Plant ash loaded cation modified chitosan-polyacrylamide efficient sludge dehydrating agent as well as preparation method and application thereof

Abstract

The invention discloses a plant ash loaded cation modified chitosan-polyacrylamide efficient sludge dehydrating agent as well as a preparation method and application thereof, and belongs to the technical field of sludge dehydration. The preparation method of the efficient sludge dehydrating agent comprises the following steps: firstly, carrying out cationic grafting modification on chitosan by adopting dimethyl diallyl ammonium chloride, and then introducing the cationic grafting modified chitosan and polyacrylamide into the surface of plant ash, so that the surface of the plant ash is obviously changed; and a discontinuous, multi-gap, disordered and irregular multi-layer structure is presented. The specific surface area of the plant ash is increased by introducing the cationic grafting modified chitosan and the polyacrylamide, and the complex surface structure is beneficial for the plant ash to generate gaps which are difficult to compress in a sludge filter cake in the sludge dewatering process, so that the dewatering performance of the sludge is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge dehydration, and more particularly relates to a wood ash-loaded cation-modified chitosan-polyacrylamide high-efficiency sludge dehydrator, and a preparation method and application thereof. Background Art

[0002] Chemical sludge conditioning refers to the use of chemicals to alter the physical and chemical properties of sludge and improve its dewatering capacity. Chemical sludge conditioning methods include acid-base conditioning, flocculation conditioning, oxidation conditioning, and the use of inert materials. Currently, flocculation conditioning is the most commonly used sludge conditioning method (hence, dewatering agents in chemical sludge conditioning are also called flocculants). It is widely used due to its simplicity and high efficiency. Inorganic flocculant conditioning involves adding inorganic cations to sludge to improve its agglomeration and settling properties through charge neutralization and bridging adsorption. Aluminum salts are the most commonly used inorganic flocculants. However, studies have shown that this type of flocculant can easily leave residual aluminum ions in the water and sludge, posing a potential threat to humans and the environment. Furthermore, their high price increases sludge treatment costs. Organic flocculant conditioning primarily involves adding organic flocculants to reduce the negative surface charge of sludge flocs, reduce electrostatic repulsion between flocs, and bridge sludge flocs, promoting floc aggregation and settling. The most common organic flocculant is polyacrylamide (PAM). However, studies have also shown that acrylamide, a monomer in PAM, poses a potential threat to humans. Acrylamide is a known neurotoxin, and long-term exposure to high concentrations of acrylamide may be harmful to the human body.

[0003] In recent years, to avoid secondary pollution, natural polymer water treatment flocculants based on polysaccharides such as starch, cellulose, and chitosan have been increasingly studied as sludge conditioners due to their abundant sources, non-toxicity, environmental friendliness, and excellent flocculation properties. These flocculants show promising application prospects in sludge conditioning and dewatering. However, conventional natural polymer flocculants generally suffer from disadvantages such as low molecular weight, low cationic content, and solubility only in acidic solutions, resulting in poor dewatering performance and a narrow range of applications. Therefore, the development of efficient sludge dewatering agents with excellent dewatering performance, biodegradability, good biocompatibility, no secondary pollution, and simple preparation methods is of great significance. Summary of the Invention

[0004] The purpose of the present invention is to provide a wood ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dewatering agent and its preparation method and application, so as to solve the problems existing in the above-mentioned prior art and realize the preparation of a high-efficiency sludge dewatering agent with excellent dehydration effect, biodegradability, good bioaffinity, no secondary pollution and simple preparation method.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is to provide a method for preparing a wood ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dehydrating agent, comprising the following steps:

[0007] Under nitrogen atmosphere, dimethyldiallylammonium chloride solution, chitosan solution and initiator are mixed and then subjected to grafting reaction to obtain cationic grafted modified chitosan;

[0008] The cationic grafted modified chitosan and polyacrylamide are dissolved in a solvent and mixed to obtain a mixed solution, and then wood ash is added to the mixed solution, and the mixture is dried to obtain the wood ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dehydrating agent.

