Composite flocculant and use method thereof

Abstract

The invention discloses a composite flocculant and a use method thereof, and belongs to the technical field of sewage treatment.The composite flocculant is prepared from, by mass, 5-10 parts of cationic polyacrylamide, 1-5 parts of polyaluminum chloride, 1-5 parts of chitosan quaternary ammonium salt, 7 parts of cationic polyacrylamide, 1 part of polyaluminum chloride and 2 parts of chitosan quaternary ammonium salt. Comprising a step of preparing a composite flocculant solution and a step of adding the solution to improve the settling performance and activity of activated sludge and strengthen the dewatering of excess sludge, and the step of preparing the composite flocculant solution comprises the following steps: S1, weighing cationic polyacrylamide, polyaluminum chloride and chitosan quaternary ammonium salt according to the proportion; according to the present invention, through the chitosan quaternary ammonium salt-polyaluminum chloride-cationic polyacrylamide gradient flocculation mode, the multiple effects of synchronously improving the activated sludge sedimentation performance, enhancing the microbial activity and enhancing the excess sludge dewatering are achieved, and the technical effects of high efficiency and biocompatibility are provided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sewage treatment, and particularly relates to a composite flocculant and a use method thereof. BACKGROUND

[0002] In the process of municipal sewage and industrial wastewater treatment, activated sludge method is the most core biochemical treatment process. However, this process often faces problems such as poor sludge settling performance (such as sludge bulking, sludge disintegration), poor microbial activity, and difficulty in dewatering of excess sludge, etc. If effective measures are not taken, these problems will often lead to deterioration of effluent quality, increase of treatment energy consumption, collapse of biochemical system, and high cost of sludge disposal. At present, the method of adding a single flocculant is often used to improve the above problems, such as using polyaluminum chloride (PAC), polyferric sulfate (PFS) or cationic polyacrylamide (CPAM). However, the single flocculant has the problems of limited effect, large dosage, possible inhibition of microbial activity, and difficulty in improving dewatering performance while considering the clarity of filtrate and the solid content of cake.

[0003] Therefore, a large number of patent schemes about composite flocculants have appeared in the industry, but through in-depth analysis, these existing technical schemes still have obvious limitations in the synergistic management of solving the above problems: such as patent number CN102285709 A, a preparation method of an ecological type composite high-efficiency composite flocculant, discloses a composite flocculant generated by the composite reaction of sodium carboxymethyl cellulose and polyaluminum salt. This scheme improves the sludge dewatering effect to some extent, but the scheme compounding two components with opposite charges reduces the active aluminum component, and the cationic charge density is low. This scheme does not involve the improvement of microbial activity in the activated sludge system, and lacks consideration of specific charge density; such as patent number CN116040775 B, a chitosan composite flocculant and a preparation method and application thereof, discloses a chitosan composite flocculant prepared by the reaction of chitosan acetic acid solution and polyaluminum chloride solution. Although this scheme uses the natural properties of chitosan, it uses chitosan acetate with low charge density. In a neutral or weak alkaline sewage environment, the solubility and the amount of positive charge carried by chitosan acetate decrease sharply, resulting in weak electric neutralization ability and unstable flocculation effect.

[0004] In summary, the composite flocculant schemes in the prior art have the following common defects: first, the function is single, or only for dewatering, or cannot consider activity improvement, or even inhibit activity; second, in component selection, high-efficiency electric neutralization, strong bridging ability and biocompatibility cannot be considered at the same time. Therefore, developing a composite flocculant based on functional gradient design of charge density and molecular weight, which can be simultaneously applied to activated sludge system improvement and end sludge dewatering, and has high efficiency and biocompatibility, has become a technical problem to be solved in the field, which is also the starting point of the present application. SUMMARY

[0005] In view of the problems of the prior art, the present application provides a composite flocculant and a use method thereof, which has the advantages of realizing the multiple effects of simultaneously improving the settling performance of activated sludge, enhancing microbial activity and strengthening the dewatering of excess sludge through the gradient flocculation mode of chitosan quaternary ammonium salt-polyaluminum chloride-cationic polyacrylamide, and having high efficiency and biocompatibility, and solves the problems of single function of the composite flocculant in the prior art, which fails to simultaneously consider high efficiency, strong bridging capacity and biocompatibility, resulting in poor effect.

