Application of composite flocculant in sewage treatment

Abstract

The application discloses application of a composite flocculant in sewage treatment and belongs to the field of sewage treatment. The system's adsorption filtering and particle capturing capacity are enhanced by adding diatomite, and the electro-neutralization effect with the negative electric particles in sewage is enhanced by selectively adding light calcium carbonate, so that the components can continuously and cooperatively play functions under the condition of integral one-step adding, and the removal rate of the suspended matters in the sewage, especially the Fenton-treated wastewater and the biochemical tank wastewater, is about 100%.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment, and more specifically, relates to the application of a composite flocculant in wastewater treatment. Background Technology

[0002] In recent years, with the continuous growth of my country's population and the rapid development of industrial and agricultural production, the demand for water resources has increased significantly, and water pollution has become increasingly serious. In the process of wastewater treatment, flocculants are added to cause tiny particles in the liquid to aggregate into larger flocs, which facilitate subsequent sedimentation or filtration separation, ultimately achieving solid-liquid separation and water purification. The application of flocculants directly affects the entire process and the final effluent quality.

[0003] Currently, flocculants used for treating industrial wastewater in my country can be classified into four categories based on their chemical composition: inorganic flocculants, organic flocculants, microbial flocculants, and composite flocculants. Among these, inorganic flocculants are the most widely used due to their low cost. In particular, inorganic polymeric flocculants offer advantages such as rapid settling and low dosage. For example, polyaluminum chloride contains a higher charge than traditional inorganic low-molecular-weight flocculants. However, inorganic flocculants are highly corrosive and have relatively low flocculation efficiency. Organic flocculants offer advantages such as a wide applicable pH range, low sludge production, good treatment effect, and low treatment cost. However, residual organic polymers, such as polyacrylamide, can exacerbate membrane fouling of nanofiltration and ultrafiltration membranes during treatment. Compared to single flocculants, composite flocculants, through the synergistic effect between different components, have significant advantages such as better flocculation effect, wider applicability, lower dosage, and superior sludge dewatering performance. Composite flocculants are gradually replacing traditional single flocculants.

[0004] Chinese invention patent application CN113044942A discloses a composite bentonite coagulant and its application in wastewater treatment. The bentonite coagulant, by mass, comprises the following components: 10-200 parts bentonite, 4-6 parts polyaluminum chloride, and 0.4-0.6 parts polyacrylamide. Adding these components to the wastewater step-by-step and stirring allows for solid-liquid separation within 5-10 minutes. However, the step-by-step addition of coagulant components in the above and similar prior art leads to complex engineering operations. Summary of the Invention

[0005] 1. The problem to be solved To address the issue that existing composite flocculants require step-by-step addition of raw materials in wastewater treatment, this invention provides an application of composite flocculants in wastewater treatment, where the composite flocculant is added to the wastewater in one step, achieving excellent removal of suspended solids.

[0006] 2. Technical Solution Existing composite flocculants often employ a high variety of components in their design to achieve better results, with some containing dozens of different components. While theoretically, composite flocculants can combine the effects of their components, in practical applications, these components may interfere with each other, weakening the flocculation effect. For example, when aluminum and iron salts are used together, an improper ratio can disrupt the hydrolysis pathway and affect polymer morphology. Furthermore, the more complex the composition, the more difficult it is to determine the optimal dosage and pH range; even slight fluctuations in wastewater composition and pH can lead to a sharp decline in treatment effectiveness. This invention, through careful design and experimentation, yields a composite flocculant with fewer components that achieves excellent wastewater treatment results through a single, integrated dosing process.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows: This invention provides an application of a composite flocculant in wastewater treatment, including the step of adding the composite flocculant as a whole into the wastewater in one step. The composite flocculant includes bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide, and the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide is (10~200):(10~200):(0.5~10):1.

[0008] When using the composite flocculant of the present invention, the pre-mixed composite flocculant is added to the wastewater to be treated in one go, followed by stirring and settling.

[0009] Preferably, the composite flocculant is composed of bentonite, polyaluminum chloride, diatomaceous earth, light calcium carbonate and polyacrylamide, and the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth, light calcium carbonate and polyacrylamide is (10~80):(10~80):(1~8):(2~30):1, and the wastewater is wastewater after Fenton treatment.

