Environment-friendly and biosafe neutral efficient sludge dewatering agent and preparation method thereof

Abstract

The invention discloses an environment-friendly and biosafe neutral efficient sludge dewatering agent and a preparation method thereof, and belongs to the technical field of sludge drying and dewatering. The preparation method of the sludge dewatering agent comprises the following steps: taking cationic polyacrylamide, sodium carboxymethylcellulose and cross-linked modified polyamino deoxyglucose as raw materials, mixing according to a mass ratio of 1: 1: 8, carrying out wet granulation, and then carrying out low-temperature drying and size stabilization on wet particles to prepare a final finished product. The sludge dewatering agent has the beneficial effects that the prepared sludge dewatering agent is neutral, has a triple synergistic flocculation mechanism of charge neutralization, adsorption bridging, network sweeping and space trapping, is excellent in dewatering performance, has extremely high environmental friendliness and biological safety, and is suitable for industrial production. The dehydrated sludge can be used for farmland fertilization, soil improvement, landscaping and composting, and the resource utilization safety and feasibility of the sludge are greatly improved.

Description

Technical Field

[0001] This invention relates to a sludge dewatering agent and its preparation method, specifically to an environmentally friendly and biosafe neutral and highly efficient sludge dewatering agent and its preparation method, belonging to the field of sludge drying and dewatering technology. Background Technology

[0002] Given that sludge treatment and disposal costs account for as much as 30%-60% of the total operating costs of wastewater treatment plants, sludge dewatering is a key step in reducing wastewater volume.

[0003] Currently, the mainstream sludge dewatering agents include: polyferric sulfate, ferric chloride, polyacrylamide (PAM), chitosan, etc.

[0004] While the aforementioned sludge dewatering agents all have dewatering effects, the dewatering time is relatively long (around 45 minutes) and it is difficult to achieve a sludge cake moisture content below 50%. Furthermore, polyferric sulfate and ferric chloride are both strong acid agents, which will not only severely corrode the treatment system (including: conveying pipelines, pumps, valves, dewatering equipment, especially centrifuges and plate and frame filter presses), but also restrict subsequent sludge disposal methods if the dewatered sludge is planned to be anaerobically digested to produce biogas. In addition, sludge cakes with extreme pH levels can change soil properties and cause land use obstacles. Moreover, when the dewatered filtrate is returned to the front end of the wastewater treatment system, it can also pose potential risks to the biological treatment system.

[0005] In summary, developing neutral and efficient sludge dewatering agents has become an inevitable trend for the industry to move towards refined and green management. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a neutral and highly efficient sludge dewatering agent with a neutral pH, a short dewatering time (30 min), and the ability to reduce the moisture content of the sludge cake to below 50%, as well as its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an environmentally friendly and biosafe neutral and highly efficient sludge dewatering agent includes the following steps: Step 1: Using polyaminodeoxyglucose with a degree of deacetylation ≥ 85% as raw material, and glutaraldehyde as crosslinking agent, crosslinking modification was carried out by reverse suspension crosslinking method to prepare crosslinked modified polyaminodeoxyglucose. Step 2: Using cationic polyacrylamide, sodium carboxymethyl cellulose and the cross-linked modified polyaminodeoxyglucose prepared in Step 1 as raw materials, they are mixed in a mass ratio of 1:1:8 and wet granulated. Then, the wet granules are dried and granulated at low temperature to obtain the final product.

