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【Excellent】50 Frequently Asked Questions and Answers in Water Treatment (Part 2)

【Excellent】50 Frequently Asked Questions and Answers in Water Treatment (Part 2)

26. What is the sludge volume index? Sludge volume index (SVI): The volume occupied by 1 gram of dry sludge after 30 minutes of sedimentation of the mixed liquor from the aeration tank outlet, measured in mL. A low SVI value indicates that the sludge particles are small, dense, and rich in inorganic matter, lacking activity and adsorption capacity; a high SVI value indicates that the sludge is difficult to settle and separate, is about to swell or has already swelled, and the cause must be investigated and measures taken. 27. What is sludge bulking, disintegration, decay, flotation, and foaming? Sludge bulking: When sludge deteriorates, it becomes difficult to settle, the SVI value increases, the sludge structure becomes loose, the volume expands, the water content increases, the clarified liquid is reduced, and the color also changes. Sludge disintegration: The phenomenon of sludge disintegration is characterized by turbid treated water, fine flocculation of sludge, and deterioration of treatment effect. Sludge decay: In the secondary sedimentation tank, anaerobic fermentation may occur due to long-term sludge retention, generating gas, resulting in the phenomenon of large chunks of sludge floating. Sludge flotation: The phenomenon of sludge floating in chunks in the secondary sedimentation tank. Foaming problem: Foaming in the aeration tank is mainly caused by the presence of a large amount of synthetic detergents or other foaming substances in the wastewater. 28. What is the activated sludge growth curve? Activated sludge microorganisms are a mixed population of multiple species, and their growth patterns are complex, but they can also be represented by a growth curve. This curve expresses the proliferation and attenuation of the number of microorganisms over time after a single sufficient addition of nutrients, when the environmental conditions such as temperature and dissolved oxygen meet the growth requirements of the microorganisms and there is a certain amount of initial microbial inoculation. The change in the growth rate of activated sludge is mainly caused by the ratio of nutrients or organic matter to microorganisms (usually expressed as F/M). The F/M value is also an important influencing factor for the organic substrate degradation rate, oxygen utilization rate, and the coagulation and adsorption performance of activated sludge. The four stages of the activated sludge growth curve: adaptation phase, logarithmic growth phase, deceleration growth phase (maximum biomass), endogenous respiration phase (best treated water quality). 29. How many processes are involved in activated sludge purification? Activated sludge purifies wastewater through three stages: In the first stage, wastewater is mainly purified through the adsorption of activated sludge. Adsorption is very rapid, generally completed within 30 minutes, and the BOD5 removal rate can reach up to 70%. It also has a partial oxidation effect, but adsorption is the main effect. The second stage, also known as the oxidation stage, mainly involves the continued decomposition and oxidation of organic matter adsorbed and absorbed in the previous stage, while continuing to adsorb some residual dissolved substances. The third stage is the solid-liquid separation stage. In this stage, activated sludge is settled and separated in the secondary sedimentation tank. Both the anabolism and catabolism of microorganisms can remove organic pollutants from wastewater, but the products are different. 30. What are the characteristics of a secondary sedimentation tank? Characteristics of secondary sedimentation tank: In terms of function, in addition to solid-liquid separation, it also performs sludge concentration, and due to changes in water quality and quantity, it also temporarily stores sludge. 31. What is a slow sand filtration system for wastewater? Slow sand filtration is the process of allowing wastewater to slowly pass through the land, purifying the wastewater through natural seepage and filtration. It is suitable for areas with good soil permeability, low evaporation, and humid climate. 32. What is a rapid sand filtration system for wastewater? Suitable for soils with very good permeability, such as sandy soil and gravelly sandy soil. After the wastewater flows to the surface of the rapid infiltration field, it quickly infiltrates into the ground and eventually enters the groundwater layer. 33. How many stages are there in anaerobic reaction? What are they? Anaerobic reaction is divided into three stages: The first stage is the decomposition of organic matter into fatty acids and other products under the action of hydrolytic and fermentative bacteria. The second stage is the further conversion of hydrogen and acetic acid-producing bacteria into hydrogen, carbon dioxide, and acetic acid. The third stage is the methanogenic fermentation stage (alkaline fermentation stage), where two different groups of methanogens act: one group converts hydrogen and carbon dioxide into methane, and the other group converts acetic acid to produce methane. 34. What is two-stage digestion? Two-stage digestion is the separation of the acid-producing stage and the methane-producing stage of anaerobic digestion of organic substrates. 35. What are the material components of sludge? The material components of sludge can be divided into organic sludge and inorganic sludge. According to the source of sludge, it can be divided into primary sedimentation sludge, excess activated sludge, humus sludge, digested sludge, and chemical sludge. 36. What kind of water does sludge contain? The water contained in sludge is divided into four categories: water in the inter-particle voids, capillary water, water adsorbed by sludge particles, and water inside the particles. Removal methods: gravity, flotation, centrifugation. 