Water treatment method
By using peracetic acid for pre-oxidation and polymer aluminum chloride flocculation in water treatment process, the problem of low turbidity removal efficiency in conventional water treatment processes is solved, and efficient algae removal and water quality improvement is achieved, with the highest flocculation efficiency reaching 92%.
Patent Information
- Application Number
- CN202411529115.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-30
- Publication Date
- 2025-01-03
AI Technical Summary
When conventional water treatment processes treat raw water containing a large amount of algae, the turbid removal efficiency is low and it is difficult to meet the increasingly stringent water quality standards.
By adding peracetic acid to the water for pre-oxidation treatment, dissolved and bound extracellular organic matter is degraded, making algae cells more likely to aggregate and settle, and after pre-oxidation, the flocculant polymerizes aluminum chloride to form a floc for precipitation. filter.
It significantly improves the removal efficiency of algae, improves water quality, and the highest flocculation efficiency can reach 92%, while reducing the generation of disinfection by-products.
Smart Images
Figure CN119240906A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of tap water purification and treatment, and in particular to a method for treating algae-containing water. Background Art
[0002] In conventional water treatment processes, treating raw water containing a large amount of algae is a very challenging task. Conventional water treatment processes, namely the "flocculation-sedimentation-filtration-disinfection" process, often show significant limitations when treating raw water containing a large amount of algae. Since the surface of algae cells usually carries a negative charge and has strong colloidal stability, it is difficult for algae cells to be effectively aggregated and precipitated during the flocculation process, resulting in unsatisfactory turbidity removal effects. The turbidity removal rate can often only reach 50% to 60%, which is difficult to meet the increasingly stringent water quality standards.
[0003] In summary, conventional water treatment processes have many limitations when treating raw water containing a large amount of algae, and it is difficult to meet the increasingly stringent water quality standards and people's demand for healthy drinking water. Therefore, it is particularly important to develop a new water treatment method that can effectively improve the algae flocculation efficiency and thus improve water quality. Summary of the invention
[0004] The main purpose of the present invention is to provide a water treatment method, aiming to solve the problem of low turbidity removal efficiency and difficulty in meeting increasingly stringent water quality standards.
[0005] The present invention provides a water treatment method, which comprises the following steps:
[0006] Obtaining water bodies containing algae;
[0007] Adding peracetic acid to the water body for pre-oxidation treatment;
[0008] A flocculant is added to the water body after the pre-oxidation treatment, and the water body is stirred to form flocs of algae in the water body. After standing, the flocs in the water body are separated.
[0009] Optionally, in the step of "adding peracetic acid to the water body for pre-oxidation treatment", the amount of peracetic acid added is 0.5 mg / L to 5 mg / L.
[0010] Optionally, in the step of "adding peracetic acid to the water body for pre-oxidation treatment", the pre-oxidation treatment time is 10 minutes to 15 minutes.
[0011] Optionally, in the step of “obtaining water containing algae”, the algae cell concentration of the water is 4×10 6 / mL~5×10 6 Pieces / mL.
[0012] Optionally, in the step of "adding a flocculant to the water body after pre-oxidation treatment", the flocculant is polyaluminium chloride, and the dosage of the polyaluminium chloride is 20mg / L to 30mg / L.
[0013] Optionally, in the step of "stirring so that the algae in the water body form flocs", the stirring time is 10 minutes to 15 minutes.
[0014] Optionally, in the step of "separating the floccules in the water body after standing still", the standing time is 20 minutes to 30 minutes.
[0015] The water treatment method of the present invention is to pre-oxidize the obtained water body by adding oxidant peracetic acid in advance, and the peracetic acid, through moderate oxidation, degrades dissolved extracellular organic matter (dEOM) and promotes the shedding of bound extracellular organic matter (bEOM) from the surface of algae, so that algae cells are more likely to aggregate and settle, and will not cause obvious cell rupture and release of intracellular organic matter. Subsequently, a flocculant polyaluminium chloride is added to flocculate the pre-oxidized water body, and then sedimentation and filtration are performed; the removal efficiency of algae is effectively improved and the water quality is improved. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.
