A sludge deep dewatering conditioner of tannin grafted polymer and its synthesis method and industrial application

Abstract

The application belongs to the technical field of sewage treatment, and specifically discloses a sludge deep dewatering conditioner based on tannin acid grafting polymer and a synthesis method and industrial application thereof. The conditioner is a novel derivative of tannin acid grafted on a synthetic polymer or natural polymer main chain by chemical bonding, which contains high-density cationic active sites and three-dimensional network chelating groups in the molecular structure, and has strong electric neutralization capacity and multi-level adsorption characteristics. The derivative is realized by directional synthesis technology for the first time and is innovatively applied in the field of sludge dewatering, can efficiently destroy the structure of sludge extracellular polymeric substances, and significantly improve the combined water release efficiency. The conditioner is precisely designed in the molecular structure, can reduce the dosage of the conditioner while realizing more than 20% increase of the sludge dewatering rate, and the grafting rate and charge density parameters constitute the core protection features, thereby breaking through the technical bottleneck of traditional flocculants in sludge deep dewatering.

Description

Technical Field

[0001] The present invention, in the field of wastewater treatment technology, specifically relates to a tannic acid-grafted polymer-based sludge deep dehydration conditioner, its synthesis method, and industrial applications. This conditioner chemically grafts tannic acid onto a synthetic or natural polymer backbone, forming a novel derivative with a high density of cationic active sites and a three-dimensional network of chelating groups. This agent effectively destroys the extracellular polymeric structure of sludge and releases bound water, significantly improving dehydration efficiency. Background Art

[0002] Sludge is a by-product of sewage treatment. Its high water content (95% to 99%) and strong colloidal properties make dehydration extremely difficult. Free water accounts for about 70% of the sludge and can be removed mechanically, while the remaining 30% of capillary water, bound water and intracellular water need to rely on chemical conditioning to achieve release. In the existing technology, although inorganic flocculants (such as polyaluminum and polyiron) have strong electrical neutralization ability, they have problems such as metal residual toxicity, corrosion of equipment and impact on sludge resource utilization; although organic polymer flocculants (such as polyacrylamide) have excellent adsorption and bridging properties, they have insufficient electrical neutralization ability and are difficult to destroy the stable structure of sludge extracellular polymers (EPS), resulting in low efficiency in bound water release.

[0003] In recent years, researchers have tried to optimize the dewatering effect by compounding agents or improving the dosing method, but have not been able to break through the structural limitations of traditional flocculants. For example, the charge density of a single cationic polymer is insufficient to effectively compress the sludge colloidal double layer; although natural polymers (such as chitosan) have good biocompatibility, their molecular chains have low rigidity and dispersed active sites, making it difficult to form a stable chelating network. In addition, existing conditioning agents generally lack the ability to destroy EPS in a targeted manner and require high dosages (2% to 5% of the dry weight of the sludge) to achieve dehydration, which is costly and prone to secondary pollution.

[0004] Tannic acid is a natural polyphenol compound, and its catechol group has strong metal chelating ability. However, direct addition is prone to non-specific binding with metal ions in sludge, resulting in waste of effective ingredients.

[0005] Currently, tannic acid is used solely for heavy metal adsorption in sludge treatment and has yet to be developed as a core component of deep dehydration conditioning agents. Furthermore, there are no reports of chemically grafting tannic acid onto polymer backbones, let alone the targeted application of such derivatives in sludge dehydration. Therefore, there is an urgent need to develop a new conditioning agent that combines high charge density, a three-dimensional chelating network, and targeted wall-breaking capabilities to overcome the bottlenecks of traditional technologies. Summary of the Invention

[0006] In view of the problems of insufficient charge density, limited ability to destroy extracellular polymeric substances (EPS), high dosage of reagent and high risk of secondary pollution of existing sludge dewatering conditioning agents, the application provides a sludge deep dewatering conditioner based on tannic acid grafted polymer and a synthesis method and industrial application thereof. The application first grafts tannic acid to a synthetic or natural polymer backbone by chemical bonding technology to form a new derivative with high-density cationic active sites and three-dimensional network chelating groups. The conditioner can efficiently destroy the stable structure of sludge EPS and significantly improve the bound water release efficiency through precise design of the molecular structure, and the dosage of the reagent is reduced by 30%-50% compared with traditional flocculants. The grafting rate of the derivative is 10%-35%, the charge density is 3-8 meq / g, and the unique chemical structure has a breakthrough application effect in the field of sludge dewatering.

