Method for removing disinfection by-products in drinking water through photocatalysis

Abstract

The invention relates to the technical field of catalytic purification of drinking water, in particular to a method for removing disinfection by-products in drinking water through photocatalysis, which comprises the following steps: S1, first pH regulation: regulating the pH value of to-be-treated drinking water containing mixed disinfection by-products to a first target pH range in situ in a water electrolysis manner to form first treated water; s2, first photocatalytic degradation: carrying out a photocatalytic reaction on the first treated water under irradiation of an ultraviolet lamp light source, and degrading a first type of disinfection by-products within a first target pH range; s3, second pH regulation: regulating the pH value of the effluent subjected to the first photocatalytic degradation to a second target pH range different from the first target pH range in situ through the water electrolysis mode to form second treated water; and S4, second photocatalytic degradation: carrying out a photocatalytic reaction on the second treated water under the irradiation of an ultraviolet lamp light source, and degrading a second type of disinfection by-products within a second target pH range. The method solves the problem that the mixed disinfection by-product is difficult to efficiently remove under the condition of single pH.

Description

Technical Field

[0001] This invention relates to the field of drinking water catalytic purification technology, specifically a method for photocatalytic removal of disinfection byproducts from drinking water. Background Technology

[0002] Drinking water disinfection is an indispensable step in safeguarding public health. However, disinfectants (such as chlorine, chloramine, and ozone) react with natural organic matter in water to generate a series of disinfection byproducts (DBPs) with potential carcinogenic, teratogenic, and mutagenic risks. These DBPs are diverse, mainly including trihalomethanes and haloacetic acids. Although their concentrations in water are low, long-term exposure poses a serious threat to human health. Advanced oxidation processes are an effective means of degrading recalcitrant organic micropollutants. Among them, photocatalytic oxidation technology shows great promise in advanced drinking water treatment due to its mild reaction conditions, thorough degradation, and environmental friendliness. This technology utilizes light irradiation to excite catalysts (such as TiO2) to generate highly oxidizing electron-hole pairs, thereby mineralizing organic matter.

[0003] However, existing photocatalytic technologies for treating DBPs face significant challenges. On one hand, different types of DBPs differ in their molecular structure, charge properties, and reactivity, leading to vastly different degradation efficiencies under a single, fixed aqueous chemical environment (such as pH). For example, trihalomethanes are more readily photocatalytically degraded under acidic conditions, while haloacetic acids exhibit higher removal rates under slightly alkaline conditions. Most existing technologies operate under a single pH condition, making it difficult to achieve simultaneous and efficient removal of complex mixed DBP populations. On the other hand, to improve photocatalytic efficiency, existing technologies often employ the addition of catalyst modifiers (such as inorganic acids like H3PO4 and H4P2O7) and co-catalysts (such as Au, Pd, and CoO). X Methods using hydrogen peroxide and small molecule organic compounds in photocatalysis include precious metals / oxides, oxidants (such as H2O2 and persulfate), and composite carriers (such as graphene oxide (GO) and biochar). For example, patent CN116495863A discloses the addition of hydrogen peroxide and small molecule organic compounds during photocatalysis, while patent CN105668880B discloses the addition of sulfates or persulfates. While these methods can increase the reaction rate, they also have drawbacks: for example, they increase the risk of secondary pollution, as the added chemicals may remain in the treated water, posing new health risks; or the additives may alter the reaction pathway, resulting in poor removal of certain disinfection byproducts; or they may increase costs and energy consumption: additional chemical addition, mixing, and reaction control require more energy. Patent CN106219839A discloses a direct photolysis method without adding chemicals, avoiding secondary pollution but with limited efficiency.

[0004] Therefore, there is an urgent need to develop a novel photocatalytic treatment method that can efficiently remove various DBPs from drinking water without introducing exogenous chemical pollution. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for photocatalytic removal of disinfection byproducts from drinking water. This method overcomes the limitations of existing technologies, which rely on a single pH condition for efficient degradation of multiple DBPs and the risk of secondary pollution from the addition of exogenous chemicals. This invention generates H₂ through in-situ water electrolysis. + and OH - This process enables precise stepwise pH control through self-supply within the process, creating optimal degradation environments for different types of DBPs. As a result, efficient, stable, and safe synergistic removal of mixed DBPs can be achieved without adding any exogenous chemicals.

