1. What is self purification of water bodies?
Self purification of water bodies: Polluted rivers undergo physical, chemical, biological, and other processes to reduce or transform the concentration of pollutants, restoring the water body to its original state or reducing it from exceeding water quality standards to equal 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 and reuse them, or convert them into harmless substances to purify sewage. 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 method, chemical treatment method, and biological treatment method according to the principle of action.
4. Five measurement indicators for water
Biochemical Oxygen Demand (BOD): refers to the amount of oxygen required by microorganisms to degrade organic matter under aerobic conditions. It is a comprehensive indicator indicating that sewage is contaminated by organic matter.
Theoretical Oxygen Demand (thOD): The theoretical oxygen demand of a certain organic compound in water. Usually refers to the theoretical value of oxygen required to completely oxidize carbon and hydrogen elements in organic matter into carbon dioxide and water (i.e., the oxygen demand calculated according to the complete oxidation reaction equation).
Total Oxygen Demand (TOD): Refers to the amount of oxygen required for substances in water that can be oxidized, mainly organic substances, to become stable oxides during combustion, expressed in mg/L of O2.
Chemical Oxygen Demand (COD): It is a chemical method used to measure the amount of reducible substances that need to be oxidized in a water sample. The oxygen equivalent of substances (usually organic compounds) that can be oxidized by strong oxidants in wastewater, wastewater treatment plant effluent, and polluted water.
Total Organic Carbon (TOC): refers to the total amount of dissolved and suspended organic matter in water containing carbon.
5. Under what circumstances is biochemical treatment used?
It is generally believed that sewage with a BOD/COD value greater than 0.3 is suitable for biochemical treatment.
6. What are the hygiene standards for drinking water in daily life?
The physical indicators of hygiene standards for drinking water include color, turbidity, odor, and taste.
7. What is eutrophication of water bodies?
Eutrophication of water bodies is a natural phenomenon that occurs in freshwater due to the sudden overgrowth of algae caused by high levels of nitrogen, phosphorus, and potassium in the water.
The main cause of eutrophication in water bodies is the discharge of elements such as nitrogen, phosphorus, and potassium into surface water bodies with slow flow rates and long renewal cycles, which leads to the massive growth and reproduction of aquatic organisms such as algae. This results in organic matter production rates far exceeding consumption rates, leading to the accumulation of organic matter in water bodies and disrupting the balance of aquatic ecology.
8. What is dissolved oxygen?
The oxygen dissolved in water is called dissolved oxygen. The organisms and aerobic microorganisms in water rely 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 method, chemical treatment method, and biological treatment method according to the principle of action.
10. What is the stability of colloids?
Colloidal stability: refers to the characteristic of colloidal particles maintaining a dispersed and suspended state in water for a long time.
11. What is an electric position?
Kinetic potential: The potential on the sliding surface of a colloid, also known as the zeta potential.
12. How do hydrophobic colloids form large particles?
For hydrophobic colloids, in order to collide with each other through Brownian motion and form large particles, it is necessary to reduce or eliminate the repulsion energy peak. The way to reduce the repulsion energy peak is to lower or eliminate the zeta potential of the colloidal particles.
13. What is the function of adsorption bridging?
Adsorption bridging refers to the adsorption and bridging of polymer substances and colloidal particles.
14. What is the function of the grille?
The function of a grille is to intercept larger suspended solids or floating impurities.
15. What are the main factors affecting the coagulation effect?
The main factors affecting the coagulation effect are water temperature, pH and alkalinity of water, suspended solids concentration in water, and hydraulic conditions.
16. How many types of sediment are there? What are they respectively?
There are four types of precipitation, which are:
Free precipitation: The particles are in a discrete state during the precipitation process, and their shape, size, and mass do not change. The settling speed is not disturbed, and they independently complete the precipitation process.
Turbulent sedimentation: During the sedimentation process, the size, mass, and settling velocity of particles all increase with depth.
Crowded sedimentation: Particles have a high concentration in water and interfere with each other during the sinking process, forming a clear interface between clear water and turbid water and gradually moving downwards.
Compressed precipitation: The concentration of particles in water is very high, and during the precipitation process, the particles come into contact with each other and are mostly supported by the compressed material, causing the gaps between the lower particles to be squeezed out.
