A method for improving the disinfection treatment effect of a clear water tank in a water plant

Abstract

The present invention relates to a method for improving the disinfection treatment effect of a water plant clear water tank, which is completed by arranging a UV-LED light source with a specific wavelength in a tap water clear water tank added with chlorine disinfectant. Compared with the prior art, the present invention can significantly reduce the amount of disinfection by-products generated in the factory water while ensuring the efficient inactivation of microorganisms, and at the same time minimize the consumption of sodium hypochlorite in the water.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment and relates to a method for improving the disinfection treatment effect of a clear water tank in a water plant. Background Art

[0002] Ultraviolet disinfection is increasingly being used in water plant disinfection because of its good bactericidal and inactivating properties, especially for chlorine-resistant microorganisms (such as Giardia and Cryptosporidium), and the fact that it does not produce highly toxic disinfection byproducts. Currently, the commonly used ultraviolet light sources are low-pressure and medium-pressure ultraviolet mercury lamps. Due to the limitations of the shape and installation of the lamp tubes, water plants usually place the ultraviolet disinfection reactor before the chlorine (amine) disinfection, that is, the disinfection is carried out in the order of ultraviolet first and then chlorine (amine). In recent years, with the rapid development of the semiconductor light-emitting diode (LED) industry, ultraviolet LED (UV-LED) as a new type of ultraviolet light source has begun to be rapidly promoted and applied in the field of disinfection. Compared with traditional low-pressure and medium-pressure mercury lamps, UV-LED has the following obvious advantages: 1) UV-LED can adjust the proportion of semiconductor material components during production to make any specific single-wavelength lamp beads, while the wavelength of traditional ultraviolet mercury lamps is fixed and cannot be adjusted; 2) UV-LED can achieve different continuous / pulse light-emitting modes, and does not require preheating, and can be used immediately after turning on; 3) UV-LED does not contain heavy metal pollution elements such as mercury, and is safe and environmentally friendly; 4) UV-LED lamp beads are very small, usually less than 1cm 2 , the application and installation are more diverse. In view of the above advantages of UV-LED, it is expected to be more flexibly applied in water plants.

[0003] The clear water tank of a waterworks is an important unit in the water supply process. It plays an important role in regulating water volume and disinfectant contact reaction. As the main unit of disinfectant contact reaction, the hydraulic retention time of the clear water tank of a waterworks is usually more than half an hour, so its volume is often large. Considering that the clear water tank contains a high concentration of chlorine disinfectant, if ultraviolet radiation can be applied to the clear water tank, the free chlorine therein can be stimulated to produce active substances such as strongly oxidizing hydroxyl radicals, forming an in-situ ultraviolet / chlorine advanced oxidation reaction, which can not only enhance the disinfection efficiency, but also is expected to reduce the generation of some highly toxic disinfection by-products. However, traditional ultraviolet mercury lamps are glass tubes, which are large and difficult to install, and contain highly toxic heavy metal mercury, so safety is difficult to guarantee.

[0004] For example, Chinese patent CN109293098A discloses a method for controlling the generation of disinfection byproducts in drinking water using a UV-LED light source, which specifically includes: (1) adding sulfuric acid or sodium hydroxide to natural drinking water to adjust the pH of the drinking water to a weak alkaline state, then adding free chlorine, and stirring to obtain a mixed solution; (2) irradiating the mixed solution under a UV-LED light with a wavelength of 270 to 280 nm until the treatment is completed. Although the patent discloses the use of a 270-280 nm UV-LED in combination with free chlorine to control disinfection byproducts, it does not specifically consider practical application improvements in engineering, making it difficult to directly use in actual projects such as water plant clear water tanks. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the disinfection treatment effect of the clear water tank of a water plant, further enhance the disinfection efficiency of the disinfectant in the clear water tank, and minimize the concentration of disinfection by-products in the effluent water to improve the water quality safety of the effluent water.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for improving the disinfection treatment effect of a clear water tank in a water plant is completed by arranging a UV-LED light source with a specific wavelength in a clear water tank of tap water added with chlorine disinfectant.

[0008] Furthermore, the wavelength of the UV-LED light source is 270-280 nm, and this preferred wavelength has better total colony inactivation efficiency and lower chlorine disinfectant consumption.

[0009] Furthermore, the wavelength of the UV-LED light source is 275 nm.

[0010] Furthermore, a plurality of guide baffles staggered up and down are arranged in the tap water clear water tank along the water inlet flow direction.

