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Get all the water treatment knowledge! Summary of water treatment knowledge (summary from eight aspects) 1. Glossary 1. Raw water: Refers to natural water or city tap water without any treatment, also called raw water 2. Clarified water: Water with suspended impurities removed from raw water. 3. Demineralized water: Demineralized water refers to water in which the cations and anions in the water are basically removed or reduced to a certain extent. Methods for removing salt include distillation, electrodialysis, reverse osmosis, ion exchange, etc. 4. Turbidity: It refers to the turbidity of water, which is an optical effect caused by the presence of certain suspended matter (including colloidal substances) in the water. The unit is expressed in NTU. Turbidity is one of the main visual characteristics that determines whether water is contaminated. The standard unit of turbidity is 1 mg SiO2. The turbidity is 1 degree. 5. Flocculant: An agent that can cause coagulation and bridging of colloidal particles to cause flocculation. 6. Total alkalinity: It refers to the total amount of substances in water that can neutralize strong acids. 7. Acidity: It refers to the total amount of substances in water that can neutralize strong alkali. 8. Hardness: It refers to certain metal ions in water that are easy to form precipitates, usually referring to the content of calcium and magnesium ions. 9. Conductivity Conductivity: It is the conductance of the solution between two parallel electrodes with a cross-sectional area of 1 square centimeter and a distance of 1 centimeter at a certain temperature. It can indirectly represent the content of dissolved salt in water. 10. Resistivity: It is also an indicator that reflects the conductivity of water. The greater the resistivity of water, the worse the conductivity of water, and the fewer ions contained in the water. Its common unit is MΩ.CM. It has a reciprocal relationship with conductivity. For example: The conductivity of water is 0.2μs/cm, then its resistivity is 1/0.2=5 (MΩ.CM). 11. TDS (total dissolved solids): It is the remaining inorganic matter after filtering out suspended solids (SS) and colloids and evaporating all water. The unit is ppm or mg/l, which can be measured with a TDS meter. It also reflects the ion content of the water. A rough correspondence between it and conductivity: For the sodium chloride reference solution, a TDS value of 1 ppm corresponds to a conductivity of 2 μs/cm. 12. pH value: The relative amounts of acid and base in a solution. pH is a measure of the negative logarithm (log) of the concentration of hydrogen ions in water. The pH value is divided into 0~14 levels. When the pH value is 7.0, the water is neutral. ； If the pH value is less than 7.0, the water is acidic ； pH value is greater than 7.0. The water is alkaline. 13. Alkalinity: Alkalinity refers to the content of substances in water that can accept ions and strong acids for neutralization reactions. The substances that produce alkalinity in water are mainly carbonate alkalinity produced by carbonates, bicarbonate alkalinity produced by bicarbonates, and hydroxide alkalinity produced by the presence of hydroxides. 14. SDI: Contamination Index - A measure of the amount of suspended solids in the raw water used in a reverse osmosis system. 15. Ozone: An unstable, highly reactive form of oxygen produced by natural lightning or high-voltage charges through the air, and is an excellent oxidant and disinfectant. 16. Residual chlorine: After the water has been chlorinated and disinfected, the available chlorine remaining in the water after contact for a certain period of time. 17. Total E. coli: Total coliform refers to a group of aerobic and facultative anaerobic gram-negative non-saccharomyces bacteria that can ferment lactose and produce acid and gas within 24 hours when grown at 37°C. Total coliform refers to the number of total coliforms contained in each liter of water sample. 18. Recovery rate: Refers to the ratio of the flow rate of product water produced by the system to the flow rate of incoming water. 19. Desalination rate: Parameters that reflect the performance of the membrane, usually the desalination rate of the primary RO membrane system is above 97%. Can be easily calculated: (Conductivity of raw water - Conductivity of product water)/Conductivity of raw water. 20. Salt content: The salinity content of water, also called salinity, indicates the amount of salts contained in the water. Since various salts in water generally exist in the form of ions, the salt content can also be expressed as the sum of the amount of various cations and anions in the water. 21. Precipitation: One of the technical methods of wastewater treatment. It can be divided into two types: physical precipitation and chemical precipitation. The precipitation usually referred to is physical precipitation, that is, the method of gravity separation. 