Water treatment method for reducing consumption by seasonal switching chlorine and reducing disinfection by-products

Abstract

The invention relates to a water treatment method for reducing chlorine consumption and disinfection by-products by seasonal switching, which comprises the following steps: adding polyaluminum chloride and ferric trichloride coagulant in a water inlet chamber in a high algae period in summer, adding chlorine, uniformly stirring, treating by flocculation and air floatation processes, filtering clarified water in a filter tank, adding ammonia, and then adding chlorine, finally, entering a clear water reservoir; polyaluminum chloride and a ferric trichloride coagulant are added into the water inlet chamber in the low-algae period in winter, uniform stirring is carried out, after flocculation and air flotation process treatment, clarified water enters the filter tank to be filtered and ammoniated, then chlorination treatment is carried out, and finally the clarified water enters the clear water reservoir. Compared with the prior art, the method provided by the invention does not need a complex and lengthy operation process, and can realize chlorine consumption reduction and effectively control the generation of disinfection by-products by changing the conventional chlorine / ammonia feeding point and sequence.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment, and more specifically relates to a method for seasonal switching of chlorine consumption reduction and reduction of disinfection by-products. Background Art

[0002] The problem of algae is a common problem faced by water plants that use surface water as their water source, especially during the high algae season in summer, which will bring about high turbidity, geosmin, dimethyl isoborneol (2-MIB) and other odor substances and algae toxins. The surface water source of long-distance water transfer has algae problems, which has its own seasonal variation law, so it is necessary to pay close attention to the seasonal changes in water quality; the water diverted from the Yangtze River by the South-to-North Water Diversion Project, as a world-renowned long-distance water transfer project, has gradually become the main source of tap water for cities along the route. The water quality of the water diverted from the Yangtze River by the South-to-North Water Diversion Project is generally good. Among them, the middle line main canal that was put into use in December 2014 is an artificially excavated canal. Before the ecosystem adapted to the canal environment was established, the main canal had abnormal algae proliferation. With the operation of the South-to-North Water Diversion Project, the seasonal changes of algae in the middle line canal have gradually formed a certain regularity. Mastering its changing law has become a major prerequisite for ensuring the water supply security of cities along the middle line.

[0003] At present, in order to kill algae and ensure the algae removal efficiency of subsequent processes, many water plants often add a high dose of sodium hypochlorite to the raw water after it enters the water plant for "pre-chlorination" to kill algae and strengthen coagulation simultaneously. Although researchers have found that pre-chlorination will generate high concentrations of disinfection by-products (DBPs) with "tri-causing" effects with algae, such as trihalomethanes (THMs) and haloacetic acids (HAAs), pre-chlorination is still a common process for many water plants to deal with seasonal high algae problems due to its good algae killing effect, low cost, and simple operation, especially its good degradation efficiency for algae odor substances; even in the low algae period, some water plants also retain the method of adding chlorine before pre-chlorination to enhance the coagulation effect. In addition, in order to facilitate operation and management, water plants usually use the same chlorination method and amount in different seasons in winter and summer, which is bound to bring high DBPs risks; at the same time, the high-dose "pre-chlorination" method all year round does not meet my country's current "low-carbon" requirements. The new version of the "Sanitary Standard for Drinking Water" (GB5749-2022) "reduced the upper limit of the 'free chlorine' index of disinfectants in factory water from 4mg / L to 2mg / L, and changed DBPs from a non-routine index to a routine index to be tested daily", indicating that the DBPs risk caused by high residual chlorine has been highly valued. In order to cope with the two new water quality indicators of algae odor substances, geosmin and 2-MIB, added in the new version of the "Sanitary Standard for Drinking Water" (GB5749-2022), the application of pre-chlorination and multi-point chlorination in water plants may become more common, which urgently requires the rational optimization of the seasonal chlorination method of water plants.

