A resource utilization method for excess sludge in a sewage treatment plant

Abstract

The present invention discloses a method for resource utilization of excess sludge from a sewage treatment plant, belonging to the technical field of sewage treatment, and comprising the following steps: adjusting the pH of the sludge obtained after elutriating the excess sludge from the sewage treatment plant, then performing hydrothermal treatment, followed by secondary elutriation and removing the precipitate to obtain a first liquid phase, flocculating the obtained first liquid phase, and finally centrifuging to separate a solid phase component and a second liquid phase. Adjust the pH of the second liquid phase to neutral and reflux it to the sewage treatment plant, and dry the solid phase component to prepare a water retaining agent, thereby realizing the resource utilization of the sludge. The present invention can, at a relatively low treatment cost, greatly recycle and utilize the excess sludge from the sewage treatment plant, thus providing technical support that takes into account both economic benefits and environmental safety for the treatment of sludge.

Description

Technical Field

[0001] The present invention belongs to the technical field of sludge resource utilization, and particularly relates to a method for resource utilization of excess sludge in a sewage treatment plant. Background Art

[0002] With the rapid economic development, continuous improvement of urbanization level and enhancement of the national environmental protection strategy, the urban domestic sewage treatment volume has been increasing year by year, which also leads to a substantial increase in the output of excess sludge. For a sewage treatment plant, the treatment cost of the sludge generated during its operation can reach 40 - 60% of the total operation cost of the sewage treatment plant, which undoubtedly increases the cost of the sewage treatment plant. Therefore, how to efficiently, low - cost and harmlessly treat and dispose of excess sludge has now become a major problem faced by sewage treatment plants.

[0003] Generally speaking, the disposal methods of excess sludge are sanitary landfill, land use, drying and incineration, building materials utilization, etc. In China, many sewage treatment plants adopt the landfill method to dispose of sludge, which occupies a large area, resulting in an effective treatment rate of less than 30% for sludge, and at the same time, it will also bring subsequent environmental problems such as secondary pollution. Land use has a high degree of resource utilization and low cost, but due to the low organic matter content and high sulfide content of sludge in China, it is difficult to make the excess sludge meet the relevant stabilization standards in China after preliminary treatment, and toxic and harmful substances such as heavy metals contained in the sludge will also enter the land without treatment.

[0004] Therefore, how to provide a treatment method for excess sludge in urban sewage treatment plants that takes into account both ecological environment safety and economic benefits, can also achieve reduction, harmless disposal, and at the same time enable its reasonable resource utilization is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0005] To solve the above - mentioned technical problems, the present invention proposes a method for resource utilization of excess sludge in a sewage treatment plant and its application. Combining the characteristics of excess sludge, the present invention uses the methods of elutriation and hydrothermal treatment to recover organic carbon sources from excess sludge, and at the same time adds flocculation materials to use the separated solid sediment as a water - retaining material, thereby realizing efficient, low - cost treatment and resource utilization of excess sludge, and solving the technical problems such as high treatment cost and difficult treatment and disposal of excess sludge in current sewage treatment plants.

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

[0007] A method for resource utilization of excess sludge in a sewage treatment plant, comprising the following steps:

[0008] The supernatant obtained after elutriating the excess sludge of the sewage treatment plant is refluxed to the sewage treatment plant. The pH of the obtained sludge is adjusted, and then it is subjected to hydrothermal treatment, followed by secondary elutriation to remove the precipitate, forming a first liquid phase. The obtained first liquid phase is flocculated, and finally, solid-liquid separation is carried out to obtain a solid component and a second liquid phase. The pH of the second liquid phase is adjusted to neutral and refluxed to the sewage treatment plant, and the solid component is dried to prepare a water-retaining agent, realizing the resource utilization of sludge.

[0009] Beneficial effects: Firstly, the elutriation method is adopted in the present invention to remove the fine colloidal and coarse colloidal substances in the sludge. These substances are easily degradable and cannot play an effective water-retaining role, belonging to the substances to be discarded. For the sludge after one elutriation, when sodium hydroxide is added to make the pH reach above 11.0, the cell membranes of the microorganisms in the sludge can be denatured, and the cell membranes are easily damaged. By adopting hydrothermal treatment, the cell membranes of the sludge microorganisms are strongly damaged, and the intracellular proteins, polysaccharides and other cell contents flow out and enter the liquid phase part. After hydrothermal treatment, secondary elutriation is carried out to separate the cell skeleton, which is the unnecessary precipitate part, while the extracellular polymers with strong binding properties (fine colloidal and coarse colloidal substances) enter the first liquid phase. The first liquid phase includes dissolved organic matter, which can be used as a carbon source for the sewage treatment plant, and the undissolved part is the extracellular polymer with strong binding properties. After adding a flocculation material for treatment, the extracellular polymer with strong binding properties forms a precipitate, and after centrifugal separation and drying, it can be used as a water-retaining material.