37. What does mechanical dewatering include? Mechanical dewatering: vacuum filtration dewatering, pressure filtration dewatering, roll pressing dewatering, sludge centrifugation dewatering. 38. What is the purpose of sludge stabilization? The purpose of sludge stabilization is to eliminate odors emitted from sludge and kill pathogenic microorganisms in sludge. 39. What is adsorption? The use of porous solids (such as activated carbon) or flocculant substances (such as polyferric) to adsorb toxic and harmful substances in wastewater onto the surface or micropores of the solid or flocculant to achieve the purpose of water purification. This treatment method is called adsorption treatment. The object of adsorption can be insoluble solid substances or soluble substances. 40. What are the characteristics of physical adsorption and chemical adsorption? Characteristics of physical adsorption: low adsorption heat, can be carried out at low temperatures, adsorption is reversible, and adsorption has basically no selectivity. Characteristics of chemical adsorption: high adsorption heat, adsorption is irreversible, and adsorption is selective. 41. What is resin density? Resin density: Generally refers to two methods of representation: wet true density and wet apparent density. Wet true density is related to the backwashing strength, expansion rate, and resin stratification of mixed beds and double-layer beds of the resin layer, while wet apparent density is used to calculate the amount of wet resin required for filling the ion exchanger. 42. What is the function of the water-spraying packing? The function of the water-spraying packing is to disperse the water droplets falling from the water distribution system into fine droplets or water films, increasing the contact area between water and air, prolonging the contact time, and thus ensuring good heat and mass exchange between air and water. 43. What is mixed liquor volatile suspended solids? Mixed liquor volatile suspended solids (MLVSS) refers to the weight of volatile substances in the dry sludge contained in a unit volume of biochemical pool mixed liquor, the unit is also mg/L. Since it does not include inorganic matter in activated sludge, it can more accurately represent the amount of microorganisms in activated sludge. 44. Why is there excess sludge? In the biochemical treatment process, the microorganisms in the activated sludge continuously consume the organic matter in the wastewater. A portion of the consumed organic matter is oxidized to provide energy for the life activities of microorganisms, while another portion is used by microorganisms to synthesize new cytoplasm, thus causing microorganisms to proliferate and reproduce. At the same time as the metabolism of microorganisms, a portion of old microorganisms die, thus producing excess sludge. 45. What is iron-carbon treatment technology? Iron-carbon treatment, also known as iron-carbon micro-electrolysis or iron-carbon internal electrolysis, is an application of metal iron wastewater treatment technology. Using the iron-carbon method as a pretreatment technology to treat toxic and harmful wastewater with high COD has a unique effect. 46. Why should the effluent pH of the neutralization sedimentation tank be adjusted to above 9? Iron-carbon effluent contains a large amount of ferrous sulfate. If it is not removed, it will affect the growth and reproduction of microorganisms in the subsequent bioreactor. Therefore, we must use lime to increase the pH of the wastewater from 5-6 to above 9, converting the water-soluble ferrous sulfate into insoluble ferrous hydroxide and calcium sulfate, and then using coagulation sedimentation to precipitate them, ensuring that the wastewater entering the bioreactor does not contain ferrous sulfate. 47. What types of flotation are there? Flotation is divided into: dissolved air flotation (divided into vacuum dissolved air flotation and pressure dissolved air flotation), dispersed air flotation, and electrolytic flotation. 48. What is flocculation? Flocculation is the addition of high-molecular flocculants to wastewater. After dissolution, high-molecular flocculants form high-molecular polymers. The structure of this polymer is linear, with one end of the line pulling a tiny particle and the other end pulling another tiny particle, playing a binding bridging role between two particles that are relatively far apart, causing the particles to gradually become larger and eventually forming large-particle flocs (commonly known as alum flocs), accelerating particle sedimentation. 49. Why is wastewater treated with polyferric for flocculation and adsorption? The ferric hydroxide flocs formed during the coagulation process of polyferric have a good ability to adsorb organic matter in wastewater. Experimental data show that after flocculation and adsorption with polyferric, wastewater can remove about 10%-20% of COD, which can greatly reduce the operating burden of the bioreactor and is conducive to the treatment of wastewater to meet discharge standards. In addition, coagulation pretreatment with polyferric can remove trace substances in wastewater that are toxic and inhibitory to microorganisms, ensuring that the microorganisms in the bioreactor can operate normally. Among many coagulants, the price of polyferric is relatively cheap (25-300 yuan/ton), so the treatment cost is relatively low, making it suitable for the pretreatment of process wastewater. 50. Why are colloidal particles in wastewater not easily naturally settled? Many impurities in wastewater with a specific gravity greater than 1, such as large particles and easily settleable suspended solids, can be removed by natural sedimentation, centrifugation, etc. However, suspended particles with a specific gravity less than 1, small, or even invisible to the naked eye, are difficult to naturally settle, such as colloidal particles, which are microparticles of 10-4-10-6 mm in size and are very stable in water. Their sedimentation rate is extremely slow, taking 200 years to settle 1 m.