[0004] Although pre-chlorination can significantly improve the turbidity of raw water and increase the removal rate of algae, the raw water contains more humus-like natural organic matter, and the dosage required for pre-chlorination is relatively high. Therefore, the use of pre-chlorination may increase the concentration of chlorine disinfection by-products to a certain extent, affecting the quality of the water leaving the factory. In addition, the damage of chlorine to algae cells will promote the dissolution of cytoplasm, which will further affect the quality of the water leaving the factory. Therefore, it is very important to determine the dosing point and the amount of chlorine. The operation mode of the water plant and the high operation cost, high drug consumption, and high risk of formation of disinfection by-products need to be solved urgently.

[0005] The invention application with application number 201811142562.4 discloses a method for degrading organic matter in water by using sunlight in combination with chlorine disinfection. The invention disinfects the object to be treated with chlorine and irradiates it at the same time, so that the halogenated disinfection byproducts that produce a significant red shift in ultraviolet visible absorption during the chlorine disinfection process can absorb light energy and degrade. However, the chlorine dosage and location are not reasonably adjusted according to the law of water quality changes, which will lead to unnecessary chlorine loss.

[0006] The invention application with application number 201610912056.3 discloses a multi-stage combined disinfection method for drinking water. The invention adopts a multi-stage disinfection method combining ultraviolet disinfection and two-point chlorination disinfection after the water is discharged from the production filter tank of the water purification plant, and adjusts the chlorine dosage in real time according to the residual chlorine and disinfection by-product monitoring data. However, the operation of the invention is relatively complicated, which increases the operating cost of the water plant, ignores the seasonal differences in the quality of raw water, and cannot effectively control disinfection by-products.

[0007] Therefore, it is very necessary to develop a method that is simple to operate, easy to control conditions, and can seasonally switch chlorine dosage to achieve the purpose of reducing chlorine consumption and effectively controlling the generation of disinfection by-products, so as to solve the problem of seasonal water discharge differences in water plants. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a water treatment method for seasonal switching to reduce chlorine consumption and reduce disinfection by-products.

[0009] The technical solution adopted by the present invention is: a water treatment method for seasonal switching to reduce chlorine consumption and disinfection by-products,

[0010] In the summer, during the high algae season, polyaluminium chloride and ferric chloride coagulants are added to the water inlet chamber, chlorine is added and stirred evenly, and after flocculation and flotation treatment, the clarified water enters the filter tank for filtration and ammonia addition, and then chlorine supplementation is carried out before finally entering the clear water reservoir;

[0011] During the low-algae period in winter, polyaluminum chloride and ferric trichloride coagulants are added to the inlet chamber, stirred evenly, and after being treated by the flocculation and air flotation processes, the clarified water enters the filter for filtration and ammonia addition, followed by chlorine addition treatment, and finally enters the clean water reservoir.

[0012] Preferably, the chlorine dosage during the high-algae period in summer is 0.3 - 0.5 mg / L, and the supplementary chlorine dosage is 0.8 - 1.0 mg / L; the chlorine dosage during the low-algae period in winter is 0.8 - 1.1 mg / L.

[0013] Preferably, the ammonia dosage is 0.2 - 0.3 mg / L.

[0014] Preferably, the concentration of polyaluminum chloride is 2 - 4 mg / L, the concentration of ferric trichloride is 4 - 5 mg / L, and after adding the flocculant, it is stirred for 5 - 10 s.

[0015] Preferably, the stirring speed during the flocculation process is 220 - 240 r / min, and the time is 25 - 30 s.

[0016] Preferably, the air flotation process is carried out in two stages, specifically: in the first stage, the stirring speed is 160 - 180 r / min, and the stirring time is 1.5 - 2 min; in the second stage, the stirring speed is 60 - 80 r / min, the stirring time is 4.5 - 5 min, and the sedimentation time is 9 - 10 min.