[0007] The technical scheme adopted by the application is as follows:

[0008] In the first aspect, the application provides a tannic acid grafted polymer sludge deep dewatering conditioner, characterized in that: a derivative is formed by grafting tannic acid to a synthetic polymer or natural polymer backbone through ester bond, amide bond or ether bond chemical bonding, and the molecular structure of the derivative comprises the following components:

[0009] (1) high-density cationic active sites: provided by synthetic polymers such as polydimethyl diallyl ammonium chloride and polyethyleneimine or natural polymers such as chitosan, with a charge density of 3-8 meq / g;

[0010] (2) three-dimensional network chelating groups: formed by coordination of the catechol group in tannic acid with metal ions in sludge, enhancing the adsorption and cross-linking ability of proteins and polysaccharides in EPS;

[0011] (3) the grafting rate of the derivative is 10%-35%, and the molecular weight is 50,000-500,000 Da.

[0012] Preferably, the synthetic polymer is polyacrylamide, polydimethyl diallyl ammonium chloride or polyethyleneimine; and the natural polymer is chitosan with a degree of deacetylation of 80% or more, lignin or carboxymethyl cellulose.

[0013] Preferably, the mass ratio of tannic acid to polymer is 1:(5-20); and the pore size of the three-dimensional network chelating groups is 2-10 nm, which can specifically bind to metal ions and hydrophobic components in EPS.

[0014] In the second aspect, the application provides a synthesis method of the tannic acid grafted polymer sludge deep dewatering conditioner, comprising the following steps:

[0015] (1) dissolving 1-10 parts by weight of tannic acid and 50-200 parts by weight of a polymer (synthetic or natural) in 200-500 parts of deionized water, adjusting the pH to 4-6, to form a homogeneous mixed solution;

[0016] (2) adding 0.5-5 parts by weight of a condensing agent (such as carbodiimide or N-hydroxysuccinimide) to the mixed solution, and reacting at 40-70° C. for 4-12 hours under nitrogen protection to achieve directional bonding between tannic acid and the polymer;

[0017] (3) After the reaction is completed, the product is purified using a dialysis membrane with a molecular weight cutoff of 3000-10000 Da, and freeze-dried to obtain a solid conditioning agent, the grafting rate of which is determined by ultraviolet spectrophotometry to be 10%-35%.

[0018] Preferably, the polydimethyldiallylammonium chloride in step (a) is an aqueous solution with a mass concentration of 5%-15%; and the chitosan needs to be pre-dissolved in a 1%-3% acetic acid solution to enhance the reaction activity.

[0019] Preferably, the reaction temperature in step (b) is controlled at 50-60° C. to balance the grafting efficiency and polymer chain stability; the condensing agent is added in two portions, with 70% of the total amount added initially and the remainder added in the middle of the reaction.

[0020] In a third aspect, the present invention provides a method for deep dehydration of sludge using the conditioner, comprising the following steps:

[0021] S1. Add the conditioning agent to the sludge with a moisture content of less than 95% at a dosage of 0.1%-2% of the dry weight of the sludge. First, stir rapidly at 200-400 rpm for 5 minutes, then stir slowly at 50-100 rpm for 10-30 minutes to promote the full combination of the conditioning agent and EPS.

[0022] S2. Transfer the conditioned sludge to a membrane filter press and filter it in stages at a pressure of 0.5-2.0 MPa: maintain the initial pressure at 0.5 MPa for 10 minutes, gradually increase it to 2.0 MPa and maintain it for 20-40 minutes, and finally reduce the sludge moisture content to below 50%.

[0023] Preferably, the conditioning agent is added in stages: the initial addition amount is 60% of the total amount, and the remaining amount is injected through the gaps between the filter plates during the filter press process to enhance the release of bound water in the later stage of dehydration.

