Knowledge Point of Water Treatment
50 Knowledge Points of Water Treatment
1. What is water self-purification?
Water self-purification: Polluted rivers through physical, chemical, biological and other aspects of the role of pollutants to reduce or transform the concentration of water to restore the original state, or from the initial exceeding water quality standards to equivalent to water quality standards.
2. What are the basic methods of sewage treatment?
The basic method of sewage treatment is to use various means and technologies to separate and remove pollutants from sewage, recycle them, or convert them into harmless substances, so that the sewage can be purified. Generally divided into water treatment and sewage treatment.
3. What are the current sewage treatment technologies?
Modern sewage treatment technology can be divided into physical treatment, chemical treatment and biological treatment according to the principle of action.
4. Five Water Measurement Indicators
Biochemical oxygen demand (BOD): refers to the amount of oxygen required to degrade organic matter under aerobic conditions due to the role of microorganisms. It is a comprehensive index indicating that sewage is polluted by organic substances.
Theoretic oxygen demand (thOD): The theoretical oxygen demand of an organic substance in water. Usually refers to the theoretical value of oxygen required for the complete oxidation of carbon and hydrogen elements in organic matter to carbon dioxide and water (that is, the oxygen demand calculated by the complete oxidation reaction formula).
Total Oxygen Demand (TOD): refers to the amount of oxygen that can be oxidized in water, mainly when organic substances become stable oxides in combustion. The result is expressed in mg/L of O2.
Chemical oxygen demand (COD): A chemical method for measuring the amount of reductive substances that need to be oxidized in water samples. Oxygen equivalent of substances (generally organic) oxidized by strong oxidants in wastewater, wastewater treatment plant effluent and polluted water.
Total Organic Carbon (TOC): refers to the total carbon content of dissolved and suspended organic matter in water.
5. What conditions are treated by biochemical method?
It is generally believed that wastewater with BOD/COD value greater than 0.3 is suitable for biochemical treatment.
6. What is the hygienic standard of drinking water?
Physical indicators of hygienic standards for drinking water: color, turbidity, odor and odor.
7. What is eutrophication?
Eutrophication is a natural phenomenon in freshwater, which is caused by the sudden over-proliferation of algae due to the excessive content of nitrogen, phosphorus and potassium in the water.
The main causes of eutrophication are that nitrogen, phosphorus, potassium and other elements are discharged into surface water bodies with slow flow and long renewal cycle, which makes algae and other aquatic organisms grow and multiply in large numbers, and makes the organic matter production rate far exceed the consumption rate, the organic matter accumulation in water bodies, and the process of destroying the aquatic ecological balance.
8. What is dissolved oxygen?
The dissolved oxygen in water is called dissolved oxygen. Biology and aerobic microorganisms in water depend on dissolved oxygen for their survival. Different microorganisms have different requirements for dissolved oxygen.
9. What are the basic methods of modern sewage treatment?
Modern sewage treatment technology can be divided into physical treatment, chemical treatment and biological treatment according to the principle of action.
10. What is colloid stability?
Colloidal stability: refers to the long-term dispersion of colloidal particles in water suspension characteristics.
11. What is the electromotive potential?
Potentiodynamic potential: the potential on the gliding surface of colloid, i.e. _potential.
12. How do hydrophobic colloids form large particles?
For hydrophobic colloids, in order to make colloids collide into large particles through Brownian motion, the repulsive peaks must be reduced or eliminated. The way to reduce the repulsive peaks is to reduce or eliminate the zeta potential of colloids.
13. What is the role of adsorption bridging?
Adsorption bridging refers to the adsorption and bridging of macromolecule and colloidal particles.
14. What is the role of grids?
The role of grille: used to intercept larger suspended matter or floating impurities.
15. What are the main factors affecting the coagulation effect?
The main factors affecting coagulation effect are water temperature, PH value and alkalinity of water, concentration of suspended solids in water and hydraulic conditions.
16. How many types of precipitation are there? What are the differences?
There are four types of precipitation, they are:
Free precipitation: Particles are discrete in the process of precipitation, and their shape, size and mass remain unchanged. The velocity of subsidence is not disturbed, and the precipitation process is completed independently of each other.
Turbulent Settlement: In the process of settling, the size, mass and settling speed of particles increase with the increase of depth.