17. What types of sedimentation tanks can be classified according to the direction of water flow in the tank?
According to the different directions of water flow in the sedimentation tank, it can be divided into horizontal flow, inclined flow, radial flow, and vertical flow.
18. What are the patterns of impurity distribution within the filter layer?
The distribution pattern of impurities in the filter material layer: At the beginning of filtration, the filter material is relatively clean, the pores are large, the water flow shear force is small, and the adhesion is strong. At this time, the particles in the water are first intercepted by the surface filter material. As the filtration time prolongs, the impurities in the filter layer increase, and the porosity gradually decreases. Especially for the surface fine filter material, the water flow shear force increases, and the shedding effect is enhanced. Finally, the particles adhered to it first fall off and move to the lower layer, and are intercepted by the lower filter material.
The result is that at a certain filtration head, the filtration rate will sharply decrease, or when the loss of the water head reaches its limit at a certain filtration head, or when the mud film cracks due to uneven force on the surface of the filter layer, a large amount of water flows out from the cracks, causing impurities in the water to penetrate the filter layer and deteriorate the quality of the effluent.
19. What are the ways to improve filtration efficiency?
Ways to improve filtration efficiency: In order to change this situation and increase the fouling capacity of the filter layer, "reverse particle size" filtration has emerged, which means that the filter material particle size decreases from large to small in the direction of water flow. Due to the complex structure of the upward and bidirectional 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 entire filter layer, and the composition and average particle size of the filter material are uniform and consistent, rather than referring to the filter material particle size being completely the same.
21. What is negative head phenomenon? What are the methods to avoid?
Negative head phenomenon: a phenomenon that occurs during the filtration process when a large amount of impurities are trapped in the filter layer, causing the head loss at a certain depth below the sand surface to exceed the water depth at that depth.
The method to avoid negative water head is to increase the water depth on the sand surface or ensure that the outlet position of the filter is equal to or higher than the surface of the filter layer. The reason why siphon filters and valve free filters do not experience negative water head is this.
How many methods are there for supplying backwash water to a regular fast filter?
There are two ways to supply backwash water for ordinary fast filter: flushing water pump and water tower.
23. What is this chlorine addition?
When the organic matter in water is mainly ammonia and nitrogen compounds, and the actual chlorine demand is met, the amount of chlorine added increases, and the amount of residual chlorine increases. However, the latter increases slowly. After a period of time, the amount of chlorine added increases, but the amount of residual chlorine decreases. Afterwards, the amount of chlorine added increases, and the amount of residual chlorine increases again. After this inflection point, free residual chlorine appears. Continuing to add chlorine for disinfection has the best effect, that is, adding chlorine at the inflection point.
24. What are the systems of activated sludge process?
The activated sludge process consists of an aeration tank, a sedimentation tank, a sludge reflux system, and a residual sludge removal system.
25. What is sludge settling ratio?
Sludge settling ratio (SV%): refers to the volume ratio (%) of settled sludge to mixed liquid in an aeration tank, which is left to settle 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 of the mixed liquid at the outlet of the aeration tank after settling for 30 minutes, measured in mL.
If the SVI value is too low, it indicates that the mud particles are small and compact, with a lot of inorganic substances, lacking activity and adsorption capacity; If the SVI value is too high, it indicates that the sludge is difficult to settle and separate, and is about to expand or has already expanded. The cause must be identified and measures taken.
27. What are sludge bulking, disintegration, corruption, floating and foam?
Sludge swelling: When the sludge deteriorates, it is not easy to settle, the SVI value increases, the structure of the sludge becomes loose, the volume expands, the moisture content increases, the clarified liquid is less, and the color also changes.
Sludge disintegration: The phenomenon of sludge disintegration occurs when the water quality is turbid, the sludge becomes finer due to coagulation, and the treatment effect deteriorates.
Sludge decay: In the secondary sedimentation tank, anaerobic fermentation may occur due to long-term retention of sludge, generating gas and resulting in the phenomenon of large pieces of sludge floating up.
Sludge floating up: The phenomenon of sludge floating up in blocks in the secondary sedimentation tank.