[0008] Preferably, in step 1, the method for preparing cross-linked modified polyaminodeoxyglucose is as follows: (1) Preparation of aqueous phase: slowly add polyaminodeoxyglucose with a degree of deacetylation ≥85% to glacial acetic acid to prepare a saturated polyaminodeoxyglucose colloidal solution; (2) Preparation of the oil phase: Mix liquid paraffin or cyclohexane and sorbitan monooleate and stir until dissolved; (3) Crosslinking: The aqueous phase is slowly added to the oil phase at a mass ratio of 1:1. The aqueous phase is dispersed into uniformly sized droplets in the oil phase by high-speed shearing and stirring. Then, glutaraldehyde aqueous solution is slowly added dropwise. The reaction system is heated to 80°C and reacted for 12 hours. (4) Post-processing: The solid microspheres were filtered out and washed with organic solvent, then soaked in a 30% sodium hydroxide solution for 1 hour, washed again, and the washed wet microspheres were dried, air-jet pulverized and vibrated to obtain 100-mesh cross-linked modified polyaminodeoxyglucose.

[0009] More preferably, in step (2), the mass ratio of liquid paraffin or cyclohexane to sorbitan monooleate is 1:3.

[0010] More preferably, in step (3), the amount of glutaraldehyde added is 30% of the mass of polyaminodeoxyglucose.

[0011] More preferably, in step (4), the method used to dry the wet microspheres is: critical point drying or vacuum low temperature drying.

[0012] Preferably, in step 2, edible alcohol is used as a wetting agent during wet granulation; and during low-temperature drying, the inlet air temperature is ≤60℃.

[0013] An environmentally friendly and biosafe neutral and highly efficient sludge dewatering agent is prepared by any of the methods described above.

[0014] The advantages of this invention are: (1) The aqueous solution of the sludge dewatering agent provided by the present invention (mass concentration of 1.5%) has a pH value in the range of 6-8 and is neutral. When added at a dosage of 5‰, it will not corrode the treatment system, restrict the subsequent sludge disposal path, or cause land use obstacles, and will not bring potential risks to the biological treatment system.

[0015] (2) The sludge dewatering agent provided by the present invention has the following properties: charge neutralization (the positive charges on the surface of cationic polyacrylamide and cross-linked modified polyaminodeoxyglucose work together to efficiently compress the double electric layer of sludge colloidal particles and destroy their stability), adsorption bridging (linear high molecular weight cationic polyacrylamide and sodium carboxymethyl cellulose rapidly bridge between sludge colloidal particles to form initial flocs), network sweeping and spatial capture (after absorbing water, cross-linked modified polyaminodeoxyglucose expands dozens of times to form a huge, water-insoluble three-dimensional network structure, like a large net that completely wraps the initial flocs, fine particles and free water). The triple synergistic flocculation mechanism (including sweeping, capturing, and forming extremely dense and robust super-large flocs) produces flocs that are large in size, compact in structure, and have high mechanical strength. The large and dense flocs result in faster settling speed, and the robust structure of the flocs is not easily damaged during mechanical dewatering. Water is more easily separated from the gaps between the flocs. The powerful network sweeping action squeezes out more water and wraps it within the skeleton. After mechanical dewatering, the moisture content of the sludge cake can be reduced to a lower level, resulting in excellent dewatering performance. It is particularly suitable for difficult-to-treat sludge (such as: excess activated sludge, digested sludge, etc.) with high organic matter content, high viscosity, and strong hydrophilicity.

[0016] (3) Both polyaminodeoxyglucose and sodium carboxymethyl cellulose are derived from natural plants and animals and can be rapidly degraded by microorganisms in the environment. Although cationic polyacrylamide is a synthetic polymer, it can also be slowly degraded by microorganisms in the environment. The sludge dewatering agent provided by this invention is biodegradable in all components and will never introduce metal ions such as aluminum and iron. It has extremely low environmental risk and is extremely environmentally friendly.

[0017] (4) Polyaminodeoxyglucose is the only known natural cationic polysaccharide that is harmless to the human body and the environment and can even be used in the food and pharmaceutical industries. The sludge dewatering agent provided by this invention is safer for the respiratory tract and skin of workers when operating on-site in sewage treatment plants, and has the ultimate biological safety.