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【Excellent】50 Frequently Asked Questions and Answers in Water Treatment (Part 1)

【Excellent】50 Frequently Asked Questions and Answers in Water Treatment (Part 1)

Q&A (Part 1) 1. What is water self-purification? Water self-purification: The process by which polluted rivers, through physical, chemical, and biological processes, reduce or transform pollutant concentrations, restoring the water body to its original state or reducing it from exceeding water quality standards to meeting them. 2. What are the basic methods of wastewater treatment? Basic methods of wastewater treatment: Employing various methods and technologies to separate and remove pollutants from wastewater, recycle them, or transform them into harmless substances, thus purifying the wastewater. This generally includes water supply treatment and wastewater treatment. 3. What wastewater treatment technologies are currently available? Modern wastewater treatment technologies can be classified into physical, chemical, and biological treatment methods based on their working principles. 4. Five water quality indicators Biochemical Oxygen Demand (BOD): The amount of oxygen required to degrade organic matter through microbial action under aerobic conditions. It is a comprehensive indicator of organic pollution in wastewater. Theoretical Oxygen Demand (ThOD): The theoretical oxygen demand of a specific organic substance in water. This usually refers to the theoretical value of oxygen required to completely oxidize the carbon and hydrogen elements in the organic matter into carbon dioxide and water (i.e., the oxygen demand calculated according to the complete oxidation reaction formula). Total Oxygen Demand (TOD): The amount of oxidizable substances in water, mainly the oxygen required for organic substances to become stable oxides during combustion, expressed as mg/L of O2. Chemical Oxygen Demand (COD): The amount of reductive substances in a water sample that can be oxidized by chemical methods. The oxygen equivalent of substances (generally organic matter) in wastewater, effluent from wastewater treatment plants, and polluted water that can be oxidized by strong oxidants. Total Organic Carbon (TOC): The total amount of carbon in dissolved and suspended organic matter in a water body. 5. When is biological treatment used? Generally, wastewater with a BOD/COD ratio greater than 0.3 is suitable for biological treatment. 6. What are the hygiene standards for drinking water? Physical indicators of drinking water hygiene standards: color, turbidity, odor, and taste. 7. What is eutrophication? Eutrophication is a natural phenomenon occurring in freshwater, caused by excessive nitrogen, phosphorus, and potassium levels leading to sudden overgrowth of algae. The main cause of eutrophication is the discharge of nitrogen, phosphorus, potassium, and other elements into slow-flowing surface waters with long renewal cycles, causing excessive growth of algae and other aquatic organisms. This leads to organic matter production exceeding consumption, accumulating organic matter in the water body, and disrupting the aquatic ecological balance. 8. What is dissolved oxygen? Oxygen dissolved in water is called dissolved oxygen. Aquatic organisms and aerobic microorganisms rely on dissolved oxygen for survival. Different microorganisms have different dissolved oxygen requirements. 9. What are the basic methods of modern wastewater treatment? Modern wastewater treatment technologies can be classified into physical, chemical, and biological treatment methods based on their working principles. 10. What is the stability of colloids? Colloid stability: The characteristic of colloidal particles remaining dispersed and suspended in water for an extended period. 11. What is electrokinetic potential? Electrokinetic potential: The potential at the slipping plane of a colloid, also known as the zeta potential. 12. How do hydrophobic colloids form larger particles? For hydrophobic colloids, to allow colloids to collide with each other through Brownian motion and form larger particles, the repulsive energy peak must be reduced or eliminated. The way to reduce the repulsive energy peak is to reduce or eliminate the zeta potential of the colloid particles. 13. What is the role of adsorption bridging? Adsorption bridging refers to the adsorption and bridging of macromolecules with colloid particles. 14. What is the function of a screen? The function of a screen: To intercept larger suspended solids or floating impurities. 15. What are the main factors affecting coagulation? Main factors affecting coagulation: water temperature, water pH and alkalinity, suspended solids concentration, and hydraulic conditions. 