22. Gray water: There are many explanations. In terms of sewage engineering, it is called reclaimed water, and in terms of factories, it is called recycled water. The distinction is generally based on water quality. Mainly refers to non-potable water that can be reused within a certain range after urban sewage or domestic sewage has been treated to meet certain water quality standards. The quality of recycled water is between upper water (drinking water) and sewer water (domestic sewage), which is also the origin of the name of gray water. People also call the system that supplies gray water as gray water system. 23. Organic pollution: Refers to certain other biodegradable synthetic organic substances such as natural organic substances in the form of carbohydrates, proteins, amino acids, fats, etc. Mainly derived from domestic sewage and industrial wastewater. 24. Concentration polarization: When reverse osmosis is operating, the salts on the membrane surface are concentrated, and there is a concentration difference between the salts in the incoming water. If the flow rate of the concentrated water is small and the flow rate is low, the water with high salt content cannot be taken away in time, and a high concentration difference will be formed on the membrane surface, which hinders the diffusion of salts. This phenomenon is called concentration polarization. 25. Suspended solids (SS): Refers to solid matter suspended in water, including inorganic matter, organic matter, mud, sand, clay, microorganisms, etc. that are insoluble in water. The content of suspended solids in water is one of the indicators to measure the degree of water pollution. It is the amount of solids obtained after filtering the water sample and drying the residue on the filter paper at a temperature of 103-105 degrees. Unit mg/l. 26. Aeration: The process of transferring O2 in the air to the mixed liquid and being utilized by microorganisms. The purpose is to provide the dissolved oxygen required by microorganisms such as activated sludge and ensure the oxygen demand for the metabolic process of microorganisms. 27. Biochemical oxygen demand (BOD): It refers to the amount of dissolved oxygen consumed by microorganisms in the process of decomposing and oxidizing organic matter in water under specified time, specified temperature, and specified conditions. The usual time used is 5 days and the temperature is 20°C. It is abbreviated as BOD5 and the unit is mg/L. 28. Chemical oxygen demand (COD): It refers to the amount of oxygen consumed by using strong oxidants to oxidize organic matter in wastewater under certain conditions. Wastewater inspection standards generally use potassium dichromate as the oxidant, and the unit is mg/L. 29. Water hammer: Also called water hammer. During the transportation of water (or other liquids), due to sudden opening or closing of valves, sudden stops of water pumps, sudden opening and closing of guide vanes, etc., the flow rate changes suddenly and the pressure fluctuates significantly. 30. Adsorption: It refers to a method that uses porous solids to absorb one or more pollutants in wastewater to recover or remove certain pollutants, thereby purifying wastewater. 31. Enzyme: It is a kind of catalyst (biocatalyst) made by biological cells. Its basic component is protein, a substance that promotes the speed of biochemical reactions. 32. Sewage: Sewage refers to the general term for water discharged during production and living activities. Human beings use a large amount of water in their daily life and production activities, and this water is often polluted to varying degrees. The polluted water is called sewage. 33. Sewage treatment: It is to use various technologies and means to separate, remove, recycle or convert pollutants contained in sewage into harmless substances so that the water can be purified. 34. Wastewater reuse: Reusing sewage or wastewater into production systems or domestic miscellaneous uses after secondary treatment and advanced treatment is called sewage reuse. When the treated effluent meets specific reuse requirements and is reused, it can also be called recycled water. 35. Scale: That is, due to poor boiler water quality, solid attachments are generated on the pipe wall where the heating surface is in contact with water after a period of operation. 36. Water slag: It refers to the solid matter in a suspended state in the boiler water and the sediment deposited in slow water flow places such as the bottom of the steam drum and the lower header. Difference from scale: The water slag is relatively loose, in the state of suspension or sediment, and some of it is easily discharged with the boiler blowdown. ； The scale can be firmly bonded to the pipe wall and is not easy to be discharged. 