Pretreatment method for high-algae raw water, composite water purifying agent for high-algae raw water, and treatment method for high-algae raw water

Abstract

The present application relates to the technical field of water treatment, and particularly relates to a pretreatment method of high-algae raw water, a composite water purifying agent for high-algae raw water and a treatment method of high-algae raw water. The pretreatment method comprises the following steps: adding a water purifying agent A into high-algae raw water to be treated, wherein the water purifying agent A is a biomass charcoal material loaded with potassium permanganate; after a predetermined time interval, continuously adding a water purifying agent B into the high-algae raw water to complete the pretreatment, wherein the water purifying agent B comprises a water-soluble divalent iron salt, a water-soluble trivalent iron salt and chitosan. The method realizes mild pre-oxidation through the slow-release effect of the loaded oxidant, inactivates the algae cells but avoids rupturing; and combines the adsorption and the agglomeration and wrapping effect of the in-situ generated iron-manganese hydrate oxide to form stable composite particles. The process can efficiently remove the algae cells and algae-derived odor substances, significantly reduces the disinfection by-product generation potential, and the formed composite particles can strengthen the subsequent conventional coagulation, thereby saving the drug consumption.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a pretreatment method for high-algae raw water, a composite water purification agent for high-algae raw water, and a treatment method for high-algae raw water. Background Technology

[0002] Many lake and reservoir water sources in my country are susceptible to seasonal algal blooms. When high-algae raw water enters water treatment plants, it significantly increases the difficulty of treatment and brings a series of complex pollution problems, such as increased production of algal cells, algal-derived odor substances, algal toxins, and disinfection byproducts, seriously threatening water supply security.

[0003] To enhance algae removal, current technologies generally employ a process combining pre-chlorination oxidation with powdered activated carbon adsorption. Pre-chlorination oxidation effectively inactivates algal cells and alters their surface properties, facilitating subsequent coagulation removal. However, for high-algae raw water, achieving sufficient algae removal often requires increasing the dosage of oxidant, which can easily lead to algal cell wall rupture, releasing large amounts of intracellular metabolites into the water. Studies show that the concentration of algal toxins and odor-causing substances inside algal cells is much higher than outside. Therefore, often in order to meet the demand for algae removal rates, the risk to water biosafety is increased, and more disinfection byproduct precursors are provided. Simultaneously, algal odor-causing substances are difficult to remove effectively using conventional processes.

[0004] Therefore, how to effectively control algal cell rupture and the release of intracellular pollutants while ensuring algae removal, and simultaneously remove algal odor substances, has become a pressing technical challenge in the field of high-algae water treatment. Summary of the Invention

[0005] To solve or partially solve the problems existing in related technologies, the present invention provides a pretreatment method for high-algae raw water, a composite water purification agent for high-algae raw water, and a treatment method for high-algae raw water.

[0006] This invention provides a pretreatment method for high-algae raw water, which includes the following steps:

[0007] Step a) Add water purification agent A to the raw water with high algae content to be treated. Water purification agent A is a biochar material loaded with potassium permanganate. Step b) After a predetermined interval, water purification agent B is added to the high-algae raw water to carry out the reaction and complete the pretreatment; the water purification agent B contains water-soluble ferrous salts, ferric salts and chitosan.

[0008] Furthermore, the water purification agent A is prepared according to the following method: Coconut shell biomass is pyrolyzed at high temperature under an inert atmosphere to obtain coconut shell biochar. The coconut shell biochar was impregnated in a potassium permanganate solution with a concentration of 2-5 wt%, and then dried to obtain water purification agent A.

[0009] Furthermore, the high-temperature pyrolysis temperature is 700-900℃; after the high-temperature pyrolysis, the coconut shell biochar also includes the following post-treatment steps: soaking the coconut shell biochar in dilute nitric acid with a concentration of 10-20wt%, and then washing it until neutral.

[0010] Furthermore, the water purification agent B comprises, by weight, 65-85 parts ferrous sulfate, 10-30 parts ferric chloride, and 5-10 parts chitosan.

[0011] Furthermore, steps a) and b) are performed at different locations in the pipeline for conveying the high-algae raw water; and / or, steps a) and b) are performed in a reaction tank or a contact tank.

[0012] Furthermore, the scheduled time is from 5 minutes to 360 minutes.

[0013] Furthermore, the dosage of water purification agent A is such that its concentration in the raw water is between 10 mg / L and 30 mg / L; the dosage of water purification agent B is such that its concentration in the raw water is between 10 mg / L and 15 mg / L.