[0017] Figure 1 is a flow chart of the water treatment method of the present invention;
[0018] Figure 2 It is a graph of the natural settling rate of algae;
[0019] Figure 3 It is a graph of algae settling rate after pre-oxidation treatment with potassium permanganate in the prior art;
[0020] Figure 4 is a graph of algae settling rate after pre-oxidation treatment using peracetic acid in the water treatment method of the present invention;
[0021] Figure 5 It is a graph of the sedimentation rate of algae cells after the pre-oxidation treatment with peracetic acid and the addition of polyaluminium chloride in the water treatment method of the present invention. DETAILED DESCRIPTION
[0022] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only embodiments of a part of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work should fall within the scope of protection of the present application.
[0023] Please refer to Figure 1-5 The present invention provides a water treatment method, which comprises the following steps:
[0024] S1. Obtaining a water body containing algae;
[0025] S2, adding peracetic acid to the water body for pre-oxidation treatment;
[0026] S3. Adding a flocculant to the water body after the pre-oxidation treatment and stirring the water body to form floccules from the algae in the water body, and separating the floccules from the water body after standing.
[0027] The water treatment method of the present invention is to perform oxidation treatment on the obtained water body by pre-adding an oxidant peracetic acid, and the peracetic acid mainly degrades dissolved extracellular organic matter (dEOM) and promotes the shedding of bound extracellular organic matter (bEOM) from the surface of algae through moderate oxidation, so that algae cells are more likely to aggregate and settle without causing obvious cell rupture and release of intracellular organic matter. Subsequently, a flocculant polyaluminium chloride is added to flocculate the pre-oxidized water body, and then sedimentation and filtration are performed; the removal efficiency of algae is effectively improved and the water quality is improved.
[0028] It should be noted that in step S1, the method of obtaining the algae-containing water body is to take a certain volume of diatoms separated from the water body of the water source and add it to sterile water to obtain a water body with an algae density similar to that of the water body of the water source, and the algae cell concentration in the water body is 4×10 6 / mL~5×10 6 / mL; water bodies containing algae can also be obtained by direct acquisition. Diatoms are one of the common algae in water bodies in water sources, especially in freshwater environments. By using diatoms from the same water source, it is possible to ensure that the experimental conditions are as close to the natural state as possible, thereby providing more accurate data and conclusions. Step S2, adding peracetic acid to the water body obtained in step S1 to pre-oxidize the water body, and the pre-oxidation treatment can improve the effect of flocculation and sedimentation. Peracetic acid is a moderate oxidant, and the degree of oxidation of algae cells is moderate. It will not over-oxidize to cause the rupture of algae cells and the release of intracellular organic matter. It degrades dissolved extracellular organic matter (dEOM) and promotes the shedding of bound extracellular organic matter (bEOM) from the algae surface, making it easier for algae cells to aggregate and settle. In addition, peracetic acid enhances the zeta potential of algae-containing water, degrades humic acid, polysaccharides, proteins and other organic matter, making it easier to remove algae cells and pollutants through the coagulation process. Through the action of peracetic acid, the suspended matter and colloidal particles in the water are more likely to aggregate into larger flocs, so that they can be effectively removed in the subsequent flocculation and sedimentation process, and the generation of disinfection by-products can also be reduced. Step S3, adding a flocculant to the water body after pre-oxidation treatment, the flocculant acts through mechanisms such as electrical neutralization, adsorption bridging and netting, and the suspended particles in the water (such as algae, suspended matter) are close to each other and adhere together to form larger flocs. Thus, the flocculation efficiency is further improved. By stirring, the algae can fully react with the added flocculant, so that the algae in the water body coagulate each other under the action of the flocculant to form flocs; after standing to allow the formed flocs to settle, the flocs in the water body are separated. Specifically, the method of separating flocs includes but is not limited to the precipitation method: by standing to allow the formed flocs to naturally settle to the bottom of the water, and then extracting clean water from the top. This method is simple and easy to implement, and is suitable for situations where the floc particles are large and easy to settle. Filtration: Use filter media such as filter screens or filter membranes to intercept flocs in the water, thereby achieving solid-liquid separation. Filtration can efficiently remove suspended matter and some soluble substances in water. Centrifugation: Use centrifugal force to separate flocs in water. This method is suitable for occasions with large processing volume and high separation efficiency requirements. Magnetic separation: For certain specific flocs, magnetic materials can be added to make them magnetic, and then separated using a magnetic field. This method is suitable for separating flocs containing magnetic substances.