37. Iron, manganese, aluminum: Trace amounts of iron and manganese can cause problems such as staining, scaling and odor. Iron exists in the form of water-soluble ferrous iron in a reducing environment. When in contact with air, it will gradually oxidize into yellow-brown colloidal ferric iron, and finally precipitate into brown iron hydroxide. The characteristics of manganese are similar to iron. Since the oxides of iron, manganese and aluminum are also one of the causes of RO membrane scaling, it is necessary to analyze their content. 38. Pure water: It refers to water that removes easy-to-remove strong dielectrics and difficult-to-remove weak electrolytes such as silicic acid and carbon dioxide to a certain extent. The salt content of pure water is below 1.0mg/L, and the conductivity is less than 3μs/cm. 39. Ultrapure water: Also known as high-purity water, it refers to water in which almost all the conductive media in the water are removed, and the non-dissociated colloidal substances, gases and organic matter in the water are removed to a very low level. The salt content of ultrapure water is below 0. 1mg/L, and the conductivity is less than 0. 1μs/cm. In addition to strict requirements on salt content or conductivity, pure water and ultrapure water also have strict restrictions on the content of various metal ions in the water, the content of organic matter, the size and number of particles, and the number of microorganisms. 40. Distilled water: The water produced by heating and vaporizing raw water and then condensing the steam is called distilled water. Generally, the conductivity of distilled water is about 10 μs/cm. Distilling once-distilled water again produces twice-distilled water. Multiple distillations produce multiple-distilled water. The conductivity can be reduced to as low as about 1.0 μs/cm. 41. Antiscalant: It is a type of agent that can disperse poorly soluble inorganic salts in water, prevent or interfere with the precipitation and scaling of poorly soluble inorganic salts on metal surfaces, and maintain good heat transfer effects on metal equipment. 42. Ion exchange resin: It is an insoluble polymer compound with functional groups (active groups that exchange ions), network structure. Usually spherical particles. 43. Ion: It refers to an atom that loses or gains one or several electrons due to the action of itself or the outside world, so that it reaches a stable structure in which the number of electrons in the outermost shell is 8 or 2 (helium atoms) or no electrons (four neutrons). This process is called ionization. 44. Water production (water flux): Refers to the production capacity of the reverse osmosis system, that is, the amount of water passing through the membrane per unit time, usually expressed in tons/hour (t/h) or gallons/day (g/d). 45.EDI: Continuous electric desalination, referred to as continuous electrolytic desalination, is a new type of ultrapure water preparation technology. It cleverly combines electrodialysis technology and ion exchange technology. 2. Explanation of basic processes of pure water treatment 1. Coarse filtration Coarse filtration: Refers to mechanical filtration to remove suspended solids, colloids, turbidity, color, odor, etc. in water. The main filtration methods include clarifiers, rapid filters, sand filters, sand filters, multi-media filters, activated carbon filters, disc filters, high-efficiency fiber filters, etc. 2. Fine filtration Fine filtration: The filter membrane made of special materials has high filtration accuracy. Common ones are microfiltration membrane and filter element filtration. 3. UltrafiltrationUltrafiltration: It is a kind of membrane filtration that removes macromolecules, colloids, bacteria, etc. The filtration precision is high, and the most common one is ultrafiltration membrane. 4. Reverse osmosis reverse osmosis: Reverse osmosis is referred to as RO. Its principle is that raw water passes through the reverse osmosis membrane under high pressure, and the solvent in the water diffuses from high concentration to low concentration to achieve the purpose of separation, purification, and concentration. Because it is opposite to the osmosis direction in nature. 5. Various inorganic salts in the ion exchange water are ionized to generate cations and anions. When passing through the hydrogen ion exchanger layer, the cations in the water are replaced by hydrogen ions, which is the desalination principle of the cation bed. ； When passing through the OH-type ion exchanger layer, the anions in the water are replaced by OH- ions, which is the desalination principle of the anion bed. Mixed bed is an ion exchange device in which cation and anion exchange resins are mixed and packed in the same exchange column in a certain proportion. 6. EDIEDI: It is a new desalination process that combines electrodialysis and ion exchange. It takes the advantages of electrodialysis and mixed bed ion exchange and uses ion exchange for in-depth treatment. It does not require regeneration with chemicals, but uses ionization to generate H+ and OH- to achieve the purpose of regenerating the resin. 