[0014] Furthermore, the algal cell density of the high-algae raw water is 1×10⁻⁶. 7 Units / L-1×10 9 per L.

[0015] The present invention also provides a composite water purifier for high-algae raw water, which is composed of water purifier A and water purifier B; wherein water purifier A is a biochar material loaded with potassium permanganate; and water purifier B contains water-soluble ferrous salts, ferric salts and chitosan.

[0016] This invention also provides a method for treating high-algae raw water, comprising: Pre-treat the high-algae raw water to be treated according to any one of the methods described above; The pretreated effluent is then transported to the subsequent water treatment unit for coagulation and sedimentation.

[0017] The pretreatment method for high-algae raw water provided by this invention can include the following beneficial effects: 1) This pretreatment method achieves slow and controllable release of oxidants by loading potassium permanganate onto a biochar carrier. This process only moderately modifies the surface of algal cells to deactivate them, effectively avoiding massive cell rupture caused by excessive oxidation, thereby controlling the release of intracellular organic matter and reducing the potential for subsequent disinfection byproducts and the risk to water quality biosafety.

[0018] 2) While biochar adsorbs algal cells and odor substances, the potassium permanganate it carries enriches and degrades target pollutants at the micro-interface. The subsequently added composite water purification agent B, through the synergistic effect of its components, generates in-situ iron-manganese hydrated oxide-biochar-algal cell composite particles, effectively encapsulating and stabilizing inactive algal cells. These particles effectively encapsulate and fix algal cells in an inactive but intact state, and their good mechanical strength can withstand hydraulic shear during transport, preventing the algal cells from redispersing.

[0019] 3) The pre-treated composite micro-nano particles have high surface activity and moderate density. After entering the coagulation process of the water plant, they can serve as excellent flocculant nuclei, significantly enhancing the formation and growth of flocs. This means that the dosage of subsequent coagulants such as aluminum salts does not need to be increased due to high algae content in the raw water, thus achieving efficient solid-liquid separation and reducing operating costs and sludge production.

[0020] 4) The adsorption and enrichment of odor substances by biochar, combined with the localized and efficient oxidation of potassium permanganate in the micropores, overcomes the problems of limited adsorption capacity or low oxidation efficiency of individual adsorption. The removal rate of typical algal odor substances can reach more than 80%.

[0021] 5) By adjusting the dosing interval between water purification agents A and B, a safe time window is established for the oxidation effect of agent A. This design aims to ensure that the oxidation reaction is limited to the necessary level of sufficient inactivation and surface modification of algal cells, thereby avoiding over-oxidation that may be caused by excessive reaction time. This effectively controls algal cell rupture and the resulting release of intracellular organic matter, reduces the total amount of precursors reacting with subsequent disinfectants, and thus significantly reduces the formation potential of disinfection byproducts such as chloroform in the effluent, improving the chemical safety of drinking water.

[0022] 6) This pretreatment process can be completed directly in the raw water transmission pipeline through point addition, without the need to build new large-scale pretreatment structures. It makes full use of existing facilities, saves investment, and is easy to operate. It is particularly suitable for water plants to deal with the emergency treatment and routine operation of raw water with seasonal high algae, and has good engineering application prospects.

[0023] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the pipeline addition implementation method in an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the reaction tank addition implementation method in this embodiment of the invention.

[0026] Figure 3This is a scanning electron microscope image of the composite particles that captured algal cells after pretreatment with water purification agents A and B in Example 2. Detailed Implementation

[0027] 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.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms “a,” “the,” and “the” used in this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0029] It should be understood that although the terms "first," "second," "third," etc., may be used in this invention to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this invention, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0030] The first embodiment of the present invention provides a pretreatment method for high-algae raw water, which includes the following steps: Step a) Add water purification agent A to the raw water with high algae content to be treated. Water purification agent A is a biochar material loaded with potassium permanganate. Step b) After a predetermined interval, water purification agent B is added to the high-algae raw water to carry out the reaction and complete the pretreatment; the water purification agent B contains water-soluble ferrous salts, ferric salts and chitosan.