[0010] Preferably, the elutriation is carried out until the sludge viscosity in the supernatant drops below 5.0 mPa·s.

[0011] Beneficial effects: Under the above conditions, more than 90% of the easily degradable substances such as fine colloidal and coarse colloidal substances can be guaranteed to be removed.

[0012] Preferably, the pH adjustment is to add liquid caustic soda to adjust the pH to 11.0 - 12.0.

[0013] Beneficial effects: Within the above pH range, the cell membranes of the microorganisms in the sludge can be more easily damaged.

[0014] Preferably, the temperature of the hydrothermal treatment is 160°C - 180°C, and the time is 30 - 60 min.

[0015] Beneficial effects: Under the above technological conditions, it can be guaranteed that the cell membranes of the microorganisms in the sludge are completely damaged, and the cell contents flow out and enter the liquid phase part.

[0016] Preferably, the flocculant for flocculation is a macromolecular polyelectrolyte, including polyacrylamide and / or polyvinyl alcohol.

[0017] Preferably, the dosage of the flocculant in the first liquid phase is 10 - 50 mg / L.

[0018] Beneficial effect: Within the above usage range, it can ensure the complete precipitation of tightly bound extracellular polymers in the first liquid phase.

[0019] The second liquid phase is adjusted to neutral pH and then recycled to the sewage treatment plant to supplement its carbon source.

[0020] Beneficial effect: The second liquid phase contains organic substances such as soluble proteins and polysaccharides that are easily utilized by microorganisms, specifically the organic substances dissolved in the liquid phase after the rupture of microbial cell membranes during the hydrothermal treatment of sludge; the carbon-nitrogen ratio of the second liquid phase exceeds 16, while the carbon-nitrogen ratio of the sewage in the sewage treatment plant is about 4, that is, the carbon-nitrogen ratio of the second liquid phase is higher than that of the sewage, and the BOD of the second liquid phase is very high; the sewage treatment plant requires carbon sources for nitrogen and phosphorus removal, and good nitrogen and phosphorus removal can only be achieved when the carbon-nitrogen ratio exceeds 4 or even 5. Therefore, the second liquid phase is a good carbon source for the sewage treatment plant and can realize the recycling of resources.

[0021] A sludge-based water retainer is obtained by using the above-mentioned resource utilization method of the surplus sludge of the sewage treatment plant.

[0022] Compared with the prior art, the present invention has the following advantages and technical effects:

[0023] The present invention can greatly recycle and utilize the surplus sludge of the sewage treatment plant at a relatively low treatment cost, thereby providing technical support that takes into account both economic benefits and environmental safety for the treatment of sludge; after washing and hydrothermal treatment of the sludge, the present invention can obtain high-quality carbon sources from the sludge, thereby reducing the cost of purchasing carbon sources externally by the sewage treatment plant. At the same time, adding flocculation materials can obtain a sludge-based water retaining material with better water retention performance, which is beneficial for land use. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0025] Figure 1 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the 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. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] To make the above objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] An embodiment of the present invention provides a method for resource utilization of excess sludge from a sewage treatment plant, as Figure 1 shown, including the following steps:

[0029] The supernatant after elutriating the excess sludge from the sewage treatment plant is refluxed to the sewage treatment plant. The elutriated sludge is adjusted in pH, then subjected to hydrothermal treatment, followed by secondary elutriation and removal of the precipitate. The obtained first liquid phase is flocculated, and finally centrifuged to obtain a solid phase component and a second liquid phase. The second liquid phase is adjusted to neutral pH and refluxed to the sewage treatment plant, and the solid phase component is dried to prepare a water retention agent, realizing the resource utilization of the sludge.

[0030] In a preferred embodiment, the elutriation is carried out until the sludge viscosity in the supernatant drops below 5.0 mPa·s.

[0031] In a preferred embodiment, the pH adjustment is to add liquid caustic soda to adjust the pH to 11.0 - 12.0.

