Summary of Q&A on Water Treatment Knowledge

1. What is water self purification?
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 the water quality standard to equal to the water quality standard.

2. 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.

3. 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, so as to purify the sewage. It is generally divided into water supply treatment and sewage treatment.

4. Five measurement indicators for water
Biochemical Oxygen Demand (BOD): refers to the amount of oxygen required to degrade organic matter under aerobic conditions due to the action of microorganisms. It is a comprehensive indicator indicating the pollution of sewage by organic matter.
On Oxygen Demand (THOD): The theoretical oxygen demand for a certain organic substance in water. Usually, it refers to the theoretical value of the oxygen required for the complete oxidation of carbon and hydrogen elements in organic matter to carbon dioxide and water (i.e. the oxygen demand calculated according to the complete oxidation reaction formula).
Total Oxygen Demand (TOD): Refers to the amount of oxygen required to oxidize substances in water, mainly organic substances, when they become stable oxides during combustion. The result is expressed in mg/L of O2.
Chemical Oxygen Demand (COD): It is a chemical method used to measure the amount of reducing substances that need to be oxidized in water samples. The oxygen equivalent of substances (usually organic matter) 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 carbon in dissolved and suspended organic matter in a water body.

5. What are the hygiene standards for drinking water?
The physical indicators of the hygiene standards for drinking water include color, turbidity, odor, and taste.

6. When is biochemical treatment used?
It is generally believed that wastewater with a BOD/COD value greater than 0.3 is suitable for biochemical treatment.

7. What is eutrophication of water bodies?
Eutrophication of water bodies is a natural phenomenon that occurs in freshwater, where the high content of nitrogen, phosphorus, and potassium in the water leads to the sudden excessive proliferation of algae.
The main reason for the formation 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, causing a large number of aquatic organisms such as algae to grow and reproduce, resulting in the production of organic matter far exceeding the consumption rate. The accumulation of organic matter in water bodies disrupts the balance of aquatic ecology.

8. What is dissolved oxygen?
The oxygen dissolved in water is called dissolved oxygen. The oxygen that organisms and aerobic microorganisms in water rely on for survival is dissolved oxygen. 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?
The stability of colloids 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?
Dynamic potential: The potential on the sliding surface of the colloid, i.e ζ Potential.

12. How do hydrophobic colloids form large particles?
For hydrophobic colloids, in order for the colloids to collide with each other and form large particles through Brownian motion, it is necessary to reduce or eliminate the repulsive energy peak. The way to reduce the repulsive energy peak is to reduce or eliminate the colloidal particles ζ Potential.

13. What is the role of adsorption bridging?
Adsorption bridging refers to the adsorption and bridging of polymer materials and colloidal particles.

14. What is the function of a grille?
The function of the grille is to intercept larger suspended solids or floating impurities.

15. What are the main factors that affect the coagulation effect?
The main factors affecting the coagulation effect include water temperature, pH and alkalinity of the water, concentration of suspended solids in the water, and hydraulic conditions.

16. How many types of precipitation are there? What are the differences?
There are four types of precipitation, which are:
Free sedimentation: The particles are in a discrete state during the sedimentation process, and their shape, size, and mass do not change. The settling speed is not disturbed, and they independently complete the sedimentation process.
Turbulent sedimentation: During the sedimentation process, the size, mass, and settling speed of particles increase with depth.
Congestion sedimentation: The concentration of particles in water is relatively high, and they interfere with each other during the sinking process, forming a clear interface between clear water and muddy water, and gradually moving downwards.
Compression 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, and the gaps between the lower particles are squeezed out.

17. What is the distribution pattern of impurities in the filter material layer?
The distribution pattern of impurities in the filter material layer: At the beginning of filtration, the filter material is relatively clean, with larger pores, smaller water flow shear force, and stronger adhesion. 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 detachment effect increases, The particles that are finally adhered to first fall off and move downwards, and are intercepted by the lower filter material.
The result is that under a certain filtration head, the filtration rate will sharply decrease, or the loss of the water head at a certain filtration rate reaches the limit value, or when the mud film cracks due to uneven force on the surface of the filter layer, a large amount of water will flow out from the cracks, causing impurities and particles in the water to penetrate the filter layer and deteriorate the water quality.

18. According to the direction of water flow in the tank, which types of sedimentation tanks can be divided into?
According to the different directions of water flow in the sedimentation tank, it can be divided into horizontal flow, oblique flow, radial flow, and vertical flow.

19. What are the ways to improve filtration efficiency?
The way to improve filtration efficiency: In order to change this situation and improve the fouling capacity of the filter layer, "reverse particle size" filtration has emerged, which means that the particle size of the filter material increases from large to small in the direction of water flow. Due to the complex structure of upward and bidirectional flow filters, it is inconvenient to wash.

20. What is the composition of a homogeneous filter material?
Homogeneous filter material composition: Homogeneous filter material refers to any cross-section in the depth direction of the entire filter layer, with uniform and consistent filter material composition and average particle size, rather than completely identical filter material particle size.