[0006] The present application is implemented in the following manner: a composite flocculant is composed of the following raw materials in mass parts: 5-10 parts of cationic polyacrylamide, 1-5 parts of polyaluminum chloride and 1-5 parts of chitosan quaternary ammonium salt, and the mass parts of the raw materials are as follows: 7 parts of cationic polyacrylamide, 1 part of polyaluminum chloride and 2 parts of chitosan quaternary ammonium salt.

[0007] Preferably, the cationic polyacrylamide has a specific viscosity greater than 10 million and an ionicity of 40%, the polyaluminum chloride has an alumina content of 30% and a salt base of 80%, and the chitosan quaternary ammonium salt has a substitution degree of 98% and a viscosity greater than 100 mPa·s.

[0008] A use method of a composite flocculant is suitable for the composite flocculant, and includes a preparation step of a composite flocculant solution and a dosing step of applying the solution to improve the settling performance and activity of activated sludge and to strengthen the dewatering of excess sludge.

[0009] Preferably, the preparation step of the composite flocculant solution includes the following steps: S1. The cationic polyacrylamide, polyaluminum chloride and chitosan quaternary ammonium salt are weighed according to the above-mentioned ratio; S2. At room temperature, the chitosan quaternary ammonium salt and the polyaluminum chloride are added to tap water with a total mass of 100 times that of the composite flocculant, and stirred at a speed of 500 r / min for 10 min; S3. The cationic polyacrylamide is added to the mixture obtained in step S2, and stirred at a speed of 1000 r / min for 60 min, and after standing and ripening, a composite flocculant solution with a concentration of 10 g / L is prepared.

[0010] Preferably, the dosing step of applying the solution to improve the settling performance and activity of activated sludge includes the following steps: the composite flocculant solution is dosed to the water inlet end of the aeration tank of the activated sludge system, the effective component dosing amount is 1-10 mg / L (relative to the volume of the sludge mixture to be treated), the dosing cycle is once a week, and the dosing opportunity is to complete the solution preparation and dosing within 1 day before the water inlet of the aeration tank.

[0011] As preferred in the present application, the dosing step for strengthening the dewatering of the residual sludge is: the composite flocculant solution is dosed into the residual sludge to be dewatered, and the effective component is dosed in an amount of 5-25 mg / L (relative to the volume of the residual sludge to be treated), and the dosing is completed within 30 minutes before the residual sludge enters the dewatering equipment.

[0012] Compared with the prior art, the present application has the following beneficial effects: the present application is innovatively designed from the perspective of the charge density and molecular weight distribution of the flocculant. The quaternary ammonium salt of chitosan has extremely high cationic charge density, can first and quickly neutralize the negative charge on the surface of the sludge colloidal particles, and effectively compress the double electric layer; the polyaluminum chloride as an inorganic pre-coagulant with medium charge density further completes the electric neutralization and forms micro-flocs; finally, the cationic PAM with relatively low ion degree but extremely high molecular weight fully plays its strong adsorption bridging and net capture and sweeping effect, connecting the micro-flocs into huge, dense and strong flocs. Through the gradient flocculation mode of "quaternary ammonium salt of chitosan (high charge density destabilization) → PAC (medium charge density pre-coagulation) → CPAM (high molecular weight bridging)", the three components form a synergistic effect of "1+1+1>3", synchronously solving the three problems of poor settling, low activity and difficult dewatering, avoiding the defects of single function of the existing flocculants, and being suitable for various activated sludge systems of sewage, significantly reducing the sludge disposal cost and operation difficulty.

[0013] Sludge activity improvement: unlike the traditional flocculants which may inhibit the microbial activity, the quaternary ammonium salt of chitosan in the present application has high efficient electric neutralization ability and biocompatibility, and its natural characteristics can be slowly degraded and utilized by microorganisms, which is a characteristic that the existing high charge density synthetic flocculants do not have. DETAILED DESCRIPTION

[0014] In order to further understand the inventive content, characteristics and effects of the present application, the following examples are exemplified and described in detail as follows.

[0015] The present application will be described in detail below.

