A method for in-situ non-mechanical sludge dewatering

Abstract

The present invention relates to a method for a method of in-situ non-mechanical sludge dewatering, and belongs to the technical field of sludge treatment. The present invention adds ionic liquid and dehydrating agent to sludge in a specific ratio, and after being fully mixed at room temperature, a rapid and stable sludge co-floating phenomenon occurs; wherein the upper solid mixture is the ionic liquid and the dehydrated sludge, and the lower layer is a high-concentration dehydrating agent solution; wherein, after the upper layer recycles the ionic liquid, the sludge solids can be directly landfilled, and the lower layer can be recycled and utilized to synthesize a highly efficient heavy metal repair agent hydroxyapatite (HAP). The present invention can simply, efficiently and effectively carry out sludge dewatering treatment, and can reduce the sludge moisture content from 99.21% to 69.63-70.21% without any mechanical dehydration operation and direct in-situ treatment. The present invention has simple operating steps, can recycle and reuse the main reagents, and can significantly reduce disposal costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of sludge treatment, and more specifically, relates to a method for in-situ non-mechanical sludge dehydration, and in particular to a method for in-situ dehydration of waste salt and sludge by synergistically treating waste salt and sludge with a dehydrating agent and an ionic liquid. Background Art

[0002] The rapid economic development and increasing urbanization in China have brought with them a series of environmental problems. Among them, sewage and sludge problems are becoming increasingly serious. According to statistics, global sludge production exceeds 100 million tons annually. Due to the high moisture content and large volume of sludge, its subsequent processing and transportation costs are extremely high. Therefore, dewatering has become a key step in sludge post-treatment. Sludge dewatering can minimize sludge volume, facilitate transportation, and even reduce leachate generated in sludge landfills. Traditional treatment methods involve chemical preconditioning or mechanical dewatering. The sludge moisture content after chemical preconditioning or mechanical dewatering alone can only reach 80-95%. Even when both methods are used in combination, the moisture content can only be reduced to 65-75%. Furthermore, traditional preconditioning methods such as acid treatment or advanced oxidation for sludge dewatering involve acidic conditions that can cause corrosion of dewatering equipment, and the inability to recover reagents can also lead to secondary pollution and other problems.

[0003] With the advancement of science and technology and the development of industry, a large amount of waste is generated in industrial production or scientific experiments. For example, a large amount of waste phosphoric acid is generated in the manufacturing process of various industries, especially the manufacturing industry. The arbitrary discharge of these waste phosphoric acid not only causes environmental pollution and water pollution, but also leads to a large amount of waste phosphoric acid in the waste liquid being wasted. At this time, the waste phosphoric acid needs to be recycled for secondary use; for example, in experiments or production, there are a large number of expired drugs. Taking potassium hydroxide as an example, recycling expired potassium hydroxide can not only protect the environment, save energy, and drive the stable and sustainable development of social benefits, but also improve the efficiency of enterprises and companies and reduce costs. Summary of the Invention

[0004] In response to current needs and the shortcomings of existing technologies, the present invention provides a process for in-situ, non-mechanical sludge dewatering. This technology can separate sludge solids and water in a single step at room temperature, significantly improving its feasibility and economic viability for industrial application. Furthermore, due to the use of ionic liquids, a new, recyclable solvent with low vapor pressure, it produces virtually no "three wastes," making it relatively environmentally friendly and addressing equipment corrosion and other environmental issues associated with traditional methods. This technology not only deeply dehydrates sludge, but also simultaneously treats waste with waste, transforming solid waste into a resource, thereby maximizing waste resource utilization.

[0005] According to the purpose of the present invention, a method for in-situ non-mechanical sludge dehydration is provided, wherein an ionic liquid and a dehydrating agent are added to the sludge and thoroughly mixed; because the dehydrating agent is more hydrophilic than the ionic liquid, water molecules are more likely to form a hydrogen bond network when close to the dehydrating agent, so that the dehydrating agent and the water in the sludge form a lower aqueous phase, and the ionic liquid and the dehydrated sludge form an upper solid phase; the upper solid phase is washed to remove the ionic liquid, thereby obtaining dehydrated sludge.

[0006] Preferably, the ionic liquid removed by washing the upper solid phase is reused for sludge dewatering.

[0007] Preferably, the dehydrating agent is phosphate.