[0017] Preferably, the filtration conditions are as follows: the diameter of the filter column is 20 - 25 mm, and the height is 1300 - 1500 mm; a double-layer filter material of quartz sand - anthracite is used. The particle size of the quartz sand filter material is 0.6 - 1.0 cm, the filter layer thickness is 500 - 600 mm, the particle size of the anthracite filter material is 1.2 - 2.5 cm, and the thickness is 300 - 400 mm; the pebble is used as the supporting layer, with a thickness of 160 - 200 mm.

[0018] Preferably, during the high-algae period in summer, the total chlorine dosage is reduced by 62 - 78%, and during the low-algae period in winter, the total chlorine dosage is reduced by 72 - 84%; the total content of disinfection by-products in summer is reduced by 77.20%, among which the degradation rate of THM reaches 80.30%, and that of HAA reaches 27.27%; while in winter, the total disinfection by-products are reduced by 79.8%, among which the degradation rate of THM reaches 83.33%, and the degradation rate of HAA reaches 9.09%.

[0019] The advantages and positive effects of the present invention are as follows: Under the condition of reducing the dosages of chlorine and ammonia, it can also ensure good water quality of the effluent, and better control the generation amount of disinfection by-products; the method of the present invention is simple to operate, the reaction conditions are easy to control, without a complex and lengthy operation process, and no other toxic and harmful substances are introduced. By changing the conventional chlorine / ammonia dosing points and sequences, chlorine consumption can be reduced and the generation of disinfection by-products can be effectively controlled, improving the water quality safety of the effluent. Description of the Drawings

[0020] Figure 1 Process flow of water treatment method for seasonal switching chlorine reduction and reduction of disinfection by-products;

[0021] Figure 2 Generated amount of disinfection by-products in the factory water in the comparative example;

[0022] Figure 3 Generated amount of disinfection by-products in the factory water in Examples 1-3; (a) Generated amount of disinfection by-products in the factory water during the high algae period in summer, (b) Generated amount of disinfection by-products in the factory water during the low algae period in winter;

[0023] Figure 4 Effect of chlorine dosage on algae density in Examples 1-3; (a) Effect of chlorine dosage during the pre-chlorination period on algae density during the high algae period in summer, (b) Generated amount of disinfection by-products in the factory water with the chlorine dosage during the pre-chlorination period during the low algae period in winter;

[0024] Figure 5 Effect on UV254 in Examples 1-3; (a) Effect on UV254 during the high algae period in summer, (b) Effect on UV254 during the low algae period in winter. Detailed implementation manner

[0025] The embodiments of the present invention will be described below with reference to the accompanying drawings.

[0026] The present invention relates to a water treatment method for seasonal switching chlorine reduction and reduction of disinfection by-products. Without adding other processes additionally, by adjusting the chlorine dosing point and controlling the dosing amount in the water treatment process according to the water quality change rules in different seasons, the disinfection effect and the water quality of the effluent are effectively guaranteed, excessive chlorine consumption is avoided, the risk of DBP generation is reduced, and at the same time, the operation cost of the water plant is also reduced. By controlling the seasonal change of the chlorine dosing amount and the dosing point, while ensuring the water quality of the effluent of the water plant, the risk of generating disinfection by-products is reduced, and the operation cost of the water plant is effectively reduced, providing a simple and easy-to-control improvement method for the water treatment of the water plant. This method is simple and practical and is easy to realize engineering application.

[0027] As Figure 1 shown is the specific process of water treatment, which specifically includes the following steps:

