Method for treating algal-containing raw water by moderate pre-oxidation with ultraviolet-activated oxidant

Abstract

The present application relates to the technical field of drinking water treatment, and particularly relates to a method for treating algal-containing raw water by using ultraviolet-activated oxidant and moderate pre-oxidation. The method comprises the following steps: 1) adding an oxidant to algal-containing raw water; 2) irradiating the algal-containing raw water containing the oxidant in step 1) by using ultraviolet light; and 3) performing coagulation and sedimentation treatment on the water body after ultraviolet irradiation. The method of the present application uses ultraviolet light as an activation switch, realizes controllable oxidation intensity by precisely controlling the ultraviolet irradiation time and irradiation dose, only changes the surface characteristics of algal cells without damaging the cell membrane, strengthens coagulation and algae removal, avoids the dissolution of intracellular organic matter and algal toxins from the root cause, and guarantees the safety of drinking water quality; the whole process does not need to add solid catalysts, the process is simple, operation and maintenance are convenient, and the method is suitable for the modification of existing processes in water plants.

Description

Technical Field

[0001] This invention relates to the field of drinking water treatment technology, and in particular to a method for moderate pre-oxidation treatment of algae-containing raw water using ultraviolet-activated oxidants. Background Technology

[0002] As eutrophication of surface water bodies intensifies, large-scale algal blooms occur in many drinking water sources across China during warmer seasons. Suspended microalgal particles in water exhibit high colloidal stability, making them difficult to remove effectively using conventional coagulation, sedimentation, and filtration processes at water plants. Algae not only increase the cost of coagulants and disinfectants but also clog filters, shorten filter media lifespan, increase backwashing frequency, and raise the operational burden on water plants. Furthermore, algae and their metabolites contain various harmful pollutants such as algal toxins and odor-causing substances. When these algal organic materials enter subsequent disinfection units, they readily generate various disinfection byproducts, posing a serious threat to the safety of urban drinking water supply.

[0003] To address the challenge of treating raw water with high algae levels, the water treatment industry currently employs a combination of pre-oxidation processes and coagulation sedimentation technology to enhance algae removal efficiency. Commonly used pre-oxidation methods include chemical oxidation, catalytic oxidation, and single ultraviolet oxidation, but existing processes suffer from numerous unavoidable problems in practical applications.

[0004] The oxidants used in conventional chemical pre-oxidation processes continuously undergo oxidation reactions after being introduced into the water. This process cannot be quickly stopped artificially and can easily cause excessive damage to algal cells. After the algal cell membranes rupture, large amounts of organic matter, toxins, and odor-causing substances inside the cells are released into the water, directly leading to the deterioration of the effluent quality and further increasing the risk of disinfection byproducts.

[0005] Some catalytic oxidation processes require the addition of solid catalysts to water bodies. During long-term operation, problems such as catalyst wear and loss may occur, which not only increases the cost of reagent replenishment, but also poses a risk of secondary pollution caused by the leaching of metal ions, and does not meet the safety requirements for drinking water quality.

[0006] Furthermore, most current pre-oxidation processes rely solely on the dosage of chemicals to roughly adjust the oxidation intensity, lacking standardized criteria for determining the degree of oxidation. Process control depends entirely on on-site experience, making it difficult to ensure both effective algae removal and stability of the original water quality. Using ultraviolet irradiation or a single oxidant alone results in insufficient oxidation capacity and low algae removal efficiency, failing to meet the treatment requirements of high-algae raw water.

[0007] Sodium percarbonate and hydrogen peroxide are environmentally friendly oxidants with weak self-oxidizing activity at room temperature and pressure. Without external activation conditions, they do not cause strong damage to algal cells, and their decomposition products are non-toxic and harmless, posing no residual pollution problems. Therefore, they have good application potential in the pre-oxidation of algae-containing raw water. How to develop a treatment process based on these oxidants and combined with activation technology, featuring controllable oxidation intensity, flexible reaction start-stop, and mild pre-oxidation, to enhance coagulation and algae removal while blocking the release of intracellular pollutants, is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing pre-oxidation algae removal technologies, such as easy over-oxidation, uncontrollable oxidation process, secondary pollution, and lack of quantitative control standards. This invention provides a method for moderate pre-oxidation treatment of algae-containing raw water using ultraviolet-activated oxidants. The method uses ultraviolet light as an activation switch, achieving controllable oxidation intensity through precise control of ultraviolet irradiation time and dosage. It only alters the surface characteristics of algal cells without damaging the cell membrane. While enhancing coagulation and algae removal, it fundamentally prevents the leaching of intracellular organic matter and algal toxins, ensuring the safety of drinking water quality. The entire process requires no external solid catalyst, is simple to operate and maintain, and is suitable for upgrading existing water plant processes.