[0011] Furthermore, the number of the guide baffles is at least 8.

[0012] Furthermore, the UV-LED light source is arranged on the guide baffle. Preferably, the UV-LED light source is arranged on the side of the guide baffle facing the water flow.

[0013] Furthermore, the UV-LED light source is arranged on a guide baffle in a flow velocity region of 0.05-0.1 m / s, which can ensure that under such hydraulic conditions, UV-LED / chlorine interacts with each other and the amount of disinfection by-products generated in the effluent water is reduced.

[0014] Furthermore, a quartz waterproof layer is installed on the outer surface of the UV-LED light source to separate it from water.

[0015] Furthermore, the hydraulic retention time of the tap water clearing tank is more than 1 hour.

[0016] The present invention uses UV-LED with a specific wavelength as the light source and arranges it on the inner wall of the clear water tank of the water plant. It can ensure the efficient inactivation of microorganisms while greatly reducing the amount of disinfection by-products generated in the water leaving the factory, and at the same time minimize the consumption of sodium hypochlorite in the water. It is simple and feasible and has good engineering application value.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1) No additional large equipment or water treatment structures are added, and the internal space of the clean water tank is fully utilized. The extremely small UV-LED is directly installed on the inner wall of the clean water tank. The renovation project is small, the cost is low, and it is easy to implement.

[0019] 2) Make full use of the high concentration of chlorine disinfectant in the clear water pool to form an advanced oxidation reaction in situ, reduce the generation of some highly toxic disinfection by-products, and at the same time enhance the removal of other difficult-to-degrade micropollutants in the water. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of a tap water purification pool combined with ultraviolet LED.

[0021] Figure 2 Schematic diagram of the hydraulic state in the clear water tank.

[0022] Figure 3 The figure shows the comparison of the inactivation effect of ultraviolet rays of different wavelengths on the total colony count in filtered water.

[0023] Figure 4 Comparison of the consumption of chlorine disinfectant in a clean water pool by UV-LEDs of different wavelengths.

[0024] Figure 5 Comparison of the generation of disinfection by-products at different hydraulic flow rates.

[0025] Figure 6 Schematic diagram of the hydraulic state of a clear water tank designed with different numbers of guide baffles.

[0026] Figure 7 Comparison of the generation of disinfection by-products under different hydraulic retention times.

[0027] Description of the markings in the figure:

[0028] 1 is a clean water pool, 2 is a guide baffle, 3 is a UV-LED light source, 4 is a water barrier, 5 is a water inlet, and 6 is a water outlet. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0030] Embodiment 1:

[0031] like Figure 1 The figure shows a schematic diagram of a treatment device formed after UV-LED is installed in a clean water tank 1, including a clean water tank 1, a plurality of guide baffles 2 (preferably more than 4) arranged in an up-and-down staggered manner along the water inlet flow direction of the clean water tank 1, and a wave-shaped flow channel with an S-shaped bend is formed in the clean water tank 1, and then, a UV-LED light source 3 is arranged on the guide baffle 2, preferably arranged on the side facing the water flow on the guide baffle 2, and at the same time, in order to improve the treatment effect and reduce the generation of disinfection by-products in the effluent, the UV-LED light source 3 is arranged on the guide baffle 2 located in the flow velocity area of ​​0.05-0.1m / s, and the water inlet 5 of the clean water tank 1 is arranged at the lower part, and the water outlet 6 is arranged at the upper part. The total hydraulic retention time of the clean water tank 1 is more than 1 hour.

[0032] The hydraulic state in the clear water tank 1 is simulated by CFD technology. The internal design of the clear water tank 1 is as follows: Figure 2 As shown, the water flow state in the first and second corridors along the water inlet direction is relatively complex, lacking sufficient stable flow rate areas, so the present invention stipulates that the UV-LED light source is set in the third and subsequent corridors where the water flow is relatively stable. The number of internal guide baffles 2 is set to 8 or more to form a subsequent corridor with a relatively stable water flow rate of 0.05-0.1m / s.

