membrane, the physical stability of the components, the cleanability, the water source, pretreatment, cleaning frequency, operation and management level, etc. According to economic analysis, it is usually more than 5 years

5. What is the difference between reverse osmosis and nanofiltration

nanofiltration is a membrane liquid separation technology between reverse osmosis and ultrafiltration. Reverse osmosis can remove the smallest solute with a molecular weight of less than 0.0001 μ M. nanofiltration can remove solute with a molecular weight of about 0.001 μ M. Nanofiltration is essentially a kind of low-pressure reverse osmosis, which is used in the situation where the purity of produced water after treatment is not particularly strict. Nanofiltration is suitable for the treatment of well water and surface water. Nanofiltration is applicable to the water treatment system without high desalination rate like reverse osmosis, but it has a high ability to remove hardness components, sometimes called "softening membrane". The nanofiltration system has low operating pressure and lower energy consumption than the corresponding reverse osmosis system

6. What is the separation capability of membrane technology

reverse osmosis is the most precise liquid filtration technology at present. The reverse osmosis membrane can intercept inorganic molecules such as soluble salts and organic substances with molecular weight greater than 100. On the other hand, water molecules can freely pass through the reverse osmosis membrane. The typical removal rate of soluble salts is 95-99%. The operating pressure ranges from 7bar (100psi) for brackish water to 69bar (1000PSI) for seawater. Nanofiltration can remove impurities with particle size of 1nm (10 angstroms) and organic matters with molecular weight greater than 200-400. The removal rate of soluble solids is 20-98%, that of salts containing monovalent anions (such as NaCl or CaCl2) is 20-80%, and that of salts containing divalent anions (such as MgSO4) is higher, forming a drum shape of 90-98%. Ultrafiltration can separate macromolecules larger than 100-1000 a (0.01-0.1 μ m). All soluble salts and small molecules can pass through the ultrafiltration membrane, and the substances that can be removed include colloids, proteins, microorganisms and macromolecular organics. The molecular weight of most ultrafiltration membranes is 1000-100000. The range of particles removed by microfiltration is about 0.1-1 μ M. generally, suspended solids and large particle colloids can be intercepted, while macromolecules and soluble salts can freely pass through the microfiltration membrane. The microfiltration membrane is used to remove bacteria, micro flocs or total suspended solids TSS. The typical pressure on both sides of the membrane is 1-3bar

7. Who sells membrane cleaners or provides cleaning services

water treatment companies can provide special membrane cleaning agents and services. Users can purchase cleaning agents for membrane cleaning according to the suggestions of membrane companies or equipment suppliers

8. What is the maximum allowable concentration of silicon dioxide in reverse osmosis membrane feed water

the maximum allowable concentration of silicon dioxide depends on the temperature, pH value and scale inhibitor. Generally, when no scale inhibitor is added, the maximum allowable concentration of silicon dioxide in concentrated water is 100ppm. Some scale inhibitors can allow the maximum concentration of silicon dioxide in concentrated water to be 240ppm. Please consult the scale inhibitor supplier

9. What effect does chromium have on RO membrane

some heavy metals, such as chromium, can catalyze the oxidation of chlorine, thus causing irreversible degradation of the membrane. This is because cr6+ is less stable than cr3+ in water. It seems that metal ions with high oxidation price have stronger destructive effect. Therefore, the concentration of chromium should be reduced in the pretreatment section or at least cr6+ should be reduced to cr3+

10. What pretreatment is generally required for RO system

the general pretreatment system consists of the following: coarse filtration (-- 80 μ m) to remove large particles, adding oxidants such as sodium hypochlorite, then precise filtration through a multi-media filter or clarifier, adding oxidants such as sodium bisulfite to reduce residual chlorine, and finally installing a security filter before the inlet of the high-pressure pump. As the name suggests, the function of the security filter is as the final insurance measure to prevent accidental large particles from damaging the impeller and membrane components of the high-pressure pump. The water source with more suspended solids usually needs a higher degree of pretreatment to meet the specified inflow requirements; For water sources with high hardness content, it is recommended to soften or add acid and scale inhibitor. For water sources with high microbial and organic content, activated carbon or anti pollution membrane elements are also required

11. Can reverse osmosis remove microorganisms such as viruses and bacteria

reverse osmosis (RO) is very dense and has a very high removal rate of viruses, bacteriophages and bacteria, at least more than 3log (removal rate of 99.9%). However, it should also be noted that in many cases, microorganisms may breed again at the water producing side of the membrane, which mainly depends on the way of assembly, monitoring and maintenance, that is, the ability of a system to remove microorganisms depends on whether the system design, operation and management are appropriate rather than the nature of the membrane element itself