[0009] To achieve the above objectives, the present invention provides a method for moderate pre-oxidation treatment of algae-containing raw water using a UV-activated oxidant, the method comprising: 1) Add an oxidant to the algae-containing raw water; 2) Irradiate the algae-containing raw water containing oxidant in step 1) with ultraviolet light; 3) Coagulation and sedimentation treatment of water bodies after ultraviolet irradiation; In step 2), the optimal ultraviolet irradiation dose is determined by one or both of the following methods: a) Detect the increase in dissolved organic matter in water after ultraviolet irradiation. When the total organic carbon or permanganate index increases by 0-30% compared to before ultraviolet irradiation, the corresponding irradiation dose is the optimal dose. b) Detect the zeta potential of the water body after ultraviolet irradiation. When the zeta potential is stable at -30~-5mV, the corresponding irradiation dose is the optimal dose.

[0010] Preferably, in step 1), the oxidant is hydrogen peroxide and / or sodium percarbonate.

[0011] Preferably, in step 1), the amount of oxidant added is 0.2~4.0 mmol / L.

[0012] Preferably, in step 1), the oxidant is added at the raw water inlet or the intake well.

[0013] Preferably, in step 2), the ultraviolet light is provided by an ultraviolet lamp with a main emission wavelength of 254nm.

[0014] Preferably, in step 2), the ultraviolet lamp is placed in a light-shielding reactor or channel, and the algae-containing raw water containing oxidant is irradiated with ultraviolet light in a flowing or static manner.

[0015] Preferably, in step 2), the ultraviolet irradiation dose is 20~140 mJ / cm². 2 .

[0016] Preferably, in step 3), the coagulant used in the coagulation treatment is selected from one or more of polyaluminum chloride, aluminum sulfate, aluminum chloride, polyferric sulfate, ferrous sulfate and ferric chloride; the dosage of the coagulant is 10~80mg / L, preferably 50~60mg / L.

[0017] Preferably, in step 3), the coagulation and sedimentation time is 40~140 min.

[0018] Preferably, the method further includes filtration and disinfection after coagulation and sedimentation.

[0019] In the above technical solution, the present invention utilizes the weak self-oxidizing ability of hydrogen peroxide or sodium percarbonate, so that when it comes into contact with algal cells without being activated by ultraviolet light, it only has a mild effect, ensuring the stability of water transport and reagent mixing stages; when the water is irradiated with ultraviolet light of a specific wavelength, hydrogen peroxide decomposes to generate highly oxidizing hydroxyl radicals. By precisely controlling the ultraviolet irradiation dose, the total amount and duration of action of free radicals can be limited, so that they only act on the surface of algal cells, changing the surface charge and structure, thereby improving the subsequent coagulation and flocculation effect.

[0020] Meanwhile, because the oxidation intensity is strictly controlled below the cell membrane penetration threshold, reactive free radicals cannot enter the cell, thus preventing the release of intracellular organic matter, algal toxins, and odor-causing substances from the source, significantly reducing the risk of disinfection byproduct generation. The "on-demand" characteristic of ultraviolet light instantly terminates the activation reaction and stops the oxidation process immediately, completely solving the problem of over-oxidation caused by continuous reactions of traditional oxidants. No particulate catalysts are required throughout the process, fundamentally avoiding secondary pollution problems such as catalyst wear, loss, and metal ion leaching. Furthermore, the quantitative judgment criteria based on TOC, permanganate index, and Zeta potential enable standardized and controllable operation of "moderate pre-oxidation."