[0033] Figure 1 and Figure 2 The clear water pool 1 shown in the case is 76m long, 35.1m wide, and 4m deep. There are 8 guide baffles 2 in the pool, which divide the pool into 9 corridors. The first water inlet corridor is 12m wide, and the remaining corridors are 8m wide. The thickness of the guide baffle 2 is very small relative to the length of the pool body and is negligible here. The diameter of the inlet and outlet pipes is 1000mm, and the flow rate of the water inlet 5 is 1.2m / s. The total hydraulic retention time of the clear water pool 1 is 3.15 hours. The UV-LED wavelength is 275nm, and it is arranged on the wall of the guide baffle 2 on the right side of the 3rd to 8th corridors. The hydraulic flow rate in the area is 0.05-0.1m / s. A quartz waterproof layer 4 is set on the outside of the UV-LED lamp bead (i.e., the UV-LED light source 3) to ensure that the circuit is not immersed in water. The number of lamp beads can be reasonably configured according to actual project needs.

[0034] Embodiment 2:

[0035] The treatment device of Example 1 was used to study the effluent from a sand filter tank of a water plant. The basic water quality parameters were: pH = 7.6, turbidity = 0.389, dissolved organic carbon (DOC) = 1.8 mg / L, total nitrogen (TN) = 1.3 mg / L, UV 254 =0.03cm -1 , total colony count = 3.98 × 10 3 CFU / mL. Different wavelengths of ultraviolet lamps were used for irradiation, with wavelengths of 254nm (low-pressure mercury lamp), 265nm (UV-LED) and 275nm (UV-LED), and the ultraviolet dose was controlled at 3mJ / cm 2 .

[0036] Depend on Figure 3 The results show that the inactivation effect of 265 and 275nm UV-LED lamps on the total bacterial colonies in the filtered water is 1.4Log, while the inactivation effect of 254nm low-pressure mercury lamp is 1.1Log, that is, the bactericidal effect of the new UV-LED light sources of 265 and 275nm is better than that of the traditional 254nm low-pressure ultraviolet mercury lamp, which proves that the light source selected by the present invention is reasonable.

[0037] Embodiment 3:

[0038] The treatment device of Example 1 was used to study the effluent from a sand filter tank of a water plant. The basic water quality parameters were the same as those of Example 2. 1 mg / L (in terms of Cl2) of sodium hypochlorite disinfectant was added to the water sample, and the hydraulic flow rate was controlled to be 0.06 m / s (equivalent G value was 2.1s -1 ), two different wavelengths of UV-LEDs, 265 and 275nm, were used to irradiate the samples, and the intensity of the UV light was controlled to be 135μW / cm 2 , sample and analyze the residual chlorine concentration at 0, 15, 30, 60 and 120 minutes reaction time, and calculate the chlorine consumption. The results are as follows Figure 4 shown.

[0039] From Example 2, it can be seen that the inactivation effect of 265 and 275 nm UV-LED on the total bacterial count in the filtered water is similar, both of which are 1.4 Log. Figure 4 Judging from the chlorine consumption shown, the 275nm UV-LED has a smaller chlorine consumption, and the advantage is more obvious when the residence time is more than 1 hour.

[0040] In the present invention, UV-LED is used in the clear water pool, on the one hand to improve the sterilization and disinfection effect, on the other hand to reduce some highly toxic disinfection byproducts, but at the same time, it is also necessary to ensure that the added sodium hypochlorite disinfectant is not consumed by excessive photolysis. Therefore, the present invention recommends the use of UV-LED with a wavelength of 270-280nm, which has obvious advantages in reducing chlorine consumption.

[0041] Embodiment 4:

[0042] The treatment device of Example 1 was used to study the effluent from a sand filter tank of a water plant. The basic water quality parameters were the same as those of Example 2. 1 mg / L (in terms of Cl2) of sodium hypochlorite disinfectant was added to the water sample, and the hydraulic flow rate was controlled to be 0, 0.06 and 0.40 m / s (equivalent G values ​​were 0, 2.1 and 16.4 s -1 ), 275nm wavelength UV-LED was used to irradiate it, and the UV light intensity was controlled to be 135μW / cm 2 The reaction time was controlled to be 30 min, and the concentrations of conventional trihalomethanes (THMs) and emerging highly toxic nitrogen-containing disinfection byproducts (N-DBPs) in the water after the reaction were measured. The results are as follows: Figure 5 shown.