Congestion precipitation: Particles in the water have a high concentration and interfere with each other in the process of sinking, forming a clear interface between clean water and muddy water, and gradually moving downward.
Compression precipitation: The concentration of particles in water is very high. In the process of precipitation, particles contact each other and are mostly supported by compressed materials. The gap between the lower particles is extruded.
17. According to the direction of flow in the tank, what kinds of sedimentation tanks can be divided into?
Depending on the direction of flow in the tank, the sedimentation tank can be divided into advection, oblique, radial and vertical flow.
18. What is the regularity of impurity distribution in the filter bed?
Distribution of impurities in the filter bed: At the beginning of filtration, the filter material is clean, the pore is large, the shear force of flow is small and the adhesion is strong. At this time, the particles in water are first intercepted by the surface filter material. With the extension of filtration time, the impurities in the filter layer increase, and the porosity decreases gradually, especially the surface fine filter material, water. With the increase of flow shear force, the shearing effect is enhanced. At last, the adhering particles first fall off and move to the lower layer and are intercepted by the lower filter material.
The results are as follows: under a certain filtration head, the filtration rate will decrease sharply, or when the loss of the head reaches the limit at a certain filtration speed, or when the mud film is cracked due to the uneven force on the surface of the filter layer, a large amount of water flows out of the crack, resulting in impurity particles in the water penetrating through the filter layer and deteriorating the quality of the effluent water.
19. What are the ways to improve filtration efficiency?
The way to improve the filtration efficiency: In order to change this situation and improve the contamination capacity of the filter layer, there is a "reverse granularity" filtration, that is, along the flow direction, the size of the filter material from large to small, because of the complex structure of upflow and bi-directional flow filter, it is inconvenient to flush and other reasons.
20. What is the composition of homogeneous filter material?
Homogeneous filter material composition: Homogeneous filter material refers to any cross-section in the depth direction of the whole filter layer. The composition and average particle size of the filter material are uniform, but not the same particle size of the filter material.
21. What is the negative head phenomenon? What are the ways to avoid it?
Negative head phenomenon: In the process of filtration, when a large number of impurities are intercepted in the filter layer, the head loss at a depth below the sand surface exceeds the water depth at that point.
The way to avoid negative water head is to increase the depth of water on the sand surface, or the outlet water level of the filter is equal to or higher than the surface of the filter layer. This is the reason why siphon and valveless filters do not have negative head.
22. How many kinds of backwash water supply modes are there in common fast filter?
There are two ways of backwashing water supply for ordinary fast filter: flushing pump and water tower.
23. What is this chlorination?
When the organic matter in water is mainly ammonia and nitride, the actual chlorine requirement is satisfied, the chlorination amount increases and the residual chlorine amount increases, but the latter increases slowly. After a period of time, the chlorination amount increases and the residual chlorine amount decreases. After that, the chlorination amount increases and the residual chlorine amount rises again. After this break point, the free residual chlorine appears and continues chlorination disinfection. The effect is the best, that is, folding point chlorination.
24. What are the systems of activated sludge process?
Activated sludge process is composed of aeration tank, sedimentation tank, sludge reflux and surplus sludge removal system.
25. What is sludge settling ratio?
Sludge Settlement Ratio (SV%): refers to the volume ratio of sludge to mixed liquor (%) in an aeration tank, which is deposited in a 1000ml measuring cylinder for 30 minutes.
26, what is sludge index?
Sludge Index (SVI): refers to the volume of dry sludge per gram at the outlet of aeration tank after 30 minutes of static precipitation.
The low value of SVI indicates that the sludge particles are small and compact, with many inorganic substances, and lack of activity and adsorption capacity. The high value of SVI indicates that sludge is difficult to settle and separate, and that it is about to expand or has already expanded. The reasons must be identified and measures taken.
27. What are sludge bulking, disintegration, decay, buoyancy and foam?
Sludge bulking: When the sludge deteriorates, the sludge is not easy to precipitate, the SVI value increases, the structure of the sludge is loose, the volume expands, the water content increases, the clarification liquid is small, and the color also varies.
Sludge Disintegration: The water quality of treated water is turbid, the sludge turbulent coagulation is fine, and the treatment effect is deteriorated, which is the phenomenon of sludge disintegration.
Sludge decomposition: In the secondary sedimentation tank, anaerobic fermentation may occur due to the long-term retention of sludge, resulting in the formation of gases, resulting in the floating of large sludge.