[0006] To address the aforementioned problems, the technical solution adopted in this invention is: a method for photocatalytic removal of disinfection byproducts from drinking water. The core of this method lies in adjusting the pH value of the reaction system in situ and stepwise using water electrolysis technology to adapt to the efficient degradation of different types of disinfection byproducts. The method includes the following steps: S1, First pH adjustment: The pH value of the drinking water containing mixed disinfection byproducts is adjusted in situ to the first target pH range by water electrolysis to form the first treated water; S2, First photocatalytic degradation: The first treated water is subjected to photocatalytic reaction under ultraviolet light source to degrade the first type of disinfection byproducts within the first target pH range; S3, Second pH adjustment: The pH value of the effluent after the first photocatalytic degradation is adjusted in situ to a second target pH range that is different from the first target pH range by water electrolysis, forming the second treated water; S4. Second photocatalytic degradation: The second treated water is subjected to photocatalytic reaction under ultraviolet light source to degrade the second type of disinfection byproducts within the second target pH range; The first type of disinfection byproducts and the second type of disinfection byproducts are different types of disinfection byproducts.

[0007] Furthermore, the pH adjustment in steps S1 and S3 is achieved through water electrolysis in the process, including diverting a portion of the water for which pH adjustment is needed and electrolyzing it to produce acidic and alkaline electrolyzed water; in-situ pH adjustment is achieved by controlling the injection amount of the acidic or alkaline electrolyzed water into the main stream. Specifically, a small portion of the water for which pH adjustment is needed is diverted into an electrolysis device (such as a membrane electrolyzer), where electrolysis produces H+-rich water. + Acidic electrolyzed water and water rich in OH- -The alkaline electrolyzed water, through precise metering, mixes the required type of electrolyzed water (acidic or alkaline) into the mainstream water in the appropriate proportion, thereby achieving precise and clean control of the pH value of the entire process.

[0008] Furthermore, the electrolysis is carried out in a membrane electrolysis device, which simultaneously produces acidic electrolyzed water and alkaline electrolyzed water.

[0009] Furthermore, the first type of disinfection byproduct includes trihalomethanes, and the first target pH range is 4.0-6.5; the second type of disinfection byproduct includes haloacetic acids, and the second target pH range is 7.5-9.5. This order can be adjusted according to the characteristics of the water quality.

[0010] Furthermore, the photocatalytic reaction is carried out in a photocatalytic reactor filled or supported with a photocatalyst, the photocatalyst including at least one of titanium dioxide, modified titanium dioxide, carbon nitride, and bismuth-based semiconductors.

[0011] Furthermore, the ultraviolet lamp light source mentioned in steps S2 and S4 is a medium-pressure mercury lamp or a xenon lamp, wherein the power of the medium-pressure mercury lamp is 300-500W, and the power of the xenon lamp is 500-1000W.

[0012] Furthermore, in steps S2 and S4, the irradiation time is 20-30 minutes.

[0013] Furthermore, the method also includes: before step S1, pre-treating the drinking water to be treated to remove suspended solids and colloids.

[0014] Compared with the prior art, the technical solution of this application has the following beneficial effects: 1. High efficiency and specificity: By adjusting the pH stepwise, the optimal degradation environment for different DBPs such as THMs and HAAs is created, achieving synergistic and efficient removal of mixed pollutants, with an overall removal rate significantly higher than that under single pH conditions.

[0015] 2. No secondary pollution: The hydrogen ions and hydroxide ions required for pH adjustment come entirely from the electrolysis of the water itself. No external acids, alkalis or oxidizing chemicals are added throughout the process, which fundamentally eliminates the risk of secondary pollution caused by chemical residues, making the effluent water safer.

[0016] 3. Low operating costs and intelligent operation: Membrane electrolysis units consume less energy and eliminate the need for purchasing, storing, and adding chemicals, thus reducing operating costs and complexity. The units can achieve feedback control via online pH sensors, resulting in a high degree of automation.