Foam problem: foam is produced in the aeration tank, which is mainly caused by a large number of synthetic washing or other foaming substances in the sewage.
28. What is the growth curve of activated sludge?
Activated sludge microorganisms are a mixed population of multiple bacterial species, and their growth patterns are relatively complex, but their growth curves can also be used to represent certain patterns. This curve expresses the proliferation and decay of microbial numbers over time after a sufficient addition of nutrients, under environmental conditions such as temperature and dissolved oxygen that meet the growth requirements of microorganisms, and with 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 on the degradation rate of organic substrates, oxygen utilization rate, coagulation and adsorption performance of activated sludge.
The four stages of the growth curve of activated sludge are: adaptation period, logarithmic growth period, deceleration growth period (with the highest biomass), and endogenous respiration period (with the best water quality treatment effect).
29. How many processes are involved in the purification of activated sludge?
The purification of wastewater by activated sludge is completed through three stages:
In the first stage, wastewater is mainly purified through the adsorption of activated sludge. The adsorption process proceeds very rapidly, usually completed within 30 minutes, and the BOD5 removal rate can reach up to 70%. It also has a partial oxidizing effect, but adsorption is the main function.
The second stage, also known as the oxidation stage. Mainly, it continues to decompose the organic matter adsorbed and absorbed 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 undergoes sedimentation and separation in the secondary sedimentation tank. Both the synthesis metabolism and decomposition metabolism of microorganisms can remove organic pollutants from wastewater, but the products are different.
What are the characteristics of a secondary sedimentation tank?
The characteristics of the secondary sedimentation tank: In terms of function, it not only separates sludge from water, but also concentrates sludge, and temporarily stores sludge due to changes in water quality and quantity.
31. What is a slow infiltration system for sewage?
Slow infiltration of sewage is the process of allowing sewage to slowly pass through the land and purify it through natural infiltration filtration. Suitable for soils with good water permeability and areas with low evaporation and humid climate.
32. What is a sewage rapid filtration system?
Suitable for soils with excellent permeability. Such as sandy soil, gravelly sandy soil, etc. After the sewage tank reaches the surface of the rapid infiltration field, it quickly infiltrates into the underground and eventually enters the groundwater layer.
How many stages are there in anaerobic reactions? What are they respectively?
Anaerobic reactions are divided into three stages:
The first stage is the decomposition of organic matter into fatty acid mechanical products under the action of hydrolysis and fermentation bacteria.
The second stage is the further conversion of hydrogen and acetic acid into hydrogen, carbon dioxide, and acetic acid under the action of bacteria.
The third stage is the methane fermentation stage (alkaline fermentation stage), which involves the action of two different groups of methane producing bacteria. One group converts hydrogen and carbon dioxide into methane, while the other group converts acetic acid to produce methane.
34. What is two-phase digestion?
Two phase digestion is the process of separating the acid production stage and methane production stage of anaerobic digestion of organic substrates.
What are the material components of sludge?
The composition of substances in sludge can be divided into organic sludge and inorganic sludge.
According to the source of sludge, it can be divided into primary sediment sludge, residual activated sludge, humic sludge, mature sludge, and chemical sludge.
What moisture does sludge contain?
The water content in sludge is divided into four categories: pore water between particles, capillary water, adsorbed water on sludge particles, and internal water of particles.
Removal methods: gravity, air flotation, centrifugation.
What does mechanical dehydration include?
Mechanical dewatering: vacuum filtration dewatering, pressure filtration dewatering, rolling dewatering, centrifugal dewatering of sludge.
What is the purpose of stabilizing sludge?
The purpose of stabilizing sludge is to eliminate the odor emitted from the sludge and kill pathogenic microorganisms in the sludge.
39. What is adsorption?
The use of porous solids (such as activated carbon) or flocs (such as polyiron) to adsorb toxic and harmful substances in wastewater onto the surface or micropores of the solids or flocs, in order to purify water quality, is called adsorption treatment. The object of adsorption can be insoluble solid substances or soluble substances.
What are the characteristics of physical adsorption and chemical adsorption?
Physical adsorption characteristics: The adsorption heat is small, it can be carried out at low temperatures, the adsorption is reversible, and the adsorption is basically non selective.