3. Manufacturers of ultrafiltration membranes, reverse osmosis membranes and EDI commonly used in engineering 1. Ultrafiltration membranes Ultrafiltration membranes: American KOCH, Dutch Norit, Shanghai Huamiao 2, reverse osmosis membrane reverse osmosis membrane: American HydraNeng, American DOW, American KOCH, American General (GE), Japanese Toray, Korean Sehan 3, EDIEDI: American GE (E-CELL), American IONPURE, American electropure, Canadian CANPURE, (European and American company, acquired by DOW), Zhejiang Dongda. 4. Commonly used water treatment processes 01 Raw water is groundwater: Sand filter + precision filter + reverse osmosis + mixed bed or EDI02 raw water is tap water: Sand filter + activated carbon filter + precision filter + RO + mixed bed or EDI03 surface water ① multi-media filter + activated carbon filter + precision filter + RO + mixed bed or EDI ② multi-media filter (or other form of filter) + ultrafiltration + precision filter + RO + mixed bed or EDI ③ disc filter + ultrafiltration + precision filter + RO + mixed bed or EDI 5. Commonly used pipe materials in water treatment projects: Carbon steel pipes Carbon steel pipes: Used for raw water inlet pipeline. UPVC pipe UPVC pipe: It is suitable for applications where the pipe diameter is less than DN150 and is easy to install. stainless steel pipe stainless steel pipe: It is used in occasions with special requirements, mostly used in small medical and pharmaceutical systems. Steel lined with rubber or plastic pipe Steel lined with rubber or plastic pipe: Used in large projects, it is reliable and difficult to construct. 6. Various uses of pure water Pure water and ultrapure water are widely used in power plants, electronics, medicine, and chemical industries. Harmful ions in the water are removed through the filtration or ion exchange of various membranes. Desalted water is commonly used in power plants. The main indicators of desalted water quality are:: The hardness is approximately zero, the conductivity is ≤0.2μs.cm, and SiO2 is ≤20ppb. Chemical plants use a variety of chemical water. Usually the water quality is not higher than that of power plants, but it may have requirements for certain ions, so the primary or secondary reverse osmosis process is commonly used. The conductivity of the effluent water quality is above 5~10μs.cm. If there are higher requirements, a mixed bed or EDI can be added later. Medical water mostly has requirements for conductivity and bacteria, and has requirements for the materials used in the system. Stainless steel products are often used. Usually, a sterilization device is added after pure water. Electronics industry The electronics industry has the highest water requirements, and most electronics have water requirements of up to 18 trillion. The requirement for resistivity is only a small part of electronic water. It has higher requirements for many of the ions, so there are special requirements for installation materials and pipelines. The selection process is also the most complicated. It is usually necessary to add polishing mixed bed, ultrafiltration, sterilization, nitrogen sealing water tank and other devices after EDI, and the cost is also very high. 7. According to the water quality requirements, the commonly used process 1 requires the conductivity of the produced water to be 10~20μs/cm, using RO pretreatment + first-level reverse osmosis (chemical industry) 2 The conductivity of the produced water is 2~9μs/cm, and the conductivity of the produced water is 2~9μs/cm, using RO pretreatment Physics + two-stage reverse osmosis (pharmaceutical, chemical industry) or use RO pretreatment + softening + one-stage reverse osmosis + EDI (pharmaceutical, chemical industry) 3 The conductivity of the produced water is less than 0.2~2μs/cm. The conductivity of the produced water is less than 0.2~2μs/cm. Use RO pretreatment + one-stage reverse osmosis + mixed bed 4 The produced water resistance is 5~13 MΩ.CM water production resistance 5~13 MΩ.CM, use R0 pretreatment + softening + first-level reverse osmosis + EDI or use RO pretreatment + second-level reverse osmosis + EDI (medicine, chemical industry, electronics, power generation) 5 water production resistance 13~17 MΩ.CM water production resistance 13~17 MΩ.CM, use R0 pretreatment + softening + first-level reverse osmosis + EDI + mixed bed or use RO pretreatment + second-level reverse osmosis + EDI + mixed bed (medicine, chemical industry, electronics, power generation) 6 water production resistance 18 MΩ.CM Water production resistance 18 MΩ.CM, use RO pretreatment + second-level reverse osmosis + EDI + mixed bed + sterilization + nitrogen sealing. 8. Questions and answers on key and difficult points in pure water treatment 1. What are the main measures to reduce acid and alkali consumption? (1) Ensure the quality of incoming water ； (2) Ensure regeneration quality and extend the water production cycle ； (3) Ensure the quality and purity of the regeneration solution and strictly control the regeneration operating procedures ； (4) Ensure the safe, reliable and normal operation of the equipment. 