A method for controlling and eliminating the generation of bromate and brominated disinfection by-products during drinking water treatment

Abstract

The present invention relates to a method for controlling and eliminating the generation of bromate and brominated disinfection by-products during drinking water treatment. The method of the present invention comprises: method one: adding a nitrite solution to a water body to be treated that has undergone a water treatment process of coagulation, precipitation, and filtration in a water plant and mixing the solution, then adding the solution to a chlorination disinfection unit, and continuously irradiating the water body with light while the water body is flowing; method two: adding a nitrite solution to a water body to be treated that has undergone a water treatment process of coagulation, precipitation, filtration, chlorination disinfection, and ozone deep treatment in a water plant and mixing the solution, and continuously irradiating the water body with light while the water body is flowing. The method of the present invention is based on the existing water treatment process, and can achieve the control of the generation of bromate and brominated disinfection by-products during drinking water treatment and the reduction of bromate and brominated disinfection by-products that have been generated in the water body by only adding illumination equipment and adding nitrite, and is easy to operate and has low process cost.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for controlling and eliminating the generation of bromate and brominated disinfection by-products in a drinking water treatment process. Background Art

[0002] At present, most water plants at home and abroad basically use conventional treatment processes with coagulation, sedimentation, filtration, and chlorine disinfection as the leading technologies to remove turbidity and bacteria. Furthermore, in order to enhance the removal of dissolved organic matter, DBPs precursors, odorous substances, etc. that cannot be effectively removed by the current process, in order to improve and ensure the safety of drinking water quality, new drinking water deep treatment processes continue to emerge, such as ozone-bioactivated carbon combination technology and various advanced oxidation technologies. However, when disinfecting raw drinking water, the bromide ions and organic matter remaining in the water will react with the disinfectant to generate brominated disinfection by-products. When the treatment process includes ozone oxidation or other advanced oxidation technologies, in addition to brominated disinfection by-products, bromide ions may also be ultimately oxidized to bromate.

[0003] The presence of bromate and brominated disinfection by-products seriously threatens the health of drinking water. The bromate limit in the U.S. Environmental Protection Agency's drinking water standards, the World Health Organization's drinking water quality standards, the European Union's drinking water quality directive, and my country's drinking water hygiene standards and drinking natural mineral water standards is 10μg / L. In recent years, surveys on the content of bromate in drinking water have shown that drinking water in many regions at home and abroad has excessive bromate. Therefore, reliable, effective and cost-controlled methods are urgently needed to control and eliminate the generation of bromate and brominated disinfection by-products. There are three main methods for controlling disinfection by-products: 1. Source control: remove precursors that can react with disinfectants from the source before disinfection. 2. Process control: reduce the generation of disinfection by-products by changing disinfection process parameters or disinfection methods. 3. Terminal control: remove disinfection by-products that have already been generated. At present, bromate control is usually carried out in tap water production at home and abroad by adding ammonia, permanganate composite oxidation, adding iron (Fe(II)), lowering pH value, optimizing ozone addition method, etc. However, most of the above methods belong to process control and are powerless to the problem of occasional excessive bromate concentration caused by changes in raw water quality parameters. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for controlling and eliminating the generation of bromate and brominated disinfection by-products in the process of drinking water treatment. The present invention can not only realize the control of brominated disinfection by-products in the existing conventional drinking water treatment process, but also eliminate the existing bromate in the water body, thereby improving the safety of drinking water, and is easy to operate and has low process cost.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] The object of the present invention is to provide a method for controlling and eliminating the generation of bromate and brominated disinfection by-products in a drinking water treatment process, comprising the following steps:

[0007] Method 1: Add nitrite solution to the water to be treated after the water treatment process of coagulation, sedimentation and filtration in the water plant and mix it, then add it to the chlorination disinfection unit, and continuously irradiate the water with light while it is flowing;

[0008] Method 2: Add nitrite solution to the water body to be treated that has undergone coagulation, sedimentation, filtration, chlorination disinfection, and ozone deep treatment in the water plant, mix them, and continuously expose them to light while the water body is flowing.

[0009] In some embodiments of the present invention, in the water body to be treated, the bromide ion concentration in the water body to be treated is 10-1000 μg / L, and the mass concentration ratio of bromide ion to DOC is 1-50%.

[0010] In some embodiments of the present invention, the nitrite in the nitrite solution is selected from sodium nitrite and / or potassium nitrite.

[0011] In some embodiments of the present invention, the light source of the illumination is ultraviolet light or simulated sunlight.