[0021] Based on the above principles, this invention exhibits several outstanding advantages in practical applications: the oxidation process is precisely controllable, relying on dual regulation of irradiation time and dosage to balance algae removal effectiveness and drinking water safety; the process is safe and environmentally friendly, with the decomposition products of the oxidant being only water, carbon dioxide, and carbonates, which are non-toxic and residue-free, and it eliminates chlorine-containing oxidation systems, avoiding toxic chlorine-containing byproducts; the process modification is simple, the oxidant addition point is flexible, the ultraviolet device can be directly installed in existing structures without large-scale civil engineering, and operation and maintenance are simple and cost-effective; it has a wide range of applications, adaptable to raw water with different algae densities, capable of both conventional treatment and emergency treatment of seasonal algal blooms, and the algal cell destabilization effect after pre-oxidation is good, which can reduce the amount of coagulant added and alleviate filter clogging; the entire process parameter system is complete and standardized, with a high degree of standardization, facilitating large-scale application in waterworks and water purification stations.

[0022] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1 The results show the proportion of viable algal cells in water after different ultraviolet irradiation doses in Examples 1, 2, 4, Comparative Examples 1 and 3-5 of the present invention. Figure 2 The TOC content in water after treatment with different ultraviolet irradiation doses in Examples 1, 2, 4, Comparative Example 1, and Comparative Examples 3-5 of the present invention; Figure 3 The zeta potential in water after treatment with different ultraviolet irradiation doses in Examples 1, 2, 4, Comparative Example 1, and Comparative Examples 3-5 of the present invention is shown. Detailed Implementation

[0024] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0026] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0027] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0028] This invention provides a method for moderate pre-oxidation treatment of algae-containing raw water using ultraviolet-activated oxidants, the method comprising: 1) Add an oxidant to the algae-containing raw water; 2) Irradiate the algae-containing raw water containing oxidant in step 1) with ultraviolet light; 3) Coagulation and sedimentation treatment of water bodies after ultraviolet irradiation; In step 2), the optimal ultraviolet irradiation dose is determined by one or both of the following methods: a) Detecting the increase in dissolved organic matter in water after UV irradiation, the optimal irradiation dose is defined as a 0-30% increase in total organic carbon or permanganate index compared to before UV irradiation. Algal cell rupture directly leads to the release of intracellular organic matter, causing a sharp increase in dissolved organic matter (TOC, permanganate index) in the water. Controlling the increase to within 30% ensures that pre-oxidation does not cause extensive cell damage. Quantitatively limiting the degree of oxidation from the perspective of organic matter leaching ensures the chemical safety of the settled water and the treated water, and reduces the potential for disinfection byproduct formation.

[0029] b) Detect the zeta potential of the water after UV irradiation. When the zeta potential stabilizes within -30 to -5 mV, the corresponding irradiation dose is optimal. Algal cells typically carry a strong negative charge (e.g., -20 to -40 mV). This stable negative charge leads to electrostatic repulsion, making coagulation difficult. Moderate oxidation can reduce the surface charge to the -30 to -5 mV range, compressing the electric double layer and facilitating coagulation destabilization, without completely destroying the cell surface structure due to the potential approaching zero. Using surface charge as a characteristic indicator of "moderate" oxidation is highly operable, allowing for real-time or rapid measurement to guide water treatment plants in dynamically adjusting the UV irradiation dose, ensuring optimal treatment conditions are always maintained.

[0030] In step 1) of this invention, the oxidant is hydrogen peroxide and / or sodium percarbonate. Hydrogen peroxide itself has a weak direct oxidizing ability against algal cells and will not significantly damage algal cells without UV activation. Sodium percarbonate, as a "solid hydrogen peroxide," dissolves in water to generate hydrogen peroxide and sodium carbonate, making it convenient to store and transport, and its reaction is mild. Both can be activated under UV irradiation to produce strong oxidizing species (·OH). In the unirradiated stage, they can maintain the integrity of algal cells and avoid uncontrollable oxidation reactions; once activated by UV light, they generate highly active free radicals, achieving precise "on-off" oxidation control, thereby strengthening coagulation and algae removal while preventing the large-scale dissolution of intracellular organic matter.

[0031] In step 1) of this invention, the dosage of the oxidant is 0.2~4.0 mmol / L, which ensures that sufficient ·OH is generated during the ultraviolet activation stage to change the surface properties of algal cells and enhance coagulation; at the same time, it avoids the generation of excessive free radicals under a given irradiation dose, which would lead to the rupture of algal cell membranes and the release of large amounts of intracellular organic matter, thereby deteriorating water quality. It ensures that sufficient oxidant precursors are converted into active species by ultraviolet light, while not exceeding the algal cell damage threshold, thus achieving the goal of "moderate pre-oxidation".

[0032] In step 1) of this invention, the oxidant is added at the raw water inlet or the intake well.