2. What are the reasons why colloids can exist in water stably? (1) The colloid surface is charged ； (2) There is a water level layer on the colloid surface ； (3) The colloid surface adsorbs certain substances that promote colloid stability. 3. What is the purpose of using coagulants? 1) Improve the floc structure to make the particles larger, stronger and heavier ； 2) Adjust the PH value and alkalinity of the treated water to achieve optimal coagulation conditions and improve the coagulation effect ； The coagulant itself has no coagulation effect, but can promote the coagulation process of impurities in the water. 4. What is the basic concept of concrete? Because the colloidal particles present in the water are negatively charged, they repel each other, and at the same time they continue to perform "Brownian motion" in the water, which is extremely stable and difficult to sink. When an appropriate amount of coagulant is added, the tiny colloidal particles in the water can destabilize, produce an adsorption bridging effect, and flocculate into flocs that sink quickly. This process is called coagulation. 5. What are the main factors affecting the coagulation effect? 1) pH of water: If PAC is added for hydrolysis, Al(OH)3 colloid will be produced. When the pH is 6.5-7.5, the dissolution will be minimal and the coagulation effect will be good. ； 2) Alkalinity of water: When the alkalinity is insufficient, the coagulant will continue to produce H+ during the hydrolysis process, causing the pH value to drop and the coagulation effect to decrease. ； 3) Water temperature: When the temperature is low, the viscosity of water is high, the hydrolysis rate is slow, the floc formation is slow, and the structure is loose, and the particles are small and difficult to settle. ； 4) Composition of impurities in water: The nature and concentration have a great influence on the coagulation effect. 6. What is the relationship between the form of carbonic acid compounds in water and the pH value? 1) When the pH value is ≤4.3, there is only CO2 (free) in the water ； 2) When the PH value = 8.3-3.4, more than 98% is HCO3-; 3) When the PH value is > 8.4, there is no CO27 in the water. What is the purpose of water treatment in the boiler? 1) Prevent the water and steam in the boiler body and ancillary systems from accumulating sediments and corroding during operation. Improve the heat transfer efficiency of the boiler. 2) Ensure steam quality, prevent scaling and corrosion of steam turbine components, reduce boiler blowdown losses and improve economic benefits while ensuring water quality. 8. How does a centrifugal pump work? The centrifugal pump works by using the centrifugal force generated by the rotation of the impeller in the water. Before starting the water pump, the pump casing and suction pipe must be filled with water, and then the motor is started so that the pump shaft drives the impeller and the water to rotate at high speed. The water is thrown toward the outer edge of the impeller under the action of centrifugal force and collected into the pump casing. It flows into the pressurized water pipeline of the water pump through the flow channel of the vortex pump casing. At the same time, a vacuum is formed in the center of the water pump impeller because the water is thrown out. The water in the suction pool is sucked into the impeller through the suction pipe under the action of atmospheric pressure. The impeller keeps rotating, and the water is constantly being thrown out and replenished. This forms a continuous water delivery by the centrifugal pump. 9. What is resin regeneration? After a period of softening or desalting, the resin loses its ability to exchange ions. ； At this time, acid, alkali or salt can be used to reduce and regenerate the resin and restore its exchange ability. This process of restoring the ability of the resin is called resin regeneration. 10. What are the main factors that affect the working exchange capacity of resin? (1) Quality of incoming water ； (2) Control indicators for exchange endpoints ； (3)Height of resin layer ； (4) Water temperature and water flow speed ； (5) The effect of exchange agent regeneration and the performance of the resin itself. 11. What are the chemical properties of resin? 1) Reversibility of ion exchange reactions, such as: RH + Na+ RNa + H+2) acidity and alkalinity: ROH R+O H- ; RH R + H+3) Selectivity: Ion exchange resins adsorb various ions differently. 4) Resin exchange capacity and size of cation resin: Fe 3+ ＞Al 3+ ＞Ca 2+ ＞Mg 2+ ＞K + ≈NH 4+＞Na+ anion resin: What are the contaminations of SO42->NO3->Cl->HCO3->His12 and mixed bed resin? 1) Suspended pollution: Mostly appear in the form of cation resin. Strengthen the pretreatment of raw water. 