Coagulant for treating low-temperature and low-turbidity water and preparation method thereof

Abstract

This invention relates to the field of wastewater treatment technology, specifically disclosing a coagulant for treating low-temperature, low-turbidity water and its preparation method. The coagulant provided by this invention utilizes composite modified polyferric chloride to provide efficient charge neutralization and colloidal destabilization capabilities at low temperatures, polyethyleneimine to enhance the rapid destabilization of colloidal particles with its high cation density, and modified carboxymethyl inulin to exert long-chain adsorption bridging and net-catching sweeping effects. The three work synergistically to achieve rapid destabilization, aggregation, and sedimentation of colloidal particles in low-temperature, low-turbidity water, effectively solving the problems of poor low-temperature activity and low turbidity removal rate of conventional coagulants.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a coagulant for treating low-temperature, low-turbidity water and its preparation method. Background Technology

[0002] Low-temperature, low-turbidity water typically refers to surface water with a temperature below 10℃ and a turbidity of less than 30 NTU. It is widely distributed in northern winter basins, southern deep-water reservoirs, and high-latitude lakes. Colloidal particles in low-temperature, low-turbidity water often carry a high negative charge, forming a thick hydration film on their surface. Furthermore, due to the reduced molecular thermal motion at low temperatures, the Brownian motion intensity of colloidal particles is significantly decreased, resulting in a marked reduction in the probability of collision and aggregation. Simultaneously, the low-temperature environment inhibits the activity of microorganisms in the water, leading to the incomplete degradation of some organic matter and further increasing the stability of the colloidal system. These characteristics make low-temperature, low-turbidity water a "challenging water body" in the water treatment industry. Improper treatment can easily lead to problems such as excessive turbidity in the effluent and low organic matter removal rates, directly threatening drinking water safety and the quality of the ecological water environment.

[0003] Currently, the most widely used coagulants in the water treatment industry mainly fall into three categories: inorganic coagulants, organic polymer coagulants, and natural polymer modified coagulants. Inorganic coagulants such as polyaluminum chloride and polyferric chloride, while possessing advantages such as readily available raw materials and low cost, exhibit significantly slower hydrolysis rates in low-temperature, low-turbidity water environments. This makes it difficult to rapidly generate highly active hydroxyl polymers, resulting in insufficient charge neutralization capacity for colloidal particles. Furthermore, the generated flocs are small in size, low in density, and slow in settling, failing to effectively remove turbidity. Organic polymeric coagulants such as polyacrylamide, while possessing strong bridging capabilities, suffer from high monomer residual toxicity and a tendency to cause secondary pollution. Moreover, in low-temperature, low-turbidity water, their molecular chain extensibility decreases, significantly weakening their bridging and trapping effect, making them ineffective against small colloidal particles. Natural polymeric modified coagulants, using starch, cellulose, sodium alginate, and other raw materials, are characterized by being green and non-toxic. However, unmodified natural polymers have few coordination sites and their molecular chains are easily degraded. When combined with inorganic coagulants, the mixture is often a simple physical mixture, lacking effective chemical bonding and synergistic mechanisms, thus failing to overcome the technical bottlenecks of difficult colloid destabilization and slow floc settling under low-temperature conditions.

[0004] Therefore, developing a stable coagulant for low-temperature, low-turbidity water has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a coagulant for treating low-temperature and low-turbidity water and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Preparation of modified carboxymethyl inulin solution Carboxymethyl inulin was dissolved in deionized water, and the pH of the system was adjusted to 9-10. Then hydrogen peroxide was added, and the reaction was heated. After the reaction was completed, the residual hydrogen peroxide was quenched with sodium sulfite after cooling. Then 2,3-epoxypropyltrimethylammonium chloride and tetrabutylammonium bromide were added to the system, and the reaction was continued. After the reaction was completed, the modified carboxymethyl inulin solution was obtained by dialysis and then used for later use.