[0008] Preferably, the phosphate is potassium phosphate;

[0009] Preferably, the potassium phosphate is synthesized from waste phosphoric acid and waste potassium hydroxide.

[0010] Preferably, a soluble calcium salt is added to the lower aqueous phase, and the soluble calcium salt reacts with phosphate to obtain hydroxyapatite.

[0011] Preferably, the dehydrating agent is carbonate.

[0012] Preferably, the ionic liquid is an imidazole ionic liquid;

[0013] Preferably, the imidazolium ionic liquid is imidazolium chloride or imidazolium bromide;

[0014] Preferably, the imidazolium chloride is 1-butyl-3-methylimidazolium chloride; and the imidazolium bromide is 1-butyl-3-methylimidazolium bromide.

[0015] Preferably, the mass ratio of the sludge, the ionic liquid and the dehydrating agent is (20-25): (1-2): (8-15).

[0016] Preferably, the dewatered sludge is directly landfilled.

[0017] Preferably, the sludge is activated sludge.

[0018] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology:

[0019] (1) In the ionic liquid and dehydrating agent system, since the dehydrating agent is more hydrophilic than the ionic liquid, water molecules are more likely to form hydrogen bond networks when close to the dehydrating agent. Therefore, the hydration shell is preferentially formed around the dehydrating agent. This causes the ionic liquid and macromolecules such as proteins and polysaccharides in the sludge to exhibit relatively high hydrophobicity at this stage. Therefore, the ionic liquid and dehydrated sludge float on the upper layer, and the lower layer is the high-concentration dehydrating agent solution, thus completing the sludge dehydration.

[0020] (2) The present invention provides a novel sludge dewatering process with industrial potential and practical application value. Compared with conventional pretreatment methods, the present technology can reduce the sludge moisture content to approximately 70% through chemical conditioning alone, significantly improving dewatering efficiency.

[0021] (3) The traditional method requires chemical pre-conditioning before transporting to another location for mechanical treatment. Not only is the transportation cost high, but the acidic conditions can also cause corrosion to the equipment. The present invention can directly perform in-situ treatment without mechanical means, greatly reducing operating costs and making it more suitable for practical applications.

[0022] (4) The present invention can be used for emergency treatment of activated sludge in emergency situations such as machine maintenance and large-scale sludge accumulation, which facilitates the establishment of a rapid response mechanism and combines normal and abnormal conditions, which is more conducive to sustainable development.

[0023] (5) The present invention preferably uses waste phosphoric acid and waste potassium hydroxide to synthesize potassium phosphate for use as a dehydrating agent. In industrial production processes such as phosphoric acid production, chemical etching, phosphoric acid phosphating, chemical cleaning, and pesticide production, a large amount of phosphoric acid-containing waste liquid is generated every year. Waste phosphoric acid has the characteristics of high pollutant concentration, complex components, poor biodegradability, and high biological toxicity. It often needs to be treated before it can be discharged. This not only requires a large amount of processing costs, but also causes a large amount of phosphorus resources to be wasted. For the common chemical raw material potassium hydroxide, not only the shelf life is relatively short, but also the storage method is relatively strict. Once it is improperly stored, such as if it is not sealed and stored, it is easy to deteriorate. As a result, a large amount of expired potassium hydroxide will be generated. Therefore, the recycling of waste phosphoric acid and expired potassium hydroxide is an urgent problem to be solved. The dehydrating agent used in the present invention is synthesized from recycled waste, which not only achieves the purpose of protecting the environment and saving energy, but also drives the stable and sustainable development of social benefits, and at the same time achieves the additional goals of treating waste with waste and converting solid waste into resources.

[0024] (6) Preferably, the lower layer solution after sludge dehydration is a high concentration phosphate solution, which can be further synthesized into a highly efficient environmental remediation agent hydroxyapatite for adsorbing heavy metal ions such as Pb in environmental water. 2+ 、Cd 2+ wait. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the main technical process flow of the method for in-situ non-mechanical sludge dewatering of the present invention.

[0026] Figure 2 Comparison of moisture content between sludge treated with different types of ionic liquids and original sludge.

[0027] Figure 3 is the moisture content of sludge after adding different ionic liquid dosages.

[0028] Figure 4 is the moisture content of sludge after adding different dehydrating agent dosages.

[0029] Figure 5 XRD comparison of commercial hydroxyapatite and synthetic hydroxyapatite.