[0018] (5) The sludge dewatering agent provided by the present invention will not cause heavy metal accumulation. The dewatered sludge can be used for farmland fertilization, soil improvement, landscaping and composting, which greatly improves the safety and feasibility of sludge resource utilization. In addition, polyaminodeoxyglucose itself has a certain inhibitory effect on plant pathogens and can improve soil aggregate structure, thus clearing the biggest obstacle to turning sludge into a valuable resource. Detailed Implementation

[0019] The present invention will be described in detail below with reference to specific embodiments.

[0020] I. Preparation of environmentally friendly and biosafe neutral high-efficiency sludge dewatering agents Step 1: Preparation of cross-linked modified polyaminodeoxyglucose (aggregate) The raw materials used to prepare crosslinked modified polyaminodeoxyglucose by mass are: 10 parts of polyaminodeoxyglucose with a degree of deacetylation ≥ 85%, 10 parts of glacial acetic acid, 6 parts of glutaraldehyde aqueous solution with a mass concentration of 50% (crosslinking agent, which reacts with the amino groups on the polyaminodeoxyglucose molecular chain to form a stable covalent crosslinking network), 15 parts of sorbitan monooleate (dispersant), and 5 parts of liquid paraffin or cyclohexane (oil phase dispersion medium).

[0021] The cross-linked modified polyaminodeoxyglucose was prepared using a reverse-phase suspension cross-linking method, the specific method of which is as follows: (1) Preparation of aqueous phase: While stirring, slowly add 10 parts of polyaminodeoxyglucose with a degree of deacetylation ≥ 85% to 10 parts of glacial acetic acid to prepare a uniform, viscous saturated polyaminodeoxyglucose colloidal solution, and let it stand to remove bubbles.

[0022] (2) Preparation of oil phase: Add 5 parts of liquid paraffin (or cyclohexane) and 15 parts of sorbitan monooleate to a reactor equipped with a stirrer and condenser, and stir until dissolved.

[0023] (3) Crosslinking: The aqueous phase is slowly added to the oil phase (mass ratio 1:1), and high-speed shear stirring (800 rpm) is turned on to disperse the aqueous phase into uniformly sized droplets in the oil phase. Then, 6 parts of glutaraldehyde aqueous solution with a mass concentration of 50% are slowly added (the amount of glutaraldehyde added is 30% of the mass of polyaminodeoxyglucose). After the addition is completed, the reaction system is heated to 80°C and the crosslinking reaction is carried out at this temperature for 12 hours (the crosslinking reaction occurs inside the polyaminodeoxyglucose droplets and gradually solidifies into spheres).

[0024] (4) Post-processing: After the reaction is completed, the reaction is terminated with a small amount of acetone (or ethanol). After the reaction solution is cooled to room temperature, it is transferred to a filter device to filter out the solid microspheres. Then, the microspheres are washed multiple times with organic solvent acetone to remove residual dispersant and unreacted substances. After that, the microspheres are soaked in a 30% sodium hydroxide solution for 1 hour to make the microsphere structure more stable. Then, the microspheres are washed multiple times with organic solvent acetone to remove residual sodium hydroxide. The washed wet microspheres are subjected to critical point drying (or vacuum low temperature drying) to maintain their porous structure to the maximum extent. Finally, the dried microspheres are subjected to air jet pulverization and vibration sieving to obtain 100-mesh cross-linked modified polyaminodeoxyglucose powder (aggregate).

[0025] Step 2: Prepare the final product The raw materials used to prepare the final product by weight are: 8 parts of cross-linked modified polyaminodeoxyglucose, 1 part of cationic polyacrylamide, and 1 part of sodium carboxymethyl cellulose.

[0026] The method for preparing the final product is as follows: (1) Premixing: The three raw materials, cross-linked modified polyaminodeoxyglucose, cationic polyacrylamide and sodium carboxymethyl cellulose, are transported to the raw material silo by airflow. The materials are then fed into the three-dimensional motion mixer (or double cone mixer) at a mass ratio of cationic polyacrylamide: sodium carboxymethyl cellulose: cross-linked modified polyaminodeoxyglucose = 1:1:8.