[0031] Addressing the challenges of existing high-algae raw water treatment methods, where increasing the dosage of oxidant is often necessary to ensure effective algae removal, but this can lead to algal cell rupture and the release of large amounts of intracellular pollutants (such as algal odor substances and algal toxins), this application presents a synergistic purification system of moderate oxidation-adsorption enrichment-in-situ coagulation. The core of this system involves loading an oxidant (potassium permanganate) onto a biochar carrier to achieve slow and controllable release, only surface-modifying and deactivating algal cells rather than completely destroying them. Subsequently, a composite coagulant (Agent B) is added at precisely controlled times, utilizing the synergistic effect between its components to generate stable iron-manganese hydrated oxide-biochar-algal cell composite micro / nano particles in situ with the pre-oxidized algal cells and carrier. These particles not only effectively encapsulate algal cells to prevent rupture but also serve as high-quality flocculant nuclei in subsequent conventional coagulation processes in water plants, achieving efficient and safe removal of algal cells and simultaneously degrading algal odor substances adsorbed and enriched by the biochar.

[0032] Step a) above is used to achieve mild pre-oxidation and adsorption enrichment of high-algae raw water. The added water purification agent A—biochar loaded with potassium permanganate—serves a dual function: Firstly, there is the controlled, slow-release oxidation: the release of potassium permanganate loaded within the biochar pores is limited by the diffusion resistance of the carrier, resulting in a slow and persistent release. This slow-release characteristic ensures a high concentration of the oxidant at the local micro-interface (biochar surface and pores), while providing a gentle boost to the overall oxidation potential of the water body. Its oxidation primarily targets the adsorbed and enriched algal cell surface, gently altering the composition of proteins and polysaccharides on the algal cell surface, reducing the absolute value of the zeta potential and increasing hydrophobicity, thereby achieving inactivation and surface modification, while minimizing the risk of cell wall penetration and rupture. Simultaneously, the prolonged contact time between odorous substances enriched within the pores and potassium permanganate leads to effective oxidative degradation.

[0033] Secondly, there is the adsorption and enrichment effect: due to its huge specific surface area and abundant pore structure, biochar rapidly adsorbs algal cells and dissolved algal odor substances (such as MIB and geosmin) in the water, enriching them on the char surface and within the pores. In addition, the loading of potassium permanganate changes the surface polarity of biochar. This modification brings additional operational advantages: on the one hand, the change in polarity helps to reduce the non-selective adsorption of common large molecular natural organic matter (NOM) in water on the char surface and the clogging in micropores, improving the material's resistance to interference in complex water quality; on the other hand, for large molecular organic matter that has entered the pores, the loaded potassium permanganate can play an oxidizing role, decomposing it into smaller molecules, thereby freeing up or giving up more adsorption sites, ensuring the material's continuous adsorption capacity and long-term performance for target algal odor substances.

[0034] Step b) above is used to achieve precise control of the pre-oxidation process, in-situ coagulation and encapsulation, and system stability. Furthermore, the timing design—adding water purification agent B after a predetermined interval of agent A's action—plays a crucial role. Specifically: Termination of Oxidation and Lock-in: The addition of Agent B, especially the rapid reaction between ferrous iron and potassium permanganate, effectively consumes the residual oxidant in the water, actively terminating the continuous oxidation process of Agent A. This ensures that the oxidation reaction is controlled within a moderate range, precisely avoiding over-oxidation that may result from excessive reaction time or oxidant accumulation, thereby significantly reducing the risk of algal cell wall damage and excessive release of intracellular organic matter.

[0035] Formation of coagulation nuclei: The ferrous salts (such as ferrous sulfate) in agent B undergo a redox reaction with the potassium permanganate released from agent A, rapidly generating in situ hydrated iron-manganese oxides (Fe-O-Mn) with abundant surface hydroxyl groups. This substance serves as the nucleus for subsequent coagulation.

[0036] Enhanced charge neutralization and coagulation: The ferric salts (such as ferric chloride) in Agent B undergo immediate hydrolysis, producing various hydroxyl complexes and releasing hydrogen ions, moderately lowering the local pH value of the algal cell micro-interface. This process further reduces the negative charge on the algal cell surface (decreases the absolute value of the zeta potential) and strongly promotes coagulation through the compression of the electric double layer.

[0037] Bridging and stabilization: Chitosan in Agent B, as a natural high-molecular polymer, bridges the already formed micro-nano particles, forming a larger and denser floc network, enhancing its mechanical strength to resist hydraulic shear in the pipeline, ensuring the stability of the encapsulation state, and preventing the micro-nano particles from depolymerizing again under strong hydraulic conditions during water transportation.

[0038] After two pretreatment steps (a) and (b), the algal cells are fixed in stable composite particles composed of biochar, iron and manganese oxides and chitosan, completing the safe transformation from live dispersed algae to inorganic-organic composite flocs, laying the foundation for efficient removal by subsequent conventional processes.