[0033] In a preferred embodiment of the present invention, the oxidant can also be added simultaneously with the coagulant at the front end of the flocculation tank; when the oxidant and coagulant are added simultaneously, the water containing the mixed reagents first flows through the ultraviolet irradiation unit to complete the irradiation activation, and then enters the flocculation and sedimentation process.

[0034] In step 2) of this invention, the ultraviolet light is provided by an ultraviolet lamp with a main emission wavelength of 254nm.

[0035] In step 2) of this invention, the ultraviolet lamp is placed in a light-shielding reactor or channel. The algae-containing raw water containing oxidant receives ultraviolet irradiation in a flowing or static manner. The ultraviolet irradiation time can be controlled by adjusting the reactor volume or the inlet and outlet water flow rate, thereby obtaining the ultraviolet irradiation dose. This makes the ultraviolet irradiation dose the only controllable variable, avoiding sunlight interference and delayed reaction, and achieving precise control of the oxidation degree. The process is simple and easy to automate.

[0036] In step 2) of this invention, the ultraviolet irradiation dose is 20~140 mJ / cm². 2 Within this dosage window, the active species generated by UV-activated peroxides act only on the surface of algal cells, moderately oxidizing cell wall components and adsorbed organic matter, reducing surface negative charge without damaging cell integrity, thereby significantly enhancing the destabilization and aggregation of algal cells in the subsequent coagulation process without causing intracellular leakage.

[0037] In step 3) of the present invention, the coagulant used in the coagulation treatment is selected from one or more of polyaluminum chloride, aluminum sulfate, aluminum chloride, polyferric sulfate, ferrous sulfate and ferric chloride; the dosage of the coagulant is 10~80mg / L, preferably 50~60mg / L.

[0038] In step 3) of this invention, the coagulation and sedimentation time is 40~140 min.

[0039] The method of the present invention further includes filtration and disinfection after coagulation and sedimentation.

[0040] By selecting and combining the above conditions, this invention provides a moderate pre-oxidation method that requires no external particulate catalyst and is precisely controlled by ultraviolet light. On the one hand, the low reactivity of peroxides ensures that algal cells are not oxidized during the addition and transportation stages; on the other hand, ultraviolet light is used as an "activation switch" to instantaneously generate hydroxyl radicals under specially designed short-time, limited-dose irradiation. These radicals act only on the surface of algal cells, moderately reducing their surface charge and partially modifying extracellular organic matter. This allows for efficient removal of algae in subsequent coagulation and sedimentation, while preventing the release of algal toxins, odor substances, and disinfection byproduct precursors caused by large-scale algal cell rupture. This significantly improves the chemical and biological safety of drinking water during periods of high algae growth.

[0041] The present invention will be described in detail below through examples, but the scope of protection of the present invention is not limited thereto. In the following examples, the drugs and pharmaceuticals are all conventional commercially available products.

[0042] • Raw water preparation: Take raw water containing algae and measure the initial water quality parameters: algal cell concentration (OD680) is 0.30, turbidity is 28.5 NTU, and ultraviolet absorbance (UV254) is 0.185 cm⁻¹. -1 The total organic carbon (TOC) was 8.2 mg / L. The algal raw water was divided into 13 equal portions and treated using the methods of Examples 1-4 and Comparative Examples 1-7, respectively.

[0043] Example 1 This embodiment employs a sealed, light-shielding reactor, inside which is equipped a low-pressure ultraviolet lamp with a main wavelength of 254nm (illuminance of 120μW / cm²). 2 Before the experiment, preheat the UV lamp for 30 minutes to ensure stable light source power. The specific steps are as follows: (1) Addition of reagents: Add sodium percarbonate as an oxidant to the algae-containing raw water to be treated at the location of the water intake well. The concentration of the addition is 0.83 mmol / L. Stir thoroughly to make the reagent and water evenly mixed.

[0044] (2) Ultraviolet pre-oxidation: The algae-containing raw water containing oxidant from step (1) is introduced into the light-shielding reactor. By adjusting the inlet and outlet water flow rates of the reactor, the ultraviolet irradiation time of the water body is controlled to be 5 minutes. The ultraviolet irradiation dose is monitored throughout the process to maintain it at 36 mJ / cm. 2 .

[0045] (3) Coagulation and sedimentation: Add polyaluminum chloride (PAC) to the water body after UV pre-oxidation in step (2) at a dosage of 55 mg / L; complete flocculation according to the conventional process of water plant, let it stand for 30 min to settle, and after sedimentation, take the supernatant to measure relevant indicators.

