A method for deep dewatering of sludge from a sewage treatment plant

Abstract

The present invention discloses a method for deep dewatering of sludge in a sewage treatment plant, belonging to the technical field of sludge dewatering. In the present invention, the sludge is first subjected to hydrodynamic cavitation treatment, and then black soldier fly pupa shell powder slurry is added for conditioning. After dewatering the conditioned sludge, a deep dewatered sludge cake with a moisture content of 60% can be formed, meeting or approaching the treatment requirements such as sludge composting and incineration. The outer shell of the black soldier fly contains substances similar to chitin, and its acid leaching products contain a large amount of hydroxyl groups (-OH) and amino groups (-NH2), which can covalently and non-covalently bind to the carbonyl groups contained in the proteins in the sludge liquid phase, thereby promoting the precipitation of hydrophilic substances such as proteins in the sludge, and further improving the sludge dewatering performance. After the sludge is subjected to hydrodynamic cavitation treatment and conditioning with pupa shell powder slurry, the dewatering performance is greatly improved. Combined with dewatering treatment, the moisture content can be reduced to below 60%.

Description

Technical Field

[0001] The present invention belongs to the technical field of sludge dewatering, and particularly relates to a method for deep dewatering of sludge from sewage treatment plants. Background Art

[0002] Sludge is a secondary product of sewage treatment plants. At present, the daily treatment capacity of urban sewage treatment plants across the country reaches 216 million cubic meters, the total annual sewage discharge is 63.90 billion cubic meters, and the dry sludge volume generated from sewage treatment reaches 13.699 million tons. If sludge is not properly treated, it may cause secondary pollution. Currently, the main methods for sludge disposal include land use, incineration, landfill, and building materials utilization. Among them, landfill and land use require the sludge moisture content to be below 60%, direct incineration requires it to be below 50%, and building materials utilization requires it to be below 40%. Dewatering is an important means to reduce the volume and weight of sludge, but due to the small size, high viscosity, and strong hydrophilicity of sludge particles, its dewatering performance is poor. Using conventional conditioning-mechanical dewatering methods, the moisture content of the sludge cake is still as high as about 80%. Generally, the moisture content of sludge composting treatment needs to be reduced to 50%-60%, the moisture content required for landfill treatment mixed into landfills is below 60%, and incineration treatment has higher requirements for moisture content. Therefore, it is particularly important to deeply treat sludge.

[0003] Existing technologies can reduce the moisture content of sludge after conditioning and mechanical dewatering to below 60%, but these technologies usually require adding a large amount of inorganic agents such as lime and iron salts to the sludge, resulting in a high content of inorganic substances and a low dry basis calorific value in the sludge cake, which is not suitable for subsequent composting and incineration treatment.

[0004] Therefore, it is particularly important to develop a deep dewatering method that can reduce the use of inorganic agents and significantly improve the dewatering performance of sludge. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a method for deep dewatering of sludge from sewage treatment plants.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for deep dewatering of sludge from sewage treatment plants, comprising the following steps: first, subject the sludge to hydrodynamic cavitation treatment, then add black soldier fly pupa shell powder slurry for conditioning, and then perform dewatering treatment to obtain a sludge cake.

[0008] Preferably, the dosage of the black soldier fly pupa shell powder slurry is 0.5%-2.0% of the volume of the sludge obtained after hydrodynamic cavitation treatment.

[0009] Preferably, the method for preparing the black soldier fly pupa shell powder slurry comprises the following steps: making the black soldier fly pupa shell into pupa shell powder, and then treating the obtained pupa shell powder with sulfuric acid to obtain the black soldier fly pupa shell powder slurry.

[0010] Preferably, the dosage of the sulfuric acid is 30%-60% (W / V) of the pupa shell powder, and the concentration of the sulfuric acid is 30% (W / V).

[0011] Preferably, the temperature of the sulfuric acid treatment is room temperature, and the time is more than 60 min.

[0012] Preferably, the parameters of the hydrodynamic cavitation treatment include: the minimum diameter of the venturi tube of the hydrodynamic cavitation device is 1 / 20 of the diameters of the front and rear sludge conveying pipes, the flow velocity of the sludge ejection is not less than 5 m / s, and the treatment time is 20-30 min.

[0013] Preferably, before the hydrodynamic cavitation treatment, the pH value of the sludge is adjusted to 2-4.