[0010] More preferably, the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth, light calcium carbonate, and polyacrylamide is (10~27):(13~27):(2~2.7):(2.5~10):1. When the content of each component is within the above range, the composite flocculant achieves a suspended solids removal rate of over 99% for the Fenton-treated wastewater, with a maximum of approximately 100%.

[0011] More preferably, the pH value of the wastewater is 5 to 7.

[0012] When the pH value of the wastewater after Fenton treatment is 5-7, the composite flocculant removes suspended solids from the wastewater after Fenton treatment at a rate of over 96%, with a maximum of approximately 100%.

[0013] More preferably, the concentration of the composite flocculant is 0.3~0.5 g / L.

[0014] When the concentration of the composite flocculant is 0.3~0.5g / L, the composite flocculant removes suspended solids from the Fenton-treated wastewater at a rate of over 99%, with a maximum of approximately 100%.

[0015] Preferably, the composite flocculant is composed of bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide, and the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide is (12~200):(12~200):(0.5~10):1. The wastewater is biological wastewater and the pH value of the wastewater is 6.5~9.

[0016] More preferably, the pH value of the wastewater is 7 to 8.5.

[0017] More preferably, the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth, and polyacrylamide is (12~100):(25~200):(3.3~8):1. When the content of each component is within the above range, the composite flocculant achieves a suspended solids removal rate of over 99% for the wastewater from the biological treatment tank, with a maximum of approximately 100%.

[0018] More preferably, the concentration of the composite flocculant is 0.1~0.6 g / L. When the concentration of the composite flocculant is 0.1~0.6 g / L, the removal rate of suspended solids in the wastewater from the biological treatment tank by the composite flocculant is above 99%, with a maximum of about 100%.

[0019] Preferably, the particle size of the composite flocculant is not greater than 100 μm.

[0020] The larger the particle size of the composite flocculant, the smaller its specific surface area and the fewer the active sites on its surface, which will reduce its charge neutralization, adsorption and bridging functions, thus affecting the wastewater treatment effect.

[0021] More preferably, the particle size of the composite flocculant can be any value taken from any of the following numerical ranges: not greater than 75μm, not greater than 50μm, not greater than 30μm, not greater than 10μm, 10~30μm, 10~50μm, 10~75μm, 10~100μm, 30~50μm, 30~75μm, 30~100μm, 50~75μm, 50~100μm, 75~100μm.

[0022] Preferably, the bentonite is sodium-based bentonite.

[0023] It should be noted that sodium-based bentonite and calcium-based bentonite are commonly used in bentonite production. Sodium-based bentonite has interlayered Na+. +It is ion-based, easily hydrated, and promotes full expansion and dispersion of crystal layers, thereby exposing a larger specific surface area and more cation exchange sites. Therefore, it is more conducive to loading active components, adsorption bridging and flocculation than calcium-based bentonite.

[0024] Preferably, the preparation method of the composite flocculant includes the following steps: grinding and mixing the raw materials at a speed of 50-500 rpm for 1-10 minutes, passing them through a 200-400 mesh sieve, and obtaining the dry powder as the composite flocculant.

[0025] The composite flocculant described in this invention utilizes the adsorption and ion exchange properties of bentonite, the charge neutralization, adsorption bridging, and netting and sweeping properties of polyaluminum chloride, the filtration and adsorption properties of diatomaceous earth, the adsorption and bridging properties of polyacrylamide, and selectively utilizes the charge neutralization properties of light calcium carbonate according to the pH value of the wastewater. This composite flocculant has an excellent effect on removing suspended solids in wastewater.

[0026] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention provides an application of a composite flocculant in wastewater treatment. By adding diatomaceous earth, the adsorption, filtration and particle capture capacity of the system are enhanced. By selectively adding light calcium carbonate, the charge neutralization effect with negatively charged particles in wastewater is strengthened. Combined with the adsorption and ion exchange effect of bentonite, the coagulation effect of polyaluminum chloride and the bridging effect of polyacrylamide, the components can continuously and synergistically perform their functions under the overall one-step addition condition. The removal rate of suspended solids in wastewater, especially wastewater after Fenton treatment and wastewater in biological treatment tanks, is up to about 100%.