[0030] Figure 6 To synthesize hydroxyapatite for heavy metal Pb 2+ adsorption amount.

[0031] Figure 7 To synthesize hydroxyapatite for heavy metal Cd 2+ adsorption amount. DETAILED DESCRIPTION

[0032] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0033] The in-situ non-mechanical sludge dehydration method of the present invention adds an ionic liquid and a dehydrating agent to activated sludge, and after thorough mixing at room temperature, the sludge rapidly and stably aggregates and floats. The upper solid layer is a mixture of the ionic liquid and dehydrated sludge, while the lower layer is a high-concentration dehydrating agent solution. The volume ratio of the upper solid layer to the lower dehydrating agent solution is approximately 1:10, indicating that a large amount of water is removed.

[0034] Preferably, soluble calcium salt is added to the obtained lower layer dehydrating agent solution for synthesizing hydroxyapatite; the upper layer solid mixture is washed several times to recover the ionic liquid and then directly used for landfill.

[0035] Preferably, in the in-situ non-mechanical sludge dewatering method of the present invention, the upper dewatered sludge is washed to separate the dewatered sludge from the ionic liquid, and the separated ionic liquid can be reused in step (1).

[0036] Preferably, in the in-situ non-mechanical sludge dewatering method of the present invention, the ionic liquid is an imidazole ionic liquid.

[0037] Preferably, in the method for in-situ non-mechanical sludge dewatering of the present invention, the imidazole ionic liquid is 1-butyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium bromide.

[0038] Preferably, in the method for in-situ non-mechanical sludge dewatering of the present invention, the dehydrating agent is at least one of carbonate and phosphate, preferably phosphate.

[0039] Preferably, in the method for in-situ non-mechanical sludge dewatering of the present invention, the phosphate is potassium phosphate.

[0040] Preferably, in the method for in-situ non-mechanical sludge dewatering of the present invention, the potassium phosphate is a product directly synthesized from waste phosphoric acid and expired potassium hydroxide.

[0041] Preferably, in the method for in-situ non-mechanical sludge dewatering of the present invention, the soluble calcium salt is calcium chloride.

[0042] Figure 1 The schematic diagram of the main process flow of the in-situ non-mechanical sludge dewatering method is shown in FIG. The in-situ non-mechanical sludge dewatering method of the present invention specifically comprises the following steps:

[0043] (1) An ionic liquid, a dehydrating agent, and activated sludge are placed in a mixing agitator and stirred at room temperature for 3 minutes. After stopping the stirring, the mixture is allowed to naturally form two phases, wherein the upper layer is the ionic liquid and the dehydrated sludge, and the lower layer is a high-concentration dehydrating agent solution; wherein the ionic liquid includes but is not limited to an imidazole ionic liquid having solubility for extracellular polymers; the most preferred is 1-butyl-3-methylimidazolium chloride. The dehydrating agent includes but is not limited to phosphates and carbonates, and the most preferred is potassium phosphate.

[0044] (2) Separate the two phases obtained in the previous step. Add a soluble calcium salt to the lower phase to ensure a calcium-phosphorus ratio of 1.67, maintain the pH at 11, and oscillate at room temperature for 5 hours and then age at room temperature for 24 hours. After the reaction is complete, separate the solid and liquid, wash the precipitate with water until neutral, and then dry it at 105°C to constant weight, which is hydroxyapatite.

[0045] (3) The upper layer of dewatered sludge and ionic liquid mixture obtained in the previous step is washed, and the ionic liquid is recovered. The washed sludge solids can be directly used for landfill.

[0046] Example 1

[0047] The method for in-situ non-mechanical sludge dewatering of the present invention comprises the following steps:

[0048] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0049] (2) Activated sludge, 1-butyl-3-methylimidazolium bromide (an imidazole ionic liquid), and potassium phosphate were mixed in a ratio of activated sludge: 1-butyl-3-methylimidazolium bromide: potassium phosphate = 2:0.15:1; and stirred thoroughly at room temperature for 3 minutes;

[0050] (3) After standing, the mixture was separated into two layers: the upper layer was a black viscous substance and the lower layer was a light yellow clear liquid. The lower layer of light yellow clear liquid was removed for the next step;

[0051] (4) Add calcium chloride to the pale yellow clear solution, maintaining the calcium-phosphorus ratio at 1.67 and the pH at 11, and shake at room temperature for 5 hours, and then age at room temperature for 24 hours. After the reaction is complete, the solid and liquid are separated, and the precipitate is washed with water until neutral and then dried at 105°C to constant weight to obtain the hydroxyapatite product;

[0052] (5) After weighing the mass of the upper black viscous material, place it in a freeze dryer for drying. After drying for 10 hours, weigh the mass of the dried solid. The difference in mass before and after drying is the water content of the dehydrated sludge, which is 73.80%;

[0053] (6) The upper black viscous material is washed multiple times, and the washing liquid is dried to obtain the regenerated ionic liquid, which is then reused.