[0027] (2) Wet granulation: The dry-mixed powder is fed into a high-speed mixing granulator and edible alcohol is sprayed in as a wetting agent (absolutely avoid using water to prevent cationic polyacrylamide and cross-linked modified polyamino deoxyglucose from swelling and sticking in advance). Under high-speed shearing, the powder is agglomerated into dense fine particles.

[0028] (3) Low temperature drying and granulation: The wet granules are immediately sent into a vacuum drying oven (or a low temperature fluidized bed dryer) and the alcohol is evaporated and recovered at a low temperature (air inlet temperature ≤ 60℃). The dried granules are then sieved with a rotary granulator to obtain a final product (light yellow granular powder) with uniform particle size (40 mesh).

[0029] The final product passes through a metal detector to ensure its purity. Vacuum packaging or nitrogen-filled packaging is used with moisture-proof and airtight materials to prevent moisture absorption.

[0030] II. Comparison of Dewatering Effects of Sludge Dewatering Agents 1. Experimental equipment A hydraulic filter press was used to simulate the effect of a real machine.

[0031] 2. Experimental raw mud Sludge from municipal solid waste and sewage treatment plants was used as the raw sludge for the experiment, and it was prepared with a moisture content of 81.5% or 82.0% for comparative experiments.

[0032] 3. Sludge dewatering agents The sludge dewatering agents used in the experiment included: polyferric sulfate, ferric chloride, polyacrylamide (PAM), chitosan, and the sludge dewatering agent prepared in this invention.

[0033] Prepare a 1.5% (w / w) solution of each reagent using deionized water and add it at a dosage of 0.5%. Set up a blank control group without adding any reagent.

[0034] 4. Dehydration effect (1) Effect of reagent type on dehydration efficiency The hydraulic filter press maintained an operating pressure that increased from 0.00 MPa to 5.00 MPa within 45 minutes, using a stacked filtration method. The raw sludge volume was 1 kg. The dewatering efficiency test results of various sludge dewatering agents are shown in Table 1.

[0035] Table 1. Dewatering efficiency test results of various sludge dewatering agents

[0036] As shown in Table 1, the moisture content of the sludge cake in Group 1 is significantly lower than that in other groups, indicating that the dewatering efficiency of the sludge dewatering agent prepared by this invention is significantly better than that of other agents.

[0037] (2) Effect of filtration time on dewatering efficiency The hydraulic filter press maintained an operating pressure that increased from 0.00 MPa to 5.00 MPa within 60 minutes, using a stacked filtration method. The raw sludge volume was 1 kg, and the raw sludge moisture content was 82.0%. In the first 25 minutes, due to the filter cloth wrapping method and equipment limitations, some sludge leakage occurred, and the data obtained was not used as a reference. Starting from the 30th minute, the moisture content was measured every 5 minutes, and the test results are shown in Table 2.

[0038] Table 2. Moisture content test results (%) under different filtration times

[0039] As shown in Table 2, after 30 minutes of filtration, the moisture content of the mud cake in Group 1 reached below 50%, which met the usage requirements. Although other groups also removed a lot of water, the moisture content of the mud cake was still above 59%, which did not meet the usage requirements. As the filtration time increased, the moisture content of the mud cake in each group continued to decrease. After 60 minutes of filtration, except for Group 1, the mud cakes in other groups still did not meet the actual usage requirements of a moisture content below 50%.

[0040] (3) Effect of filter press pressure on dewatering efficiency The hydraulic filter press maintained an operating pressure that increased from 0.00 MPa to 0.50 MPa, 1.00 MPa, 1.50 MPa, 2.00 MPa, 2.50 MPa, 3.00 MPa, 3.50 MPa, 4.00 MPa, 4.50 MPa, 5.00 MPa, or 5.50 MPa within 45 minutes. Filtration was performed using a stacked filtration method. The raw sludge volume was 1 kg, and the raw sludge moisture content was 82.0%. The dewatering efficiency test results of various sludge dewatering agents under different filtration pressures are shown in Tables 3-1 and 3-2.

