1. Sewage
Sewage refers to the water that has been used, which contains various pollutants such as organic, inorganic, pathogens, etc. Sewage mainly comes from industrial wastewater, domestic sewage, and agricultural drainage.
2. Industrial wastewater
Industrial wastewater refers to the wastewater and waste liquid discharged in the process of process production, which contains industrial production materials, intermediate products, by-products and pollutants generated in the production process that are lost with water, which is an important cause of environmental pollution, especially water pollution, and the water quality composition is complex and changeable.
3. Domestic sewage

Domestic sewage generally refers to the discharge water produced by various kitchen water, washing water and toilet water used in human life, which is mostly non-toxic inorganic salts, and domestic sewage contains more nitrogen, phosphorus, sulfur, and more pathogenic bacteria.

4. Agricultural drainage
It refers to the excessive surface water, soil water and groundwater in the farmland, which is less polluted and can be recycled, and generally does not do special treatment.
5. Sewage treatment
Sewage treatment is the use of various (technologies and means) to remove (remove), (recycle) (utilize) or convert the pollutants contained in sewage into harmless substances, so that water can be purified.

6. 3 major sewage treatment methods
Sewage treatment is mainly divided into three types: (physical) sewage treatment method, (biological) sewage treatment method, and (chemical) sewage treatment method.
7. What is the (physical) sewage treatment method?
The physical treatment method is a treatment method that separates and recovers insoluble and suspended pollutants in sewage through physical action.
8. What is the (biological) sewage treatment method?
Biological treatment is a treatment method that uses microorganisms to suck, decompose and oxidize the organic matter in the sewage, and degrade the unstable organic matter into stable and harmless substances, so that the sewage can be purified.
9. What is the (chemical) sewage treatment method?
Chemical treatment is a treatment method that adds chemicals to sewage and uses chemical reactions to separate and recover pollutants in sewage, or convert them into harmless substances.

10. What are the common (physical) pretreatment processes for sewage?
In the process of sewage treatment, the common pretreatment processes are mainly as follows: grid, air flotation tank, regulating tank, secondary sedimentation tank and so on.
11. What is the role of the grid in sewage treatment?
In front of the sewage treatment system or pumps, a grid must be installed to intercept suspended solids and large solid contaminants in the sewage before they can cause damage to the pumps or process lines of the subsequent treatment unit.
In general, the sewage treatment process is set up with two grids, and the sewage first passes through the coarse grid and then through the fine grid.
12. What is the function of air flotation tank in sewage treatment?
Air flotation tank refers to a kind of pool that mainly uses a large number of microbubbles to capture and adsorb fine particles of glue to make it float and achieve the effect of solid-liquid separation.

The working principle of the air flotation process is that part of the treated wastewater circulates into the dissolved air tank, in the pressurized air state, the air is supersaturated and dissolved, and then mixed with the raw water with the addition of flocculant at the entrance of the air flotation tank, due to the decrease in pressure, the supersaturated air is released, forming tiny bubbles, which are quickly attached to the suspended solids and lifted to the surface of the air flotation tank. As a result, a floating layer of sludge is formed that is easily removed, and the heavier solids that settle at the bottom of the pond are also removed.
13. What is the function of the regulating tank in sewage treatment?
A regulating tank is a structure used to regulate the flow of inlet and outlet water. It mainly plays the role of regulating the quantity and quality of water, as well as the adjustment of sewage pH value and water temperature, and can also be used as accident drainage.
14. What is the function of the secondary sedimentation tank in sewage treatment?
The secondary sedimentation tank, also known as the secondary sedimentation tank, is an important part of the activated sludge system, and its function is mainly to separate the sludge, make the mixed liquid clear, concentrate and return the activated sludge.
15. Activated sludge system
Activated Sludge SystemThe activated sludge system consists of an aeration tank, a sedimentation tank, sludge return and a residual sludge removal system.

16. Activated sludge process
Activated sludge processes include A-B process, SBR process, A2/O process, oxidation ditch process, etc.
17. A-B process
The A-B process actually refers to the adsorption-biodegradation process. Among them, the bioreactor in section A is called the adsorption tank, which plays the function of bacteria adsorbing organic matter in wastewater, and then enters the sedimentation tank for sludge water separation, part of the sludge is refluxed, and the remaining sludge is discharged.
The effluent of the intermediate sedimentation tank then enters section B, and the biological reaction tank of section B is a conventional aeration tank, which plays the role of activated sludge in the degradation, removal and transformation of organic matter or other pollutants in wastewater, and finally enters the sedimentation tank for sludge water separation, part of the sludge is refluxed, and the remaining sludge is discharged.