[0039] In step a), water purification agent A is preferably prepared according to the following method: Coconut shell biomass is pyrolyzed at high temperature under an inert atmosphere to obtain coconut shell biochar. The coconut shell biochar was impregnated in a potassium permanganate solution with a concentration of 2-5 wt%, and then dried to obtain water purification agent A.

[0040] In this preferred embodiment, water purifier A uses coconut shell biomass as the carbon-loaded raw material. Coconut shell biomass has a dense structure and high hardness. The biochar obtained after pyrolysis has a well-developed microporous structure and high mechanical strength, providing stable and abundant loading sites for potassium permanganate. Simultaneously, it possesses excellent adsorption properties. More importantly, from the perspective of drinking water treatment safety, coconut shell, as a natural plant-based material, does not contain any toxic or harmful components. After high-temperature pyrolysis and carbonization, volatile organic compounds are fully removed, resulting in biochar with stable chemical properties and good biocompatibility. It is not prone to leaching harmful substances during long-term contact with water, ensuring the basic safety of the water purification material. Its stable carbon skeleton structure also helps to firmly load potassium permanganate, reducing uncontrolled dissolution of manganese ions during subsequent treatment processes, thereby ensuring the safety of the effluent water quality.

[0041] Before pyrolysis, coconut shell biomass preferably undergoes a step of pulverizing the coconut shells into powder. The advantages of pulverization include increasing the specific surface area of ​​the raw material, making the pyrolysis process more uniform and thorough, facilitating the formation of biochar with a more developed pore structure, and improving the penetration and loading efficiency of potassium permanganate solution in subsequent impregnation steps. To remove dust, soluble impurities, and some pigments adhering to the surface of the coconut shells, ensuring the purity of the raw material, and preventing impurities from adversely affecting the pyrolysis process or clogging the subsequently formed pores, a step of washing and drying the coconut shell biomass is also preferred before pulverization. Specifically, the preferred method is to wash and dry the coconut shell biomass, then pulverize it to obtain coconut shell powder with a diameter of less than 0.15 mm, before pyrolysis. The inert gas atmosphere for pyrolysis can be nitrogen.

[0042] The preferred pyrolysis temperature is 700-900℃. Compared to the conventional pyrolysis temperature (approximately 300-400℃), the higher pyrolysis temperature used in this embodiment aims to effectively eliminate volatile organic compounds and reducing active sites that may exist on the surface and inside the coconut shell biochar through deep carbonization. This reduces the reduction consumption of the biochar itself by the subsequently loaded oxidant (potassium permanganate), helping to maintain the oxidizing activity and stability of potassium permanganate, laying the foundation for its controllable and mild oxidizing effect in pretreatment. The preferred pyrolysis time is 1-3 hours, with 2 hours being the most preferred. After pyrolysis, the furnace is allowed to cool naturally to room temperature under continuous ventilation protection to obtain coconut shell biochar.

[0043] Furthermore, after high-temperature pyrolysis, the coconut shell biochar undergoes the following post-treatment step: the coconut shell biochar is soaked in a 10-20 wt% dilute nitric acid solution, and then washed until neutral. The purpose of this step is to utilize the strong oxidizing properties of dilute nitric acid to further oxidize and remove any trace amounts of reducing substances that may remain on the surface of the coconut shell biochar after high-temperature pyrolysis, or to inertize its surface, thus achieving surface passivation. This process reduces the ineffective reduction of potassium permanganate by the biochar carrier, ensuring that the loaded potassium permanganate has the expected and stable oxidizing capacity, thereby guaranteeing the controllability and reproducibility of the pre-oxidation stage.

[0044] The water purification agent B added in step b) includes: ferrous salt, ferric salt, and chitosan. The components work synergistically to achieve algal cell aggregation, encapsulation, and system stability: the main function of the ferrous salt is to react with potassium permanganate from water purification agent A in a redox reaction, rapidly generating hydrated iron-manganese oxide Fe-O-Mn with a high specific surface area and abundant surface hydroxyl groups. This substance serves as the core adsorption site, exhibiting strong specific adsorption and complexation capabilities for algal cells whose surface properties have changed after pre-oxidation in step a). The role of the ferric salt lies in its rapid hydrolysis characteristics; the various hydroxyl polymers and hydrogen ions generated during hydrolysis can moderately regulate the pH of the algal cell micro-interface region. The H value further reduces the absolute value of the zeta potential on the surface of algal cells and strengthens the charge neutralization and aggregation process between Fe-O-Mn and algal cells and biochar through the compression of the electric double layer. Chitosan, as a natural cationic polymer, mainly functions by adsorbing and bridging the preliminarily aggregated algal cells-biochar-Fe-O-Mn micro-nano particles through its long molecular chains, promoting the formation of larger and denser floc structures, thereby significantly enhancing the mechanical strength and shear resistance of the composite particles, ensuring their structural stability during transportation, and preventing the redispersibility of algal cells.