[0009] Preferably, the concentration of the dimethyldiallylammonium chloride solution is 1-2.5 wt %; the chitosan solution is an acetic acid solution of chitosan; the concentration of the chitosan solution is 0.5-1.5 wt %; and the initiator includes one or more of cerium sulfate, potassium persulfate and ammonium persulfate.

[0010] Preferably, the volume ratio of the dimethyl diallyl ammonium chloride solution to the chitosan solution is 1:1-2; and the mass of the initiator is 1.5-2.5% of the mass of the chitosan in the chitosan solution.

[0011] Preferably, the grafting reaction temperature is 50-60° C., and the time is 2-3 hours.

[0012] Furthermore, after the grafting reaction is completed, the product is sequentially subjected to the steps of precipitation with anhydrous ethanol, washing and filtration, drying, purification and drying; the drying method independently includes oven drying or freeze drying; the purification includes reflux extraction in a Soxhlet extractor using anhydrous ethanol.

[0013] Preferably, the solvent comprises one or more of acetic acid, formic acid and hydrochloric acid.

[0014] Preferably, in the mixed solution, the concentration of the cationic grafted modified chitosan is 0.5-1 wt%, and the concentration of polyacrylamide is 1.5-2.5 wt%; and the usage ratio of the wood ash to the mixed solution is 2-3 g:100 mL.

[0015] Preferably, the mixing temperature is 50-55°C and the time is 1.5-2.5 hours; the drying temperature is 40-50°C.

[0016] The second technical solution of the present invention is to provide a wood ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dewatering agent prepared by the above preparation method.

[0017] The third technical solution of the present invention is to provide the application of the above-mentioned wood ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dewatering agent in sludge chemical conditioning.

[0018] The fourth technical solution of the present invention is to provide a method for chemical conditioning of sludge, comprising the following steps:

[0019] The plant ash-loaded cation-modified chitosan-polyacrylamide high-efficiency sludge dehydrating agent is added to the sludge at a dosage of 13-17 mg / g to chemically condition the sludge.

[0020] The technical mechanism of the present invention is as follows:

[0021] The present invention first uses dimethyldiallylammonium chloride to perform cationic grafting modification on chitosan. The purpose of using dimethyldiallylammonium chloride is to introduce highly water-soluble quaternary ammonium salt cationic groups. Cationic grafting modification of chitosan with dimethyldiallylammonium chloride significantly enhances the material's water solubility and stability, strengthens the chitosan's cationic charge density, and thus significantly improves the sludge dewatering performance of the sludge dewatering agent.

[0022] During the cationic grafting modification of chitosan, the grafting reaction parameters and raw material ratio have a significant impact on the grafting effect. An appropriate amount of monomer facilitates chain growth, while an excessive amount may impair the grafting reaction due to steric hindrance. A low initiator concentration can easily lead to insufficient reaction, while a high initiator concentration can exacerbate chain termination. Reaction temperature also affects the balance between initiator decomposition and chain growth, thereby affecting grafting efficiency. By optimizing these factors, modified chitosan with excellent grafting performance can be obtained.

[0023] Secondly, the prepared cationic grafted modified chitosan and polyacrylamide are attached to the surface of wood ash to construct a synergistic dehydration system. The wood ash acts as a skeleton material, and the modified chitosan and polyacrylamide attached to it play an electrical neutralization and adsorption bridging role, thereby significantly improving the dehydration performance of the prepared sludge dehydrator.

[0024] The present invention uses cationic grafted modified chitosan in combination with polyacrylamide and wood ash to condition sludge. Cationic grafted modified chitosan is a modified natural polymer material, which has the advantages of excellent flocculation effect, abundant sources, non-toxicity, and environmental friendliness. It can reduce the use of synthetic polymer flocculants such as polyacrylamide to a certain extent; polyacrylamide is a synthetic organic water treatment agent, which can reduce the negative charge on the surface of sludge flocs and reduce the electrostatic repulsion between flocs during sludge dewatering, as well as bridge sludge flocs to promote floc aggregation and sedimentation; wood ash is a common agricultural waste, which can produce difficult-to-compress voids in the sludge filter cake during sludge dewatering, thereby promoting dewatering efficiency. The synergistic effect of the three is manifested as follows: cationic modified chitosan exerts an electrical neutralization effect to destabilize sludge particles, polyacrylamide agglomerates and settles sludge particles through adsorption and bridging, and wood ash produces difficult-to-compress voids inside the sludge filter cake, reducing sludge specific resistance and improving water discharge efficiency.