[0014] Preferably, after the conditioning, the pH value of the conditioned sludge is adjusted to 6-9.

[0015] Preferably, the dehydration treatment method is high-pressure plate and frame dehydration.

[0016] Preferably, the water content of the sludge cake is 50%-57%.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects:

[0018] In the present invention, by first performing hydrodynamic cavitation treatment on the sludge, then adding the black soldier fly pupa shell powder slurry for conditioning, and performing dehydration treatment on the conditioned sludge, a deeply dehydrated sludge cake with a water content of 60% can be formed, meeting the treatment requirements such as sludge composting and incineration. The black soldier fly outer shell has a substance similar to chitin, and its acid leaching product contains a large amount of hydroxyl groups (-OH) and amino groups (-NH 2 ), which can covalently and non-covalently bind to the carbonyl groups contained in the proteins in the sludge liquid phase, thereby promoting the precipitation of hydrophilic substances such as proteins in the sludge, and further improving the sludge dehydration performance. After the sludge is treated by hydrodynamic cavitation and conditioned with the pupa shell powder slurry, the dehydration performance is greatly improved. Combined with the dehydration treatment, the water content can be reduced to less than 60%. Description of the Drawings

[0019] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0020] Figure 1 It is the process flow diagram of Examples 1-4;

[0021] Figure 2 Schematic diagram of the hydrodynamic cavitation device in Examples 1-4; wherein, 1 is a control valve, 2 is a pressure gauge, 3 is a Venturi tube, 4 is a first sludge storage tank, 5 is a stainless steel self-priming vortex pump, and 6 is a second sludge storage tank. Detailed implementation mode

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0023] To make the above objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation modes.

[0024] The embodiment of the present invention provides a method for deep dewatering of sludge in a sewage treatment plant, which includes the following steps: first, perform hydrodynamic cavitation treatment on the sludge, then add black soldier fly pupa shell powder slurry for conditioning, and then perform dewatering treatment to obtain sludge cakes.

[0025] In a preferred embodiment, the sludge is thickened sludge; the water content of the sludge is 96%-98%.

[0026] In a preferred embodiment, the parameters of the hydrodynamic cavitation treatment include: the minimum diameter of the Venturi tube of the hydrodynamic cavitation device is 1 / 20 of the diameters of the front and rear sludge conveying pipes, the flow velocity of the ejected sludge is not less than 5 m / s, and the treatment time is 20-30 min. The present invention uses a hydrodynamic cavitation device equipped with a Venturi tube for hydrodynamic cavitation treatment. In the Venturi tube, the jet rate of the sludge suddenly increases, and high-speed frictional forces will be generated between the sludge particles. At the same time, the cavitation bubbles generated by the high-speed jet burst instantaneously, generating huge energy, which promotes the generation of ·OH and ·H by water molecules. ·OH can covalently and non-covalently bind to the carbonyl groups contained in the proteins in the sludge liquid phase, thereby promoting the precipitation of hydrophilic substances such as proteins in the sludge, and then improving the sludge dewatering performance.

[0027] In a preferred embodiment, before the hydro-cavitation treatment, it further includes adjusting the pH value of the sludge to 2-4; the reagent for adjusting the pH value of the sludge is sulfuric acid; specifically, adjusting the pH value of the sludge to 2-4 means: slowly adding sulfuric acid to the sludge and continuously stirring to make the sulfuric acid and the sludge mix evenly, and stop adding sulfuric acid after detecting that the pH of the sludge is adjusted to 2-4, and let it stand for 10-60 min. When the pH value of the sludge is lower than 4.0, advanced oxidation can occur, and at the same time, the low pH value can denature the proteins in the extracellular polymeric substances of the sludge and damage the microbial cell membranes in the sludge. Furthermore, under the synergistic effect of the denaturation of the proteins on the cell membrane surface, advanced oxidation, and the high-speed frictional force between sludge particles, etc., it promotes the rupture of the sludge cell membrane. Thus, the microbial cell contents in the sludge are released, and the microbial cytoplasm in the sludge is transformed into easily removable moisture such as free water.