[0054] Example 2

[0055] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0056] (2) Activated sludge, 1-butyl-3-methylimidazolium chloride (an imidazole ionic liquid), and potassium phosphate were mixed in a ratio of activated sludge: 1-butyl-3-methylimidazolium chloride: potassium phosphate = 2:0.15:1; and stirred thoroughly at room temperature for 5 minutes;

[0057] (3) After standing, the mixture was separated into two layers: the upper layer was a black viscous substance and the lower layer was a light yellow clear liquid. The lower layer of light yellow clear liquid was removed for the next step;

[0058] (4) Add calcium chloride to the pale yellow clear solution, maintaining the calcium-phosphorus ratio at 1.67 and the pH at 11, and shake at room temperature for 5 hours, and then age at room temperature for 24 hours. After the reaction is complete, the solid and liquid are separated, and the precipitate is washed with water until neutral and then dried at 105°C to constant weight to obtain the hydroxyapatite product;

[0059] (5) After weighing the mass of the black viscous substance on the upper layer, place it in a freeze dryer for drying. After drying for 10 hours, weigh the mass of the dried solid. The difference in mass before and after drying is the water content of the dehydrated sludge, which is 70.21%;

[0060] (6) The upper black viscous material is washed multiple times, and the washing liquid is dried to obtain the regenerated ionic liquid, which is then reused.

[0061] Figure 2 The water content of the original sludge, Example 1, and Example 2 was compared. The results showed that when the selected ionic liquid was 1-butyl-3-methylimidazolium chloride, its sludge dehydration effect was better than that of 1-butyl-3-methylimidazolium bromide. Therefore, the dosage of 1-butyl-3-methylimidazolium chloride was further optimized, and the sludge moisture content after optimization was ( Figure 3 )See Examples 2-4.

[0062] Example 3

[0063] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0064] (2) Activated sludge, 1-butyl-3-methylimidazolium chloride (an imidazole ionic liquid), and potassium phosphate were mixed in a ratio of activated sludge: 1-butyl-3-methylimidazolium chloride: potassium phosphate = 2:0.1:1; and stirred thoroughly at room temperature for 5 minutes;

[0065] (3) After standing, the mixture was separated into two layers: the upper layer was a black viscous substance and the lower layer was a light yellow clear liquid. The lower layer of light yellow clear liquid was removed for the next step;

[0066] (4) Add calcium chloride to the pale yellow clear solution, maintaining the calcium-phosphorus ratio at 1.67 and the pH at 11, and shake at room temperature for 5 hours, and then age at room temperature for 24 hours. After the reaction is complete, the solid and liquid are separated, and the precipitate is washed with water until neutral and then dried at 105°C to constant weight to obtain the hydroxyapatite product;

[0067] (5) After weighing the mass of the upper black viscous material, place it in a freeze dryer for drying. After drying for 10 hours, weigh the mass of the dried solid. The difference in mass before and after drying is the water content of the dehydrated sludge, which is 75.50%;

[0068] (6) The upper black viscous material is washed multiple times, and the washing liquid is dried to obtain the regenerated ionic liquid, which is then reused.

[0069] Example 4

[0070] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0071] (2) Activated sludge, 1-butyl-3-methylimidazolium chloride (an imidazole ionic liquid), and potassium phosphate were mixed in a ratio of activated sludge: 1-butyl-3-methylimidazolium chloride: potassium phosphate = 2:0.2:1; and stirred thoroughly at room temperature for 5 minutes;

[0072] (3) After standing, the mixture was separated into two layers: the upper layer was a black viscous substance and the lower layer was a light yellow clear liquid. The lower layer of light yellow clear liquid was removed for the next step;