[0028] (1) During the high-algae period in summer, polyaluminum chloride and ferric trichloride coagulants are added to the inlet chamber, chlorine is added and stirred evenly. The concentration of polyaluminum chloride is 2 - 4 mg / L, the concentration of ferric trichloride is 4 - 5 mg / L, the chlorine dosage is 0.3 - 0.5 mg / L, and the stirring time for even mixing is 5 - 10 s. After treatment by the flocculation and air flotation processes, the specific flocculation process is as follows: the stirring speed is 220 - 240 r / min and the time is 25 - 30 s. The air flotation process is carried out in two stages. Specifically, in the first stage, the stirring speed is 160 - 180 r / min and the stirring time is 1.5 - 2 min; in the second stage, the stirring speed is 60 - 80 r / min and the stirring time is 4.5 - 5 min, and the sedimentation time is 9 - 10 min. The clarified water enters the filter for filtration. The specific filtration process is as follows: the filter column diameter is 20 - 25 mm and the height is 1300 - 1500 mm; a double-layer filter material of quartz sand - anthracite is used. The particle size of the quartz sand filter material is 0.6 - 1.0 cm, the filter layer thickness is 500 - 600 mm, the particle size of the anthracite filter material is 1.2 - 2.5 cm, and the thickness is 300 - 400 mm; the pebble is used as the supporting layer with a thickness of 160 - 200 mm. After filtration, ammonia is added with a dosage of 0.2 - 0.3 mg / L, and then chlorine supplementation treatment is carried out with a chlorine dosage of 0.8 - 1.0 mg / L, and finally it enters the clear water reservoir.

[0029] (2) During the low-algae period in winter, polyaluminum chloride and ferric trichloride coagulants are added to the inlet chamber and stirred evenly. The concentration of polyaluminum chloride is 2 - 4 mg / L, the concentration of ferric trichloride is 4 - 5 mg / L, and the stirring time for even mixing is 5 - 10 s. After treatment by the flocculation and air flotation processes, the specific flocculation process is as follows: the stirring speed is 220 - 240 r / min and the time is 25 - 30 s. The air flotation process is carried out in two stages. Specifically, in the first stage, the stirring speed is 160 - 180 r / min and the stirring time is 1.5 - 2 min; in the second stage, the stirring speed is 60 - 80 r / min and the stirring time is 4.5 - 5 min, and the sedimentation time is 9 - 10 min. The clarified water enters the filter for filtration. The specific filtration process is as follows: the filter column diameter is 20 - 25 mm and the height is 1300 - 1500 mm; a double-layer filter material of quartz sand - anthracite is used. The particle size of the quartz sand filter material is 0.6 - 1.0 cm, the filter layer thickness is 500 - 600 mm, the particle size of the anthracite filter material is 1.2 - 2.5 cm, and the thickness is 300 - 400 mm; the pebble is used as the supporting layer with a thickness of 160 - 200 mm. After filtration, ammonia is added with a dosage of 0.2 - 0.3 mg / L, and then chlorine addition treatment is carried out with a chlorine dosage of 0.8 - 1.1 mg / L, and finally it enters the clear water reservoir.

[0030] In the above steps, polyaluminum chloride and ferric trichloride are used as coagulants, which can promote the formation of flocs. The staged air flotation is adopted, and the staged air flotation fully improves the contact efficiency between the air flotation bubbles and the suspended substances, making the suspended pollutants float to the water surface more fully and improving the water treatment effect. Then, the filter media is used to filter the suspended substances after air flotation, so as to achieve the purpose of improving the effluent water quality. Experiments can prove that through the above method for water treatment, good effluent water quality can be achieved with low chlorine dosage, and the generation amount of disinfection by-products can be better controlled.

[0031] This embodiment is implemented on the premise of the technical solution of the present invention. Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0032] In the following embodiments, unless otherwise specified for raw materials or treatment techniques, it means that they are all conventional reagents or raw materials in the art to achieve the corresponding functions.

[0033] Example 1

[0034] The water used in the example is the raw water of the diverted river water in July - August in summer and November - December in winter of the same year. The water temperature in summer is 27.0 - 28.4 °C, and the water temperature in winter is 9.8 - 15.2 °C. A method for seasonal switching of chlorine reduction and reduction of disinfection by-products includes the following steps:

[0035] (1) In the high - algae period in summer, 3 mg / L of polyaluminum chloride and 4 mg / L of ferric trichloride coagulants are added to the inlet chamber, 0.3 mg / L of chlorine is added and stirred for 6 s. After being treated by the flocculation and air flotation processes, the clarified water enters the filter for filtration and 0.2 mg / L of ammonia is added, and then 0.8 mg / L of chlorine is added, and finally it enters the clear water reservoir.