[0046] Example 2 The implementation was carried out in accordance with Example 1, except that step (2) was modified to "control the ultraviolet irradiation time of the water body to 5 minutes, monitor the ultraviolet irradiation dose throughout the process, and maintain it at 36 mJ / cm²". 2 Replace "Control the ultraviolet irradiation time of the water body to 10 minutes, monitor the ultraviolet irradiation dose throughout the process, and maintain it at 72 mJ / cm²" with " 2 "Under the same conditions, after the precipitation is complete, take the supernatant and measure the relevant indicators."

[0047] Example 3 The process was carried out in accordance with Example 1, except that "adding sodium percarbonate as an oxidant" in step (1) was replaced with "adding hydrogen peroxide as an oxidant". Other conditions remained unchanged. After precipitation, the supernatant was taken to measure relevant indicators.

[0048] Example 4 The procedure was carried out in accordance with Example 1, except that in step (1), "sodium percarbonate was added as an oxidant to the algae-containing raw water to be treated at the location of the water intake well, with a concentration of 0.83 mmol / L" was replaced with "sodium percarbonate was added as an oxidant to the algae-containing raw water to be treated at the location of the water intake well, with a concentration of 1.66 mmol / L". Other conditions remained unchanged. After the sedimentation was completed, the supernatant was taken to measure the relevant indicators.

[0049] Comparative Example 1 Using the same batch of algae-containing raw water from Example 1, without adding any oxidant or undergoing ultraviolet light treatment, polyaluminum chloride (PAC) was added to the water at a dosage of 55 mg / L; flocculation was completed according to the conventional process of the water plant, and the mixture was allowed to stand for 30 minutes to settle. After the sedimentation was completed, the supernatant was taken to measure relevant indicators.

[0050] Comparative Example 2 The algae-containing raw water from the same water source as in Example 1 was treated using a traditional prechlorination-enhanced coagulation method. The chlorination dosage was 2 mg / L, and the coagulant dosage, stirring speed, and stirring time were the same as in Example 1. After sedimentation, the supernatant was taken to measure relevant indicators.

[0051] Comparative Example 3 The implementation was carried out in accordance with Example 1, except that step (2) was modified to "control the ultraviolet irradiation time of the water body to 5 minutes, monitor the ultraviolet irradiation dose throughout the process, and maintain it at 36 mJ / cm²". 2 Replace "Control the ultraviolet irradiation time of the water body to 60 minutes, monitor the ultraviolet irradiation dose throughout the process, and maintain it at 144 mJ / cm²" with " 2 "Under the same conditions, after the precipitation is complete, take the supernatant and measure the relevant indicators."

[0052] Comparative Example 4 The implementation was carried out in accordance with Example 1, except that step (2) was modified to "control the ultraviolet irradiation time of the water body to 5 minutes, monitor the ultraviolet irradiation dose throughout the process, and maintain it at 36 mJ / cm²". 2 Replace "Control the ultraviolet irradiation time of the water body to 2 minutes, and monitor the ultraviolet irradiation dose throughout the process to maintain it at 14.4 mJ / cm²" with " 2 "Under the same conditions, after the precipitation is complete, take the supernatant and measure the relevant indicators."

[0053] Comparative Example 5 The implementation was carried out in accordance with Example 1, except that step (2) was modified to "control the ultraviolet irradiation time of the water body to 5 minutes, monitor the ultraviolet irradiation dose throughout the process, and maintain it at 36 mJ / cm²". 2 Replace "Control the ultraviolet irradiation time of the water body to 40 minutes, and monitor the ultraviolet irradiation dose throughout the process to maintain it at 288 mJ / cm²" with " 2 "Under the same conditions, after the precipitation is complete, take the supernatant and measure the relevant indicators."

[0054] Comparative Example 6 This comparative example uses a closed, light-shielded reactor, inside which is equipped a low-pressure ultraviolet lamp with a main wavelength of 254nm (illuminance of 120μW / cm²). 2 Before the experiment, preheat the UV lamp for 30 minutes to ensure stable light source power. The specific steps are as follows: (1) Ultraviolet irradiation: The algae-containing raw water to be treated was introduced into the light-shielding reactor. The ultraviolet irradiation time of the water was controlled to be 5 minutes by adjusting the inlet and outlet flow rates of the reactor. The ultraviolet irradiation dose was monitored throughout the process and maintained at 36 mJ / cm. 2 .