[0027] (2) When treating sewage, the composite flocculant provided by the present invention adjusts the composition of the composite flocculant according to the pH value of the sewage. Light calcium carbonate is added to acidic and neutral sewage, while light calcium carbonate is removed from neutral and alkaline sewage, so as to achieve the effect of maximizing the advantages and avoiding the disadvantages. Attached Figure Description

[0028] Figure 1 The suspended solids removal rate of the composite flocculants prepared in Examples 1-16 of Test Example 1 of this invention on Fenton-treated wastewater; Figure 2 The suspended solids removal rate of the composite flocculant prepared in Example 12 with different dosage concentrations in Test Example 2 of the present invention on Fenton-treated wastewater; Figure 3 This is a comparison chart of the effects of the composite flocculant prepared in Example 12 with a concentration of 0.3 g / L on Fenton-treated wastewater before (left) and after (right) treatment. Figure 4The suspended solids removal rate of the composite flocculant prepared in Examples 17-32 of Test Example 5 of this invention is shown to be achieved by the composite flocculant in the biological treatment tank wastewater. Detailed Implementation

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0030] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0031] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0032] The functions of each component in the composite flocculant provided by this invention are as follows: Bentonite: The main component of bentonite is montmorillonite, which has a layered structure and a large specific surface area, enabling it to adsorb pollutants in water; the interlayers of montmorillonite contain exchangeable cations (such as Na+). + Ca² + When it comes into contact with wastewater containing heavy metals, it undergoes an ion exchange reaction; it can disperse into colloidal particles in water, acting as a flocculant to remove suspended solids and some organic matter, thereby improving treatment efficiency.

[0033] Polyaluminum chloride: Through three actions—electrode neutralization, adsorption bridging, and netting and sweeping—colloidal particles and suspended solids in water are destabilized, aggregated, and form large flocs, thereby achieving rapid sedimentation and separation.

[0034] Diatomaceous earth: It has a unique porous structure, high specific surface area and surface chemical properties. It removes suspended solids, colloids, microorganisms and some dissolved pollutants from water through multiple mechanisms such as mechanical filtration, adsorption, flocculation and ion action.

[0035] Light calcium carbonate: The calcium ions produced in the wastewater react with the negatively charged particles suspended in the wastewater to neutralize the charge, thereby destabilizing the particulate colloids in the wastewater and removing large suspended particles.

[0036] Polyacrylamide: It enables the rapid adsorption and bridging of neutralized colloidal particles and very fine colloidal particles, increasing the density of flocs and thus enhancing the flocculation and sedimentation effects.

[0037] The bentonite (sodium bentonite) used in the embodiments of the present invention was purchased from Maclean (item number 85049-30-5), polyaluminum chloride was purchased from Maclean (item number 1327-41-9), diatomaceous earth was purchased from Maclean (item number 61790-53-2), light calcium carbonate was purchased from Maclean (item number 471-34-1), and polyacrylamide was purchased from Maclean (item number 9003-05-8).

[0038] The formula for calculating the suspended solids removal rate in the test examples of this invention is as follows: Suspended solids removal rate = (Suspended solids concentration before treatment - Suspended solids concentration after treatment) × 100% / Suspended solids concentration before treatment It should be noted that when the concentration of suspended solids in wastewater treated with composite flocculants is extremely low, it may exceed the detection limit of the testing instrument. In this case, the concentration of suspended solids after treatment will be marked as "not detected", and the removal rate of suspended solids is approximately 100%.

[0039] In the Fenton oxidation process, to ensure efficient reaction, the pH of the wastewater usually needs to be adjusted to an acidic range. Therefore, the wastewater after Fenton treatment typically remains acidic. The pH of the wastewater in the biological treatment tank is usually close to neutral to alkaline, generally between 6.5 and 8.5. In the embodiments of this invention, both the wastewater after Fenton treatment and the wastewater in the biological treatment tank come from a sewage treatment plant.

[0040] The present invention will be further described below with reference to specific embodiments.

[0041] Example 1 This embodiment provides a composite flocculant and its preparation method: Weigh out 40g of bentonite, 40g of polyaluminum chloride, 4g of diatomaceous earth, 10g of light calcium carbonate, and 1g of polyacrylamide. Add them to a mixer and grind and mix them at 400rpm for 30s, then at 80rpm for 5min. Finally, pass the mixture through a 300-mesh sieve. The resulting dry powder is the composite flocculant.