[0036] (2) In the low - algae period in winter, 3 mg / L of polyaluminum chloride and 4 mg / L of ferric trichloride coagulants are added to the inlet chamber and stirred for 6 s. After being treated by the flocculation and air flotation processes, the clarified water enters the filter for filtration and 0.2 mg / L of ammonia is added, and then 0.8 mg / L of chlorine is added, and finally it enters the clear water reservoir.

[0037] (3) The air flotation process in steps (1) and (2) is divided into two stages. In the first stage, the stirring speed is 160 r / min and the stirring time is 1.5 min; in the second stage, the stirring speed is 65 r / min and the stirring time is 4.5 min, and the sedimentation time is 9 min.

[0038] (4) The filtration processes in steps (1) and (2) are carried out in an acrylic filter column with a diameter of 25 mm and a height of 1500 mm. A double-layer filter material of quartz sand - anthracite is used. The particle size of the quartz sand filter material is 1.0 cm, and the filter layer thickness is 500 mm; the particle size of the anthracite filter material is 2.0 cm, and the thickness is 300 mm. Pebbles are used as the supporting layer with a thickness of 200 mm.

[0039] Compare the effluents in the high - algae period in summer in step (1) and the low - algae period in winter in step (2) with other chlorine - dosing methods. From Figure 2 it can be seen that chloramine disinfection can reduce the generation amounts of THMs, HAAs, and N - DBPs by about 60 - 90%. The method of dosing chlorine and ammonia after filtration has the lowest chlorine consumption and the fewest types of disinfection by - products generated. Compared with the conventional chlorine - dosing method, the total chlorine dosage of seasonal switching chlorine dosing is greatly reduced, significantly reducing the operating cost; at the same time, the generation of HANs is avoided, and the total generation amount of disinfection by - products is significantly reduced.

[0040] Example 2

[0041] In the examples, the water used is the raw water of the diverted river water in July - August in summer and November - December in winter of the same year. The water temperature in summer is 27.0 - 28.4 °C, and the water temperature in winter is 9.8 - 15.2 °C. A method for seasonal switching of chlorine reduction and reduction of disinfection by - products includes the following steps:

[0042] (1) In the high - algae period in summer, 3.5 mg / L of polyaluminum chloride and 4.8 mg / L of ferric trichloride coagulants are added to the inlet chamber, 0.4 mg / L of chlorine is added and stirred for 8 s. After being treated by the flocculation and air - flotation processes, the clarified water enters the filter for filtration and 0.3 mg / L of ammonia is added, and then 0.8 mg / L of chlorine is added, and finally it enters the clear water reservoir.

[0043] (2) In the low - algae period in winter, 3.5 mg / L of polyaluminum chloride and 5.0 mg / L of ferric trichloride coagulants are added to the inlet chamber and stirred for 10 s. After being treated by the flocculation and air - flotation processes, the clarified water enters the filter for filtration and 0.2 mg / L of ammonia is added, and then 0.9 mg / L of chlorine is added, and finally it enters the clear water reservoir.

[0044] (3) The air - flotation processes in steps (1) and (2) are both divided into two stages. In the first stage, the stirring speed is 165 r / min and the stirring time is 1.5 min; in the second stage, the stirring speed is 70 r / min and the stirring time is 4.5 min, and the sedimentation time is 9.5 min.

[0045] (4) The filtration processes in steps (1) and (2) are carried out in an acrylic filter column with a diameter of 25 mm and a height of 1400 mm. A double-layer filter material of quartz sand - anthracite is used. The particle size of the quartz sand filter material is 0.8 cm, and the filter layer thickness is 550 mm; the particle size of the anthracite filter material is 1.5 cm, and the thickness is 350 mm. Pebbles are used as the supporting layer with a thickness of 180 mm.