Sludge floatation: Sludge floats in bulk in the secondary sedimentation tank.
Foam problem: Foam is produced in the aeration tank. The main reason is that there are a lot of synthetic washing or other foaming substances in the sewage.
28. What is the activated sludge growth curve?
Activated sludge microorganism is a mixed group of multi-bacteria. Its growth law is complex, but it can also be expressed by its growth curve. The curve expresses the law of microbial growth and attenuation with time when nutrients are sufficiently added at a time when environmental conditions such as temperature and dissolved oxygen meet the requirements of microbial growth and there is a certain amount of initial microbial inoculation.
The change of the growth rate of activated sludge is mainly caused by the ratio of nutrients or organic matter to microorganisms (usually expressed as F/M). F/M value is also an important factor affecting the degradation rate of organic substrate, oxygen utilization rate, aggregation and adsorption performance of activated sludge.
There are four stages in the growth curve of activated sludge: adaptation period, logarithmic growth period, deceleration growth period (biomass maximum), endogenous respiration period (water quality treatment effect is the best).
29. How many processes are involved in the purification of activated sludge?
Activated sludge purification wastewater is accomplished in three stages:
In the first stage, the wastewater is purified mainly through the adsorption of activated sludge. Adsorption proceeds very quickly, usually within 30 minutes, and the removal rate of BOD5 can be as high as 70%. At the same time, it has partial oxidation, but adsorption is the main role.
The second stage, also known as oxidation stage. It is mainly to continue to decompose the adsorbed and absorbed organic substances in the pre-oxidation stage, while continuing to adsorb some residual dissolved substances.
The third stage is the mud-water separation stage. In this stage, activated sludge is precipitated and separated in secondary clarifier. Microbial anabolism and catabolism can remove organic pollutants from sewage, but the products are different.
30. What are the characteristics of the secondary sedimentation tank?
The characteristics of secondary sedimentation tank: In addition to sludge separation, it also concentrates sludge, and temporarily stores sludge due to changes in water quality and quantity.
31. What is sewage slow infiltration system?
Slow infiltration of sewage is to let the sewage slowly pass through the land, because of the role of natural infiltration and filtration to purify the sewage. It is suitable for areas with good permeability, small evaporation and humid climate.
32. What is a sewage rapid infiltration system?
It is suitable for soil with very good permeability. Such as sandy soil, gravel sandy soil, etc. Soon after the sewage tank reaches the surface of the fast infiltration field, it seeps into the underground and finally into the groundwater layer.
33. How many stages are anaerobic reactions? What are the differences?
Anaerobic reaction can be divided into three stages:
The first stage is the decomposition of organic matter into fatty acid machine products under the action of hydrolysis and fermentation bacteria.
In the second stage, hydrogen-producing acetic acid is further converted into hydrogen, carbon dioxide and acetic acid under the action of bacteria.
The third stage is the methane fermentation stage (alkaline fermentation stage), through the action of two different groups of methanogens, one group converts hydrogen and carbon dioxide into methane, the other group is acetic acid degassing to methane.
34. What is biphasic digestion?
Two-phase digestion is to separate the acid and methane production stages of anaerobic digestion of organic substrates.
35. What is the material composition of sludge?
The substances in sludge can be divided into organic sludge and inorganic sludge.
According to the source of sludge, it can be divided into primary sedimentation sludge, residual activated sludge, humic sludge, mature sludge and chemical sludge.
36. What moisture does the sludge contain?
Water content in sludge can be divided into four categories: interstitial water between particles, capillary water, water absorbed by sludge particles and water inside particles.
Removal methods: gravity, air flotation and centrifugation.
37. What does mechanical dehydration include?
Mechanical dewatering: vacuum filtration dewatering, pressure filtration dewatering, rolling dewatering, centrifugal dewatering of sludge.
38. What is the purpose of sludge stabilization?
The purpose of sludge stabilization is to eliminate the odor emitted from sludge and kill pathogenic microorganisms in sludge.
39. What is adsorption?
Porous solids (such as activated carbon) or flocs (such as polyferric) are used to adsorb toxic and harmful substances in wastewater onto the surface or micro-pore of solids or flocs to purify water quality. This treatment method is called adsorption treatment. The object of adsorption can be either insoluble solid substance or soluble substance.