2) Organic pollution: Mainly occurs in strong base cation resin. Main methods of resuscitation: Soak the resin in a mixed solution of NaOH (1-4%) and NaCl (5-12%) for 24 hours. 3) Heavy metal ion iron pollution: It is mostly formed in anion resin, which strengthens the corrosion of pipelines and equipment, reduces the Fe content of incoming water, and increases iron removal measures. 13. What are the main reasons for the degradation of RO membrane performance? 1) Chemical changes in the membrane itself: Hydrolysis of the membrane, oxidation interference of free chlorine and active chlorine 2) Physical changes of the membrane itself: The densification of the membrane reduces the water permeability and increases the salt removal rate. ； Membrane is contaminated: Scale, microorganisms, and solid particles contaminate and block the membrane surface or within the membrane. 14. What is the process principle of the security filter? It is a mechanical filtration using a 5um pore pp filter element, so that the trace suspended particles, colloidal microorganisms, etc. remaining in the water are trapped or adsorbed on the surface and gaps of the filter element. As the water production time increases, the resistance of the filter element increases due to solid objects. When the pressure difference between the inlet and outlet increases to 0.1MPa, it should be replaced. ； The filter element of the filter is a replaceable cartridge filter rod. 15. How to prevent RO membrane scaling? 1) Pre-treat raw water to ensure SOI <4, and add bactericide to prevent the growth of microorganisms ； 2) Appropriate working pressure must be maintained during RO operation. Generally, as the working pressure increases, the water production also increases, but if the working pressure is too high, the membrane will be compacted. 3) During RO operation, the flocculation state of concentrated water should be maintained to reduce the concentration polarization of the solution on the membrane surface and avoid the precipitation of insoluble salts on the membrane surface. ； 4) When the RO is out of operation, it should be flushed with chemicals in the short term, and CH2O protection solution should be added for long-term protection. 5) When the RO water production decreases significantly or the salt content increases, the surface is scaled or contaminated, and chemical cleaning should be performed. 16. What is the role of adding NaHCO3 during the desalination process of the RO unit? Eliminate or reduce the residual chlorine content in the water to ensure the stability of the RO element. Our company's residual chlorine is less than 0.1mg/L. 17. What is the purpose of installing an electric slow-opening automatic valve in front of the RO membrane module? This prevents the sudden start and stop of the high-pressure pump from boosting the pressure during RO operation, causing high-pressure impact on the RO membrane element and causing water hammer to damage the RO membrane. 18. What is the filtration cycle? How many links does it include? What is the function of each link? Filtration cycle is the actual running time between two backwashes including: There are three steps of filtration, backwashing and forward washing. Backwashing is to remove the dirt accumulated during the filtration process and restore the dirt interception capacity of the filter medium. Is forward washing to ensure the filtration operation? It is a necessary step to ensure that the water is qualified. Only after the main washing is qualified can the periodic operation of water production be entered. 19. Principle of chlorine removal by activated carbon. The removal of residual chlorine by activated carbon is not physical adsorption, but a chemical reaction. When free residual chlorine passes through the activated carbon, it produces a catalytic effect on its surface. The free residual chlorine quickly hydrolyzes out oxygen atoms [O] and chemically reacts with carbon atoms to generate carbon dioxide. At the same time, HCLO in the raw water is also quickly converted into CO2 gas. Comprehensive response: C+2Cl2+2H2O→4Hcl+CO2↑According to the above, the activated carbon in the reaction vessel will gradually decrease according to the residual chlorine content in the raw water, and should be replenished appropriately every year. 20. Principle of reverse osmosis process RO uses the water-permeable and salt-impermeable characteristics of a semi-permeable membrane to remove most of the salt in the water. Pressurize the raw water side of the RO so that part of the pure water in the raw water passes through the membrane in the direction perpendicular to the membrane. The salts and colloidal substances in the water are concentrated on the membrane surface, and the remaining raw water takes away the concentrated substances in the direction parallel to the membrane. There is only a small amount of salt in the permeated water, and the purpose of desalination is achieved by collecting the permeated water.