[0007] In this step, the mass ratio of carboxymethyl inulin, deionized water, hydrogen peroxide, 2,3-epoxypropyltrimethylammonium chloride, and tetrabutylammonium bromide is 5-10:100:4-8:0.8-1.5:0.02-0.05.

[0008] In this step, the hydrogen peroxide has a mass fraction of 30%.

[0009] In this step, the heating temperature is 50-55℃, and the heating time is 1-3 hours.

[0010] In this step, the reaction continues at a temperature of 55-60℃ for 2-4 hours.

[0011] In this step, the mild oxidizing effect of hydrogen peroxide is used to introduce aldehyde and carboxyl active sites onto the carboxymethyl inulin molecule, enhancing its water solubility, coordination ability, and reactivity, providing binding sites for subsequent compounding. Subsequently, 2,3-epoxypropyltrimethylammonium chloride and tetrabutylammonium bromide are added, and under alkaline conditions, the epoxy groups react with the hydroxyl and carboxyl groups on the carboxymethyl inulin, grafting the quaternary ammonium salt cationic groups onto the molecular chain, improving the charge neutralization of the carboxymethyl inulin, enabling it to rapidly expand in low-temperature water, and possessing both adsorption bridging and charge neutralization destabilization capabilities.

[0012] S2, Preparation of composite modified polyferric chloride Cerium salt and ferric chloride were dissolved in deionized water, the pH of the solution was adjusted to 1-2, and the solution was kept at 60-70℃ for 1-2 hours. Then, KH560 hydrolysate was added and stirred for 1-2 hours. Subsequently, the solution was aged at room temperature, concentrated under reduced pressure, and then freeze-dried to obtain composite modified polyferric chloride.

[0013] In this step, the mass ratio of cerium salt, ferric chloride, and KH560 hydrolysate is 1-2:6-10:10-15.

[0014] In this step, the cerium salt is selected from cerium nitrate or cerium chloride.

[0015] In this step, the mass fraction of KH560 hydrolysate is 5-10%.

[0016] In this step, the preparation method of KH560 hydrolysate is as follows: add 5-10g of KH560 to 100g of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), stir at room temperature for 2h, and the KH560 hydrolysate is obtained.

[0017] In this step, cerium salt and ferric chloride are dissolved in water, and the pH is adjusted to 1-2 to inhibit the rapid hydrolysis of metal ions. The solution is then kept at 60-70℃ for 1-2 hours, allowing ferric ions to gradually hydrolyze and form polyferric chloride via hydroxyl bridging. Simultaneously, cerium ions are uniformly incorporated into the polyferric chloride. Utilizing the high charge and catalytic properties of rare earth cerium ions, the charge density and low-temperature hydrolysis activity of the polyferric chloride are enhanced. Then, pre-hydrolyzed KH560 hydrolysate is added. The silanol groups of silane undergo dehydration condensation with the hydroxyl groups on the surface of the polyferric chloride, introducing epoxy groups to strengthen the binding strength between the polyferric chloride and other components in the system, thereby improving the structural stability of the coagulant.

[0018] S3, Preparation of coagulant The composite modified polyferric chloride and polyethyleneimine were added to the modified carboxymethyl inulin solution, ultrasonically dispersed evenly, and aged at room temperature. After aging, the mixture was filtered, vacuum dried, pulverized and sieved to obtain a coagulant for treating low-temperature and low-turbidity water.

[0019] In this step, the mass ratio of the composite modified polyferric chloride, polyethyleneimine, and modified carboxymethyl inulin solution is 4-8:1-2:60-80.

[0020] In this step, the maturation time is 16-24 hours.