[0024] Preferably, the mass ratio of the conditioning agent to EPS in the sludge is 1:(10-30); after dehydration, the capillary water release rate of the sludge is increased by ≥40%, the bound water release efficiency is ≥25%, and the filtrate COD is reduced by 30%-50%.

[0025] In a fourth aspect, the present invention discloses the application of the tannic acid grafted polymer in the deep dehydration of municipal sludge, oily sludge and printing and dyeing wastewater sludge, the core mechanism of which includes:

[0026] (1) Electrical neutralization and adsorption bridging: High-density cationic active sites quickly compress the sludge colloidal double layer and achieve inter-particle bridging through long polymer chains to form dense flocs;

[0027] (2) Targeted wall breaking: three-dimensional network chelating groups bind to metal ions (such as Ca 2 +, Mg2+) specifically binds to it, destroying its gel structure and releasing internal bound water;

[0028] (3) Synergistic dehydration: The hydrophobic benzene ring of tannic acid promotes protein folding and cross-linking, reducing the number of hydrophilic functional groups and further improving dehydration efficiency.

[0029] The present invention has been verified through laboratory pilot and industrialization, showing that, compared with traditional polyacrylamide, the conditioner can reduce the sludge moisture content from 98% to 48% and increase the dehydration rate by 22% when the dosage is only 0.8%; the filtrate turbidity is reduced by 60%, and no metal ions remain, thus meeting the requirements for subsequent resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 Schematic diagram of wavelengths for inventing tannic acid and tannic acid grafted polydimethyldiallylammonium chloride;

[0032] Figure 2 This is the UV spectrum of the tannic acid grafted polydimethyldiallylammonium chloride aqueous solution of the present invention;

[0033] Figure 3 This is a SEM comparison of the original sludge of the present invention and the dewatered sludge after adding TA-PEI-3; DETAILED DESCRIPTION

[0034] The technical solution of the present invention is described in detail below in conjunction with examples and comparative tests. The present invention provides a sludge deep dehydration conditioner based on tannic acid grafted polymer, which directionally grafts tannic acid to a synthetic or natural polymer backbone through chemical bonding to form a new derivative with both high charge density and a three-dimensional chelating network. The conditioner can efficiently destroy the structure of sludge extracellular polymers (EPS) and significantly improve the dehydration efficiency. In the following examples, the raw materials used are all commercially available chemically pure reagents, and the sludge samples were taken from a municipal sewage treatment plant with an initial moisture content of 98%.

[0035] Example 1: Synthesis of tannic acid grafted polydimethyldiallylammonium chloride (PDMDAAC)

[0036] 5 parts by weight of tannic acid (≥95% purity) was mixed with 100 parts by weight of polydimethyldiallyl ammonium chloride (PDMDAAC, molecular weight 200,000 Da, 10% aqueous solution), then 300 parts of deionized water was added and stirred until completely dissolved. The pH of the solution was adjusted to 5.0 with 1 mol / L hydrochloric acid. 3 parts by weight of EDC and 1.5 parts by weight of N-hydroxysuccinimide (NHS) were added to the mixture, and nitrogen was purged. The reaction was maintained at 50°C for 8 hours. During the reaction, the condensing agent was added in two portions (70% initially and the remaining 30% after 4 hours). After the reaction, the solution was transferred to a dialysis bag with a molecular weight cutoff of 8000 Da and dialyzed against deionized water for 48 hours to remove unreacted tannic acid and byproducts. After freeze-drying, the product was obtained as a white solid, designated TA-PDMDAAC-1.

[0037] The grafting efficiency was determined to be 28.5% by UV-Vis spectrophotometry (280 nm), the charge density was determined to be 6.2 meq / g by colloid titration, and the molecular weight was determined to be 180,000 Da by gel permeation chromatography (GPC).