[0042] Examples 2-32 The composite flocculants and their preparation methods provided in Examples 2-32 are similar to those in Example 1, except that the amounts of each component are different, as shown in Table 1.

[0043] Table 1. Components of the composite flocculants prepared in Examples 1-32

[0044] Test Example 1 0.15g of the composite flocculant prepared in Examples 1-16 was added to 500ml of Fenton-treated wastewater with a pH of approximately 4.5. The mixture was rotated at 400rpm for 30s, then at 80rpm for 5min, and allowed to settle naturally for 30s. The wastewater before and after treatment was then tested according to the "Determination of Suspended Solids in Water - Gravimetric Method" (GB 11901-89). The suspended solids concentration in the supernatant of the wastewater before treatment was 920mg / L. The suspended solids concentration in the supernatant of the wastewater after treatment and the results of the suspended solids removal rate of the composite flocculant are as follows: Figure 1 As shown in Table 2.

[0045] Depend on Figure 1 As shown in Table 2, the composite flocculants prepared in Examples 1-16 all achieved a suspended solids removal rate of over 94% for the Fenton-treated wastewater, demonstrating excellent removal performance. The orthogonal experimental analysis in Table 2 revealed that the influence of each component on the suspended solids removal rate, from largest to smallest, was: polyacrylamide > polyaluminum chloride > light calcium carbonate > bentonite > diatomaceous earth. The composite flocculants prepared in Examples 12, 14, and 16 achieved a suspended solids removal rate of approximately 100%. Considering that the hygroscopicity of polyaluminum chloride would affect the preparation and storage of the composite flocculant, and that the addition of polyacrylamide would exacerbate subsequent membrane fouling, the composite flocculant prepared in Example 12, containing less of the aforementioned two components, was selected for further research.

[0046] Table 2. Removal rate of suspended solids from Fenton-treated wastewater by the composite flocculants prepared in Examples 1-16

[0047] Test Example 2 0.05 g, 0.10 g, 0.15 g, 0.20 g, and 0.25 g of the composite flocculant prepared in Example 12 were added to 500 ml of Fenton-treated wastewater with a pH of approximately 4.5. The mixture was rotated at 400 rpm for 30 s, then at 80 rpm for 5 min, and allowed to settle naturally for 30 s. The wastewater before and after treatment was tested according to the "Determination of Suspended Solids in Water - Gravimetric Method" (GB 11901-89). The suspended solids concentration in the supernatant of the wastewater before treatment was 920 mg / L. The suspended solids concentration in the supernatant of the wastewater after treatment and the results of the suspended solids removal rate of the composite flocculant are shown below. Figure 2 As shown in Table 3.

[0048] Depend on Figure 2As shown in Table 3, when the dosage concentration is 0.3 g / L, the suspended solids removal rate reaches 100%, and when the dosage concentration increases to 0.5 g / L, the suspended solids removal rate begins to decrease. Figure 3 The image shows a comparison of the treated (left) and untreated (right) wastewater after Fenton treatment using the composite flocculant prepared in Example 12 at a concentration of 0.3 g / L. The excellent treatment effect of the composite flocculant on suspended solids is clearly evident.

[0049] The light calcium carbonate contained in the composite flocculant prepared in Example 12 can provide Ca in water. 2+ Ions neutralize negatively charged colloids and fine particles, causing them to destabilize and aggregate. However, when the dosage is too high, the Ca in the system... 2+ The significantly increased ionic strength of inorganic salts can easily lead to excessive neutralization or even charge reversal on the particle surface, causing destabilized particles to undergo restabilization, resulting in a certain amount of fine particles remaining in the supernatant. Simultaneously, light calcium carbonate itself consists of fine solid particles; under conditions of short-term stirring and short-term natural settling, some calcium carbonate fine powder that has not fully participated in flocculation or has not completely settled may also enter the supernatant and be counted as suspended solids by gravimetric method.

[0050] Table 3. Removal rate of suspended solids from Fenton-treated wastewater by composite flocculants prepared in Example 12 at different dosage concentrations.