[0055] (2) Coagulation and sedimentation: Polyaluminum chloride (PAC) was added to the water after ultraviolet irradiation in step (1) at a dosage of 55 mg / L; flocculation was completed according to the conventional process of the water plant, and the water was allowed to settle for 30 min. After sedimentation, the supernatant was taken to measure relevant indicators.

[0056] Comparative Example 7 (1) Addition of reagents: Add sodium percarbonate as an oxidant to the algae-containing raw water to be treated at the location of the water intake well. The concentration of the addition is 0.83 mmol / L. Stir thoroughly to make the reagent and water evenly mixed.

[0057] (2) Coagulation and sedimentation: The algae-containing raw water containing oxidant in step (1) is passed into the light-shielding reactor. The water body is controlled to stay in the reactor for 5 minutes by adjusting the inlet and outlet water flow rates. Polyaluminum chloride (PAC) is added to the water body at a dosage of 55 mg / L. Flocculation is completed according to the conventional process of the water plant. After settling for 30 minutes, the supernatant is taken to measure relevant indicators.

[0058] Detection Example 1 The algae-containing raw water treated in Examples 1-4 and Comparative Examples 1-7 was tested for relevant indicators. The specific test indicators and methods are as follows: • Algal cell concentration (OD680, absorbance at 680 nm): Using ultrapure water / blank raw water as a reference, measure the absorbance (OD680) of the water sample at a wavelength of 680 nm. If the absorbance is >1.0, measure after serial dilution with blank water, and multiply the result by the dilution factor. An OD680-microscopic algal cell counting standard curve can be established in advance to convert the absorbance into algal cell concentration (cells / L).

[0059] Turbidity was tested in accordance with GB / T5750.4-2023 "Standard Examination Methods for Drinking Water - Part 4: Sensory Characteristics and Physical Indicators".

[0060] • Ultraviolet absorbance (UV254): The water sample was filtered through a 0.45 μm filter membrane, and the absorbance was measured at a wavelength of 254 nm using ultrapure water as a blank reference.

[0061] • Total organic carbon (TOC) was tested in accordance with GB / T5750.7-2023 "Standard Examination Methods for Drinking Water - Part 7: Comprehensive Index of Organic Matter".

[0062] • Trihalomethane formation potential (THMFP) was determined according to the detection method in "The role of nitrobenzene on the yield of trihalomethane formation potential in aqueous solutions with Microcystisaeruginosa" Water Research, 2011, 45(19), 6489-6495.

[0063] • Algal cell removal rate = (C0-C1) / C0×100%, where C0 is the original algal cell concentration in the water, in cells / L, and C1 is the algal cell concentration in the treated water, in the same unit as C0.

[0064] The results are shown in Table 1.

[0065] Table 1 As shown in Table 1, compared to Comparative Example 1, the method of the present invention can significantly improve algae removal efficiency. There is no substantial difference in overall algae removal efficiency and post-settling water quality between Examples 1 and 3, indicating that percarbonate and hydrogen peroxide are both suitable for the method of the present invention. Compared to Examples 1-2 and Example 4, moderately increasing the irradiation dose and oxidant dosage can further improve the coagulation and algae removal effect, but it also leads to an increase in algae-related organic matter indicators (TOC and THMFP) in the post-settling water. However, when the irradiation dose exceeds the range defined by the present invention, the oxidation effect in Comparative Example 4 is not significant due to insufficient irradiation dose, resulting in overall poor coagulation and algae removal. The effect was not good; in Comparative Example 5, the excessive irradiation dose caused a sharp increase in the algal organic matter-related indicators (TOC and THMFP) in the sedimentation water; although Comparative Example 3 just exceeded the irradiation dose limit of the present invention, the algal organic matter-related indicators (TOC and THMFP) in the sedimentation water still increased significantly, proving that precise control of the ultraviolet irradiation dose is the key step to achieve moderate oxidation-enhanced coagulation and algae removal; Comparative Examples 6 and 7 show that neither UV nor peroxide alone can achieve the ideal coagulation and algae removal effect; compared with Comparative Example 2, the present invention can significantly reduce the concentration of algal organic matter in the sedimentation water and improve the water supply quality.