[0046] Example 3

[0047] In the examples, the water used is the raw water from the diverted river water in July - August in summer and November - December in winter of the same year. The water temperature in summer is 27.0 - 28.4 °C, and the water temperature in winter is 9.8 - 15.2 °C. A method for seasonal switching of chlorine reduction and reduction of disinfection by-products includes the following steps:

[0048] (1) In the high - algae period in summer, 4.0 mg / L of polyaluminum chloride and 5.0 mg / L of ferric trichloride coagulants are added to the inlet chamber, 0.5 mg / L of chlorine is added and stirred for 5 s. After being treated by the flocculation and air - flotation processes, the clarified water enters the filter for filtration and 0.2 mg / L of ammonia is added, and then 0.8 mg / L of chlorine is added, and finally it enters the clear water reservoir.

[0049] (2) In the low - algae period in winter, 3.5 mg / L of polyaluminum chloride and 5.0 mg / L of ferric trichloride coagulants are added to the inlet chamber and stirred for 10 s. After being treated by the flocculation and air - flotation processes, the clarified water enters the filter for filtration and 0.2 mg / L of ammonia is added, and then 1.1 mg / L of chlorine is added, and finally it enters the clear water reservoir.

[0050] (3) The air - flotation processes in steps (1) and (2) are both divided into two stages. In the first stage, the stirring speed is 180 r / min and the stirring time is 2.0 min; in the second stage, the stirring speed is 70 r / min and the stirring time is 5.0 min, and the sedimentation time is 10 min.

[0051] (4) The filtration processes in steps (1) and (2) are carried out in an acrylic filter column with a diameter of 25 mm and a height of 1400 mm. A double - layer filter material of quartz sand - anthracite is used. The particle size of the quartz sand filter material is 1.0 cm, and the filter layer thickness is 600 mm; the particle size of the anthracite filter material is 2.5 cm, and the thickness is 400 mm. Pebbles are used as the supporting layer with a thickness of 160 mm.

[0052] Comparative example

[0053] 4.0 mg / L of polyaluminum chloride and 5.0 mg / L of ferric trichloride coagulants are added to the inlet chamber, 4.5 mg / L of chlorine is added and stirred for 5 s. After being treated by the flocculation process, the clarified water enters the filter for filtration, and then 0.8 mg / L of chlorine is added and finally it enters the clear water reservoir.

[0054] The water entering the clear water tank is detected to measure the content of disinfection by-products, and the results are as Figure 2 shown.

[0055] The effluent water quality of Examples 1-3 and the comparative examples is detected, and the contents of disinfection by-products, algae, and UV254 in the water are measured respectively. Figure 3 The following is the detection of disinfection by-products in the effluent obtained from the treatment in Examples 1-3. By comparison, it can be seen that the water treatment method of the present invention can significantly reduce the content of disinfection by-products in the effluent. In summer, the total content of disinfection by-products is reduced by 77.20%, among which the degradation rate of THM reaches 80.30% and that of HAA reaches 27.27%; in winter, the total disinfection by-products are reduced by 79.8%, among which the degradation rate of THM reaches 83.33% and the degradation rate of HAA reaches 9.09%. Moreover, the lower the pre-chlorination dosage, the lower the content of disinfection by-products. With the increase of the pre-chlorination dosage, the amount of disinfection by-products in the factory water shows an upward trend. Seasonal switching of chlorine dosing can avoid unnecessary chlorine consumption through simple operation, solve the problem of the negative impact on the environment caused by excessive chlorine dosing, effectively control the generation of disinfection by-products, and improve the effluent water quality of the water plant.