[0012] In some embodiments of the present invention, the wavelength of the light source of the illumination is 200-390 nm.

[0013] Specifically, the light source used in the present invention includes ultraviolet light or simulated sunlight, and can be one of the four light sources of xenon lamp, low-pressure mercury lamp, medium-pressure mercury lamp, and monochromatic light-emitting diode with emission wavelength in the range of 200-230nm and 300-390nm, or a combination of any several light sources.

[0014] When using simulated sunlight as the light source, the irradiance is 800-1200W / m 2 , which is close to the light irradiance value on the surface at noon.

[0015] In some embodiments of the present invention, in method 1, the molar concentration ratio of the nitrite solution to bromide ions is 2-3.

[0016] In some embodiments of the present invention, in method 2, the water to be treated contains bromate and bromide ions, the molar concentration ratio of the nitrite solution to bromate is 3 to 4; and the concentration of the bromate is 10 to 1000 μg / L.

[0017] In some embodiments of the present invention, stirring or aeration is used to keep the water in a flowing state.

[0018] In some embodiments of the present invention, the continuous illumination time in the flowing water state is more than 60 minutes.

[0019] In the present invention, certain improvements are made on the basis of the existing treatment process of the water plant, and the appropriate section for adding nitrite and irradiation is selected according to the specific process conditions.

[0020] When the treatment process of the water plant is coagulation, sedimentation, filtration, and chlorine disinfection, nitrite is added to the water before the chlorination operation. During the chlorination disinfection process, the light source is turned on for illumination. At the same time, the water body is kept in a certain flow state through mechanical stirring or aeration, so as to achieve process control of the generation of brominated disinfection by-products. For the specific process, see Figure 3 .

[0021] When the treatment process of the water plant is coagulation, sedimentation, filtration, chlorine disinfection, ozone / bioactivated carbon (O3 / PAC) deep treatment, nitrite is added to the water that has completed the deep treatment, and the light source is turned on for illumination. At the same time, the water body is kept in a certain flow state through mechanical stirring or aeration, so as to achieve the end control of the generation of bromate and brominated disinfection by-products. The specific process is shown in Figure 4 .

[0022] The principle of the method for controlling and eliminating bromate and brominated disinfection by-products of the present invention is:

[0023] After raw water containing bromide ions and dissolved organic matter is disinfected with chlorine, hypochlorous acid, as a disinfectant, will oxidize bromide ions into hypobromous acid. Hypobromous acid can then attack DOM in the water to form organic bromine-containing substances, and finally form brominated disinfection by-products under the action of liquid chlorine. See Formula 1-Formula 3 for details.

[0024] HClO+Br - →HBrO+Cl - (1)

[0025] HBrO+DOM→Br-DOM (2),

[0026] Br-DOM+HClO→Br-DBPs (3),

[0027] When light and nitrite are introduced into the water during the chlorine disinfection process, on the one hand, nitrite can react with hypobromous acid to generate nitryl bromide, and further react with nitryl bromide to generate nitrate and bromide ions, thereby avoiding the production of hypobromous acid as a bromination reagent, as shown in Formula 4-Formula 6.

[0028] NO2 - +HBrO→NO2Br (4),

[0029] NO2 - +NO2Br→N2O4+Br - (5)

[0030] N2O4+H2O→NO2 - +NO3 - +2H + (6)

[0031] On the other hand, nitrite can be photolyzed under light conditions to produce highly reactive intermediates such as: ·NO, ·OH, ·NO2 and e aq - , see Formula 7-Formula 14.

[0032]

[0033] OH+NO2 - → NO2+OH - (8)

[0034] ·OH+·NO2→ONOO - (9)

[0035] ·NO+·NO2→N2O3 (10),

[0036] N2O3+H2O→2H + +2NO2 - (11)

[0037] 2. NO2+H2O→NO2 - +NO3 - +2H + (12)

[0038]

[0039] O2+e aq - →O2 - (14)

[0040] These highly active intermediates can attack DOM, causing the electron density of the DOM structure to decrease or decompose, thereby reducing the probability of DOM being attacked by hypobromous acid to produce organic bromine-containing substances.

[0041] When raw water containing bromide ions and dissolved organic matter undergoes chlorine disinfection and ozone deep treatment, the bromide ions may be eventually oxidized by ozone into bromate (Formula 15-16) or generate brominated disinfection by-products with the participation of DOM, see Formula 1-Formula 3, Formula 17-Formula 18.