[0017] 4. Strong system adaptability: This method can flexibly set two-stage pH target values ​​and reaction sequence according to the dominant types of DBPs in the raw water, and has good adaptability to different water qualities.

[0018] 5. Environmentally friendly catalyst: The entire process is carried out in a mild chemical environment, which helps maintain the long-term activity stability of the photocatalyst and avoids the corrosion of the catalyst by strong acids, strong bases or strong oxidants. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of a photocatalytic method for removing disinfection byproducts from drinking water according to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: This embodiment of the invention discloses a method for photocatalytic removal of disinfection byproducts from drinking water, referring to... Figure 1 The drinking water to be treated contains approximately 30 μg / L of chloroform and approximately 20 μg / L of dichloroacetic acid.

[0022] 1. Pretreatment: The drinking water to be treated is pretreated to remove suspended particles and control the turbidity to <1 NTU.

[0023] 2. First pH Adjustment (S1): Most of the pretreated drinking water serves as the main stream, while a small portion (approximately 5% of the total flow) is pumped into a membrane electrolysis unit (using a homogeneous anion exchange membrane, with a titanium-coated ruthenium-iridium anode and a stainless steel cathode). Electrolysis produces stable concentrations of acidic electrolyzed water (pH 2.5) and alkaline electrolyzed water (pH 11.0). An online pH meter monitors the pH of the main stream water, and a metering pump precisely injects acidic electrolyzed water into the main stream water to stabilize the first target pH range of the mixed first-treatment water at 5.5 ± 0.2.

[0024] 3. First photocatalytic degradation (S2): The treated water is fed into a photocatalytic reactor filled with a supported TiO2 catalyst. A 500W medium-pressure mercury lamp is used as the ultraviolet light source, and the irradiation time is 25 minutes. Under these acidic conditions, chloroform is efficiently degraded.

[0025] 4. Second pH adjustment (S3): The effluent after the first photocatalytic degradation is electrolyzed again to adjust the pH in situ, so that the second target pH range of the mixed second treated water is adjusted to 8.5±0.2.

[0026] 5. Second photocatalytic degradation (S4): The second batch of treated water is fed into the photocatalytic reactor and irradiated with the same light source for 25 minutes. Under these alkaline conditions, dichloroacetic acid is efficiently degraded.

[0027] 6. Post-treatment: The effluent after the second photocatalytic degradation is further adjusted in situ by electrolysis to bring the pH to approximately 7.2, thus obtaining purified effluent.

[0028] Results Testing: Samples of the purified effluent obtained in step 6 were taken for testing. The removal rate of chloroform reached 94%, and the removal rate of dichloroacetic acid reached 91%. A full scan analysis of anions and cations (chloride ions, sulfate ions, sodium ions, calcium ions, etc.) in the effluent was performed, and no abnormal increases were found. The effluent was clear and odorless.

[0029] Example 2 The difference from Example 1 is that the drinking water to be treated contains dichloroacetonitrile (approximately 15 μg / L) and 2,4,6-trichlorophenol (approximately 10 μg / L); the first target pH range is 5.0, and the second target pH range is 9.0; the ultraviolet lamp source is a 1000W xenon lamp, and the photocatalytic irradiation time for each stage is 25 minutes.

[0030] Results showed that the removal rate of dichloroacetonitrile was >88%, and the removal rate of 2,4,6-trichlorophenol was >95%.

[0031] Comparative Example 1 The difference from Example 1 is that instead of stepwise pH adjustment, the pH is kept at 7.0 throughout the process, and the total irradiation time is 50 minutes.

[0032] Results showed that the removal rate of chloroform was 68% and the removal rate of dichloroacetic acid was 62%.

[0033] Comparative Example 2 The difference from Example 1 is that instead of stepwise pH adjustment, the pH is kept at 5.0 throughout the process, and the total irradiation time is 50 minutes.

[0034] Results showed that the removal rate of chloroform was 85%, and the removal rate of dichloroacetic acid was 58%.

[0035] Comparative Example 3 The difference from Example 1 is that instead of stepwise pH adjustment, the pH is kept at 9.0 throughout the process, and the total irradiation time is 50 minutes.

[0036] Results showed that the removal rate of chloroform was 45%, and the removal rate of dichloroacetic acid was 86%.