[0029] In general, through the above steps, we can effectively remove diatoms and other suspended particles from the water body of the water source, thereby improving the water quality. First, the use of diatoms from the same water source ensures that the experimental conditions are as close to the natural state as possible, providing more accurate data and conclusions. Secondly, the pre-oxidation treatment significantly improves the effect of flocculation and sedimentation, making it easier for suspended matter and colloidal particles in the water to aggregate into larger flocs, which not only helps to more effectively remove these substances in the subsequent flocculation and sedimentation process, but also reduces the generation of disinfection by-products. Then, by adding flocculants and utilizing their electrical neutralization, adsorption bridging and netting mechanisms, suspended particles in the water (such as algae and suspended matter) are close to each other and adhere to each other to form larger flocs, further improving the flocculation efficiency. Finally, through the stirring and standing process, it is ensured that the algae and flocculants fully react and form settled flocs, thereby achieving effective solid-liquid separation. Not only does it improve the efficiency and effect of water treatment, but it also helps to ensure the water quality safety of the water body of the water source.
[0030] As a further example, please refer to Figures 2 to 5 In the step of "adding peracetic acid to the water body for pre-oxidation treatment", the amount of peracetic acid added is 0.5mg / L to 5mg / L. In the step of "adding peracetic acid to the water body for pre-oxidation treatment", the time of pre-oxidation treatment is 10min to 15min. In the step of "obtaining a water body containing algae", the algae cell concentration of the water body is 4×106 / mL to 5×106 / mL. In the step of "adding a flocculant to the water body after pre-oxidation treatment", the flocculant is polyaluminum chloride, and the amount of polyaluminum chloride added is 20mg / L to 30mg / L. In the step of "stirring to form flocs in the algae in the water body", the stirring time is 10min to 15min. In the step of "standing for a period of time to allow the flocs to settle", the standing time is 20min to 30min.
[0031] The following experiment shows that the flocculation efficiency can reach up to 92% when peracetic acid is used as the oxidant for pre-oxidation treatment and then added with polyaluminium chloride as the flocculant. The experimental process is as follows:
[0032] First, two control groups and two experimental groups are set up, and the final experimental results are obtained by comparing the data between the experimental group and the control group.
[0033] (1) Control group 1 - natural sedimentation rate experiment of algae cells
[0034] The concentration of algae cells in the water is 4×10 6 / mL~5×10 6 / mL of water, stir for 10min~15min and then let it stand for 20min~30min.
[0035] Experimental results: Without adding oxidants and flocculants, the sedimentation rate of algae cells is as follows: Figure 2 As shown in the figure, the natural sedimentation efficiency of the algae liquid without the addition of flocculants and pre-oxidation treatment varies with time, but the sedimentation rate is basically below 30%. This phenomenon shows that relying solely on the natural sedimentation process to remove algae in water is limited and inefficient. Since natural sedimentation relies on gravity to sink suspended particles to the bottom of the water, but due to the small size of algae cells and their density similar to that of water, their sedimentation rate is slow. In the absence of external assistance, the interaction between algae cells is weak, and it is difficult to form large aggregates, resulting in low sedimentation efficiency.
[0036] Pre-oxidation treatment can change the surface properties of suspended matter in water by adding oxidants, promote aggregation between particles, and create favorable conditions for subsequent flocculation and precipitation. Oxidants can also partially degrade organic matter and improve water quality safety. Different oxidants have different oxidizing abilities and scopes of application. For example, chlorine is a common oxidant suitable for disinfection and control of microbial growth. Ozone has a strong oxidizing ability and can effectively remove organic matter and odor in water. Potassium permanganate is often used to remove heavy metal elements such as iron and manganese. The selection of a suitable oxidant requires consideration of the characteristics of the raw water and the treatment target. In this embodiment, potassium permanganate oxidant is used as one of the control groups. The type of oxidant is selected, and the dosage of the oxidant also directly affects the effect of pre-oxidation. Excessive or insufficient dosage may lead to unsatisfactory treatment effects. Therefore, it is necessary to accurately control the dosage of the oxidant according to the water quality of the water body. For example, in potassium permanganate pre-oxidation, it is necessary to control its dosage to avoid the generation of Mn2+ with genotoxic effects. In addition, the oxidation reaction time is one of the important factors affecting the pre-oxidation effect. Too short a reaction time may result in insufficient oxidation reaction, while too long a reaction time may waste resources.