[0025] The present invention discloses the following technical effects:

[0026] 1. The present invention graft-modifies chitosan to obtain cationic graft-modified chitosan, which improves chitosan's solubility and flocculation and dewatering properties. Furthermore, attaching the cationic graft-modified chitosan and polyacrylamide to the surface of wood ash allows the wood ash to act as a skeleton conditioner during sludge dewatering, improving the sludge dewatering effect. Furthermore, the use of wood ash can reduce the amount of cationic graft-modified chitosan and polyacrylamide used in actual use, thereby reducing costs.

[0027] 2. The high-efficiency sludge dewatering agent prepared using this invention can reduce the use of synthetic polymer flocculants during the sludge dewatering process, lowering the residual rate of synthetic polymer flocculants and thus reducing the risk of secondary pollution. Furthermore, the product obtained by this technical solution can effectively condition sludge. The introduction of cationic-modified chitosan can reduce the zeta potential of the sludge itself, significantly improving the filtration performance of the conditioned sludge.

[0028] 3. The present invention introduces cationic grafted modified chitosan and polyacrylamide into the surface of wood ash, which can cause its surface to change significantly, presenting a discontinuous, multi-porous, disorderly and irregular multi-layer structure, indicating that the introduction of cationic grafted modified chitosan and polyacrylamide increases the specific surface area of ​​wood ash. This complex surface structure is conducive to the formation of difficult-to-compress gaps in the sludge filter cake during the sludge dewatering process, thereby improving the dewatering performance of the sludge.

[0029] 4. The preparation conditions of the present invention are simple, and the obtained high-efficiency sludge dewatering agent ensures good sludge dewatering effect and can be better used in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a physical picture of the high-efficiency sludge dewatering agent product obtained in Example 1.

[0031] Figure 2 This is the condition of the sludge after being conditioned using the high-efficiency sludge dehydrating agent obtained in Example 1.

[0032] Figure 3 The changes in sludge moisture content and sludge specific resistance after conditioning with the high-efficiency sludge dehydrating agent obtained in Example 1 are shown.

[0033] Figure 4 This shows the change in sludge moisture content after conditioning with commercially available conventional sludge dehydrating agents.

[0034] Figure 5 This shows the change in sludge specific resistance after treatment with commercially available conventional sludge dewatering agents.

[0035] Figure 6 This is the change of sludge moisture content and sludge specific resistance after conditioning with the addition of wood ash alone.

[0036] Figure 7 These are SEM images of the wood ash and the resulting high-efficiency sludge dehydrating agent described in Example 1, wherein the left image is the wood ash and the right image is the high-efficiency sludge dehydrating agent.

[0037] Figure 8 This is the XRD pattern of the cationic grafted modified chitosan described in Example 1.

[0038] Figure 9 These are SEM images of the chitosan described in Example 1 before and after cationic grafting modification, wherein the left image is the chitosan before cationic grafting modification, and the right image is the chitosan after cationic grafting modification.

[0039] Figure 10 This is the thermogravimetric curve of the chitosan before and after cationic grafting modification described in Example 1.

[0040] Figure 11 This is the FITR spectrum of the chitosan described in Example 1 before and after cationic grafting modification.

[0041] Figure 12 The figure shows the effect curve of the dosage of sludge dewatering agent obtained under different preparation conditions on the moisture content of sludge filter cake and sludge specific resistance; among them, a corresponds to the mass ratio of cationic modified chitosan, polyacrylamide and wood ash of 1:1:8, b corresponds to the mass ratio of cationic modified chitosan, polyacrylamide and wood ash of 1:2:7, and c corresponds to the mass ratio of cationic modified chitosan, polyacrylamide and wood ash of 1:4:5.

[0042] Figure 13 The influence of parameters in the chitosan grafting modification process and the amount of raw materials on the properties of cationic grafted modified chitosan. DETAILED DESCRIPTION

[0043] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0044] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0045] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0046] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0047] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0048] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0049] Unless otherwise specified, the raw materials used in the present invention are all commercially available products, and the sources of the commercially available products do not affect the technical effects of the present invention.