[0028] In a preferred embodiment, the dosage of the black soldier fly pupa shell powder slurry is 0.5%-2.0% of the volume of the sludge obtained after hydro-cavitation treatment. In the present invention, the dosage of the black soldier fly pupa shell powder slurry is controlled within the above range, which has the advantages of less material consumption and low cost. If the dosage of the black soldier fly pupa shell powder slurry is too low, the designed dehydration requirement cannot be achieved. If it is too high, it will increase the sludge quality, increase the cost, and the improvement of the dehydration effect is not obvious.

[0029] In a preferred embodiment, the preparation method of the black soldier fly pupa shell powder slurry includes the following steps: making the black soldier fly pupa shell into pupa shell powder, and then treating the obtained pupa shell powder with sulfuric acid to obtain the black soldier fly pupa shell powder slurry. In the present invention, sulfuric acid is used to treat the pupa shell powder, thereby obtaining an acid-leaching product containing a large amount of hydroxyl groups (-OH) and amino groups (-NH 2 ) The hydroxyl groups (-OH) and amino groups (-NH 2 ) can covalently and non-covalently bind to the carbonyl groups contained in the proteins in the sludge liquid phase, thereby promoting the precipitation of hydrophilic substances such as proteins in the sludge, and further improving the sludge dewatering performance.

[0030] In a preferred embodiment, the particle size of the pupa shell powder is 1.0-10 μm; the preparation method of the pupa shell powder includes: grinding the black soldier fly pupa shell to obtain the pupa shell powder.

[0031] In a preferred embodiment, the dosage of sulfuric acid is 30%-60% (W / V) of the pupa shell powder, and the concentration of sulfuric acid is 30% (W / V). In the present invention, the dosage of sulfuric acid is controlled within the above range, which has the advantages of less material consumption and significant dehydration effect. If the dosage of sulfuric acid is too low, the proteins in the microbial cell membranes in the sludge cannot be denatured, and thus the sludge cell membranes cannot be damaged, ultimately resulting in the inability to transform the water in the microbial cells into easily removable free water, affecting the dehydration effect. If it is too high, it will increase the cost and increase the sludge quality.

[0032] In a preferred embodiment, the temperature of the sulfuric acid treatment is room temperature, and the time is more than 60 min.

[0033] In a preferred embodiment, after conditioning, the pH value of the conditioned sludge is adjusted to 6-9; the reagent for adjusting the pH value of the conditioned sludge is an alkaline agent; the alkaline agent includes one or more of sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0034] In a preferred embodiment, the dehydration treatment method is high-pressure plate-and-frame dehydration; the pressure of the high-pressure plate-and-frame dehydration is 13-15 MPa, and the pressure filtration time is 20 min.

[0035] In a preferred embodiment, the water content of the sludge cake is 50%-57%.

[0036] In the embodiments of the present invention, room temperature refers to "25±2°C".

[0037] Unless otherwise specified, the raw materials in the embodiments of the present invention are all obtained through commercial channels.

[0038] Example 1

[0039] A method for deep dehydration of sewage treatment plant sludge, the process flow is shown in Figure 1 , specifically including the following steps:

[0040] Take the concentrated sludge with a water content of 98% from a sewage treatment plant, adjust the pH value of the sludge to 3 with sulfuric acid, stir and mix evenly, then let it stand for 30 min, and then carry out hydrodynamic cavitation treatment. The minimum diameter of the venturi tube of the hydrodynamic cavitation device is 1 / 20 of the diameter of the front and rear sludge conveying pipes, the flow velocity of the sludge ejection is 5 m / s, and the treatment is continued for 30 min to obtain the sludge after hydrodynamic cavitation treatment. Add the black soldier fly pupa shell powder slurry to the above-mentioned sludge after hydrodynamic cavitation treatment at a ratio of 0.5% (V / V), mix evenly, and then add sodium hydroxide to adjust the pH value of the sludge to 8 to obtain the conditioned sludge. Pump the conditioned sludge into a high-pressure plate-and-frame dehydrator for dehydration treatment. After 20 min of treatment, a sludge cake with a water content of 57% is obtained;

[0041] Among them, the preparation method of the black soldier fly pupa shell powder slurry is: grind the discarded outer shell after extracting black soldier fly pupae with a crusher to obtain pupa shell powder with a particle size of 1-10 μm; add 30% (W / V) sulfuric acid to the above pupa shell powder, the concentration of sulfuric acid is 30% (W / V), and treat it at 25°C for 60 min to obtain the black soldier fly pupa shell powder slurry.