[0066] Detection Example 2 The changes in the proportion of viable algal cells, TOC, and zeta potential in the water of Examples 1, 2, 4, Comparative Examples 1, and Comparative Examples 3-5 after treatment with different UV irradiation doses (without coagulation and sedimentation treatment) were detected, and the results are as follows: Figure 1-3 As shown.

[0067] Figure 1This indicates that ultraviolet radiation dose has a significant impact on algal cell integrity. When the irradiation dose exceeds the upper limit of 140 mJ / cm² specified in this invention, the effect is even greater. 2 The proportion of viable cells subsequently decreased sharply, and in severe cases, less than 1% of the algal cells were able to maintain their intact morphology (Comparative Examples 3 and 5); while when the irradiation dose was within the range defined by this invention (20~140 mJ / cm²), the proportion of viable cells decreased sharply. 2 When the concentration is below the lower limit, the vast majority of cells can be preserved intact (Examples 1, 2, 4, Comparative Examples 1 and 4). Figure 2 This indicates that excessive exposure to ultraviolet radiation leads to a rapid increase in TOC, especially when the radiation dose reaches 288 mJ / cm². 2 At that time (Comparative Example 5), the TOC increase rate was 148%, which seriously affected the safety of the treated water quality. Figure 3 This indicates that appropriate ultraviolet radiation catalytic oxidation of algae-containing water can effectively increase the zeta potential of the solution. When the irradiation dose is within the range defined in this invention (20~140 mJ / cm²), 2 When the irradiation dose is above the upper limit (Examples 1, 2, 4, Comparative Examples 3 and 5), the zeta potential in algae-containing water can increase significantly, which is beneficial for coagulation and algae removal. When the irradiation dose is insufficient (Comparative Examples 1 and 4), the zeta potential change is not significant. Taking into account both the final effluent quality and algae removal efficiency, this invention proposes to use the TOC change rate and the zeta potential of the algae-containing water after oxidation as a standard for judging appropriate oxidation, so as to achieve the goal of enhancing coagulation and avoiding excessive oxidation from affecting the final water supply quality.

[0068] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0069] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0070] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for moderate pre-oxidation treatment of algae-containing raw water using ultraviolet-activated oxidants, characterized in that, The method includes: 1) Add an oxidant to the algae-containing raw water; 2) Irradiate the algae-containing raw water containing oxidant in step 1) with ultraviolet light; 3) Coagulation and sedimentation treatment of water bodies after ultraviolet irradiation; In step 2), the optimal ultraviolet irradiation dose is determined by one or both of the following methods: a) Detect the increase in dissolved organic matter in water after ultraviolet irradiation. When the total organic carbon or permanganate index increases by 0-30% compared to before ultraviolet irradiation, the corresponding irradiation dose is the optimal dose. b) Detect the zeta potential of the water body after ultraviolet irradiation. When the zeta potential is stable at -30~-5mV, the corresponding irradiation dose is the optimal dose.

2. The method according to claim 1, characterized in that, In step 1), the oxidant is hydrogen peroxide and / or sodium percarbonate.

3. The method according to claim 1 or 2, characterized in that, In step 1), the amount of oxidant added is 0.2~4.0 mmol / L.

4. The method according to claim 1, characterized in that, In step 1), the oxidant is added at the raw water inlet or the intake well.

5. The method according to claim 1, characterized in that, In step 2), the ultraviolet light is provided by an ultraviolet lamp with a main emission wavelength of 254nm.

6. The method according to claim 1, characterized in that, In step 2), the ultraviolet lamp is placed in a light-shielding reactor or water treatment channel, and the algae-containing raw water containing oxidant is irradiated with ultraviolet light in a continuous flow or static setting manner.

7. The method according to claim 1, characterized in that, In step 2), the ultraviolet radiation dose is 20~140 mJ / cm². 2 .

8. The method according to claim 1, characterized in that, In step 3), the coagulant used in the coagulation treatment is selected from one or more of polyaluminum chloride, aluminum sulfate, aluminum chloride, polyferric sulfate, ferrous sulfate, and ferric chloride; Preferably, the dosage of the coagulant is 10~80 mg / L, and more preferably 50~60 mg / L.

9. The method according to claim 1, characterized in that, In step 3), the coagulation and sedimentation time is 40~140 min.

10. The method according to claim 1, characterized in that, The pre-oxidation treatment method further includes filtration and disinfection after coagulation and sedimentation.

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