[0037] The following is the sedimentation rate of algae cells when potassium permanganate, a commonly used oxidant, is used for pre-oxidation treatment:
[0038] (2) Experiment on the sedimentation rate of algae cells after 2-potassium permanganate pre-oxidation in the control group
[0039] Experimental conditions: Algal cell concentration in water: 4×10 6 / mL~5×10 6 / mL; pre-oxidation treatment time: 10min~15min; stirring time: 10min~15min; flocculation sedimentation time: 20min~30min.
[0040] Experimental results: Under the above experimental conditions, the flocculation and sedimentation efficiency of algae cells after pre-oxidation treatment with potassium permanganate, a common pre-oxidant, was as follows: Figure 3Compared with the untreated water, the algae cell sedimentation efficiency after adding potassium permanganate for pretreatment is 18%-52%, and the effect of potassium permanganate on the algae liquid sedimentation efficiency increases with the increase of concentration. The algae cell sedimentation efficiency under 10 mg / L potassium permanganate treatment is 52%.
[0041] Due to the use of potassium permanganate for pre-oxidation treatment, color residue will be produced in the water body. For this, a color remover can be used for color removal, such as vitamin C solution, oxalic acid solution, citric acid solution, hydrogen peroxide solution, sodium thiosulfate solution and sodium sulfite solution.
[0042] It can be seen from the experimental results of the above control group that compared with the water body without adding any oxidant, the sedimentation efficiency of algae cells in the water body with potassium permanganate added increases with the increase of the addition concentration of potassium permanganate; but its sedimentation efficiency is 52% under the treatment of 10 mg / L potassium permanganate, and there will be color residue.
[0043] It has been found that the use of peracetic acid as an oxidant for pre-oxidation treatment in algae-containing water treatment processes can significantly improve the sedimentation efficiency of algae. Peracetic acid decomposes to produce acetic acid, water and oxygen, and does not produce toxic by-products, which can further improve water quality. The following is an experiment using peracetic acid as an oxidant for pre-oxidation treatment:
[0044] (3) Experimental group 1-2% peracetic acid pre-oxidation treatment of algal cells sedimentation efficiency experiment
[0045] Experimental conditions: Algal cell concentration in water: 4×10 6 / mL~5×10 6 / mL; pre-oxidation treatment time: 10min~15min; stirring time: 10min~15min; flocculation sedimentation time: 20min~30min; 2% peracetic acid dosage: 0.5mg / L, 1mg / L, 2.5mg / L, 5mg / L.
[0046] Experimental results: The flocculation and sedimentation efficiency of algae cells after pre-oxidation treatment with 2% peracetic acid at different concentrations is as follows: Figure 4 As shown. Compared with the water bodies that settled naturally without treatment and pre-treated with potassium permanganate, the algae cell settling efficiency was significantly improved after pre-oxidation treatment with peracetic acid, and the settling efficiency was 62%-82%. Moreover, the algae liquid settling efficiency could reach more than 60% under low concentration of peracetic acid (0.5mg / L), which was more significant than the algae cell settling efficiency improvement after pre-treatment with high concentration of potassium permanganate.
[0047] It should be noted that peracetic acid also has excellent bactericidal ability and can remove a variety of microorganisms and pollutants in water. In addition, it does not produce toxic byproducts during the auxiliary disinfection process. Its main decomposition products are acetic acid and water, which purifies drinking water and improves the quality of drinking water. Even at low concentrations, it can still exert excellent bactericidal and oxidative abilities, and can use its strong oxidizing properties to remove trace pollutants in water, and has the ability to continuously disinfect.
[0048] Only adding peracetic acid for pre-oxidation treatment can increase the sedimentation efficiency of algae cells in water to 82%, but this is not the best effect. Experiments have found that after using peracetic acid for pre-oxidation treatment, the sedimentation efficiency of algae cells is still improved after adding flocculants. In this embodiment, polyaluminum chloride is selected as a flocculant for use in combination with the oxidant peracetic acid. The selection of polyaluminum chloride as a flocculant in this embodiment does not limit the protection scope of the present invention.
[0049] (4) Experimental Group 2 - Experiment on the Sedimentation Efficiency of Algal Cells after Peracetic Acid Oxidation by Adding Polyaluminium Chloride
[0050] Experimental conditions: Algal cell concentration in water: 4×10 6 / mL~5×10 6 / mL; pre-oxidation treatment time: 10min~15min; coagulation stirring time: 10min~15min; dosage of polyaluminium chloride: 20mg / L~30mg / L; dosage of 2% peracetic acid: 0.5mg / L, 1mg / L, 2.5mg / L, 5mg / L; flocculation sedimentation time: 20min~30min.