[0042] Example 2

[0043] A method for deep dehydration of sewage treatment plant sludge, the process flow is shown in Figure 1 , specifically including the following steps:

[0044] Take the concentrated sludge with a water content of 96% from the sewage treatment plant, adjust the pH value of the sludge to 3 with sulfuric acid, stir and mix evenly, let it stand for 30 min, then carry out hydrodynamic cavitation treatment. The minimum diameter of the venturi tube of the hydrodynamic cavitation device is 1 / 20 of the diameters of the sludge conveying pipes before and after it, the flow velocity of the ejected sludge is 10 m / s, and the treatment lasts for 30 min to obtain the sludge after hydrodynamic cavitation treatment. Add the black soldier fly pupa shell powder slurry into the above-mentioned sludge after hydrodynamic cavitation treatment at a ratio of 0.5% (V / V), mix evenly, and then add sodium hydroxide to adjust the pH value of the sludge to 8 to obtain the conditioned sludge. Pump the conditioned sludge into a high-pressure plate and frame filter press for dehydration treatment. After 20 min of treatment, a sludge cake with a water content of 56% is obtained;

[0045] The preparation method of the black soldier fly pupa shell powder slurry is the same as that in Example 1.

[0046] Example 3

[0047] A method for deep dehydration of sludge from a sewage treatment plant, the process flow is shown in Figure 1 , specifically including the following steps:

[0048] Take the concentrated sludge with a water content of 97% from the sewage treatment plant, adjust the pH value of the sludge to 3 with sulfuric acid, stir and mix evenly, let it stand for 30 min, then carry out hydrodynamic cavitation treatment. The minimum diameter of the venturi tube of the hydrodynamic cavitation device is 1 / 20 of the diameters of the sludge conveying pipes before and after it, the flow velocity of the ejected sludge is 5 m / s, and the treatment lasts for 30 min to obtain the sludge after hydrodynamic cavitation treatment. Add the black soldier fly pupa shell powder slurry into the above-mentioned sludge after hydrodynamic cavitation treatment at a ratio of 2% (V / V), mix evenly, and then add sodium hydroxide to adjust the pH value of the sludge to 8 to obtain the conditioned sludge. Pump the conditioned sludge into a high-pressure plate and frame filter press for dehydration treatment. After 20 min of treatment, a sludge cake with a water content of 50% is obtained;

[0049] The preparation method of the black soldier fly pupa shell powder slurry is the same as that in Example 1.

[0050] Example 4

[0051] A method for deep dehydration of sludge from a sewage treatment plant, the process flow is shown in Figure 1 , specifically including the following steps:

[0052] Take the concentrated sludge with a water content of 98% from the sewage treatment plant, adjust the pH value of the sludge to 3 with sulfuric acid, stir and mix evenly, let it stand for 30 min, then carry out hydrodynamic cavitation treatment. The minimum diameter of the venturi tube of the hydrodynamic cavitation device is 1 / 20 of the diameters of the sludge conveying pipes before and after it. The flow velocity of the ejected sludge is 10 m / s, and the treatment lasts for 30 min to obtain the sludge after hydrodynamic cavitation treatment. Add the black soldier fly pupa shell powder slurry to the sludge after the above-mentioned hydrodynamic cavitation treatment at a ratio of 2% (V / V), mix evenly, and then add sodium hydroxide to adjust the pH value of the sludge to 8 to obtain the conditioned sludge. Pump the conditioned sludge into a high-pressure plate and frame filter press for dehydration treatment. After 20 min of treatment, a sludge cake with a water content of 53% is obtained;

[0053] The preparation method of the black soldier fly pupa shell powder slurry is the same as that in Example 1.

[0054] Figure 1 It is the process flow chart of Examples 1 - 4. From Figure 1 It can be seen that in the present invention, first, concentrated sludge is added with sulfuric acid to adjust the pH value to 2 - 4, and then subjected to hydrodynamic cavitation treatment to form hydrodynamically cavitated conditioned sludge. Then, the pupa shell powder formed by treating the black soldier fly pupa shell with sulfuric acid is added to the hydrodynamically cavitated conditioned sludge to form pupa shell powder - hydrodynamically cavitated combined treated sludge. Finally, an alkaline agent is added to adjust the pH value to 6 - 9 to form the conditioned sludge. After the conditioned sludge is mechanically dehydrated, deeply dehydrated sludge with a water content of about 60% is formed.