[0073] (4) Add calcium chloride to the pale yellow clear solution, maintaining the calcium-phosphorus ratio at 1.67 and the pH at 11, and shake at room temperature for 5 hours, and then age at room temperature for 24 hours. After the reaction is complete, the solid and liquid are separated, and the precipitate is washed with water until neutral and then dried at 105°C to constant weight to obtain the hydroxyapatite product;

[0074] (5) After weighing the mass of the black viscous substance on the upper layer, place it in a freeze dryer for drying. After drying for 10 hours, weigh the mass of the dried solid. The difference in mass before and after drying is the water content of the dehydrated sludge, which is 69.53%;

[0075] (6) The upper black viscous material is washed multiple times, and the washing liquid is dried to obtain the regenerated ionic liquid, which is then reused.

[0076] Figure 3 It shows that the dehydration effect is relatively good in Examples 2 and 4. Taking into account the economic cost, the optimal dosage is determined to be Example 2. Subsequently, different phosphate dosages are compared, see Example 2, Example 5, and Example 6.

[0077] Example 5

[0078] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0079] (2) Mixing activated sludge, 1-butyl-3-methylimidazolium chloride (an imidazole ionic liquid) and potassium phosphate in a ratio of activated sludge: 1-butyl-3-methylimidazolium chloride: potassium phosphate = 5:0.375:2; stirring thoroughly at room temperature for 5 minutes;

[0080] (3) After standing, the mixture was separated into two layers: the upper layer was a black viscous substance and the lower layer was a light yellow clear liquid. The lower layer of light yellow clear liquid was removed for the next step;

[0081] (4) Add calcium chloride to the pale yellow clear solution, maintaining the calcium-phosphorus ratio at 1.67 and the pH at 11, and shake at room temperature for 5 hours, and then age at room temperature for 24 hours. After the reaction is complete, the solid and liquid are separated, and the precipitate is washed with water until neutral and then dried at 105°C to constant weight to obtain the hydroxyapatite product;

[0082] (5) After weighing the mass of the upper black viscous material, place it in a freeze dryer for drying. After drying for 10 hours, weigh the mass of the dried solid. The difference in mass before and after drying is the water content of the dehydrated sludge, which is 75.92%;

[0083] (6) The upper black viscous material is washed multiple times, and the washing liquid is dried to obtain the regenerated ionic liquid, which is then reused.

[0084] Example 6

[0085] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0086] (2) Activated sludge, 1-butyl-3-methylimidazolium chloride (an imidazole ionic liquid), and potassium phosphate were mixed in a ratio of activated sludge: 1-butyl-3-methylimidazolium chloride: potassium phosphate = 5:0.375:3; and stirred thoroughly at room temperature for 5 minutes;

[0087] (3) After standing, the mixture was separated into two layers: the upper layer was a black viscous substance and the lower layer was a light yellow clear liquid. The lower layer of light yellow clear liquid was removed for the next step;

[0088] (4) Add calcium chloride to the pale yellow clear solution, maintaining the calcium-phosphorus ratio at 1.67 and the pH at 11, and shake at room temperature for 5 hours, and then age at room temperature for 24 hours. After the reaction is complete, the solid and liquid are separated, and the precipitate is washed with water until neutral and then dried at 105°C to constant weight to obtain the hydroxyapatite product;

[0089] (5) After weighing the mass of the upper black viscous material, place it in a freeze dryer for drying. After drying for 10 hours, weigh the mass of the dried solid. The difference between the mass before and after drying is the water content of the dehydrated sludge, which is 69.87%;

[0090] (6) The upper black viscous material is washed multiple times, and the washing liquid is dried to obtain the regenerated ionic liquid, which is then reused.

[0091] Figure 4 The sludge moisture content diagram after the phosphate dosage is optimized is shown in FIG. The dehydration effects of Examples 2 and 6 are relatively good. Taking into account the sludge dehydration effect, in order to save economic costs, the preferred phosphate dosage is Example 2.

[0092] In summary, compared with the above embodiments, embodiment 2 is the best solution.

[0093] Example 7

[0094] The hydroxyapatite product synthesized in Example 2 was characterized by XRD and its structure was compared with that of commercial hydroxyapatite. Figure 5 0.03 g of synthetic hydroxyapatite was accurately weighed and added to 50 mL of Pb(NO3)2 solution at 100, 200, 400, 800, and 1000 mg / L, respectively. The mixture was reacted in a constant temperature oscillating box at 25°C and 400 r / min for 24 h. The samples were then taken and filtered through a 0.22 μm filter. The Pb content was determined by ICP. 2+ concentration, calculate the hydroxyapatite to Pb 2+ The adsorption capacity of hydroxyapatite on Pb 2+ It has good adsorption effect, and the maximum adsorption capacity can reach 616mg / g (such as Figure 6 shown).