[0045] The water purification agent B preferably comprises, by weight: 65-85 parts ferrous sulfate, 10-30 parts ferric chloride, and 5-10 parts chitosan. More preferably, it comprises: 70 parts ferrous sulfate, 20 parts ferric chloride, and 10 parts chitosan.

[0046] The timing of adding water purification agent B in step b) (i.e., the interval between step a) is a crucial operational parameter. It is not a simple matter of sequential addition, but rather a control of the oxidation reaction time window to limit the extent of the first stage (oxidative modification) before initiating the second stage (coagulation and encapsulation), achieving a balance between efficient inactivation of algal cells and structural preservation. The predetermined interval is preferably 5 to 360 minutes, more preferably 10 to 360 minutes. The inventors of this application have discovered that controlling the oxidation time within 360 minutes keeps the concentration of dissolved organic matter released by oxidation at a low level (e.g., less than 0.05 mg / L); if the oxidation time is extended further, the concentration of released dissolved organic matter tends to increase. Therefore, 360 minutes satisfies both the algae removal effect and ensures water quality safety.

[0047] Regarding the dosage of water purifier A and water purifier B at their respective stages, this embodiment preferably specifies the following: the dosage of water purifier A is such that its concentration in the raw water is 10-30 mg / L; the dosage of water purifier B is such that its concentration in the raw water is 10-15 mg / L. At this concentration, water purifier A can provide sufficient supported potassium permanganate and adsorption sites to ensure effective pre-oxidation and adsorption enrichment. At this concentration, water purifier B can provide sufficient iron salt to fully consume residual oxidant and form sufficient iron-manganese hydrated oxides and hydrolysis products, and can also provide an appropriate amount of chitosan to achieve effective bridging. Thus, while ensuring the pretreatment effect, it avoids potential problems such as increased cost, increased effluent color, or increased metal ion concentration caused by excessive dosage of reagents.

[0048] Steps a) and b) above can be performed at different points in the pipeline transporting the high-algae raw water, or in the reaction tank or contact tank. For the former, please refer to [reference needed]. Figure 1 , Figure 1 This is a schematic diagram of the pipeline dosing implementation method. The diagram shows the raw water delivery pipeline, and the dosing points for water purification agent A and water purification agent B are marked sequentially along the water flow direction. The pipeline length (L) between the two points and the water flow velocity (v) together determine the hydraulic residence time (HRT) between steps a) and b), i.e., the predetermined interval time. For the latter, please refer to... Figure 2 , Figure 2This diagram illustrates the implementation method of adding water purification agent A to a reaction tank containing raw water. Step a) is completed by controlling the stirring or settling time. Then, water purification agent B is added to the same reaction tank for step b). This method achieves the predetermined interval time by controlling the stirring or settling time. This application preferably adopts the former approach, which has the following advantages: it can fully utilize existing raw water transmission pipelines as the reaction site, eliminating the need for constructing additional large reaction structures, thus saving infrastructure investment and land area; the reaction time can be easily and flexibly controlled by adjusting the pipeline flow rate and the distance to the addition point, making it easy to integrate with existing water plant systems and achieve rapid emergency response and routine operation.

[0049] The pretreatment method for high-algae raw water provided in this embodiment enables safe and efficient pretreatment of algal cells in high-algae raw water. Its core lies in the gentle oxidation process, which inactivates algal cells and alters their surface properties without causing extensive cell rupture. Subsequently, these cells are effectively encapsulated and aggregated into stable particles by in-situ generated composite flocs. This pretreatment primarily targets the algal cells themselves and the extracellular and some intracellular odor substances they release, creating favorable conditions for subsequent conventional treatment processes. This method is suitable for algal cell densities of 1×10⁻⁶ cells / year. 7 Raw water with an algal cell density of 1×10⁶ cells / L is particularly suitable for algal cell densities of 1×10⁶ cells / L. 7 Units / L-1×10 9 Raw water per liter.