40. What are the characteristics of physical and chemical adsorption?
Physical adsorption characteristics: adsorption heat is small, low temperature can be carried out, adsorption is reversible, adsorption is basically non-selective.
Chemical adsorption characteristics: the adsorption heat is large, the adsorption is irreversible, and the adsorption is selective.
41. What is resin density?
Resin density: generally refers to wet true density and wet apparent density. The wet true density is related to the backwashing strength, expansion rate of resin layer and the resin stratification of mixed bed and double bed. The wet apparent density is used to calculate the quantity of wet resin needed for ion exchanger.
42. What's the function of water filling?
The function of water-spraying filler is to make water droplets splashed by water distribution system into tiny water droplets or water film by multiple splashes, increase the contact area between water and air, prolong the contact time, thus ensuring good heat and mass exchange between air and water.
43. What is volatile suspended solids in mixed liquids?
Volatile suspended solids (MLVSS) of mixed liquor refers to the weight of volatile substances in the dry sludge contained in the mixed liquor of a unit volume biochemical pond, which is also mg/L. Because it does not include inorganic substances in the activated sludge, it can more accurately represent the number of microorganisms in the activated sludge.
44. Why is excess sludge produced?
In the process of biochemical treatment, microorganisms in activated sludge continuously consume organic substances in wastewater.
Among the consumed organic substances, some organic substances are oxidized to provide energy for microbial life activities, while others are utilized by microorganisms to synthesize new cytoplasm, so that microorganisms multiply and reproduce, while the metabolism of microorganisms is accompanied by the death of some old microorganisms. The excess sludge was removed.
45. What is needle carbon technology?
Iron-carbon treatment, also known as iron-carbon micro-electrolysis or iron-carbon internal electrolysis, is an application form of iron-metal wastewater treatment technology. It has a unique effect to treat toxic, harmful and highly concentrated COD wastewater with iron-carbon pretreatment technology.
46. Why should the effluent pH of the neutralization sedimentation tank be above 9?
Iron-carbon effluent contains a large amount of ferrous sulfate, if not removed, it will affect the growth and reproduction of microorganisms in subsequent biochemical ponds.
Therefore, we must use lime to raise the pH value of wastewater from 5-6 to above 9, so that water-soluble ferrous sulfate can be converted into insoluble ferrous hydroxide and calcium sulfate, and then they can be precipitated by coagulation and sedimentation to ensure that the wastewater entering the biochemical pond does not contain ferrous sulfate.
47. What are the types of air flotation?
Air flotation can be divided into dissolved air flotation (vacuum dissolved air flotation and pressurized dissolved air flotation), dispersed air flotation and electrolytic air flotation.
48. What is flocculation?
Flocculation is the addition of polymer coagulant agent in wastewater. When the polymer coagulant agent dissolves, it will form a polymer. The structure of this polymer is a linear structure. One end of the line pulls a tiny particle and the other pulls another tiny particle. It acts as a bridge between two particles far apart, making the particles gradually larger and eventually forming large particles of flocculant (commonly known as alum flower) to accelerate particle sedimentation
49. Why should the wastewater be treated with Polyferric flocculation and adsorption?
Polyferric hydroxide floc formed during coagulation process has a good ability to adsorb organic substances in wastewater. The experimental data show that the COD in wastewater can be removed by flocculating and adsorbing with polyferric oxide, which can greatly reduce the operating burden of biochemical ponds and is conducive to the discharge of wastewater up to the standard.
In addition, coagulation pretreatment with Polyferric can remove trace substances which are toxic and inhibiting to microorganisms in wastewater, so as to ensure the normal operation of microorganisms in biochemical ponds. Among many coagulants, the price of Polyferric is relatively cheap (25-300 yuan/ton), so the cost of treatment is relatively low, which is more suitable for the pretreatment of process wastewater.
50. Why is it difficult for colloidal particles in wastewater to precipitate naturally?
Many impurity suspended substances, large particles and easily settled suspended substances with a proportion of more than 1 in wastewater can be removed by natural sedimentation and centrifugation.
However, it is difficult for suspended particulates whose specific gravity is less than 1, small or even invisible to the naked eye to settle naturally. For example, colloidal particulates are 10-4-10-6 mm in size, which are very stable in water and have a very slow settling speed. It takes 200 years for a meter to settle.
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