[0050] Example 1

[0051] This embodiment provides a preparation of an efficient sludge dehydrating agent, and the specific steps are as follows:

[0052] An appropriate amount of chitosan was weighed and dissolved in a dilute acetic acid solution to prepare a chitosan solution with a concentration of 1 wt %; in a closed container, a water bath was adjusted to 55° C., and a slow flow of nitrogen was continuously introduced for 15 min to exhaust oxygen; the temperature was controlled, a 0.5 wt % cerium sulfate solution (the mass of cerium sulfate was 2% of the mass of chitosan) was added, and stirred for 2 min, followed by addition of a 3 wt % dimethyldiallyl ammonium chloride solution with the same volume as the chitosan solution, and the mixture was reacted at a constant temperature for 2.5 h, cooled, precipitated with anhydrous ethanol, washed and filtered several times, dried to constant weight, and ground to obtain a milky white powder, i.e., a crude grafted product; the crude grafted product was placed in a Soxhlet extractor, refluxed with anhydrous ethanol, and the extracted product was dried to constant weight to obtain a cationic grafted modified chitosan.

[0053] 0.5 wt% cationic grafted chitosan and 2 wt% polyacrylamide were dissolved in 100 mL of 1 wt% acetic acid solution. A constant-temperature magnetic stirrer was set at 50°C, 100 rpm, and run for 2 hours until the mixture was completely dissolved. 2.5 g of wood ash powder was then added and thoroughly stirred to mix. The mixture was then dried in a vacuum drying oven at 45°C to obtain a highly efficient sludge dehydrator.

[0054] Figure 1 This is a physical picture of the high-efficiency sludge dewatering agent product obtained in Example 1.

[0055] Figure 2 This is the condition of the sludge after being conditioned using the high-efficiency sludge dehydrating agent obtained in Example 1.

[0056] Figure 3 The changes in sludge moisture content and sludge specific resistance after conditioning with the high-efficiency sludge dehydrating agent obtained in Example 1 are shown.

[0057] Figure 7 These are SEM images of the wood ash and the resulting high-efficiency sludge dehydrating agent described in Example 1, wherein the left image is the wood ash and the right image is the high-efficiency sludge dehydrating agent.

[0058] Figure 8 This is the XRD pattern of the cationic grafted modified chitosan described in Example 1.

[0059] Figure 9 These are SEM images of the chitosan described in Example 1 before and after cationic grafting modification, wherein the left image is the chitosan before cationic grafting modification, and the right image is the chitosan after cationic grafting modification.

[0060] Figure 10 This is the thermogravimetric curve of the chitosan before and after cationic grafting modification described in Example 1.

[0061] Figure 11This is the FITR spectrum of the chitosan described in Example 1 before and after cationic grafting modification.

[0062] Figure 7 The left picture shows that the surface of wood ash is smooth. After the modified chitosan and polyacrylamide are attached to the surface of wood ash, the surface of the modified wood ash changes significantly, as shown in the right picture, showing a discontinuous, multi-void, disorderly and irregular multi-layer structure, indicating that the introduction of modified chitosan and polyacrylamide increases the surface area of ​​wood ash, which can prove that the material is successfully attached to the surface of wood ash.

[0063] Depend on Figure 8 Chitosan and grafted chitosan exhibit distinct crystallization peaks. The peaks at 2θ = 12° and 20° correspond to the characteristic chitosan 020 and 110 reflections, respectively. These peaks are significantly weakened and broadened in the modified chitosan, indicating a lower crystallinity in the grafted chitosan. This change is attributed to the introduction of DMDAAC monomer during the grafting reaction, which disrupts the chitosan's original structure and reduces intermolecular hydrogen bonding. Analysis of the XRD spectrum demonstrates the successful grafting of DMDAAC monomer into the chitosan molecular chain.