[0038] Example 2: Synthesis of tannic acid grafted chitosan (CTS)

[0039] Chitosan (85% deacetylation) was dissolved in 2% acetic acid to a concentration of 8% by weight. Insoluble matter was removed by filtration. 80 parts by weight of the chitosan solution was mixed with 8 parts by weight of tannic acid, and 200 parts by weight of deionized water were added to adjust the pH to 4.5. Two parts by weight of EDC was added and the mixture was reacted at 60°C for 10 hours under nitrogen. The product was purified by dialysis (molecular weight cut-off 5000 Da) and freeze-dried to obtain a pale yellow solid product, labeled TA-CTS-2.

[0040] The grafting efficiency was determined to be 22.3% by UV-Vis spectrophotometry (280 nm), the charge density was determined to be 4.8 meq / g by colloid titration, and the molecular weight was determined to be 120,000 Da by gel permeation chromatography (GPC).

[0041] Example 3: Synthesis of tannic acid grafted polyethyleneimine (PEI)

[0042] Dissolve 3 parts by weight of tannic acid and 150 parts by weight of polyethyleneimine (PEI, molecular weight 50,000 Da) in 400 parts of deionized water and adjust the pH to 5.5. Add 4 parts by weight of EDC and react at 45°C for 6 hours. After dialysis (molecular weight cut-off 3000 Da), freeze-drying, a brown solid product was obtained, labeled TA-PEI-3.

[0043] The grafting efficiency was determined to be 18.7% by UV-Vis spectrophotometry (280 nm), the charge density was determined to be 7.5 meq / g by colloid titration, and the molecular weight was determined to be 220,000 Da by gel permeation chromatography (GPC).

[0044] Dewatering performance test: Add conditioner to 1L of sludge with a moisture content of 98% (the amount added is based on the dry weight of the sludge), first stir quickly at 300rpm for 5 minutes, and then stir slowly at 80rpm for 20 minutes. Use a diaphragm filter press, maintain an initial pressure of 0.5MPa for 10 minutes, gradually increase to 2.0MPa and maintain for 30 minutes. The moisture content was tested by drying method (105℃ to constant weight), the water release efficiency was combined by differential scanning calorimetry (DSC), and the filtrate COD was tested by potassium dichromate method. The test results are shown in Table 1: Table 1. Comparison of dehydration effects of tannic acid grafted polydimethyldiallyl ammonium chloride (TA-PDMDAAC-1) and other common coagulants

[0045]

[0046]

[0047] Table 2. Comparison of dehydration effects of tannic acid grafted chitosan (TA-CTS-2) and other common coagulants

[0048]

[0049] Table 3. Comparison of dehydration effects of tannic acid grafted polyethyleneimine (TA-PEI-3) and other common coagulants

[0050]

[0051] Table 4. Comparison of TA-PEI-3 on sludge dewatering effect in different sewage treatment plants

[0052]

[0053]

[0054] Table 5. Zeta potential changes with TA-PEI-3 dosage (formula: tannic acid: PEI = 3:150)

[0055]

[0056] At a dosage of only 24%-48% of that of conventional PAM, the conditioner reduces moisture content to below 50% after dehydration, and the efficiency of bound water release is more than doubled. The filtrate COD decreases significantly, demonstrating that the conditioner effectively reduces organic matter dissolution and mitigates the risk of secondary pollution.

[0057] Application examples:

[0058] Treatment of printing and dyeing wastewater sludge. The tested printing and dyeing wastewater sludge had a moisture content of 97% and a COD of 12,000 mg / L. TA-PEI-3 was added at a dosage of 1.0% (dry weight) in two separate doses (60% initially and 40% mid-filter).

[0059] After dehydration, the final sludge moisture content is 42.5%, and the filtrate COD is 650 mg / L (58% lower than the traditional method).

[0060] Key mechanism verification:

[0061] Electroneutralization ability: Zeta potential test showed that after adding TA-PDMDAAC-1, the sludge colloid potential increased from -25mV to +8mV, and the double layer was significantly compressed.

[0062] Chelation network effect: XPS analysis showed that the tannic acid catechol group and Ca 2 +Forms a stable coordination bond (binding energy 532.1eV).

[0063] EPS destruction: Three-dimensional fluorescence spectroscopy showed that the characteristic peak intensities of protein (Ex / Em=280 / 350nm) and polysaccharide (Ex / Em=320 / 420nm) in the conditioned sludge decreased by 60%-70%.