16. What are the types of sedimentation? There are four types of sedimentation: Free settling: Particles remain discrete during sedimentation, their shape, size, and mass remain unchanged, and their settling velocity is not affected, each completing the sedimentation process independently. Flocculent settling: During sedimentation, the size, mass, and settling velocity of particles increase with depth. Hindered settling: The concentration of particles in water is high, and they interfere with each other during settling, forming a clear interface between clear water and turbid water, which gradually moves downward. Compression settling: The concentration of particles in water is very high, and during sedimentation, the particles come into contact with each other and are mostly supported by the compressed material, and the gaps between the lower particles are squeezed out. 17. According to the flow direction in the basin, what types of sedimentation tanks are there? According to the flow direction in the basin, sedimentation tanks can be classified into horizontal flow, inclined flow, radial flow, and vertical flow types. 18. What is the distribution pattern of impurities within the filter media layer? Distribution pattern of impurities within the filter media layer: In the initial stage of filtration, the filter media is relatively clean, the pores are larger, and the water flow shear force is smaller, and the adhesion is stronger. At this time, the particles in the water are first intercepted by the surface filter media. As the filtration time increases, the impurities in the filter layer increase, and the porosity gradually decreases, especially the surface fine filter media. The water flow shear force increases, and the detachment effect is enhanced. Finally, the particles that are adhered to first detach and move to the lower layer and are intercepted by the lower layer filter media. As a result, under a certain filtration head, the filtration rate will decrease sharply, or under a certain filtration rate, the head loss will reach the limit value, or due to uneven stress on the filter layer surface, cracks will occur in the mud film, causing a large amount of water to flow out from the cracks, causing the impurities in the water to penetrate the filter layer and deteriorating the effluent water quality. 19. What are the ways to improve filtration efficiency? Ways to improve filtration efficiency: In order to change this situation and improve the ability of the filter layer to hold impurities, "reverse particle size" filtration has emerged, that is, the particle size of the filter media is from large to small in the direction of water flow. Due to the complex structure of upward flow and two-way flow filter pools and the inconvenience of washing, etc. 20. What is a homogeneous filter media composed of? Composition of homogeneous filter media: Homogeneous filter media refers to a filter media where the composition and average particle size are uniform across any cross-section in the depth direction of the entire filter layer, not that the particle size of the filter media is exactly the same. 21. What is the negative head phenomenon? What are the methods to avoid it? Negative head phenomenon: A phenomenon that occurs during filtration when a large amount of impurities are intercepted by the filter layer, causing the head loss at a certain depth below the sand surface to exceed the water depth at that location. Methods to avoid negative head: Increase the water depth above the sand surface, or the filter pool outlet is at or above the filter layer surface. Siphon filters and valveless filters will not experience negative head for this reason. 22. How many ways are there to supply backwash water for ordinary rapid filters? There are two ways to supply backwash water for ordinary rapid filters: wash water pumps and water towers. 23. What is breakpoint chlorination? When the main organic matter in water is ammonia and nitrogenous compounds, after the actual chlorine demand is met, the amount of chlorine added increases, and the residual chlorine increases, but the latter increases slowly. After a period of time, the amount of chlorine added increases, and the residual chlorine decreases. After that, the amount of chlorine added increases, and the residual chlorine increases again. After this breakpoint, free residual chlorine appears, and the disinfection effect is best when chlorine is added continuously, which is breakpoint chlorination. 24. What systems are included in the activated sludge process? The activated sludge process consists of an aeration tank, a sedimentation tank, sludge return, and excess sludge removal systems. 25. What is sludge settling ratio? Sludge settling ratio (SV%): The ratio (%) of the volume of settled sludge to the volume of mixed liquor in a 1000ml cylinder after settling for 30min. Disclaimer: The content is from Water Treatment New Vision. We remain neutral on the views in the article, and it is for reference and exchange purposes only. The copyright of the reprinted articles and pictures belongs to the original authors and institutions. If there is any infringement, please contact us for deletion!