[0064] Figure 9 The left image shows a scanning electron micrograph of chitosan before grafting modification. The surface of the chitosan before modification is regular. However, after DMDAAC is grafted onto the chitosan molecular chain, as shown in the right image, the surface of the modified chitosan undergoes significant changes, breaking up the chitosan surface into a fragmented, irregular porous structure. This significantly increases the specific surface area of ​​the modified chitosan. This leads to the conclusion that a graft copolymerization reaction has occurred between chitosan and the grafting monomer DMDAAC.

[0065] like Figure 10 As shown, the thermal gravimetric loss curves of chitosan and modified chitosan exhibit similar peak shapes, but differ in peak value. The first weight loss of chitosan occurs between 20°C and 270°C, with a weight loss of 5%, likely due to evaporation of adsorbed and bound water on the sample surface. The second weight loss of chitosan occurs between 270°C and 800°C. The first weight loss of the modified chitosan occurs between 20°C and 230°C, while the second weight loss occurs between 230°C and 800°C. This second thermal decomposition of the modified product is primarily due to the instability of the quaternary ammonium salt and the gradual decomposition of organic matter with increasing temperature. The final residual weights of chitosan and modified chitosan are 34.5% and 35.5% respectively. Overall, the grafted product is less thermally stable than chitosan. This is because the introduction of the DMDAAC monomer into the chitosan chain significantly reduces the number of hydroxyl groups on the chitosan chain, weakening hydrogen bonding within the molecule. This is partly due to the instability of the quaternary ammonium salt. The thermogravimetric curves of the grafted product and chitosan once again proved that the monomer DMDAAC was successfully grafted onto the chitosan backbone.

[0066] Figure 11 In 2868cm -1 , 1079cm -1 The 3442cm in the infrared spectrum of original chitosan is the CH stretching vibration absorption peak in the methyl group of chitosan and the CO stretching vibration absorption peak in the alcohol group. -1 Redshift to 3419 cm -1 The absorption peak at 2922 cm -1 and 2868cm -1 Move to 2929cm -1 and 2887cm -1 This is due to the introduction of -CH3 in the monomer DMDAAC structure; according to the structural analysis of infrared spectroscopy, the monomer DMDAAC has been successfully grafted onto the chitosan chain.

[0067] Example 2

[0068] Verify the influence of parameters and raw material dosage in the chitosan grafting modification process on the performance of cationic grafted chitosan: the specific experimental steps are as follows:

[0069] The orthogonal experimental method was used to verify the effects of parameters and raw material dosage in the grafting modification process of chitosan on the performance of cationic grafted modified chitosan. The grafting rate and dehydration performance of the modified material were used as reference standards. The modification experimental steps were as follows: weigh an appropriate amount of chitosan and dissolve it in dilute acetic acid solution to prepare a chitosan solution with a concentration of 1wt%; in a closed container, the water bath was adjusted to 55°C, and a slow flow of nitrogen was continuously introduced for 15 minutes to exhaust the oxygen; the temperature was controlled, a certain amount of 0.5wt% cerium sulfate solution was added, stirred for 2 minutes, and then a certain amount of 3wt% dimethyldiallylammonium chloride solution was added, and the reaction was carried out at a constant temperature for 2.5 hours, cooled, precipitated with anhydrous ethanol, washed and filtered several times, dried to constant weight, and ground to obtain a milky white powder, i.e., a crude grafted product; the crude grafted product was loaded into a Soxhlet extractor and refluxed with anhydrous ethanol. The extracted product was dried to constant weight to obtain a cationic grafted modified chitosan.

[0070] The dehydration experiment steps are as follows: the modified chitosan powder with different grafting rates is added into pure water and stirred until completely dissolved to prepare a solution with a concentration of 0.5wt%. Equal amounts of modified chitosan solutions with different grafting rates are added to 100mL of municipal sludge, and stirred rapidly at a stirring speed of 200r / min for 2min, and then slowly stirred at a speed of 80r / min for 15min. After stirring, the sludge is settled for 15min, and the moisture content and sludge specific resistance of the sludge after settlement are measured.

[0071] The specific parameters of the orthogonal experiment are shown in Table 1, and the data on the influence of parameters and material ratios on the grafting rate of modified chitosan during the modification process are shown in Table 2.