[0051] Experimental results: The flocculation and sedimentation efficiency of algae cells after adding different concentrations of 2% peracetic acid and 20 mg / L polyaluminium chloride is as follows: Figure 5 Compared with the water without polyaluminium chloride, the algae cell settling efficiency in the water after adding the flocculant polyaluminium chloride was significantly improved, and the highest settling efficiency could reach 92%. Therefore, adding the flocculant polyaluminium chloride can further improve the settling efficiency of algae cells.
[0052] From the above experimental data, it can be seen that the sedimentation efficiency of algae cells is more significantly improved than other oxidants by selecting 2% peracetic acid as an oxidant for pre-oxidation treatment of water bodies, and the minimum can reach 62%; after using peracetic acid for pre-oxidation treatment and then using it with flocculant polyaluminium chloride, the flocculation efficiency of algae cells can reach up to 92%. Specifically, peracetic acid, as an oxidant, degrades dissolved extracellular organic matter (dEOM) and promotes the shedding of bound extracellular organic matter (bEOM) from the surface of algae, making it easier for algae cells to aggregate and settle without causing obvious cell rupture and release of intracellular organic matter. It helps the subsequent flocculation process and can also reduce the potential harm of algae to water quality. The oxidation of peracetic acid can also partially degrade other organic pollutants in water, such as pesticide residues, endocrine disruptors, etc., thereby further improving water quality safety. The aluminum ions ionized by polyaluminium chloride in water have a strong adsorption capacity and can aggregate the tiny algae cell fragments and suspended matter produced during the pre-oxidation process into larger flocs. Due to their high density, these floccules are more likely to settle to the bottom of the water under the action of gravity, thus achieving solid-liquid separation. Polyaluminium chloride can also further improve the flocculation effect by adjusting the pH value of water and optimizing the flocculation conditions. Therefore, the pre-oxidation treatment of peracetic acid creates favorable conditions for the flocculation of polyaluminium chloride, allowing polyaluminium chloride to act more effectively on the partially degraded algal cell fragments to form larger floccules. This synergistic effect not only improves the sedimentation efficiency of algal cells, but also may reduce the amount of flocculants used and reduce treatment costs. The combined use of peracetic acid and polyaluminium chloride can not only improve the sedimentation efficiency of algal cells, but also effectively remove other suspended matter and colloidal substances in the water, thereby improving the transparency and clarity of the water quality. This process also helps to reduce the content of organic matter in water, reduce the odor and color in the water, and further improve the water quality. Compared with the use of peracetic acid or polyaluminium chloride alone, the combined use of the two can more effectively control algae and other suspended matter in the water and reduce their impact on water quality.
[0053] The above is only for explaining the implementation mode of the present invention and is not intended to limit the present invention. For those skilled in the art, any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention without creative work should be included in the protection scope of the present invention.
Claims
1. A water treatment method, characterized in that: The following steps are involved: Obtaining water bodies containing algae; Adding peracetic acid to the water body for pre-oxidation treatment; A flocculant is added to the water body after the pre-oxidation treatment, and the water body is stirred to form flocs of algae in the water body. After standing, the flocs in the water body are separated.
2. The water treatment method according to claim 1, characterized in that: In the step of "adding peracetic acid to the water body for pre-oxidation treatment", the amount of peracetic acid added is 0.5 mg / L to 5 mg / L.
3. The water treatment method according to claim 1, characterized in that: In the step of "adding peracetic acid to the water body for pre-oxidation treatment", the pre-oxidation treatment time is 10 minutes to 15 minutes.
4. The water treatment method according to claim 1, characterized in that: In the step of "obtaining water containing algae", the algae cell concentration of the water is 4×10 6 / mL~5×10 6 Pieces / mL.
5. The water treatment method according to any one of claims 1 to 4, characterized in that: In the step of "adding a flocculant to the water body after pre-oxidation treatment", the flocculant is polyaluminium chloride, and the dosage of the polyaluminium chloride is 20mg / L to 30mg / L.
6. The water treatment method according to claim 5, characterized in that: In the step of "stirring to make the algae in the water body form flocs", the stirring time is 10 minutes to 15 minutes.
7. The water treatment method according to claim 6, characterized in that: In the step of "separating the floccules in the water body after standing still", the standing time is 20 minutes to 30 minutes.