[0021] In this step, the composite modified polyferric chloride and polyethyleneimine are added to the modified carboxymethyl inulin solution, and the components are uniformly mixed by ultrasonic dispersion to avoid local agglomeration and promote full contact between molecules. During the curing process, polyethyleneimine (PEI) contains a large number of primary and secondary amines, which can undergo "epoxy-amine ring-opening addition reaction" with the epoxy groups in step S2 at room temperature. At the same time, the amino group of PEI can also undergo Schiff base reaction with the aldehyde group generated by oxidation in step S1 to form a stable inorganic-organic composite system. This covalent network is extremely difficult to break under the shear force of water flow, and the floc strength is very high at low temperature.

[0022] The present invention also provides a coagulant for treating low-temperature, low-turbidity water prepared by the above preparation method.

[0023] Compared with the prior art, the present invention has the following beneficial effects: (1) The coagulant provided by the present invention has a composite modified polyferric chloride that provides efficient charge neutralization and colloidal destabilization at low temperature, polyethyleneimine enhances the rapid destabilization of colloidal particles with its high cation density, and modified carboxymethyl inulin plays a role in long-chain adsorption bridging and net trapping sweeping. The three work together to achieve rapid destabilization, aggregation and sedimentation of colloidal particles in low-temperature and low-turbidity water, effectively solving the problems of poor low-temperature activity and low turbidity removal rate of conventional coagulants.

[0024] (2) This invention utilizes the mild oxidizing effect of hydrogen peroxide to introduce aldehyde and carboxyl active sites on carboxymethyl inulin molecules, thereby improving its water solubility, coordination ability and reactivity, and providing binding sites for subsequent composites; then 2,3-epoxypropyltrimethylammonium chloride and tetrabutylammonium bromide are added, and under alkaline conditions, the epoxy groups react with the hydroxyl and carboxyl groups on carboxymethyl inulin, grafting the quaternary ammonium salt cationic groups onto the molecular chain, thereby improving the charge neutralization of carboxymethyl inulin, enabling it to spread rapidly in low-temperature water, and combining adsorption bridging and charge neutralization destabilization capabilities.

[0025] (3) In this invention, cerium ions are uniformly doped into polyferric chloride. By utilizing the high charge and catalytic properties of rare earth cerium ions, the charge density and low-temperature hydrolysis activity of polyferric chloride are improved. Then, pre-hydrolyzed KH560 hydrolysate is added. The silanol groups of silane undergo dehydration condensation with the hydroxyl groups on the surface of polyferric chloride. By introducing epoxy groups, the binding strength between polyferric chloride and other components in the system is enhanced, thereby improving the structural stability of the coagulant. Detailed Implementation

[0026] The present invention will be further described in detail below through specific preferred embodiments, but the present invention is not limited to the following embodiments.

[0027] It should be noted that, unless otherwise specified, all chemical reagents involved in this invention were purchased through commercial channels.

[0028] The preparation method of KH560 hydrolysate provided in this embodiment of the invention is as follows: 5g of KH560 is added to 100g of ethanol aqueous solution (the volume ratio of ethanol to water is 4:1), and stirred at room temperature for 2h to obtain KH560 hydrolysate.

[0029] The hydrogen peroxide has a mass fraction of 30%.

[0030] The average relative molecular weight of polyethyleneimine is 3000. Example 1

[0031] A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Dissolve 8g of carboxymethyl inulin in 100g of deionized water, adjust the pH of the system to 9, then add 6g of hydrogen peroxide, heat at 50℃ for 3h. After the reaction is complete, cool and quench the residual hydrogen peroxide with 0.5g of sodium sulfite. Then add 1g of 2,3-epoxypropyltrimethylammonium chloride and 0.04g of tetrabutylammonium bromide to the system, and continue to react at 60℃ for 2h. After the reaction is complete, purify by dialysis to obtain the modified carboxymethyl inulin solution for later use. S2. Dissolve 1g of cerium nitrate and 6g of ferric chloride in 100g of deionized water, adjust the pH of the solution to 1.5, keep warm at 60℃ for 2h, then add 10g of KH560 hydrolysate, stir for 2h, then age at room temperature, concentrate under reduced pressure and freeze dry to obtain composite modified polyferric chloride. S3. Add 6g of composite modified polyferric chloride and 1.5g of polyethyleneimine to 60g of modified carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature for 24h. After maturation, filter, vacuum dry, and pulverize through a 200-mesh sieve to obtain a coagulant for treating low-temperature and low-turbidity water. Example 2