[0042] O3+Br - +H2O→HBrO+O2+OH - (15)

[0043] HBrO+2O3→BrO3 - +2O2+H + (16)

[0044] O3+Br - →HBrO+O2 (17),

[0045] Br-DOM+O3→Br-DBPs (18).

[0046] When light and nitrite are introduced into a water body where bromate and brominated disinfection by-products have already been generated, bromate will first be reduced to hypobromous acid under the action of light. The generated hypobromous acid will then react with nitrite to generate nitryl bromide and further generate nitrate and bromide ions, thereby eliminating the existing bromate, see Formula 19, Formula 4-Formula 6.

[0047] BrO3 - +UV→HBrO (19)

[0048] The highly active intermediates produced by the photolysis of nitrite under light conditions can attack the brominated disinfection by-products that have been generated, causing them to debrominate, thereby reducing the toxicity of the brominated disinfection by-products that have been generated. In the drinking water treatment process, the small bromine-containing organic matter produced after liquid chlorine or chloramine disinfection is generally called brominated disinfection by-products, such as bromoform, dibromoacetonitrile, tribromoacetonitrile, bromoacetic acid, etc.; bromate is an inorganic salt.

[0049] The above technical solution of the present invention has the following advantages compared with the prior art:

[0050] The present invention is based on the existing water treatment process, and the method adopted by the present invention is based on the clear generation mechanism of bromate and brominated disinfection byproducts. For the process without ozone deep treatment, the control of possible brominated disinfection byproducts can be achieved by providing a light source and nitrite in the chlorine disinfection tank. For the process containing ozone deep treatment, the control of possible bromate and brominated disinfection byproducts can be achieved by adding nitrite to the water body after ozone deep treatment and providing a light source. Therefore, no matter whether the existing process of the water plant has ozone deep treatment or not, the generation of bromine-containing harmful products can be significantly reduced.

[0051] The introduced illumination system is a commonly used device in water treatment. The nitrate formed by the transformation of the introduced nitrite under illumination or deep treatment will not exceed the limit value (nitrate (in terms of N) 10 mg / L) specified in the Sanitary Standard for Drinking Water of the People's Republic of China (GB5749-2022). While achieving a significant reduction in brominated disinfection by-products, it can also ensure that the bromate content of the treated water is less than 10 μg / L. Therefore, the method adopted by the present invention is easy to implement, green and efficient, has high operability, and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0053] Figure 1 The present invention relates to a schematic diagram of the generation and process control of brominated disinfection by-products in the conventional drinking water treatment process.

[0054] Figure 2 The present invention relates to a schematic diagram of the generation and back-end elimination of bromate in a drinking water treatment process involving ozone deep treatment.

[0055] Figure 3 It is a specific flow chart of method 1 of the present invention.

[0056] Figure 4 It is a specific flow chart of method 2 of the present invention. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0058] (1) Two brominated disinfection by-products, bromoform and dibromoacetonitrile, were selected as representative substances, and the specific determination methods were based on the methods of USEPA.

[0059] First, the water samples were pretreated.

[0060] For bromoform, extract 20 mL of the terminated water sample with 2 mL of n-pentane and fully vibrate on an oscillator for 2 minutes to ensure that the extraction is complete. After the extraction is completed, let it stand for 30 minutes and take the organic solution layer for determination and analysis.

[0061] For dibromoacetonitrile, add 2 mL of concentrated sulfuric acid to 20 mL of the terminated water sample and quickly add 1 g of CuSO4·5H2O. After shaking and mixing, quickly add 4 g of Na2SO4 to the water sample, shake it to dissolve it, add 2 ml of methyl tert-butyl ether as the extractant and place it on a test tube shaker for 2 minutes, then let it stand for 10 minutes. Use a pipette to draw 1 mL of the upper layer of the extractant solution and place it in a sample injection bottle. Place the sample injection bottle in an automatic sampler and use a gas chromatograph-mass spectrometer.

[0062] The chromatographic conditions were a quartz capillary column (30m×0.25μm×0.25μm). The column temperature was programmed with an initial temperature of 50°C. After holding for 2 min, the temperature was increased to a final temperature of 250°C at a rate of 20°C / min and held for 10 min. The detector temperature was 230°C, the column flow rate was 1mL / min, the carrier gas was helium, and split injection was adopted with a split ratio of 10:1.

[0063] (2) The determination method of bromide ion and bromate is as follows: using an ion chromatograph (ICS-1100 model) equipped with an automatic sample injector, a conductivity detector, an anion chromatographic column, and a current suppressor. The temperature of the conductivity detection cell is 30 degrees Celsius, the mobile phase is KOH solution, the mobile phase flow rate is 1 mL / min, the injection volume is 100 μL, and the suppressor current is 25 mA.