Chemical adsorption characteristics: high adsorption heat, irreversible adsorption, selective adsorption.
41. What is resin density?
Resin density: generally refers to two methods of expression: wet true density and wet apparent density. The wet true density is related to the backwash strength and expansion rate of the resin layer, as well as the resin stratification of the mixed bed and double bed. The wet apparent density is used to calculate the amount of wet resin required to fill the ion exchanger.
What is the function of water filling material?
The function of water spraying filler is to disperse the water droplets splashed in the water distribution system into fine droplets or water films after multiple splashes, increase the contact area between water and air, prolong the contact time, and ensure good heat and mass exchange between air and water.
43. What is a mixed liquid volatile suspended solid?
Mixed liquid volatile suspended solids (MLVSS) refers to the weight of volatile substances in the dry sludge contained in the mixed liquid of a biochemical tank per unit volume, also in mg/L. Since it does not include inorganic substances in activated sludge, it can accurately represent the number of microorganisms in activated sludge.
Why is there excess sludge generated?
During the biochemical treatment process, microorganisms in activated sludge continuously consume organic matter in wastewater.
In the consumed organic matter, a portion of the organic matter is oxidized to provide the energy required for microbial life activities, while another portion is utilized by microorganisms to synthesize new cytoplasm, thereby promoting microbial reproduction. While microorganisms metabolize, some old microorganisms die, resulting in the production of excess sludge.
45. What is needle charcoal technology?
Iron carbon treatment method, also known as iron carbon microelectrolysis method or iron carbon internal electrolysis method, is an application form of metal iron wastewater treatment technology. Using iron carbon method as a pretreatment technology to treat toxic and harmful, high concentration COD wastewater has a unique effect.
Why is the pH of the effluent from the neutralization sedimentation tank adjusted to above 9?
Iron charcoal effluent contains a large amount of ferrous sulfate, which, if not removed, will affect the growth and reproduction of microorganisms in the subsequent biochemical pool.
Therefore, we must use lime to increase the pH value of the wastewater from 5-6 to above 9, so as to convert water-soluble ferrous sulfate into insoluble ferrous hydroxide and calcium sulfate, and then precipitate them through coagulation and sedimentation to ensure that the wastewater entering the biochemical tank does not contain ferrous sulfate.
What are the types of air flotation?
Air flotation is divided into dissolved air flotation (divided into vacuum dissolved air flotation and pressurized dissolved air flotation), dispersed air flotation, and electrolytic air flotation.
48. What is flocculation?
Flocculation is the process of adding high molecular weight coagulants to wastewater, which dissolve to form high molecular weight polymers. The structure of this polymer is a linear structure, with one end of the line pulling a tiny particle and the other end pulling another tiny particle, playing a role in bonding and bridging between two particles that are far apart, gradually increasing the size of the particles and ultimately forming a large particle floc (commonly known as alum flower), accelerating particle settling.
Why is it necessary to use polyiron for coagulation and adsorption treatment of wastewater?
During the coagulation process, polyiron forms iron hydroxide flocs, which have excellent ability to adsorb organic substances in wastewater. Experimental data shows that after using polyiron coagulation to adsorb wastewater, about 10% -20% of COD in the wastewater can be removed, which can greatly reduce the operational burden of the biochemical tank and facilitate the standard discharge of wastewater treatment.
In addition, using polyiron for coagulation pretreatment can remove trace substances that are toxic and inhibitory to microorganisms in wastewater, ensuring the normal operation of microorganisms in the biochemical tank. Among many coagulation agents, the price of polyiron is relatively cheap (25-300 yuan/ton), so the treatment cost is relatively low and it is more suitable for the pretreatment of process wastewater.
Why are colloidal particles in wastewater difficult to naturally precipitate?
Many impurities, suspended solids, large particles, and easily settling suspended solids with a specific gravity greater than 1 in wastewater can be removed by natural settling, centrifugation, and other methods.
However, suspended particles with a specific gravity less than 1, which are small and even invisible to the naked eye, are difficult to naturally settle. For example, colloidal particles are small particles with a size of 10-4-10-6mm, which are very stable in water. Their settling speed is extremely slow, and it takes 200 years to cultivate them for every 1 meter of settling.