[0095] Example 8

[0096] Accurately weigh 0.05 g of synthetic hydroxyapatite and add it to 50 mL of Cd(NO3)2·4H2O solution with concentrations of 50, 100, 200, 400, and 600 mg / L, respectively. After reacting in a constant temperature oscillating box at 25°C and 400 r / min for 24 h, samples were taken and filtered through a 0.22 μm filter. Cd was determined by ICP. 2+ concentration, calculate the hydroxyapatite to Cd 2+ The adsorption capacity of hydroxyapatite for Cd2+ It has good adsorption effect, and the maximum adsorption capacity can reach 283mg / g (such as Figure 7 shown).

[0097] Comparative Example 1

[0098] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0099] (2) Mixing activated sludge and 1-butyl-3-methylimidazolium chloride in a ratio of activated sludge: ionic liquid = 2:0.15; stirring thoroughly at room temperature for 3 minutes;

[0100] (3) There was no phase separation after standing, which was compared with Examples 1 and 2. This showed that the ionic liquid alone could not separate the phases, indicating that the dehydration failed.

[0101] Comparative Example 2

[0102] (1) Sludge from the secondary sedimentation tank of a municipal sewage treatment plant in Wuhan was collected. Before the experiment, all sludge samples were sieved using a 1mm pore stainless steel sieve to remove large sand and gravel particles and other impurities. The sludge was then stored in a refrigerator at 4°C. All experiments were completed within one week of sludge collection.

[0103] (2) Mix activated sludge and potassium phosphate in a ratio of activated sludge: potassium phosphate = 2:1; stir thoroughly at room temperature for 3 minutes;

[0104] (3) There was no phase separation after standing, which was compared with Examples 1 and 2. This showed that phosphate alone could not separate the phases, indicating that dehydration failed.

Claims

1. A method for in-situ non-mechanical sludge dewatering, characterized in that: An ionic liquid and a dehydrating agent are added to the sludge and mixed thoroughly, wherein the dehydrating agent is a phosphate; since the dehydrating agent is more hydrophilic than the ionic liquid, water molecules are more likely to form a hydrogen bond network when close to the dehydrating agent, so that the dehydrating agent and water in the sludge form a lower aqueous phase, and the ionic liquid and the dehydrated sludge form an upper solid phase; the upper solid phase is washed to remove the ionic liquid, thereby obtaining dehydrated sludge; A soluble calcium salt is added to the lower aqueous phase, and the soluble calcium salt reacts with the phosphate to obtain hydroxyapatite.

2. The method for in-situ non-mechanical sludge dewatering according to claim 1, characterized in that: The ionic liquid removed by washing the upper solid phase is used again for sludge dewatering.

3. The method for in-situ non-mechanical sludge dewatering according to claim 1, characterized in that: The phosphate is potassium phosphate.

4. The method for in-situ non-mechanical sludge dewatering according to claim 3, characterized in that: The potassium phosphate is synthesized from waste phosphoric acid and waste potassium hydroxide.

5. The method for in-situ non-mechanical sludge dewatering according to claim 1, characterized in that: The ionic liquid is an imidazole ionic liquid.

6. The method for in-situ non-mechanical sludge dewatering according to claim 5, characterized in that: The imidazolium ionic liquid is imidazolium chloride or imidazolium bromide.

7. The method for in-situ non-mechanical sludge dewatering according to claim 6, characterized in that: The imidazolium chloride is 1-butyl-3-methylimidazolium chloride; the imidazolium bromide is 1-butyl-3-methylimidazolium bromide.

8. The method for in-situ non-mechanical sludge dewatering according to claim 1, characterized in that: The mass ratio of the sludge, the ionic liquid and the dehydrating agent is (20-25): (1-2): (8-15).

9. The method for in-situ non-mechanical sludge dewatering according to claim 1, characterized in that: The dewatered sludge is directly landfilled.

10. The method for in-situ non-mechanical sludge dewatering according to claim 1, characterized in that: The sludge is activated sludge.

Images