[0032] In a preferred embodiment, the temperature of the hydrothermal treatment is 160°C - 180°C, and the time is 30 - 60 min.

[0033] In a preferred embodiment, the flocculant for flocculation is a macromolecular polyelectrolyte, including polyacrylamide and / or polyvinyl alcohol.

[0034] In a preferred embodiment, the usage amount of the flocculant in the first liquid phase is 10 - 50 mg / L.

[0035] The second liquid phase is adjusted to neutral pH and refluxed to the sewage treatment plant to supplement its carbon source.

[0036] An embodiment of the present invention also provides a sludge-based water retention agent obtained by using the above method for resource utilization of excess sludge from a sewage treatment plant.

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

[0038] Among them, the concentrated excess sludge in the embodiments of the present invention is taken from the sludge thickening tank of a municipal sewage treatment plant, and its composition includes bacteria, inorganic particles, plant organic residues, colloids, etc.;

[0039] The liquid caustic soda in the embodiments of the present invention is liquid sodium hydroxide.

[0040] Normal temperature or room temperature in the embodiments of the present invention both refer to 25 ± 3°C.

[0041] The "effluent from sewage treatment plant" used in the examples refers to the effluent from the sewage treatment plant whose various indicators have reached the standards after various treatments.

[0042] Example 1

[0043] A method for resource utilization of excess sludge from a sewage treatment plant, comprising the following steps:

[0044] (1) Primary elutriation: Take the concentrated excess sludge with a solids content of 2% from the municipal sewage treatment plant, and first use the effluent from the sewage treatment plant to conduct primary elutriation on the sludge to remove fine colloidal and coarse colloidal substances until the sludge viscosity of the supernatant drops to 4.0 mPa·s.

[0045] (2) Hydrothermal treatment: Add liquid alkali to the elutriated sludge to adjust the pH to 11.6. Add the sludge with adjusted pH to a high-pressure reaction kettle and conduct hydrothermal treatment at 160 °C for 50 min.

[0046] (3) Secondary elutriation: Conduct secondary elutriation on the sludge after hydrothermal treatment to remove sludge precipitation to obtain a first liquid phase part, and the obtained precipitation enters the sludge system for treatment;

[0047] (4) Flocculation separation: Add a polyacrylamide solution (mass concentration of 0.1%) to the first liquid phase part obtained in step (3) until the concentration of polyacrylamide in the first liquid phase part is 10 mg / L, and then conduct centrifugal separation on it to obtain a solid phase part and a second liquid phase.

[0048] (5) Recycling: The solid phase part is made into a sludge-based water retention agent after air drying treatment, and the second liquid phase is adjusted to neutral pH and then recycled to the sewage treatment plant for reuse.

[0049] The carbon source COD in the second liquid phase obtained through this process flow is 3500 mg / L, and the carbon-nitrogen ratio is 14. The prepared sludge-based water retention agent has a high water absorption rate, the water absorption amount in 10 min of natural water absorption is 630 g / g, and the brine absorption ratio is 28 g / g. The 12 h water retention rate of the sludge-based water retention agent prepared in this example is 96.5%, the 24 h water retention rate is 83%, the 48 h water retention rate is 52%, the 72 h water retention rate is 16%, and the 96 h water retention rate is 4.1%.

[0050] Example 2

[0051] A method for resource utilization of excess sludge from a sewage treatment plant, comprising the following steps:

[0052] (1) Primary elutriation: Take the concentrated excess sludge with a solids content of 3% from the municipal sewage treatment plant, and first use the effluent from the sewage treatment plant to conduct primary elutriation on the sludge to remove fine colloidal and coarse colloidal substances until the sludge viscosity of the supernatant drops to 5.0 mPa·s.

[0053] (2) Hydrothermal treatment: Add liquid caustic soda to the washed sludge to adjust the pH to 11.4. Add the sludge with adjusted pH into a high-pressure reaction kettle and conduct hydrothermal treatment at 180 °C for 30 min.

[0054] (3) Secondary washing: Wash the sludge after hydrothermal treatment twice to remove sludge precipitation to obtain the first liquid phase part, and the obtained precipitation enters the sludge system for treatment;

[0055] (4) Flocculation separation: Add polyacrylamide solution (mass concentration is 0.1%) to the first liquid phase part obtained in step (3) until the concentration of polyacrylamide in the first liquid phase part is 30 mg / L, and then conduct centrifugal separation on it to obtain a solid phase part and a second liquid phase.