[0032] A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Dissolve 5g of carboxymethyl inulin in 100g of deionized water, adjust the pH of the system to 9, then add 4g of hydrogen peroxide, heat at 50℃ for 3h. After the reaction is complete, cool and quench the residual hydrogen peroxide with 0.5g of sodium sulfite. Then add 0.8g of 2,3-epoxypropyltrimethylammonium chloride and 0.02g of tetrabutylammonium bromide to the system, and continue to react at 60℃ for 2h. After the reaction is complete, purify by dialysis to obtain the modified carboxymethyl inulin solution for later use. S2. Dissolve 2g of cerium nitrate and 10g of ferric chloride in 100g of deionized water, adjust the pH of the solution to 1.5, keep warm at 60℃ for 2h, then add 15g of KH560 hydrolysate, stir for 2h, then age at room temperature, concentrate under reduced pressure and freeze dry to obtain composite modified polyferric chloride. S3. Add 4g of composite modified polyferric chloride and 1g of polyethyleneimine to 60g of modified carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature for 24h. After maturation, filter, vacuum dry, and pulverize through a 200-mesh sieve to obtain a coagulant for treating low-temperature and low-turbidity water. Example 3

[0033] A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Dissolve 10g of carboxymethyl inulin in 100g of deionized water, adjust the pH of the system to 9, then add 8g of hydrogen peroxide, heat at 50℃ for 3h. After the reaction is complete, cool and quench the residual hydrogen peroxide with 0.5g of sodium sulfite. Then add 1.5g of 2,3-epoxypropyltrimethylammonium chloride and 0.05g of tetrabutylammonium bromide to the system, and continue to react at 60℃ for 2h. After the reaction is complete, purify by dialysis to obtain the modified carboxymethyl inulin solution for later use. S2. Dissolve 1.5g cerium nitrate and 8g ferric chloride in 100g deionized water, adjust the pH of the solution to 1.5, keep warm at 60℃ for 2h, then add 12g KH560 hydrolysate, stir for 2h, then age at room temperature, concentrate under reduced pressure and freeze dry to obtain composite modified polyferric chloride. S3. Add 8g of composite modified polyferric chloride and 2g of polyethyleneimine to 80g of modified carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature for 24h. After maturation, filter, vacuum dry, and pulverize through a 200-mesh sieve to obtain a coagulant for treating low-temperature and low-turbidity water. Comparative Example 1

[0034] A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Dissolve 8g of carboxymethyl inulin in 100g of deionized water to obtain a carboxymethyl inulin solution for later use. S2. Dissolve 1g of cerium nitrate and 6g of ferric chloride in 100g of deionized water, adjust the pH of the solution to 1.5, keep warm at 60℃ for 2h, then add 10g of KH560 hydrolysate, stir for 2h, then age at room temperature, concentrate under reduced pressure and freeze dry to obtain composite modified polyferric chloride. S3. Add 6g of composite modified polyferric chloride and 1.5g of polyethyleneimine to 60g of carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature for 24h. After maturation, filter, vacuum dry, and pulverize through a 200-mesh sieve to obtain a coagulant for treating low-temperature and low-turbidity water.