[0050] The second embodiment of the present invention provides a composite water purification agent for high-algae raw water, which is composed of water purification agent A and water purification agent B; water purification agent A is a biochar material loaded with potassium permanganate; water purification agent B contains water-soluble divalent iron salt, trivalent iron salt and chitosan.

[0051] The function of water purifier A is to provide a material with both adsorption and controlled slow-release oxidation capabilities, used for the initial adsorption of algal cells and odor substances, and for the gentle surface oxidative modification of algal cells. The function of water purifier B is to provide a composite agent with charge neutralization, coagulation and bridging functions, used to consume residual oxidants, generate coagulation nuclei, reduce the surface charge of algal cells, and coagulate and encapsulate the modified algal cells with water purifier A and other substances into stable composite particles.

[0052] The second embodiment of the present invention provides a method for treating high-algae raw water, comprising: The high-algae raw water to be treated is pretreated according to the method of the first embodiment described above; The pretreated effluent is then transported to subsequent water treatment units for coagulation and sedimentation. For example, the pretreated effluent can be transported to conventional treatment units such as mixing, flocculation, and sedimentation tanks in a waterworks, where coagulants such as aluminum or iron salts are added. The system is then operated according to the standard stirring intensity, flocculation time, and sedimentation load used when treating low-algae raw water, thus achieving efficient removal of algae cells. After pretreatment, the water contains a large number of micro- and nano-particles that can serve as excellent flocculant nuclei, thereby enhancing the removal effect of conventional coagulation and sedimentation processes on algae cells and reducing the process load.

[0053] The pretreatment method for high-algae raw water provided in this embodiment of the invention has the following advantages: 1) This pretreatment method achieves slow and controllable release of oxidants by loading potassium permanganate onto a biochar carrier. This process only moderately modifies the surface of algal cells to deactivate them, effectively avoiding massive cell rupture caused by excessive oxidation, thereby controlling the release of intracellular organic matter and reducing the potential for subsequent disinfection byproducts and the risk to water quality biosafety.

[0054] 2) While biochar adsorbs algal cells and odor substances, the potassium permanganate it carries enriches and degrades target pollutants at the micro-interface. The subsequently added composite water purification agent B, through the synergistic effect of its components, generates in-situ iron-manganese hydrated oxide-biochar-algal cell composite particles, effectively encapsulating and stabilizing inactive algal cells. These particles effectively encapsulate and fix algal cells in an inactive but intact state, and their good mechanical strength can withstand hydraulic shear during transport, preventing the algal cells from redispersing.

[0055] 3) The pre-treated composite micro-nano particles have high surface activity and moderate density. After entering the coagulation process of the water plant, they can serve as excellent flocculant nuclei, significantly enhancing the formation and growth of flocs. This means that the dosage of subsequent coagulants such as aluminum salts does not need to be increased due to high algae content in the raw water, thus achieving efficient solid-liquid separation and reducing operating costs and sludge production.

[0056] 4) The adsorption and enrichment of odor substances by biochar, combined with the localized and efficient oxidation of potassium permanganate in the micropores, overcomes the problems of limited adsorption capacity or low oxidation efficiency of individual adsorption. The removal rate of typical algal odor substances can reach more than 80%.

[0057] 5) By adjusting the dosing interval between water purification agents A and B, a safe time window is established for the oxidation effect of agent A. This design aims to ensure that the oxidation reaction is limited to the necessary level of sufficient inactivation and surface modification of algal cells, thereby avoiding over-oxidation that may be caused by excessive reaction time. This effectively controls algal cell rupture and the resulting release of intracellular organic matter, reduces the total amount of precursors reacting with subsequent disinfectants, and thus significantly reduces the formation potential of disinfection byproducts such as chloroform in the effluent, improving the chemical safety of drinking water.

[0058] 6) This pretreatment process can be completed directly in the raw water transmission pipeline through point addition, without the need to build new large-scale pretreatment structures. It makes full use of existing facilities, saves investment, and is easy to operate. It is particularly suitable for water plants to deal with the emergency treatment and routine operation of raw water with seasonal high algae, and has good engineering application prospects.