[0056] (5) Recycling: The solid phase part is made into a sludge-based water retention agent after air drying treatment, and the pH of the second liquid phase is adjusted to neutral and then recycled to the sewage treatment plant for reuse.

[0057] The carbon source COD in the second liquid phase obtained through this process flow is 4000 mg / L, and the carbon-nitrogen ratio is 15. The prepared sludge-based water retention agent has a high water absorption rate, the water absorption amount in 10 min of natural water absorption is 680 g / g, and the brine absorption ratio is 30 g / g. The 12-h water retention rate of the sludge-based water retention agent prepared in this example is 97.2%, the 24-h water retention rate is 85%, the 48-h water retention rate is 55%, the 72-h water retention rate is 18%, and the 96-h water retention rate is 4.5%.

[0058] Example 3

[0059] A resource utilization method for the surplus sludge of a sewage treatment plant, comprising the following steps:

[0060] (1) Primary washing: Take the concentrated surplus sludge with a solid content of 3% from the urban sewage treatment plant, first use the effluent of the sewage treatment plant to conduct primary washing on the sludge to remove fine colloidal and coarse colloidal substances until the sludge viscosity of the supernatant drops to 3.0 mPa·s.

[0061] (2) Hydrothermal treatment: Add liquid caustic soda to the washed sludge to adjust the pH to 12.0. Add the sludge with adjusted pH into a high-pressure reaction kettle and conduct hydrothermal treatment at 170 °C for 40 min.

[0062] (3) Secondary washing: Wash the sludge after hydrothermal treatment twice to remove sludge precipitation to obtain the first liquid phase part, and the obtained precipitation enters the sludge system for treatment;

[0063] (4) Flocculation separation: Add polyacrylamide solution (mass concentration of 0.1%) to the first liquid phase part obtained in step (3) until the concentration of polyacrylamide in the first liquid phase part reaches 40 mg / L, and then perform centrifugal separation on it to obtain a solid phase part and a second liquid phase.

[0064] (5) Recycling: After air-drying the solid phase part, a sludge-based water retaining agent is prepared, and the second liquid phase is adjusted to neutral pH and then recycled to the sewage treatment plant for reuse.

[0065] The carbon source COD in the second liquid phase obtained through this process flow is 5000 mg / L, and the carbon-nitrogen ratio is 20. The prepared sludge-based water retaining agent has a high water absorption rate, with a water absorption of 650 g / g in 10 minutes of natural water absorption and a brine absorption ratio of 25 g / g. The 12-hour water retention rate of the sludge-based water retaining agent prepared in this example is 96.8%, the 24-hour water retention rate is 82%, the 48-hour water retention rate is 50%, the 72-hour water retention rate is 15%, and the 96-hour water retention rate is 3.8%.

[0066] Example 4

[0067] A resource utilization method for the excess sludge of a sewage treatment plant, comprising the following steps:

[0068] (1) Primary elutriation: Take the concentrated excess sludge with a solids content of 2% from the urban sewage treatment plant, and first use the effluent of the sewage treatment plant to conduct primary elutriation on the sludge to remove fine colloidal and coarse colloidal substances until the sludge viscosity of the supernatant drops to 5.0 mPa·s.

[0069] (2) Hydrothermal treatment: Add liquid caustic soda to the elutriated sludge to adjust the pH to 11.8. Add the sludge with adjusted pH to a high-pressure reaction kettle and conduct hydrothermal treatment at 160 °C for 60 minutes.

[0070] (3) Secondary elutriation: Conduct secondary elutriation on the sludge after hydrothermal treatment to remove sludge precipitation to obtain a first liquid phase part, and the obtained precipitation enters the sludge system for treatment;

[0071] (4) Flocculation separation: Add polyacrylamide solution (mass concentration of 0.1%) to the first liquid phase part obtained in step (3) until the concentration of polyacrylamide in the first liquid phase part reaches 50 mg / L, and then perform centrifugal separation on it to obtain a solid phase part and a second liquid phase.

[0072] (5) Recycling: After air-drying the solid phase part, a sludge-based water retaining agent is prepared, and the second liquid phase is adjusted to neutral pH and then recycled to the sewage treatment plant for reuse.