[0051] Test Example 3 The composite flocculant prepared in Example 12 was added to Fenton-treated wastewater at different pH values ​​at a concentration of 0.3 g / L. The mixture was rotated at 400 rpm for 30 s, then at 80 rpm for 5 min, and allowed to settle naturally for 30 s. The wastewater before and after treatment was tested according to the "Determination of Suspended Solids in Water by Gravimetric Method" (GB 11901-89). The suspended solids concentration in the supernatant of the wastewater before treatment was 920 mg / L. The suspended solids concentration in the supernatant of the wastewater after treatment and the results of the suspended solids removal rate of the composite flocculant are shown in Table 4.

[0052] As shown in Table 4, the removal rate of suspended solids by the composite flocculant prepared in Example 12 increased with the increase of wastewater pH, reaching 100% at pH 7. This trend is mainly due to the synergistic pH sensitivity of the inorganic coagulant polyaluminum chloride and the polymeric flocculant polyacrylamide in the composite flocculation system. Under slightly acidic conditions, the degree of hydrolysis of polyaluminum chloride is relatively limited, resulting in fewer effective coagulation morphologies and weaker netting and sweeping effects, leading to insufficient destabilization of fine particles. As the pH rises to near neutral, polyaluminum chloride more easily forms hydrolytic polymerization products with strong adsorption, charge neutralization, and netting capabilities, thus fully destabilizing colloidal particles. On this basis, the adsorption-bridging effect of polyacrylamide on destabilized particles is conducive to the formation of larger and denser flocs and rapid sedimentation. Therefore, the best solid-liquid separation effect can be obtained at pH=7.

[0053] Table 4. Removal rate of suspended solids from Fenton-treated wastewater at different pH values ​​by the composite flocculant prepared in Example 12.

[0054] Test Example 4 Wastewater from the biological treatment tank with a pH of approximately 8.5 was tested according to the "Determination of Suspended Solids in Water - Gravimetric Method" (GB 11901-89), and the suspended solids concentration was found to be 3358 mg / L. The composite flocculant prepared in Example 12 was added to the wastewater at a concentration of 0.3 g / L. The mixture was rotated at 400 rpm for 30 seconds, then at 80 rpm for 5 minutes, and allowed to settle naturally for 30 seconds. However, the flocculation effect was found to be poor, and the amount of sludge produced was large.

[0055] The function of light calcium carbonate is to provide calcium. 2+ Ions neutralize negatively charged particles, promoting colloid destabilization. However, in an alkaline system at pH 8.5, light calcium carbonate tends to remain as insoluble, fine solid particles rather than fully dissolving Ca. 2+ The addition of ions weakens their effective contribution to charge neutralization and increases the solid load of the system in the form of inorganic fine powder, which is directly converted into sludge and results in a large amount of sludge production.

[0056] Test Example 5 0.15g of the composite flocculant prepared in Examples 17-32 (without light calcium carbonate) was added to 500ml of biological wastewater at a pH of approximately 8.5. The mixture was rotated at 400rpm for 30s, then at 80rpm for 5min, and allowed to settle naturally for 30s. The wastewater before and after treatment was then tested according to the "Determination of Suspended Solids in Water - Gravimetric Method" (GB 11901-89). The suspended solids concentration in the supernatant of the wastewater before treatment was 3358mg / L. The suspended solids concentration in the supernatant of the wastewater after treatment and the results of the suspended solids removal rate of the composite flocculant are as follows: Figure 4 As shown in Table 5.

[0057] Depend on Figure 4 As shown in Table 5, the composite flocculants prepared in Examples 17-32 all achieved a removal rate of over 97% for suspended solids in the biological treatment tank wastewater, demonstrating excellent performance. Compared to the composite flocculants prepared in Examples 1-16, the composite flocculants prepared in Examples 17-32 do not contain light calcium carbonate. Under the alkaline conditions of the biological treatment tank wastewater, the removal of light calcium carbonate avoids its residual insoluble fine powder, increased ionic strength, and adverse effects on coagulation / bridging synergy in the alkaline system. This allows the coagulation destabilization of polyaluminum chloride, the adsorption framework effect of bentonite and diatomaceous earth, and the bridging effect of polyacrylamide to more effectively synergistically generate dense flocs and settle, thereby achieving lower sludge production and better operational performance while maintaining a high removal rate.