[0043] like Figure 5 It can be seen that a total of four THMs were detected, including trichloromethane (TCM), dichlorobromomethane (BDCM), monobromodichloromethane (DBCM) and tribromoform (TBM); a total of four N-DBPs were detected, including trichloropicrin (TCNM), dichloroacetonitrile (DCAN), bromochloroacetonitrile (BCAN) and dibromoacetonitrile (DBAN). From the perspective of the total amount of disinfection by-products, when the flow rate is higher than 0.06m / s, the application of 275nm wavelength UV-LED irradiation (i.e., UV-LED / chlorine combination) in the clear water pool containing chlorine disinfectant has a lower total amount of disinfection by-products in the effluent than the chlorine disinfection alone, and the faster the flow rate, the lower the concentration. However, considering the design standards of the clear water pool, if the flow rate is too large, the pool body will be too large on the basis of ensuring the retention time, which is not economical and practical, and it is often difficult to have large areas of high flow rate in the actual clear water pool.

[0044] After comprehensive consideration, the present invention recommends placing 270-280nm UV-LEDs in the 0.05-0.1m / s flow rate area to achieve a good disinfection by-product reduction effect.

[0045] In order to ensure the disinfection contact time, a clean water pool with disinfection function usually needs to be equipped with baffles to form multiple corridors. However, the number of baffles will affect the effect of the combination with UV-LED in the present invention. Figure 6 The following are three clear water tank design schemes with the same other dimensions and different only in the number of guide baffles. Figure 6 (a) is the scheme used in Examples 1-3, and the number of baffles is 8. Figure 6 (b) The number of baffles is 6. Figure 6 (c) The number of baffles is 18. By comparison, among the three schemes, only Figure 6In (a) and (c), the flow rate is stable in the 0.05-0.1m / s region, which is suitable for UV-LED deployment. Figure 6 (b) Due to the insufficient number of baffles, the flow velocity in the corridor is generally lower than 0.02m / s. Figure 5 The results show that the risk of disinfection by-products generation is higher when UV-LED is deployed in areas with flow rates lower than 0.02 m / s. Therefore, there should be no less than 8 diversion baffles in the clean water tank.

[0046] Embodiment 5:

[0047] The treatment device of Example 1 was used to study the effluent from a sand filter tank of a water plant. The basic water quality parameters were the same as those of Example 2. 1 mg / L (in terms of Cl2) of sodium hypochlorite disinfectant was added to the water sample, and the hydraulic flow rate was controlled to be 0.06 m / s (equivalent G value was 2.1s -1 ), 275nm wavelength UV-LED was used to irradiate it, and the UV light intensity was controlled to be 135μW / cm 2 The reaction time was controlled at 0.5, 1 and 2 h, and the concentrations of conventional trihalomethanes (THMs) and emerging highly toxic nitrogen-containing disinfection byproducts (N-DBPs) in the water after the reaction were measured. The results are as follows: Figure 7 shown.

[0048] Depend on Figure 7 The results show that extending the hydraulic retention time, that is, increasing the hydraulic retention time, the combined application of UV-LED / chlorine can further reduce the generation of THMs and N-DBPs, especially the more toxic N-DBPs when the retention time is extended to more than 1h, the generation is close to 0μg / L; for chlorine disinfection alone, extending the hydraulic retention time, the total amount of THMs has a slight downward trend, but the more toxic N-DBPs show a significant increase.

[0049] Therefore, the present invention recommends that when a 270-280nm UV-LED is used in a chlorine-containing disinfectant clean water tank, the total hydraulic retention time should be controlled to be more than 1h to achieve a better disinfection by-product reduction effect.

[0050] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for improving the disinfection effect of a clear water tank in a waterworks, characterized in that: Arrange the UV-LED light source of specific wavelength in a clean water pool with tap water added with chlorine disinfectant, and it is complete; The wavelength of the UV-LED light source is 270-280nm; The tap water clear water tank is also provided with a plurality of diversion baffles staggered up and down along the water inlet flow direction, and the diversion baffles are provided with at least 8 pieces; The UV-LED light source is arranged on a side of the guide baffle facing the water flow in a flow velocity region of 0.05-0.1 m / s.

2. A method for improving the disinfection treatment effect of a clear water tank in a waterworks according to claim 1, characterized in that: The wavelength of the UV-LED light source is 275 nm.

3. A method for improving the disinfection treatment effect of a clear water tank in a waterworks according to claim 1, characterized in that: The outer surface of the UV-LED light source is also provided with a quartz material water-proof layer to separate it from water.

4. A method for improving the disinfection treatment effect of a clear water tank in a waterworks according to claim 1, characterized in that: The hydraulic retention time of the tap water clearing tank is more than 1 hour.

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