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Technical Process Analysis of MVR Device in Ningxia and Ninghe Chemical Liquid Zero Discharge Project

Technical Process Analysis of MVR Device in Ningxia and Ninghe Chemical Liquid Zero Discharge Project

To treat the high-salt wastewater generated by the membrane process of the Ningxia and Ninghe chemical projects, and to achieve zero liquid discharge and resource utilization, Honzon Think (Beijing) Environmental Engineering Co., Ltd. designed and provided an MVR device. The qualified condensate water produced by the MVR device (BOD5≤5mg/L, CODcr≤10mg/L, NH3-N≤10mg/L, dissolved solids ≤200mg/L) is sent to the recycled water tank and can be used in the production system to replace fresh water. The concentrated liquid is treated by crystallization to obtain mixed salts, ultimately achieving zero liquid discharge. This article introduces the technical process of the MVR device in this project, elaborates on its process characteristics, and can provide reference for the application of MVR evaporation crystallization technology to treat industrial wastewater to achieve zero liquid discharge.

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Methods for treating high-salinity wastewater

Methods for treating high-salinity wastewater

Methods for Treating High-Salinity Wastewater 1. Add alkali to the high-salinity water for chemical reaction, producing calcium carbonate and magnesium hydroxide, removing some precipitates and suspended solids, and then treating the high-salinity wastewater through a membrane device. The water produced by the membrane device can be adjusted to a suitable pH range by adding acidic substances, and then enter the membrane desalination device for desalination. 2. The water produced by the nanofiltration membrane device is mainly sodium chloride solution. The sodium chloride solution enters the membrane concentration device for concentration. The fresh water after the device can be further recovered, and the remaining concentrated water can enter the weakly acidic cation bed to further weaken the water hardness. After the acidic cation bed, the water enters the decarbonization device for decarbonization. After CO2 removal, the remaining water enters the evaporator, and evaporative crystallization forms sodium chloride crystals. The dried salt can be used as industrial salt. 3. Most of the concentrated water produced by the nanofiltration membrane device is sodium sulfate solution, which is frozen and crystallized to form mirabilite. Mirabilite is obtained by thermal evaporation crystallization of sodium sulfate. The treated mirabilite mother liquor continues to be reverse osmosis concentrated, and the water is reused. Then, the concentrated water is sent to an evaporative crystallization device or a flue gas evaporation or ash mixing treatment device.

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Treatment of high-salt wastewater to reduce the discharge of high-salt wastewater

Treatment of high-salt wastewater to reduce the discharge of high-salt wastewater

High-salinity wastewater treatment devices are mainly used to purify wastewater with a salt content exceeding 1%. Many industrial processes generate a large amount of wastewater that cannot be directly recycled. However, direct discharge will cause great environmental pollution. Therefore, this equipment is needed to purify high-salinity wastewater to reduce its discharge. 1. Reduce the discharge of high-salinity wastewater, avoid the discharge of highly toxic and refractory substances, and solve wastewater treatment problems. 2. Reducing the discharge of high-salinity wastewater allows for wastewater reuse, reduces industrial water consumption, and recovers wastewater. High-salinity wastewater treatment can save water resources, alleviate the current serious shortage of water resources, and achieve zero discharge of high-salinity wastewater. 3. High-salinity wastewater treatment can solve the problem of end-of-pipe wastewater discharge. In many places, digging wastewater treatment ponds to treat end-of-pipe wastewater not only wastes land resources but also, in severe cases, threatens the groundwater environment. How to solve the partial blockage problems involved in high-salinity wastewater treatment?

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High-salt wastewater treatment technology

High-salt wastewater treatment technology

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