[0041] Table 3-1 Moisture content test results under different filtration pressures (I) (%)

[0042] Table 3-2 Moisture content test results under different filtration pressures (II) (%)

[0043] As shown in Tables 3-1 and 3-2, when the filter press pressure reaches 4.00 MPa, the moisture content of the sludge cake in Group 1 reaches 50%, which can meet the usage requirements, while the moisture content of the sludge cake in other groups is still above 57%, which does not yet meet the usage requirements.

[0044] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. A method for preparing an environmentally friendly and biosafe neutral and highly efficient sludge dewatering agent, characterized in that, Includes the following steps: Step 1: Using polyaminodeoxyglucose with a degree of deacetylation ≥ 85% as raw material, and glutaraldehyde as crosslinking agent, crosslinking modification was carried out by reverse suspension crosslinking method to prepare crosslinked modified polyaminodeoxyglucose. Step 2: Using cationic polyacrylamide, sodium carboxymethyl cellulose and the cross-linked modified polyaminodeoxyglucose prepared in Step 1 as raw materials, they are mixed in a mass ratio of 1:1:8 and wet granulated. Then, the wet granules are dried and granulated at low temperature to obtain the final product.

2. The preparation method of the environmentally friendly and biosafe neutral high-efficiency sludge dewatering agent according to claim 1, characterized in that, In step 1, the method for preparing cross-linked modified polyaminodeoxyglucose is as follows: (1) Preparation of aqueous phase: slowly add polyaminodeoxyglucose with a degree of deacetylation ≥85% to glacial acetic acid to prepare a saturated polyaminodeoxyglucose colloidal solution; (2) Preparation of the oil phase: Mix liquid paraffin or cyclohexane and sorbitan monooleate and stir until dissolved; (3) Crosslinking: The aqueous phase is slowly added to the oil phase at a mass ratio of 1:

1. The aqueous phase is dispersed into uniformly sized droplets in the oil phase by high-speed shearing and stirring. Then, glutaraldehyde aqueous solution is slowly added dropwise. The reaction system is heated to 80°C and reacted for 12 hours. (4) Post-processing: The solid microspheres were filtered out and washed with organic solvent, then soaked in a 30% sodium hydroxide solution for 1 hour, washed again, and the washed wet microspheres were dried, air-jet pulverized and vibrated to obtain 100-mesh cross-linked modified polyaminodeoxyglucose.

3. The preparation method of the environmentally friendly and biosafe neutral high-efficiency sludge dewatering agent according to claim 2, characterized in that, In step (2), the mass ratio of liquid paraffin or cyclohexane to sorbitan monooleate is 1:

3.

4. The preparation method of the environmentally friendly and biosafe neutral high-efficiency sludge dewatering agent according to claim 2, characterized in that, In step (3), the amount of glutaraldehyde added is 30% of the mass of polyaminodeoxyglucose.

5. The preparation method of the environmentally friendly and biosafe neutral high-efficiency sludge dewatering agent according to claim 2, characterized in that, In step (4), the wet microspheres are dried by either critical point drying or vacuum low-temperature drying.

6. The method for preparing the environmentally friendly and biosafe neutral high-efficiency sludge dewatering agent according to claim 1, characterized in that, In step 2, during wet granulation, edible alcohol is used as a wetting agent.

7. The preparation method of the environmentally friendly and biosafe neutral high-efficiency sludge dewatering agent according to claim 1, characterized in that, In step 2, during low-temperature drying, the inlet air temperature is ≤60℃.

8. An environmentally friendly and biosafe neutral high-efficiency sludge dewatering agent, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

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