[0016] Example 1: Preparation of the composite flocculant solution: 7 g of cationic polyacrylamide with a specific viscosity greater than 100 million, 1 g of polyaluminum chloride with an aluminum oxide content of 30% and a basicity of 80%, and 2 g of quaternary ammonium salt of chitosan with a degree of substitution of 98% and a viscosity greater than 100 mPa.s were weighed. At room temperature, the polyaluminum chloride and the quaternary ammonium salt of chitosan were added to 1 L of tap water, stirred at a speed of 500 r / min for 10 min, then the cationic polyacrylamide was added, and stirred at a speed of 1000 r / min for 60 min. After standing for 30 minutes, 10 g / L of the composite flocculant solution was obtained.

[0017] Application experiment of the flocculation performance of the composite flocculant: Selecting the isoelectric point 4-5, in neutral and weakly basic negative, electrically similar to activated sludge kaolin suspension as the application object, by the composite flocculant of the application and other types of flocculants, model and manufacturer see table 1, respectively, 10g / L solution, take 4g / L calcined kaolin suspension 100mL into 100mL beaker, respectively, 0, 0.5, 1, 2.5, 5, 10mg / L effective component of different dosages are added to the above solution, with 100r / min stirring speed, 1min, 10min, with pipette to take supernatant at 550nm wavelength to determine its absorbance, the lower the supernatant absorbance value, the better the flocculation performance, the comparative data are shown in table 2.

[0018] The results show that, in addition to 40% ionic cationic polyacrylamide flocculation performance slightly lower than the application, the flocculation performance of other single substance flocculants and biological sedimentation aid is far lower than the application, the flocculant of the application in the treatment of 4g / L kaolin suspension, with the increase of the dosage, the flocculation effect shows the trend of first increasing and then decreasing, the optimal dosage is 1mg / L, at this time, the flocculation rate is 96.32%.

[0019] Table 1

[0020] Table 2

[0021] Example 2: preparation of composite flocculant solution: same as example 1.

[0022] Application test for improving the settling performance of activated sludge under aeration state: Take the activated sludge mixed liquor from the end of the aeration tank of the wastewater station of Dongying Tianzheng Chemical Co., Ltd., the MLSS is 4500mg / L, SV 30 85% (poor settling performance), SVI is 189mL / g, in the state of slight sludge bulking, the supernatant is slightly turbid. The 40% ionic cationic PAM of Wuxi Lanbo Chemical Co., Ltd., PAC, the degree of substitution of 98%, viscosity >100mPa.s of chitosan quaternary ammonium salt of Guangdong Qianjin Chemical Reagent Co., Ltd., biological sedimentation aid of Mianjin Environmental Protection Mianjin Environmental Protection Technology (Shanghai) Co., Ltd. and the application for improving the settling performance of activated sludge under aeration state are compared, and they are respectively configured into 10g / L solution before dosing.

[0023] Take 8 1L measuring cylinders, each add 1L of the above sludge mixture, add aeration head, and continuously aerate at 0.5L / min, and each device is dosed under the condition of aeration. The blank group does not add any reagent; the experimental groups 1-3 add 0.1 mL, 0.5 mL, and 1 mL (the effective component dosing amount is 1 mg / L, 5 mg / L, and 10 mg / L, respectively) of the composite flocculant solution; the comparison group 4 adds 1 mL (the effective component dosing amount is 10 mg / L) of 40% ionic cation PAM solution; the comparison group 5 adds 1 mL (the effective component dosing amount is 10 mg / L) of PAC solution; the comparison group 6 adds 1 mL (the effective component dosing amount is 10 mg / L) of chitosan quaternary ammonium salt solution; and the comparison group 7 adds 1 mL (the effective component dosing amount is 10 mg / L) of biological subsidence aid solution; after dosing the reagent, aerate for 5 min, 1 d, and 3 d, and then measure the supernatant OD 550 , SV 30 after 30 min of static settling. The results are shown in Table 3.

[0024] The results show that after adding 10 mg / L of the composite flocculant of the present application to the activated sludge mixture under the condition of continuous aeration, the SV 30 decreases from 85% to 45%, and as the aeration time is prolonged, the sludge settling performance is slightly improved, and the supernatant turbidity gradually increases, but the change is small. Compared with other flocculants, the activated sludge settling performance improvement effect of the present application is best under the same dosing amount and aeration condition.