[0072] Table 1 Orthogonal experiment table

[0073]

[0074] Table 2 Orthogonal experiment results and result analysis

[0075] serial number A B C D G / ％ 1 1 45 2.5 1:1 63.2 2 1 55 3.5 1:3 87.22 3 1 65 4.5 1:5 79.31 4 2 45 3.5 1:5 78.75 5 2 55 4.5 1:1 79.55 6 2 65 2.5 1:3 88.32 7 3 45 4.5 1:3 78.5 8 3 55 2.5 1:5 78 9 3 65 3.5 1:1 55.13 ∑G1j / 3 76.58％ 73.48％ 76.51％ 65.96％ - ∑G2j / 3 82.21％ 81.59％ 73.70％ 84.68％ - ∑G3j / 3 70.54％ 74.25％ 79.12％ 78.69％ - ΔG 11.67％ 8.11％ 5.42％ 18.72％ -

[0076] The results are as follows: The grafting efficiency first increases and then decreases with increasing dimethyldiallylammonium chloride monomer mass. When the chitosan mass is constant, an appropriate amount of monomer promotes chain growth by increasing the reaction probability. However, an excess of monomer inhibits intermolecular interactions due to steric hindrance, inducing homopolymerization and resulting in a decrease in the grafting efficiency. Initiator concentration significantly affects the grafting efficiency: at low concentrations, the number of free radicals increases, accelerating chain growth. However, excessive initiator leads to excessive free radical concentration, increasing the chain termination probability while reducing polymer molecular weight, which is detrimental to flocculation performance. The temperature reaches an optimal value at 55°C, where the initiator decomposition rate is balanced with the chain growth rate. Further increases in temperature trigger explosive free radical generation, resulting in the chain termination rate dominating the reaction. Reaction time has no significant effect within the selected range. Based on the range of influence, the factors affecting the grafting efficiency are, from greatest to least, D (chitosan / DMDAAC mass ratio) > A (initiator percentage in chitosan mass) > B (temperature) > C (time). The optimal preparation conditions combined with economic factors were: chitosan / DMDAAC mass ratio of 1:3, initiator mass percentage of chitosan of 2%, reaction temperature of 55°C, and reaction time of 2.5h.

[0077] The influence of grafting rate of materials on sludge dewatering performance is as follows Figure 13 shown.

[0078] Depend on Figure 13 It can be seen that as the grafting rate increases, the water content of the filter cake first decreases and then increases. The increase in grafting rate helps to increase the molecular weight. When the cationic degree is similar, the adsorption and bridging effect plays a dominant role in the entire flocculation process. Therefore, when the grafting rate is low, the adsorption and bridging effect is weak, so the flocculation effect is poor. When the grafting rate is too high, the relative molecular weight is too large, resulting in an increase in relative viscosity at the same addition amount, and it cannot be fully mixed with the sludge. At this time, the charge neutralization effect and bridging adsorption effect are seriously limited. The grafting rate of modified chitosan with the best dehydration effect is about 85%.

[0079] Example 3

[0080] Verify the effects of parameters and raw material dosage during the preparation of high-efficiency sludge dewatering agent on its performance:

[0081] According to the material ratios listed in Table 3, a 0.5wt% cationic grafted chitosan solution and a 2wt% polyacrylamide solution were mixed in the specified proportions. A constant-temperature magnetic stirrer was maintained at 50°C, 100 rpm, and run for 1 hour until the two materials were evenly mixed. Wood ash powder was then added in a specified proportion and stirred thoroughly to achieve a uniform mixture. The mixture was then dried in a vacuum drying oven at 45°C to produce three highly efficient sludge dewatering agents with different material ratios.

[0082] The three obtained sludge dehydrating agents were dissolved into 1wt% solution, and the sludge dehydrating agent solutions were added to 100mL of municipal sludge according to a certain dosage gradient, and then rapidly stirred at a stirring speed of 200r / min for 2min, and then slowly stirred at a speed of 80r / min for 15min. After the stirring was completed, the sludge was settled for 15min, and the moisture content and sludge specific resistance of the sludge after settlement were measured.

[0083] The material quality ratio is shown in Table 3:

[0084] Table 3 Material mass ratio

[0085]

[0086]

[0087] The results are as follows Figure 12 shown.