[0035] Compared with Example 1, no modification treatment was performed on carboxymethyl inulin in Comparative Example 1. Comparative Example 2

[0036] A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Dissolve 8g of carboxymethyl inulin in 100g of deionized water, adjust the pH of the system to 9, then add 6g of hydrogen peroxide, heat at 50℃ for 3h, and after the reaction is complete, dialysis is used to purify the solution to obtain the modified carboxymethyl inulin solution for later use. S2. Dissolve 1g of cerium nitrate and 6g of ferric chloride in 100g of deionized water, adjust the pH of the solution to 1.5, keep warm at 60℃ for 2h, then add 10g of KH560 hydrolysate, stir for 2h, then age at room temperature, concentrate under reduced pressure and freeze dry to obtain composite modified polyferric chloride. S3. Add 6g of composite modified polyferric chloride and 1.5g of polyethyleneimine to 60g of modified carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature for 24h. After maturation, filter, vacuum dry, and pulverize through a 200-mesh sieve to obtain a coagulant for treating low-temperature and low-turbidity water.

[0037] Compared with Example 1, Comparative Example 2 did not use 2,3-epoxypropyltrimethylammonium chloride to further modify carboxymethyl inulin. Comparative Example 3

[0038] A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Dissolve 8g of carboxymethyl inulin in 100g of deionized water, adjust the pH of the system to 9, then add 6g of hydrogen peroxide, heat at 50℃ for 3h. After the reaction is complete, cool and quench the residual hydrogen peroxide with 0.5g of sodium sulfite. Then add 1g of 2,3-epoxypropyltrimethylammonium chloride and 0.04g of tetrabutylammonium bromide to the system, and continue to react at 60℃ for 2h. After the reaction is complete, purify by dialysis to obtain the modified carboxymethyl inulin solution for later use. S2. Dissolve 6g of ferric chloride in 100g of deionized water, adjust the pH of the solution to 1.5, keep it at 60℃ for 2h, then age it at room temperature, concentrate it under reduced pressure and freeze dry it to obtain polyferric chloride. S3. Add 6g of polyferric chloride and 1.5g of polyethyleneimine to 60g of modified carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature for 24h. After maturation, filter, vacuum dry, and pulverize through a 200-mesh sieve to obtain a coagulant for treating low-temperature and low-turbidity water.

[0039] Compared with Example 1, Comparative Example 3 did not involve any modification treatment of polyferric chloride. Comparative Example 4

[0040] A method for preparing a coagulant for treating low-temperature, low-turbidity water includes the following steps: S1. Dissolve 8g of carboxymethyl inulin in 100g of deionized water, adjust the pH of the system to 9, then add 6g of hydrogen peroxide, heat at 50℃ for 3h. After the reaction is complete, cool and quench the residual hydrogen peroxide with 0.5g of sodium sulfite. Then add 1g of 2,3-epoxypropyltrimethylammonium chloride and 0.04g of tetrabutylammonium bromide to the system, and continue to react at 60℃ for 2h. After the reaction is complete, purify by dialysis to obtain the modified carboxymethyl inulin solution for later use. S2. Dissolve 6g of ferric chloride in 100g of deionized water, adjust the pH of the solution to 1.5, keep warm at 60℃ for 2h, then add 10g of KH560 hydrolysate, stir for 2h, then age at room temperature, concentrate under reduced pressure and freeze dry to obtain modified polyferric chloride. S3. Add 6g of modified polyferric chloride and 1.5g of polyethyleneimine to 60g of modified carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature for 24h. After maturation, filter, vacuum dry, and pulverize through a 200-mesh sieve to obtain a coagulant for treating low-temperature and low-turbidity water.

[0041] Compared to Example 1, Comparative Example 4 did not involve cerium doping of polyferric chloride.

[0042] The performance of the coagulants prepared in Examples 1-3 and Comparative Examples 1-4 was tested, as follows: Low-temperature, low-turbidity water (temperature 5℃, turbidity 8.7 NTU, COD 36.35 mg / L) samples were taken from a water plant. 100 mL of the water was placed in each of seven beakers, and then the coagulants prepared in Examples 1-3 and Comparative Examples 1-4 were added respectively. The coagulant dosage was 20 mg / L. After the coagulant was added, the mixture was mechanically stirred at 300 rpm for 1 minute, then at 50 rpm for 10 minutes. After standing for 10 minutes, the supernatant was collected, and the turbidity and COD content of the supernatant were measured. The turbidity removal rate and COD removal rate were calculated. The test results are shown in Table 1.