[0064] Embodiment 1:

[0065] The DOC concentration of the water to be treated is 2.5 mg / L, and the bromide ion concentration is 200 μg / L. The process control of the generation of brominated disinfection by-products in the water is carried out as follows:

[0066] Step 1: Coagulation, sedimentation and filtration of the water body. This step is a routine water treatment step in the water plant, so it will not be described here.

[0067] Step 2: Add sodium nitrite solution to the water body treated in step 1, so that the concentration of sodium nitrite in the water body reaches 500 μg / L, that is, ensure that the molar concentration ratio of nitrite to bromide ion in the water body is 2.9.

[0068] Step 3: Introduce the water treated in step 2 into the chlorination disinfection unit. Turn on the xenon lamp as the light source while chlorinating. Turn on the mechanical stirring device to keep the water flowing. Ensure that the hydraulic retention time of the water to be treated in the chlorination disinfection unit is 60 minutes.

[0069] After the water body has been treated in the above steps, it is sampled and allowed to stand for 24 hours before measurement (24 hours is used to refer to the time it takes for tap water to be delivered from the water plant to the user). The measured results are shown in Table 1.

[0070] Comparative Example 1:

[0071] The water treatment process of this comparative example is obtained by removing the increased illumination and addition of nitrite in Example 1. After the treated water is sampled, it is allowed to stand for 24 hours before measurement (24 hours is used to refer to the time it takes for tap water to be transported from the water plant to the user). The measured results are shown in Table 1.

[0072] Table 1

[0073] index Bromoform(μg / L) Dibromoacetonitrile (μg / L) Tribromoacetonitrile (μg / L) Comparative Example 1 67.5 81.6 36.3 Example 1 15.2 9.3 1.6

[0074] As can be seen from Table 1, the combined treatment of light and nitrite during chlorination of water bodies can significantly reduce the amount of brominated disinfection by-products in the effluent, thereby improving the safety of drinking water.

[0075] Embodiment 2:

[0076] The DOC concentration of the water to be treated is 6.5 mg / L, and the bromide ion concentration is 90 μg / L. The end-point control of the formation of bromate and brominated disinfection by-products in the water is carried out as follows:

[0077] Step 1: The water body is subjected to coagulation, sedimentation, filtration, chlorination disinfection, and ozone deep treatment. This step is a common water treatment step in water plants, so it is not described here. The concentrations of brominated disinfection byproducts and bromate in the treated water body were measured. Bromate was measured at 53.5 μg / L, bromoform at 35.8 μg / L, dibromoacetonitrile at 67.4 μg / L, and tribromoacetonitrile at 38.9 μg / L.

[0078] Step 2: Add sodium nitrite solution to the water treated in step 1 to make the concentration of sodium nitrite in the water reach 100 μg / L, that is, ensure that the molar concentration ratio of nitrite in the water to bromate generated after deep ozone treatment is 3.5.

[0079] Step 3: Illuminate the water treated in step 2 with a low-pressure mercury lamp, and turn on the mechanical stirring device to keep the water flowing, ensuring that the hydraulic retention time of the water to be treated under illumination and flow conditions reaches 60 minutes.

[0080] After the water body has been treated in the above steps, it is sampled and allowed to stand for 24 hours before measurement (24 hours is used to refer to the time it takes for tap water to be delivered from the water plant to the user). The measured results are shown in Table 2.

[0081] Comparative Example 2:

[0082] The water treatment process of this comparative example is obtained by removing step 2 and step 3 in Example 2. After the treated water is sampled, it is allowed to stand for 24 hours before measurement (24 hours is used to refer to the time for tap water to be transported from the water plant to the user). The measured results are shown in Table 2.

[0083] Table 2

[0084]

[0085] As can be seen from Table 2, after the water body has undergone coagulation, sedimentation, filtration, chlorination disinfection, ozone deep treatment and other steps, the combined treatment of light and nitrite can reduce the content of brominated disinfection by-products, especially bromate, in the effluent, thereby improving the safety of drinking water.

[0086] Embodiment 3:

[0087] The DOC concentration of the water to be treated is 3.0 mg / L, and the bromide ion concentration is 460 μg / L. The process control of the generation of brominated disinfection by-products in the water is carried out as follows:

[0088] Step 1: Coagulation, sedimentation and filtration of the water body. This step is a routine water treatment step in the water plant, so it will not be described here.