[0025] Table 3

[0026] Example 3: Preparation of the composite flocculant solution: same as Example 1.

[0027] Application test of strengthening sludge dewatering performance: Take the concentrated residual sludge (its water content is 97.5%) of the wastewater station of Hubei Yitai Pharmaceutical Co., Ltd. as the application object, and compare the sludge dewatering performance of the present application with 40% ionic cation PAM, PAC, and PAM and PAC component mixture of Wuxi Lanbo Chemical Co., Ltd. The reagents are respectively configured into 10 g / L solution before dosing.

[0028] The sludge specific resistance (SRF) is determined by using a Buchner funnel filtration method, a blank group is the original sludge without adding reagent, the experimental groups 1-5 are added with the composite flocculant solution of the application (the effective component adding amount is converted to 5, 10, 15, 20, 25 mg / L respectively), the comparison group 6 is added with PAC solution (the effective component adding amount is converted to 20 mg / L), the comparison group 7 is added with 40% ionicity cationic PAM solution (the effective component adding amount is converted to 20 mg / L), and the comparison group 8 is added with PAC and PAM two-component composite flocculant (the effective component adding amount of PAC and PAM is converted to 6 mg / L and 14 mg / L respectively), and the results are shown in Table 4.

[0029] The results show that when the adding amount reaches 20 ppm, the dewatering effect of the composite flocculant of the application is much better than that of each comparison group, the sludge specific resistance (SRF) is the lowest, which is reduced from 15.8*1012 m / kg to 1.5*1012 m / kg, the moisture content of the sludge cake is the lowest, and the comprehensive dewatering performance is the best. A very good effect can be achieved at a lower adding amount (10-15 ppm), and there is a significant economic advantage.

[0030] Table 4

[0031] It should be noted that the relational terms herein such as first and second and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0032] Although the embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, alternatives, and variations can be made thereto without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A composite flocculant, characterized in that, It is composed of the following raw materials in parts by weight: 5-10 parts cationic polyacrylamide, 1-5 parts polyaluminum chloride, and 1-5 parts chitosan quaternary ammonium salt. The mass ratio of the raw materials is: 7 parts cationic polyacrylamide, 1 part polyaluminum chloride, and 2 parts chitosan quaternary ammonium salt.

2. The composite flocculant as described in claim 1, characterized in that: The cationic polyacrylamide has an intrinsic viscosity greater than 10 million and an ionicity of 40%. The polyaluminum chloride has an alumina content of 30% and a basicity of 80%. The chitosan quaternary ammonium salt has a degree of substitution of 98% and a viscosity greater than 100 mPa·s.

3. A method for using a composite flocculant, characterized in that, The composite flocculant according to any one of claims 1-2 includes the step of preparing the composite flocculant solution and the step of adding the solution to improve the settling performance and activity of activated sludge and enhance the dewatering of excess sludge.

4. The method of using a composite flocculant as described in claim 3, characterized in that: The preparation steps of the composite flocculant solution include: S1. Weigh out cationic polyacrylamide, polyaluminum chloride and chitosan quaternary ammonium salt according to the above ratio; S2. At room temperature, add chitosan quaternary ammonium salt and polyaluminum chloride to tap water with a total mass of 100 times that of the composite flocculant, and stir at 500 r / min for 10 min. S3. Add cationic polyacrylamide to the mixture obtained in step S2, stir at 1000 r / min for 60 min, and let it stand to mature to obtain a composite flocculant solution with a concentration of 10 g / L.

5. The method of using a composite flocculant as described in claim 4, characterized in that: The solution is used in the following steps to improve the settling performance and activity of activated sludge: the composite flocculant solution is added to the inlet of the aeration tank of the activated sludge system, the effective component dosage is 1-10 mg / L (relative to the volume of the mixed liquid of the sludge to be treated), the addition cycle is once a week, and the addition time is to complete the solution preparation and addition within 1 day before the aeration tank is filled with water.

6. The method of using a composite flocculant as described in claim 4, characterized in that: The solution is applied to enhance the dewatering of excess sludge as follows: the composite flocculant solution is added to the excess sludge to be dewatered, with an effective component dosage of 5-25 mg / L (relative to the volume of the excess sludge to be treated), and the addition is completed within 30 minutes before the excess sludge enters the dewatering equipment.

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