[0037] Comparative Example 4 The difference from Example 1 is that stepwise pH adjustment (5.5→8.5) is used, but the pH adjustment method is to add exogenous chemicals (using 0.1 mol / L HCl solution and 0.1 mol / L NaOH solution for pH adjustment).

[0038] Results showed that chloroform removal rate was 92% and dichloroacetic acid removal rate was 90%. However, ion chromatography analysis of the effluent revealed the presence of Cl... - and Na + The concentrations were significantly higher than those of the original water, increasing by approximately 12 mg / L and 8 mg / L, respectively.

[0039] The test results of Examples 1-2 and Comparative Examples 1-4 are shown in the table below: Table 1: Comparison of process effects between embodiments of the present invention and comparative examples

[0040] Results analysis: The above examples and comparative examples demonstrate that the "in-situ water electrolysis-stepwise pH adjustment" photocatalytic method provided by this invention achieves a significantly higher overall removal efficiency for mixed disinfection byproducts than any single constant pH condition process, without introducing exogenous ions. Furthermore, compared to methods that also employ stepwise pH adjustment but use exogenous chemicals, this invention completely eliminates the risk of secondary pollution caused by chemical residues while ensuring high efficiency, achieving a balance between treatment performance and effluent safety.

[0041] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the structure of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for photocatalytic removal of disinfection byproducts from drinking water, characterized in that, Includes the following steps: S1, First pH adjustment: The pH value of the drinking water containing mixed disinfection byproducts is adjusted in situ to the first target pH range by water electrolysis to form the first treated water; S2, First photocatalytic degradation: The first treated water is subjected to photocatalytic reaction under ultraviolet light source to degrade the first type of disinfection byproducts within the first target pH range; S3, Second pH adjustment: The pH value of the effluent after the first photocatalytic degradation is adjusted in situ to a second target pH range that is different from the first target pH range by water electrolysis, forming the second treated water; S4. Second photocatalytic degradation: The second treated water is subjected to photocatalytic reaction under ultraviolet light source to degrade the second type of disinfection byproducts within the second target pH range; The first type of disinfection byproducts and the second type of disinfection byproducts are different types of disinfection byproducts.

2. The method for photocatalytic removal of disinfection byproducts from drinking water according to claim 1, characterized in that: The pH adjustment in steps S1 and S3 is achieved by electrolyzing water in the process, including diverting a portion of the water body whose pH needs to be adjusted and electrolyzing it to produce acidic electrolyzed water and alkaline electrolyzed water; and achieving in-situ pH adjustment by controlling the amount of acidic or alkaline electrolyzed water injected into the main water.

3. The method for photocatalytic removal of disinfection byproducts from drinking water according to claim 2, characterized in that: The electrolysis is carried out in a membrane electrolysis device.

4. The method for photocatalytic removal of disinfection byproducts from drinking water according to claim 1, characterized in that: The first type of disinfection byproduct includes trihalomethanes, and the first target pH range is 4.0-6.5; the second type of disinfection byproduct includes haloacetic acids, and the second target pH range is 7.5-9.

5.

5. The method for photocatalytic removal of disinfection byproducts from drinking water according to claim 1, characterized in that: In steps S2 and S4, the photocatalytic reaction is carried out in a photocatalytic reactor filled or supported with a photocatalyst, wherein the photocatalyst includes at least one of titanium dioxide, modified titanium dioxide, carbon nitride, and bismuth semiconductor.

6. The method for photocatalytic removal of disinfection byproducts from drinking water according to claim 1, characterized in that: In steps S2 and S4, the ultraviolet lamp light source is a medium-pressure mercury lamp or a xenon lamp, wherein the power of the medium-pressure mercury lamp is 300-500W and the power of the xenon lamp is 500-1000W.

7. The method for photocatalytic removal of disinfection byproducts from drinking water according to claim 1, characterized in that: In steps S2 and S4, the irradiation time is 20-30 minutes.

8. The method for photocatalytic removal of disinfection byproducts from drinking water according to claim 1, characterized in that: The method further includes: before step S1, pre-treating the drinking water to be treated to remove suspended solids and colloids.

Images