[0056] Figure 4 The following is the detection of the algae content in the effluent water quality of Examples 1-3. Seasonal switching of chlorine dosing can achieve an overall algae removal rate of 97%-100%, with a higher algae removal rate, reduce the clogging and backwashing frequency of the filter, greatly reduce the filter load in actual production, and thus reduce production costs. Seasonal switching of chlorine dosing can achieve efficient algae removal at a lower chlorine dosing amount, reduce the types and concentrations of disinfection by-products, and ensure the safety and reliability of the effluent water quality. Figure 5 The following is the UV254 content in the effluent of Examples 1-3. As one of the indicators of organic matter, the reduction of UV254 can also reduce the generation of disinfection by-products. The overall UV254 removal rate of seasonal switching of chlorine dosing can reach 31%-36%. Seasonal chlorine dosing can not only ensure the removal of UV254 in summer and winter, but also ensure that the effluent indicators such as permanganate index meet the national standards.

[0057] The above has described the embodiments of the present invention in detail, but the content described is only the preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still fall within the scope covered by the patent of the present invention.

Claims

1. A water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products, characterized in that: In the high-algae period in summer, polyaluminum chloride and ferric trichloride coagulants are added to the inlet chamber, chlorine is added and stirred evenly. After being treated by the flocculation and air flotation processes, the clarified water enters the filter for filtration and ammonia is added, and then supplementary chlorine treatment is carried out, and finally it enters the clear water reservoir; In the low-algae period in winter, polyaluminum chloride and ferric trichloride coagulants are added to the inlet chamber, stirred evenly. After being treated by the flocculation and air flotation processes, the clarified water enters the filter for filtration and ammonia is added, and then chlorine addition treatment is carried out, and finally it enters the clear water reservoir.

2. The water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products according to claim 1, characterized in that: In the high-algae period in summer, the chlorine addition amount is 0.3 - 0.5 mg / L, and the supplementary chlorine dosage is 0.8 - 1.0 mg / L; in the low-algae period in winter, the chlorine addition dosage is 0.8 - 1.1 mg / L.

3. The water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products according to claim 2, characterized in that: The ammonia addition dosage is 0.2 - 0.3 mg / L.

4. The water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products according to any one of claims 1 - 3, characterized in that: The concentration of polyaluminum chloride is 2 - 4 mg / L, the concentration of ferric trichloride is 4 - 5 mg / L, and after adding the flocculant, it is stirred for 5 - 10 s.

5. The water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products according to claim 4, characterized in that: The stirring speed during the flocculation process is 220 - 240 r / min, and the time is 25 - 30 s.

6. The water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products according to any one of claims 1 - 3, characterized in that: The air flotation process is carried out in two stages, specifically: in the first stage, the stirring speed is 160 - 180 r / min, and the stirring time is 1.5 - 2 min; in the second stage, the stirring speed is 60 - 80 r / min, the stirring time is 4.5 - 5 min, and the sedimentation time is 9 - 10 min.

7. The water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products according to any one of claims 1 - 3, characterized in that: The filtration conditions are that the filter column diameter is 20 - 25 mm and the height is 1300 - 1500 mm; a double-layer filter material of quartz sand - anthracite is used. The particle size of the quartz sand filter material is 0.6 - 1.0 cm, the filter layer thickness is 500 - 600 mm, the particle size of the anthracite filter material is 1.2 - 2.5 cm, and the thickness is 300 - 400 mm; pebbles are used as the supporting layer, and the thickness is 160 - 200 mm.

8. The water treatment method for seasonal switching of chlorine reduction and reduction of disinfection by-products according to any one of claims 1 - 7, characterized in that: During the high-algae period in summer, the total chlorine dosage decreased by 62 - 78%, and during the low-algae period in winter, the total chlorine dosage decreased by 72 - 84%. The total content of disinfection by-products in summer decreased by 77.20%, among which the degradation rate of THM reached 80.30% and that of HAA reached 27.27%. In winter, the total disinfection by-products decreased by 79.8%, among which the degradation rate of THM reached 83.33% and the degradation rate of HAA reached 9.09%.

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