[0073] The COD of the carbon source in the second liquid phase obtained through this process flow is 4,600 mg / L, and the carbon-nitrogen ratio is 17. The prepared sludge-based water retainer has a high water absorption rate, with a water absorption of 600 g / g in 10 minutes of natural water absorption and a brine absorption ratio of 26 g / g. The 12-hour water retention rate of the sludge-based water retainer prepared in this example is 97.5%, the 24-hour water retention rate is 87%, the 48-hour water retention rate is 58%, the 72-hour water retention rate is 19%, and the 96-hour water retention rate is 4.8%.

[0074] Comparative Example 1

[0075] A resource utilization method for the excess sludge of a sewage treatment plant, which is different from Example 1 in that it does not include the primary elutriation and secondary elutriation steps. Other process steps and parameters are the same as those in Example 1.

[0076] The COD of the carbon source in the second liquid phase obtained through this process flow is only 650 mg / L, and the carbon-nitrogen ratio is 6. The prepared sludge-based water retainer has a low water absorption rate, with a water absorption of only 250 g / g in 10 minutes of natural water absorption and a brine absorption ratio of 16 g / g. The 12-hour water retention rate of the sludge-based water retainer prepared in this example is 93.5%, the 24-hour water retention rate is 78%, the 48-hour water retention rate is 46%, the 72-hour water retention rate is 12%, and the 96-hour water retention rate is 3.2%.

[0077] Comparative Example 2

[0078] A resource utilization method for the excess sludge of a sewage treatment plant, which is different from Example 1 in that the temperature of hydrothermal treatment in step (2) is 120 °C. Other process steps and parameters are the same as those in Example 1.

[0079] The COD of the carbon source in the second liquid phase obtained through this process flow is 890 mg / L, and the carbon-nitrogen ratio is 8. The natural water absorption of the prepared sludge-based water retainer in 10 minutes is 320 g / g, and the brine absorption ratio is 18 g / g. The 12-hour water retention rate of the sludge-based water retainer prepared in this example is 92.8%, the 24-hour water retention rate is 74%, the 48-hour water retention rate is 44%, the 72-hour water retention rate is 11%, and the 96-hour water retention rate is 3.1%.

[0080] Comparative Example 3

[0081] A resource utilization method for the excess sludge of a sewage treatment plant, which is different from Example 1 in that in step (4), a polyacrylamide solution (mass concentration of 0.1%) is added to a part of the first liquid phase obtained in step (3) until the concentration of polyacrylamide in the first liquid phase part reaches 5 mg / L. Other process steps and parameters are the same as those in Example 1.

[0082] The COD of the carbon source in the second liquid phase obtained through this process flow is 1600 mg / L, and the carbon-nitrogen ratio is 11. The water absorption of the sludge-based water retainer prepared within 10 minutes of natural water absorption is 420 g / g, and the brine absorption ratio is 22 g / g. The water retention rate of the sludge-based water retainer prepared in this example is 93.1% at 12 h, 76% at 24 h, 47% at 48 h, 13% at 72 h, and 3.5% at 96 h.

[0083] The above are only the preferred specific embodiments 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 resource utilization method for the excess sludge of a sewage treatment plant, characterized in that, It includes the following steps: Adjust the pH of the sludge obtained after elutriating the excess sludge of the sewage treatment plant, then conduct hydrothermal treatment, followed by secondary elutriation and removal of the precipitate to obtain a first liquid phase. Flocculate the obtained first liquid phase, and finally perform centrifugal separation to obtain a solid phase component and a second liquid phase. Adjust the pH of the second liquid phase to neutral and reflux it to the sewage treatment plant, and dry the solid phase component to prepare a water-retaining agent, thereby realizing the resource utilization of the sludge; The elutriation is carried out until the sludge viscosity in the supernatant drops below 5.0 mPa·s; Adjusting the pH means adding liquid caustic to adjust the pH to 11.0 - 12.0; The temperature of the hydrothermal treatment is 160°C - 180°C, and the time is 30 - 60 min; The flocculant for flocculation is a macromolecular polyelectrolyte, including polyacrylamide and / or polyvinyl alcohol; The concentration of the flocculant in the first liquid phase is 10 - 50 mg / L.

2. The resource utilization method of excess sludge in a sewage treatment plant according to claim 1, characterized in that, After adjusting the pH of the second liquid phase to neutral, it is refluxed to the sewage treatment plant as a carbon source.

3. A sludge-based water retaining agent, characterized in that, Obtained by using the method for resource utilization of excess sludge of a sewage treatment plant according to claim 1 or 2.

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