[0059] The technical solution of the present invention will be further described below with reference to specific embodiments: Example 1 - Preparation of Composite Water Purification Agent 1. Preparation of water purification agent A 1) After washing, the coconut shell biomass is dried and then pulverized to obtain coconut shell powder with a diameter of less than 0.15 mm; 2) The coconut shell powder obtained in step 1) is placed in a tube furnace and heated to 800°C under a nitrogen atmosphere for 2 hours for pyrolysis. After pyrolysis, the furnace is allowed to cool naturally to room temperature under continuous ventilation protection to obtain coconut shell biochar. 3) Soak the coconut shell biochar obtained in step 2) in 18wt% dilute nitric acid for 15 hours, then wash with water until neutral; 4) The coconut shell biochar treated in step 3) is immersed in a 3wt% potassium permanganate solution, and then evaporated at 60°C under low temperature and reduced pressure until the water is removed. Heating is stopped immediately to obtain solid powder water purification agent A.

[0060] 2. Preparation of water purification agent B Mix the following parts by weight of raw materials evenly to obtain water purification agent B: 70 parts ferrous sulfate, 20 parts ferric chloride, and 10 parts chitosan.

[0061] For subsequent use, dissolve water purifier B in water to prepare a 10wt% solution. This concentration is based on the total mass of ferrous sulfate, ferric chloride, and chitosan.

[0062] The high-algae raw water in the following examples and comparative examples all came from a certain water source reservoir, and its algae density was measured (via optical density OD at 680 nm). 680The raw water (measured) had an algae content of 12 million cells / L, a pH of 8.02, dissolved organic carbon (DOC) of 3.2 mg / L, methyl isochorol-2 concentration of 25 ng / L, and geosmin concentration of 36 ng / L. 1L of this high-algae raw water was taken as a sample for treatment in each example and comparative example.

[0063] In the following examples, the concentration of a certain material is X, which means that the amount of the material added is equal to its concentration of X in the raw water.

[0064] Example 2 1. Pour the water sample into a beaker, add 20 mg / L of water purification agent A, stir slowly to simulate the raw water transportation process, react for 10 minutes, then add 12 mg / L of water purification agent B, and continue to stir slowly for another 10 minutes.

[0065] The scanning electron microscope image of the raw water after this step is shown below. Figure 3 As shown, Figure 3 Images a and b in the figure are scanning electron microscope (SEM) images of captured algal cells at different scales, produced by... Figure 3 It can be seen that the algal cells are encapsulated in dense composite particles composed of biochar fragments, iron and manganese oxides, and organic polymers. Figure 3 a shows the overall morphology of multiple composite particles. Figure 3 The higher magnification image (b) clearly shows the microstructure of a single algal cell tightly wrapped and fixed by the surrounding inorganic-organic matrix. This result directly confirms that the method of the present invention can effectively capture and stabilize algal cells through in-situ formed composite flocs without rupturing the cells, providing morphological evidence for the efficient removal of algal cells in subsequent coagulation and sedimentation processes.

[0066] 2. Simulate the coagulation and sedimentation process of a waterworks. First, stir rapidly (250 rpm) for 1 minute, then add 15 mg / L aluminum sulfate and stir at medium speed (150 rpm) for 5 minutes, then stir slowly (40 rpm) for 10 minutes and let stand for 30 minutes.

[0067] Example 3 1. Pour the water sample into a beaker, add 10 mg / L of water purification agent A, stir slowly to simulate the raw water transportation process, react for 360 minutes, then add 15 mg / L of water purification agent B, and continue to stir slowly for 10 minutes.

[0068] 2. Same as step 2 in Example 2.

[0069] Comparative Example 1 1. Pour the water sample into a beaker, add NaOCl solution until the chlorine concentration is 0.5 mg / L, and stir rapidly for 5 minutes.

[0070] 2. Add KMnO4 solution to the water sample until its concentration is 30 µM, and stir rapidly (250 rpm) for 5 minutes; then add FeSO4 solution until the Fe(II) concentration is 90 µM, and stir at 200 rpm for 2 minutes and then at 40 rpm for 15 minutes in sequence.

[0071] 3. Same as step 2 in Example 2.

[0072] Comparative Example 2 The only difference between this comparative example and Comparative Example 1 is that in step 1, the amount of NaOCl solution added is increased to a chlorine concentration of 1.0 mg / L. All other steps are the same as those in Comparative Example 1.

[0073] Comparative Example 3 1. Pour the water sample into a beaker, add 20 mg / L of coconut shell biochar and 20 mg / L of potassium permanganate, stir slowly to simulate the raw water transportation process, react for 10 minutes, then add 12 mg / L of water purification agent B, and continue to stir slowly for another 10 minutes.

[0074] 2. Same as step 2 in Example 2.