[0088] Depend on Figure 12 It can be seen that when the mass ratio of modified chitosan: polyacrylamide: wood ash is 1:4:5, the best dehydration effect can be obtained, and the moisture content of the mud cake is reduced from 83.5% to the lowest 69.2%; the sludge specific resistance is reduced from 1.25×10 13 m / kg decreased to 8.4×10 11 m / kg.

[0089] Example 4

[0090] Verify the moisture content and sludge specific resistance of the sludge filter cake at different dosages of the high-efficiency sludge dehydrating agent obtained in Example 1:

[0091] The residual sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Baotou City was selected as the treatment object. Sludge dehydrating agent solution was added to 100 mL of municipal sludge according to a certain dosage gradient. Then, the sludge was rapidly stirred at a stirring speed of 200 r / min for 2 minutes, and then slowly stirred at a speed of 80 r / min for 15 minutes. After stirring, the sludge was settled for 15 minutes. The moisture content and sludge specific resistance of the sludge after settlement were measured.

[0092] The results are as follows Figure 3 shown.

[0093] Figure 3 The moisture content and sludge resistance of the sludge filter cake under different dosages of the high-efficiency sludge dehydrating agent obtained in Example 1 are shown in Table 1. Figure 3 It can be seen that with the increase of the dosage, the moisture content of the sludge filter cake and the sludge specific resistance show a trend of first rapidly decreasing to the optimal value and then slightly increasing. When the flocculant is excessively added, a downward trend will appear. The optimal dosage is 14 mg / gDS. Under this dosage, MC is 69.2% and SRF is 8.4×10 11 m / kg. This is because the new flocculant contains a large number of cationic groups on its surface, which neutralize the negatively charged sludge particles, causing them to destabilize and aggregate, leading to a continuous decrease in MC and SRF values. When excessive flocculant addition causes the sludge dewatering effect to deteriorate, the analysis shows that the excessive amount of polymer materials in the sludge makes it difficult for the molecular chains to stretch normally, resulting in excessively large sludge floc particles, which worsens the dewatering process. As a result, MC and SRF rise again, and the sludge settling performance weakens.

[0094] Comparative Example 1

[0095] Commercially available cationic polyacrylamide CPAM (purchased from Tianjin Zhonglian Chemical Reagent Co., Ltd.) was used alone as a dehydrating agent.

[0096] Comparative Example 2

[0097] Commercially available polyacrylamide (PAM) (purchased from Tianjin Zhonglian Chemical Reagent Co., Ltd.) was used alone as a dehydrating agent.

[0098] Comparative Example 3

[0099] Chitosan was used alone as a dehydrating agent.

[0100] Comparative Example 4

[0101] Wood ash is used alone as a dehydrating agent.

[0102] Performance testing:

[0103] The dehydrating agents obtained in Example 1 and Comparative Examples 1 to 4 were used to condition the sludge. The specific method is as follows:

[0104] The dehydrating agents described in Example 1 and Comparative Examples 1 to 4 were added to the sludge (residual sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Baotou City) in an amount of 0 to 20 mg / g DS, and the sludge was subjected to a conditioning process of rapid stirring at 200 r / min for 3 minutes, slow stirring at 80 r / min for 15 minutes, and sedimentation treatment for 20 minutes. The results are shown in FIG. Figures 3 to 6 shown.

[0105] Depend on Figure 3It can be seen that with the increase of the dosage of high-efficiency sludge dewatering agent, the moisture content of sludge filter cake and sludge specific resistance showed a trend of rapid decrease, reaching the optimal value and then slightly increasing. The optimal dosage was 14 mg / gDS. Under this dosage, MC was 69.2% and SRF was 8.4×10 11 The effect is better than that of the four commercially available sludge dewatering agents in Comparative Example 1, Comparative Example 2, Comparative Example 3 and Comparative Example 4.

[0106] Depend on Figure 4 It can be seen that when cationic polyacrylamide is added alone at the optimal dosage, the moisture content of the sludge filter cake is 72.1%, the moisture content of the sludge filter cake after chitosan treatment is 73.5%, and the moisture content of the sludge filter cake after polyacrylamide treatment is 73.2%.