[0055] Figure 2 It is the schematic diagram of the hydrodynamic cavitation device in Examples 1 - 4. From Figure 2 It can be seen that the sludge in the first sludge storage tank 4 is pumped by a stainless steel self - priming vortex pump 5. The control valve 1 is adjusted, and the reading of the pressure gauge 2 is observed to make the flow velocity of the sludge reach the design requirement after passing through the venturi tube 3. The sludge after hydrodynamic cavitation is stored in the second sludge storage tank 6.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that the black soldier fly pupa shell powder slurry is added to the sludge after hydrodynamic cavitation treatment at a ratio of 4% (V / V), and the other steps are the same as those in Example 1; a sludge cake with a water content of still 57% is obtained.

[0058] Comparative Example 2

[0059] The difference from Example 1 is that the black soldier fly pupa shell powder slurry is added to the sludge after hydrodynamic cavitation treatment at a ratio of 0.2% (V / V), and the other steps are the same as those in Example 1; a sludge cake with a water content of 62% is obtained.

[0060] Comparative Example 3

[0061] It is different from Example 1 in that the black soldier fly pupa shell powder slurry is not added, and the remaining steps are the same as those in Example 1; a sludge cake with a water content of 78% is obtained.

[0062] Comparative Example 4

[0063] It is different from Example 1 in that the black soldier fly pupa shell powder slurry is added to the sludge after hydrocavitation treatment at a ratio of 2% (V / V), and the pH value of the sludge is adjusted to 5 with sulfuric acid. The remaining steps are the same as those in Example 1; a sludge cake with a water content of 63% is obtained.

[0064] Comparative Example 5

[0065] It is different from Example 1 in that the preparation method of the black soldier fly pupa shell powder slurry is as follows: the discarded outer shell after extracting black soldier fly pupae is ground with a crusher to obtain pupa shell powder with a particle size of 2 - 8 μm; 30% (W / V) water is added to the above pupa shell powder and treated at 25°C for 60 min to obtain the black soldier fly pupa shell powder slurry. The remaining steps are the same as those in Example 1; a sludge cake with a water content of 77% is obtained.

[0066] The above is only the preferred specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for deep dehydration of sludge from a sewage treatment plant, characterized in that: The following steps are involved: The sludge is first subjected to a hydraulic cavitation treatment, and then a black soldier fly pupa shell powder slurry is added for conditioning, and then a dehydration treatment is performed to obtain a sludge cake; the amount of the black soldier fly pupa shell powder slurry is 0.5%-2.0% of the volume of the sludge obtained after the hydraulic cavitation treatment; The method for preparing the black soldier fly pupa shell powder slurry comprises the following steps: preparing black soldier fly pupa shells into pupa shell powder, and then treating the obtained pupa shell powder with sulfuric acid to obtain the black soldier fly pupa shell powder slurry; the amount of sulfuric acid used is 30%-60% (W / V) of the pupa shell powder, and the concentration of sulfuric acid is 30% (W / V); the temperature of the sulfuric acid treatment is room temperature, and the time is 60 minutes.

2. The deep dehydration method of sewage treatment plant sludge according to claim 1, characterized in that: The parameters of the hydrodynamic cavitation treatment include: the minimum diameter of the venturi tube of the hydrodynamic cavitation device is 1 / 20 of the diameter of the sludge conveying pipes before and after it, the flow rate of the sludge spraying is not less than 5m / s, and the treatment time is 20-30min.

3. The deep dehydration method of sewage treatment plant sludge according to claim 1, characterized in that: The process also includes adjusting the pH value of the sludge to 2-4 before the hydrodynamic cavitation treatment.

4. The deep dehydration method of sewage treatment plant sludge according to claim 1, characterized in that: The conditioning also includes adjusting the pH value of the conditioned sludge to 6-9.

5. The deep dehydration method of sewage treatment plant sludge according to claim 1, characterized in that: The dehydration treatment method is high-pressure plate and frame dehydration.

6. The deep dehydration method of sewage treatment plant sludge according to claim 1, characterized in that: The moisture content of the sludge cake is 50%-57%.

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