12. What is the effect of temperature on water yield

the higher the temperature, the higher the water yield, and vice versa. When operating at a higher temperature, the operating pressure should be reduced to keep the water yield unchanged, and vice versa. For the temperature correction factor TCF of water yield change, please refer to the relevant sections

13. What is particle and colloid contamination? How to determine

once the reverse osmosis or nanofiltration system is blocked by particles and colloids, it will seriously affect the water yield of the membrane, and sometimes reduce the desalination rate. The early symptom of colloidal fouling is the increase of system pressure difference. The sources of particles or colloids in the membrane water source vary from place to place, often including bacteria, sludge, colloidal silicon, iron corrosion products, etc. the drugs used in the pretreatment part, such as polyaluminum and ferric chloride or cationic polydielectrics, may also cause fouling if they cannot be effectively removed in the clarifier or medium filter. In addition, cationic polydielectrics will also react with anionic scale inhibitors, and their precipitates will pollute and block the membrane elements. SDI15 is used to evaluate whether such pollution blocking tendency or pretreatment in water is qualified. Please refer to the detailed introduction in relevant chapters

14. How long is the maximum allowable shutdown without system flushing

if the system uses a post inhibitor, when the water temperature is between 20-38 ℃, about 4 hours; Under 20 ℃, about 8 hours; If no scale inhibitor is used in the system, about 1 day. 15. how to reduce the energy consumption of membrane system

low energy consumption membrane elements can be used, but it should be noted that their desalination rate is slightly lower than that of standard membrane elements

15. Can the reverse osmosis pure water system be started and stopped frequently

the membrane system is designed based on continuous operation, but in actual operation, there will always be certain frequency of startup and shutdown. Ipul has set a new standard for pultrusion molding. When the membrane system is shut down, its produced water or qualified water after pretreatment must be used for low-pressure flushing to replace the concentrated water with high concentration but containing scale inhibitor from the membrane element. Measures shall also be taken to prevent the introduction of air due to water leakage in the system, because irreversible loss of water production flux may occur if the components are dried up. If the shutdown is less than 24 hours, no measures need to be taken to prevent microbial breeding. However, if the shutdown time exceeds the above provisions, the protective solution shall be used for system preservation or periodic flushing of the membrane system

16. How to determine the direction of the brine seal ring installed on the membrane element

the brine seal ring on the membrane element is required to be installed at the water inlet end of the element, and the opening faces the water inlet direction. When water is supplied to the pressure vessel, its opening (LIP) will be further opened to completely seal the bypass flow between the membrane element and the inner wall of the pressure vessel

17. How to remove silicon from water

silicon in water exists in two forms, active silicon (monomer silicon) and colloidal silicon (poly silicon): colloidal silicon has no ionic characteristics, but its scale is relatively large. Colloidal silicon can be intercepted by fine physical filtration processes, such as reverse osmosis. It can also reduce the content in water through coagulation technology, such as coagulation clarifier, but those separation technologies that rely on the characteristics of ionic charge, Such as ion exchange resin and continuous electrodeionization process (CDI), the effect of colloidal silicon removal is very limited

the size of active silicon is much smaller than colloidal silicon, so most physical filtration technologies such as coagulation clarification, filtration and air flotation cannot remove active silicon. The processes that can effectively remove active silicon are reverse osmosis, ion exchange and continuous electrodeionization

18. What is the effect of pH on removal rate, water yield and membrane life

the corresponding pH range of reverse osmosis membrane products is generally 2-11. PH has little effect on the membrane performance itself, which is one of the remarkable characteristics different from other membrane products. However, the characteristics of many ions in water are greatly affected by pH. for example, weak acids such as citric acid are mainly in non-ionic state under low pH conditions, but in ionic state under high pH values. As the same ion has a high degree of charge, the removal rate of the membrane is high. If the degree of charge is low or no charge, the removal rate of the membrane is low. Therefore, pH has a great impact on the removal rate of some impurities

19. What is the relationship between inlet TDS and conductivity

when the water inlet conductivity value is obtained, it must be converted into TDS value so that it can be input during software design. For most water sources, the ratio of conductivity/tds is between 1.2 and 1.7. In order to carry out Rosa design, 1.4 ratio is selected for seawater and 1.3 ratio is selected for brackish water. Generally, a better approximate conversion rate can be obtained

20. How do I know if the membrane has been contaminated

the following is

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