[0043] Table 1 Performance test results for different groups

[0044] As shown in Table 1, Examples 1-3 of the present invention achieved a turbidity removal rate of 95% and a COD removal rate of 82% when treating low-temperature, low-turbidity water at 5℃ and a turbidity of 8.7 NTU, significantly better than the comparative examples. Comparative Example 1, without modification of carboxymethyl inulin, had insufficient adsorption bridging and charge neutralization capabilities; Comparative Example 2 lacked quaternary ammonium salt cation grafting, resulting in decreased colloidal destabilization; Comparative Example 3 used unmodified ordinary polyferric chloride, exhibiting poor low-temperature activity and floc strength; Comparative Example 4 did not introduce cerium doping, leading to reduced low-temperature hydrolysis efficiency. The coagulant provided by the present invention utilizes composite modified polyferric chloride to provide efficient charge neutralization and colloidal destabilization capabilities at low temperatures, polyethyleneimine to enhance rapid destabilization of colloidal particles with its high cation density, and modified carboxymethyl inulin to exert long-chain adsorption bridging and net-trapping effects. The synergistic effect of these three components enables rapid destabilization, aggregation, and sedimentation of colloidal particles in low-temperature, low-turbidity water, effectively solving the problems of poor low-temperature activity and low turbidity removal rate of conventional coagulants.

[0045] Finally, it should be noted that the above embodiments do not limit the present invention in any way. Those skilled in the art can make modifications and improvements based on the present invention. Therefore, any modifications or improvements made without departing from the spirit of the present invention are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a coagulant for treating low-temperature, low-turbidity water, characterized in that, Includes the following steps: S1. Dissolve carboxymethyl inulin in deionized water, adjust the pH of the system to 9-10, then add hydrogen peroxide, heat the reaction, and after the reaction is complete, cool it and quench the residual hydrogen peroxide with sodium sulfite. Then add 2,3-epoxypropyltrimethylammonium chloride and tetrabutylammonium bromide to the system and continue the reaction. After the reaction is complete, purify by dialysis to obtain the modified carboxymethyl inulin solution for later use. S2. Dissolve cerium salt and ferric chloride in deionized water, adjust the pH of the solution to 1-2, keep it at 60-70℃ for 1-2 hours, then add KH560 hydrolysate, stir for 1-2 hours, then age at room temperature, concentrate under reduced pressure and freeze dry to obtain composite modified polyferric chloride. S3. Add the composite modified polyferric chloride and polyethyleneimine to the modified carboxymethyl inulin solution, disperse evenly by ultrasonication, and mature at room temperature. After maturation, filter, vacuum dry, pulverize and sieve to obtain the coagulant for treating low-temperature and low-turbidity water.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of carboxymethyl inulin, deionized water, hydrogen peroxide, 2,3-epoxypropyltrimethylammonium chloride and tetrabutylammonium bromide is 5-10:100:4-8:0.8-1.5:0.02-0.

05.

3. The preparation method according to claim 1, characterized in that, In step S1, the heating temperature is 50-55℃ and the heating time is 1-3h.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of cerium salt, ferric chloride, and KH560 hydrolysate is 1-2:6-10:10-15.

5. The preparation method according to claim 1, characterized in that, In step S2, the mass fraction of KH560 hydrolysate is 5-10%.

6. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of the composite modified polyferric chloride, polyethyleneimine, and modified carboxymethyl inulin solution is 4-8:1-2:60-80.

7. The preparation method according to claim 1, characterized in that, In step S3, the aging process takes 16-24 hours.

8. The coagulant for treating low-temperature, low-turbidity water prepared by the preparation method according to any one of claims 1-7.

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