[0107] Depend on Figure 5 It can be seen that when cationic polyacrylamide is added alone at the optimal dosage, the sludge resistance is 2×10 12 m / kg, the moisture content of the sludge cake after chitosan treatment was 2.5×10 12 m / kg, the moisture content of the sludge cake after polyacrylamide treatment is 2×10 12 m / kg.

[0108] Depend on Figure 6 It can be seen that with the increase of the amount of wood ash added, the sludge specific resistance and the moisture content of the mud cake continue to decrease. Under the condition of 1000 mg / g DS addition, the sludge specific resistance is the lowest at 2.3×10 12 m / kg, and the moisture content of the sludge filter cake is 75%.

[0109] From the above tests, it can be seen that the sludge dewatering agent is better than the conventional sludge dewatering agents on the market in conditioning sludge, and has the advantages of good effect and small dosage.

[0110] cost:

[0111] The preparation conditions in Example 1 proved to be optimal for the efficient sludge dewatering agent. A cost analysis of the sludge dewatering agent prepared using the method described in Example 1 was conducted. The specific calculations are as follows: During the preparation of modified chitosan, the optimal chitosan:DMDAAC monomer ratio for optimal treatment is 1:3. Therefore, a minimum of 0.25 tons of chitosan and 0.75 tons of DMDAAC monomer are required to produce 1 ton of modified chitosan, resulting in a cost of 25,595 yuan. Wood ash costs 800 yuan per ton, and PAM costs 12,000 yuan per ton. The efficient sludge dewatering agent prepared using the ratios in Example 1 (i.e., a modified chitosan:polyacrylamide:wood ash ratio of 1:4:5) results in a cost of approximately 8,000 yuan per ton. The costs of other commercially available dewatering agents are shown in Table 4.

[0112] Table 4

[0113]

[0114]

[0115] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0116] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a wood ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dehydrating agent, characterized in that: The steps include: Under nitrogen atmosphere, dimethyldiallylammonium chloride solution, chitosan solution and initiator are mixed and then subjected to grafting reaction to obtain cationic grafted modified chitosan; The cationic grafted modified chitosan and polyacrylamide are dissolved in a solvent and mixed to obtain a mixed solution, and then wood ash is added to the mixed solution, and the mixture is dried to obtain the wood ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dehydrating agent.

2. The preparation method according to claim 1, characterized in that The concentration of the dimethyldiallylammonium chloride solution is 1 to 2.5 wt %; and / or the chitosan solution is an acetic acid solution of chitosan; the concentration of the chitosan solution is 0.5 to 1.5 wt %; and / or the initiator includes one or more of cerium sulfate, potassium persulfate and ammonium persulfate.

3. The preparation method according to claim 1, characterized in that The volume ratio of the dimethyl diallyl ammonium chloride solution to the chitosan solution is 1:1-2; the mass of the initiator is 1.5-2.5% of the mass of the chitosan in the chitosan solution.

4. The preparation method according to claim 1, characterized in that The grafting reaction temperature is 50-60° C. and the time is 2-3 hours.

5. The preparation method according to claim 1, characterized in that The solvent includes one or more of acetic acid, formic acid and hydrochloric acid.

6. The preparation method according to claim 1, characterized in that In the mixed solution, the concentration of cationic grafted modified chitosan is 0.5-1 wt%, and the concentration of polyacrylamide is 1.5-2.5 wt%. The usage ratio of the wood ash to the mixed solution is 2-3 g:100 mL.

7. The preparation method according to claim 1, characterized in that The mixing temperature is 50-55°C and the time is 1.5-2.5 hours; and / or the drying temperature is 40-50°C.

8. The wood ash-loaded cation-modified chitosan-polyacrylamide high-efficiency sludge dewatering agent prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the wood ash-loaded cation-modified chitosan-polyacrylamide high-efficiency sludge dewatering agent according to claim 8 in sludge chemical conditioning.

10. A method for chemical conditioning of sludge, characterized in that: The steps include: The plant ash-loaded cationic modified chitosan-polyacrylamide high-efficiency sludge dehydrating agent according to claim 8 is added to the sludge in an amount of 13 to 17 mg / g to chemically condition the sludge.

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