18. SBR process
SBR is the abbreviation of sequential batch activated sludge method, which is an activated sludge wastewater treatment technology that operates according to the intermittent aeration method. Its main feature is the orderly and intermittent operation in operation, the core of SBR technology is the SBR reaction tank, which integrates the functions of homogenization, primary sedimentation, biodegradation, secondary sedimentation and other functions in one pool, no sludge reflux system. It is especially suitable for the occasion of insufficient construction space, intermittent discharge and large flow rate changes.
19. A2/O process
The A2/O process is the simplest and most widely used denitrification and phosphorus removal process. The A2/O process is also known as the A-A-O process (anaerobic-anoxic-aerobic).
20. Oxidation ditch process
The oxidation ditch process, also known as the oxidation ditch process, is a variant of the activated sludge process. It is named because its structure is a closed annular ditch. Because sewage and activated sludge are constantly circulating in the aeration channel, some people call them "circulating aeration tanks" and "non-terminal aeration tanks".

21. The proportional relationship between carbon source, nitrogen source and phosphorus source
The proportional relationship of the three major nutrients (carbon source, nitrogen source and phosphorus source) is generally BOD:N:P=100:5:1.
22. How to understand the sludge index (SVI)?
Sludge index refers to the volume (in ml) of 1g of dry sludge occupied by the corresponding 1g of dry sludge after 30min of static sedimentation of the mixture of aeration tank, i.e., SVI = sludge deposition (ml) / dry weight of sludge (g) after 30min static sedimentation of the mixture
The SVI value can better reflect the looseness and coagulation and sedimentation performance of activated sludge. Good activated sludge SVI is often between 50~300, and the sludge concentration is too high, and the SVI value measured at the same concentration is valuable. In addition, because the size of the measurement container has a certain impact on the number of measurements, it is necessary to measure the containers uniformly.

23. What temperature range is the most suitable for microorganisms to grow and reproduce?
In the biological treatment of wastewater, the optimal temperature range for microorganisms is generally 16-30 °C, and the maximum temperature is 37-43 °C, when the temperature is lower than 10 °C, microorganisms will no longer grow. In the appropriate temperature range, for every 10°C increase in temperature, the metabolic rate of microorganisms will increase correspondingly, and the removal rate of COD will also increase by about 10%. Conversely, for every 10°C decrease in temperature, the removal rate of COD decreases by 10%, so the biochemical removal rate of COD in winter is significantly lower than in other seasons.
24. What is the most suitable pH range for microorganisms?
The life activities and metabolism of microorganisms are closely related to the pH value. Most microorganisms are adapted to a pH range of 4.5-9, while the optimal pH range is 6.5-7.5. When the pH is lower than 6.5, the fungus begins to compete with the bacteria, and when the pH reaches 4.5, the fungus will have a complete dominance in the biochemical tank, and the result is that the sedimentation of the sludge will be seriously affected, and when the pH exceeds 9, the metabolic rate of the microorganisms will be hindered. Different microorganisms have different requirements for the pH range. In aerobic biological treatment, the pH can vary between 6.5-8.5, and in anaerobic biological treatment, the pH requirements for microorganisms are stricter, and the pH should be between 6.7-7.4.

25. Cohesion
In the wastewater with positive ions of coagulation agent, a large number of positive ions exist between colloidal particles to eliminate the electrostatic repulsion between colloidal particles, so that the particles coalesce, this method by adding positive ions electrolyte, the process of colloidal particles coalescing with each other is called coagulation. Commonly used coagulants include aluminum sulfate, ferrous sulfate, alum, ferric chloride, etc.
26. Flocculation
Flocculation is the addition of polymer coagulation agent to wastewater, and after the polymer coagulation agent is dissolved, a polymer polymer will be formed. The structure of this polymer is a linear structure, one end of the line pulls a tiny particle, the other end pulls another tiny particle, which plays the role of bonding and bridging between two particles far apart, so that the particles gradually become larger, and finally form a large particle of floc (commonly known as alum flower), accelerating the particle sedimentation.
Commonly used flocculants are polyacrylamide (PAM), polyiron (PE), etc.

27. Coagulation

The process used in combination of coagulation and flocculation is the coagulation process. Coagulation is often used in experiments or engineering, such as adding ferrous sulfate and other agents to water to eliminate electrostatic repulsion between colloidal particles, and then adding polyacrylamide (PAM) to make the particles gradually larger, forming visible alum flowers, and finally producing sedimentation.
28. What are the common sewage treatment agents in sewage treatment?
(1) Acid: sulfuric acid, hydrochloric acid, oxalic acid
(2) Alkali: lime, sodium hydroxide (caustic soda)
(3) Flocculant: polyacrylamide 
(4) Coagulant: polyaluminum chloride, aluminum sulfate, ferric chloride 
(5) Oxidant: hydrogen peroxide (hydrogen peroxide), sodium hypochlorite
(6) Reducing agent: sodium metabisulfite, sodium sulfide, sodium bisulfite
(7) Functional agents: ammonia nitrogen remover, phosphorus remover, heavy metal scavenger, decolorizing agent, defoamer, ......
Other agents: antiscalants, demulsifiers, citric acid......