[0075] Comparative Example 4 1. Pour the water sample into a beaker, add 20 mg / L of water purification agent A, stir slowly to simulate the raw water transportation process, react for 10 minutes, then add 12 mg / L of ferrous sulfate, and continue to stir slowly for another 10 minutes.

[0076] Same as step 2 in Example 2.

[0077] For the water samples treated in Examples 2-3 and Comparative Examples 1-4, the supernatant was taken and its pH, algal density, DOC, methyl isoborneol-2 concentration, geosmin concentration and manganese ion concentration were tested; the test results are listed in Table 1.

[0078] For the water samples treated in Examples 2-3 and Comparative Examples 1-4, the supernatant was taken, filtered through a 0.45 μm filter membrane, and the formation potential of the disinfection byproduct chloroform was tested according to the "Standard Examination Methods for Drinking Water" (GB / T 5750). The specific steps are as follows: Chlorination reaction: Add an appropriate amount of sodium hypochlorite solution to the water sample, adjust the pH to 7.0±0.2 with phosphate buffer, and react at 25℃ in the dark for 24 h. If the free chlorine concentration is still 1.0±0.2 mg / L after the reaction, it indicates that the reaction is complete.

[0079] Reaction termination: After the reaction is complete, immediately add an appropriate amount of sodium thiosulfate solution to quench the residual chlorine.

[0080] Sample determination: Immediately determine the concentration of chloroform using headspace gas chromatography as specified in GB / T 5750.10. This concentration represents the formation potential of the disinfection byproduct chloroform. The test results are listed in Table 2.

[0081] The state of flocs in the water samples treated with Examples 2-3 and Comparative Examples 1-4 was observed and recorded. The test results are listed in Table 2.

[0082] Table 1. Relevant indicators of water samples after treatment in Examples 2-3 and Comparative Examples 1-4

[0083] Table 2. Disinfection byproduct formation potential and floc state of water samples treated in Examples 2-3 and Comparative Examples 1-4

[0084] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A pretreatment method for high-algae raw water, characterized in that, Includes the following steps: Step a) Add water purification agent A to the raw water with high algae content to be treated. Water purification agent A is a biochar material loaded with potassium permanganate. Step b) After a predetermined interval, water purification agent B is added to the high-algae raw water to carry out the reaction and complete the pretreatment; the water purification agent B contains water-soluble ferrous salts, ferric salts and chitosan.

2. The pretreatment method according to claim 1, characterized in that, The water purification agent A is prepared according to the following method: Coconut shell biomass is pyrolyzed at high temperature under an inert atmosphere to obtain coconut shell biochar. The coconut shell biochar was impregnated in a potassium permanganate solution with a concentration of 2-5 wt%, and then dried to obtain water purification agent A.

3. The pretreatment method according to claim 2, characterized in that, The temperature of the high-temperature pyrolysis is 700-900℃; The coconut shell biochar, after high-temperature pyrolysis, also includes the following post-processing steps: The coconut shell biochar was soaked in dilute nitric acid with a concentration of 10-20 wt%, and then washed until neutral.

4. The pretreatment method according to claim 1, characterized in that, The water purification agent B comprises, by weight, 65-85 parts ferrous sulfate, 10-30 parts ferric chloride, and 5-10 parts chitosan.

5. The pretreatment method according to claim 1, characterized in that, Steps a) and b) are performed at different locations in the pipeline for transporting the high-algae raw water; and / or, steps a) and b) are performed in a reaction tank or a contact tank.

6. The pretreatment method according to claim 1, characterized in that, The scheduled time is from 5 minutes to 360 minutes.

7. The pretreatment method according to claim 1, characterized in that, The dosage of water purification agent A is such that its concentration in the raw water is between 10 mg / L and 30 mg / L; the dosage of water purification agent B is such that its concentration in the raw water is between 10 mg / L and 15 mg / L.

8. The pretreatment method according to claim 1, characterized in that, The algal cell density of the high-algae source water is 1×10⁻⁶. 7 Units / L-1×10 9 per L.

9. A composite water purification agent for high-algae raw water, characterized in that, It consists of water purification agent A and water purification agent B; The water purification agent A is a biochar material loaded with potassium permanganate; the water purification agent B contains water-soluble ferrous salts, ferric salts and chitosan.

10. A method for treating high-algae raw water, characterized in that, include: The high-algae raw water to be treated is pretreated according to the method described in any one of claims 1-8; The pretreated effluent is then transported to the subsequent water treatment unit for coagulation and sedimentation.

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