[0064] In conjunction with the instructions Figure 1 and attached Figure 2 , Figure 1 Schematic diagram of wavelengths for inventing tannic acid and tannic acid grafted polydimethyldiallylammonium chloride;

[0065] Figure 2 This is the UV spectrum of the tannic acid grafted polydimethyldiallylammonium chloride aqueous solution of the present invention;

[0066] The tannin acid grafted polydimethyl diallyl ammonium chloride aqueous solution has different PH values, corresponding to different wavelengths and absorption light intensity.

[0067] Industrial application examples

[0068] A municipal sludge treatment plant uses TA-PDMDAAC-1 (dosing amount 0.8%) to replace the traditional PAM. The operation results show that the dewatering cycle is shortened by 30%, the daily average treatment capacity is increased to 120 tons, the sludge cake heat value is increased to 12 MJ / kg, meeting the incineration requirements, and the annual reagent cost is reduced by 45%.

[0069] The above examples demonstrate that the present application realizes efficient, low consumption and greenization of sludge deep dewatering through the unique structural design of tannin acid grafted polymer, and has significant industrial application value.

[0070] It should be noted that, in this text, relational terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or equipment. Without more limitations, the element defined by the statement "including a" does not exclude the presence of another identical element in the process, method, article or equipment including the element.

[0071] The basic principles and main features of the present application and the advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A tannic acid grafted polymer sludge deep dehydration conditioner, characterized in that: The derivative is formed by grafting tannic acid onto a synthetic polymer backbone through chemical bonding. The molecular structure of the derivative contains high-density cationic active sites and three-dimensional network chelating groups. The grafting rate of the derivative is 10%-35%, and the charge density is 3-8 meq / g. The synthetic polymer is any one of polyacrylamide, polydimethyldiallylammonium chloride, and polyethyleneimine; The chemical bonding method is an ester bond, an amide bond or an ether bond; The synthesis method of a tannic acid grafted polymer sludge deep dehydration conditioner comprises the following steps: (a) dissolving 1-10 parts by weight of tannic acid and 50-200 parts by weight of a synthetic polymer in 200-500 parts of deionized water, and adjusting the pH to 4-6 to obtain a mixed solution; (b) adding 0.5-5 parts by weight of a condensing agent to the mixed solution, and reacting at 40-70° C. for 4-12 hours under nitrogen protection; (c) after the reaction is completed, the product is dialyzed for purification and freeze-dried to obtain the tannic acid grafted polymer; The condensing agent is any one or a combination of carbodiimide compounds and N-hydroxysuccinimide, and the molecular weight cut-off of the dialysis purification is 3000-10000Da; The synthetic polymer in step (a) is a polydimethyldiallylammonium chloride aqueous solution with a mass concentration of 5%-15%.

2. A dehydration method using the tannic acid grafted polymer sludge deep dehydration conditioner according to claim 1, characterized in that: The following steps are involved: S1. Add the conditioning agent to the sludge with a moisture content of less than 95% at a dosage of 0.1%-2% of the dry weight of the sludge and stir for 10-30 minutes; S2. Place the sludge treated in step S1 in a filter press and filter press it at a pressure of 0.5-2.0 MPa for 20-50 minutes to reduce the moisture content of the sludge to below 50%.

3. The dehydration method according to claim 2, characterized in that The filter press is a diaphragm filter press or a plate and frame filter press; the conditioning agent is added in stages, with the initial addition amount being 50%-70% of the total amount, and the remaining amount being added gradually during the filtration process.

4. The dehydration method according to claim 3, characterized in that The mass ratio of the conditioning agent to the extracellular polymers in the sludge is 1:(10-30); and the bound water release efficiency of the sludge after dehydration is increased by ≥25%.

5. Use of the tannic acid grafted polymer sludge deep dehydration conditioner according to claim 1 in the deep dehydration treatment of municipal sludge, industrial wastewater sludge or oily sludge, characterized in that: The application includes simultaneously achieving structural destruction of sludge extracellular polymers and release of bound water during the dehydration process, and the total dosage of the agent is reduced by 30%-50% compared with traditional flocculants.

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