[0089] Step 2: Add sodium nitrite solution to the water treated in step 1 to make the sodium nitrite concentration in the water reach 850 μg / L, that is, ensure that the molar concentration ratio of nitrite to bromide ion in the water is within the range of 2.1.

[0090] Step 3: Introduce the water treated in step 2 into the chlorination disinfection unit. While performing chlorination disinfection, turn on the medium-pressure mercury lamp as the light source, turn on the mechanical stirring device to keep the water in a flowing state, and ensure that the hydraulic retention time of the water to be treated in the chlorination disinfection unit is 60 minutes.

[0091] After the water body was treated by the above steps, it was sampled and left to stand for 24 hours before measurement (24 hours is used to refer to the time it takes for tap water to be transported from the water plant to the user). The measured results are shown in Table 3.

[0092] Comparative Example 3:

[0093] The water treatment process of this comparative example is obtained by removing the increased illumination and addition of nitrite in Example 3. After the treated water is sampled, it is allowed to stand for 24 hours before measurement (24 hours is used to refer to the time it takes for tap water to be transported from the water plant to the user). The measured results are shown in Table 3.

[0094] Table 3

[0095] index Bromoform(μg / L) Dibromoacetonitrile (μg / L) Tribromoacetonitrile (μg / L) Comparative Example 3 97.2 96.7 49.2 Example 3 17.4 8.9 1.9

[0096] It can be seen from Table 3 that the combined treatment of light / nitrite with chlorination of water bodies can significantly reduce the amount of brominated disinfection by-products in the effluent, thereby improving the safety of drinking water.

[0097] Embodiment 4:

[0098] The DOC concentration of the water to be treated is 8.5 mg / L, and the bromide ion concentration is 780 μg / L. The water body is subjected to terminal control of the formation of bromate and brominated disinfection by-products.

[0099] Step 1: The water body is subjected to coagulation, sedimentation, filtration, chlorination disinfection, and ozone deep treatment. This step is a common water treatment step in water plants, so it is not described here. The concentrations of brominated disinfection byproducts and bromate in the treated water were measured, and the measured values ​​were 460 μg / L of bromate, 127.8 μg / L of bromoform, 254.3 μg / L of dibromoacetonitrile, and 99.7 μg / L of tribromoacetonitrile.

[0100] Step 2: Add sodium nitrite solution to the water body treated in step 1 to make the sodium nitrite concentration in the water body reach 1000 μg / L. At this time, the molar concentration ratio of nitrite in the water body to bromate generated after deep ozone treatment is 4.

[0101] Step 3: Irradiate the water treated in step 2 with a medium-pressure mercury lamp, and turn on the mechanical stirring device to keep the water flowing, ensuring that the hydraulic retention time of the water to be treated in the chlorination disinfection unit is 60 minutes.

[0102] After the water body has been treated in the above steps, it is sampled and allowed to stand for 24 hours before measurement (24 hours is used to refer to the time it takes for tap water to be delivered from the water plant to the user). The measured results are shown in Table 2.

[0103] Comparative Example 4:

[0104] The water treatment process of this comparative example is obtained by removing step 2 and step 3 in Example 4. After the treated water is sampled, it is allowed to stand for 24 hours before measurement (24 hours is used to refer to the time for tap water to be transported from the water plant to the user). The measured results are shown in Table 2.

[0105] Table 4

[0106]

[0107] As can be seen from Table 4, after the water body has undergone steps such as coagulation, sedimentation, filtration, chlorination disinfection, and ozone deep treatment, the combined treatment of light / nitrite can reduce the content of brominated disinfection by-products, especially bromate, in the effluent, thereby improving the safety of drinking water.

[0108] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for eliminating bromate and brominated disinfection by-products in a drinking water treatment process, characterized in that: The following steps are involved: A nitrite solution is added to the water body to be treated that has been subjected to coagulation, sedimentation, filtration, chlorination disinfection and ozone deep treatment in a water plant, and the mixture is continuously irradiated with light while the water body is flowing; the wavelength of the light source for the irradiation is 200-390 nm; the water body to be treated contains bromate and bromide ions, the molar concentration ratio of the nitrite solution to bromate is 3-4; the concentration of the bromate is 10-1000 μg / L; and the continuous irradiation time while the water body is flowing is more than 60 minutes.

2. The method according to claim 1, characterized in that The nitrite in the nitrite solution is selected from sodium nitrite and / or potassium nitrite.

3. The method according to claim 1, characterized in that In order to keep the water flowing, stirring or aeration is used.

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