[0058] The orthogonal experimental analysis in Table 5 shows that the influence of each component on the suspended solids removal rate, from largest to smallest, is: polyaluminum chloride > bentonite > anionic polyacrylamide > diatomaceous earth. The suspended solids removal rates of the composite flocculants prepared in Examples 25, 29, 30, and 32 are approximately 100%, while the suspended solids removal rate of the composite flocculant prepared in Example 21 is 99.94%, close to 100%. Considering that the water absorption of polyaluminum chloride will affect the preparation and storage of the composite flocculant, and that the addition of polyacrylamide will exacerbate subsequent membrane fouling, the composite flocculant prepared in Example 21, containing less of the aforementioned two components, was selected for further research.

[0059] Table 5. Removal rate of suspended solids from biological treatment pond wastewater by the composite flocculants prepared in Examples 17-32.

[0060] Test Example 6 0.05 g, 0.10 g, 0.15 g, 0.20 g, and 0.25 g of the composite flocculant prepared in Example 21 were added to 500 ml of biological wastewater with a pH of approximately 8.5. The mixture was rotated at 400 rpm for 30 s, then at 80 rpm for 5 min, and allowed to settle naturally for 30 s. The wastewater before and after treatment was tested according to the "Determination of Suspended Solids in Water by Gravimetric Method" (GB 11901-89). The concentration of suspended solids in the supernatant of the wastewater before treatment was 3358 mg / L. The concentration of suspended solids in the supernatant of the wastewater after treatment and the results of the suspended solids removal rate of the composite flocculant are shown in Table 6.

[0061] As shown in Table 6, when the concentration of the composite flocculant prepared in Example 21 is 0.1 g / L, its suspended solids removal rate for the wastewater in the biological treatment tank is 99.82%. When the concentration is increased to 0.3 g / L or above, its suspended solids removal rate for the wastewater in the biological treatment tank is approximately 100%.

[0062] Table 6. Removal rate of suspended solids from biological wastewater by the composite flocculant prepared in Example 21 at different dosage concentrations.

[0063] The above description provides an illustrative overview of the present invention and its embodiments. This description is not restrictive, and the embodiments shown are merely one example of the invention's implementation. Actual implementations are not limited to these examples. Therefore, if those skilled in the art are inspired by this description and design similar implementations and examples without departing from the spirit of the invention, such designs should fall within the scope of protection of the present invention.

Claims

1. The application of a composite flocculant in wastewater treatment, characterized in that: The method includes the step of adding a composite flocculant into the wastewater in one step. The composite flocculant includes bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide, and the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide is (10~200):(10~200):(0.5~10):

1.

2. The application according to claim 1, characterized in that: The composite flocculant is composed of bentonite, polyaluminum chloride, diatomaceous earth, light calcium carbonate and polyacrylamide, and the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth, light calcium carbonate and polyacrylamide is (10~80):(10~80):(1~8):(2~30):

1. The wastewater is wastewater after Fenton treatment.

3. The application according to claim 2, characterized in that: The mass ratio of bentonite, polyaluminum chloride, diatomaceous earth, light calcium carbonate and polyacrylamide is (10~27):(13~27):(2~2.7):(2.5~10):

1.

4. The application according to claim 2 or 3, characterized in that: The pH value of the wastewater is 5-7.

5. The application according to claim 2 or 3, characterized in that: The concentration of the composite flocculant is 0.3~0.5 g / L.

6. The application according to claim 1, characterized in that: The composite flocculant is composed of bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide, and the mass ratio of bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide is (12~200):(12~200):(0.5~10):

1. The wastewater is biological wastewater and the pH value of the wastewater is 6.5~9.

7. The application according to claim 6, characterized in that: The mass ratio of bentonite, polyaluminum chloride, diatomaceous earth and polyacrylamide is (12~100):(25~200):(3.3~8):

1.

8. The application according to claim 6 or 7, characterized in that: The concentration of the composite flocculant is 0.1~0.6 g / L.

9. The application according to claim 1, characterized in that: The particle size of the composite flocculant is no greater than 100 μm.

10. The application according to claim 1, characterized in that: The bentonite is sodium-based bentonite.

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