Method for preparing high-concentration liquid carbon source based on primary sludge fermentation

Abstract

The invention discloses a method for preparing a high-concentration liquid carbon source based on primary sludge fermentation, which is characterized by comprising the following steps: adding soluble sugar into primary sludge to prepare a mixture with the C / N ratio of (15-25): 1, then sequentially carrying out micro-aerobic fermentation and anaerobic fermentation, taking clear liquor, carrying out adsorption reaction to remove nitrogen and phosphorus components, and then carrying out dehydration treatment to obtain the high-concentration liquid carbon source. The method provided by the invention can realize recycling of the primary sludge, and has the advantages of high fatty acid yield and high recycling efficiency of biomass resources in the sludge.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge treatment in sewage treatment plants, and specifically relates to a method for preparing a high-concentration liquid carbon source based on fermentation of primary sludge. Background Art

[0002] A primary sedimentation tank is a sedimentation tank used for primary treatment in sewage treatment plants, following interception by the inlet screen and grit settling in the grit chamber. It is primarily used to reduce the concentration of suspended solids in wastewater and is also known as a primary sedimentation tank. After the screen intercepts large floating and suspended solids, and the grit chamber removes suspended particles with a density greater than 1.5 g / cm3, many suspended particles with slightly lower density or smaller particle size remain. These particles are primarily composed of organic matter. If these substances enter the biological treatment phase directly, they would increase the organic load in the aeration tank and even affect the microbial oxidation, decomposition, and nitrification of organic matter, affecting the effluent quality of the secondary sedimentation tank. Therefore, they are removed through the primary sedimentation tank. The resulting sludge is called primary sludge.

[0003] The treatment characteristics of primary sedimentation tanks result in a high concentration of organic matter in primary sludge, with a VS / TS ratio (the ratio of organic matter volatile at 600°C to the total solid matter in the water) typically ranging from 40-60%. Traditional disposal methods for primary sludge involve dewatering followed by landfill or incineration, which is costly and wasteful.

[0004] In some subsequent steps of wastewater treatment, when insufficient carbon sources are present in the water, carbon sources often need to be added to enhance the nitrifying bacteria's activity. Sewage treatment plants generally face carbon source shortages. Volatile fatty acids (VFAs) are commonly used as carbon sources for wastewater treatment, but purchasing or re-culturing VFAs is costly. Primary sludge contains a large amount of organic matter, which can be considered for use in the production of VFA carbon sources, further maximizing waste utilization.

[0005] CN201810090767.6 once disclosed a method for promoting anaerobic fermentation of sludge to produce volatile fatty acids. Fatty acids can be obtained through sludge treatment, cultivation and fermentation. However, the patent did not complete the separation of fatty acids and sludge, and the fatty acid cultivation process was relatively simple. The maximum fatty acid yield was only 2673.8 mg / L, and the problem of nitrogen and phosphorus release was not solved. The overall resource recycling efficiency was low.

[0006] Therefore, how to utilize primary sludge to better obtain a high-concentration carbon source with fatty acids as the main component and improve the recycling efficiency of biomass resources in sludge has become a problem that needs to be considered and solved by those skilled in the art. Summary of the Invention

[0007] In response to the above-mentioned shortcomings of the prior art, the present invention aims to provide a method for producing a high-concentration liquid carbon source through fermentation of primary sludge, which has a high fatty acid yield and high efficiency in recycling biomass resources in the sludge, thereby better realizing the comprehensive utilization of primary sludge.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: A method for preparing a high-concentration liquid carbon source based on primary sludge fermentation, characterized in that the primary sludge is added with soluble sugar to form a mixture with a C / N ratio of 15-25:1, and then subjected to microaerobic fermentation and anaerobic fermentation in sequence, and the clarified liquid is taken to remove nitrogen and phosphorus components through adsorption reaction, and then dehydrated to obtain a high-concentration liquid carbon source.

[0009] In this way, soluble sugar is first added in the present method to adjust the appropriate carbon-nitrogen ratio of the sludge, thereby better providing a suitable nutrient ratio for subsequent fermentation microorganisms, accelerating the rate of subsequent organic matter decomposition, and ensuring the effect and efficiency of the fermentation process. During fermentation, microaerobic fermentation is first performed to rapidly degrade macromolecular organic matter, and then converted into fatty acids through anaerobic fermentation. After a large amount of liquid fatty acids are generated, they are clarified to the upper layer together with the water in the sludge. The clarified liquid is then taken and subjected to an adsorption reaction to remove nitrogen and phosphorus components, thereby avoiding the introduction of a large amount of nitrogen and phosphorus to cause pollution when the carbon source is used for sewage treatment. The liquid after the nitrogen and phosphorus components are then dehydrated through an ultrafiltration membrane to obtain a high-concentration liquid carbon source. Therefore, it has a higher fatty acid yield and a faster treatment conversion rate.

[0010] In this solution, sludge and waste molasses are mixed at a C / N ratio of 15-25:1 to ensure even distribution of the materials, reduce localized concentration fluctuations, and thus improve the reaction conversion rate. Microorganisms decompose organic matter requiring appropriate carbon and nitrogen sources to build their cell structures and carry out metabolic activities. A C / N ratio within the 15-25:1 range provides the microorganisms with an optimal nutrient ratio, promoting their growth and reproduction. During the subsequent sludge fermentation process, this appropriate C / N ratio accelerates the decomposition of organic matter, making the fermentation process more efficient. By replacing pure carbon sources with molasses or fruit and vegetable wastewater, raw material costs can be reduced by over 40%.

[0011] Furthermore, the primary sludge has a moisture content of 90-92%. If the moisture content is too high, it will be detrimental to the subsequent fermentation process and reduce the treatment efficiency. If the moisture content is too low, the sludge fluidity may deteriorate, which is not conducive to the transfer and connection between various treatment steps.

[0012] Furthermore, the soluble sugar is industrial waste honey (sugar factory waste) or fruit and vegetable processing waste liquid. In this way, industrial waste can be better utilized to supplement soluble sugars, achieving the effect of turning waste into treasure.

[0013] Furthermore, during microaerobic fermentation, the sludge oxygen content is controlled at a DO of 0.2-0.5 mg / L. This can better promote the rapid degradation of large organic molecules by facultative bacteria (such as Bacillus). A DO of 0.2-0.5 mg / L allows the synergistic effects of aerobic, facultative, and some anaerobic microorganisms. This environment allows aerobic and facultative anaerobic bacteria to utilize trace amounts of oxygen to degrade small organic molecules, while simultaneously eliminating the toxic effects of organic acids and oxygen on methanogens, thereby achieving efficient organic degradation. Microaerobic fermentation is generally controlled to a duration of approximately 24 hours, preferably sufficient to complete the degradation of large organic molecules.

[0014] Furthermore, during anaerobic fermentation, an acid-producing composite bacterial agent is added to assist the fermentation, and the acid-producing composite bacterial agent includes Klebsiella acidophilus and Lactobacillus buchneri.

[0015] In this way, microaerobic fermentation is followed by anaerobic treatment. Through the metabolic activity of anaerobic microorganisms, the complex organic matter in the sludge is gradually broken down into small-molecule organic acids such as VFAs. During fermentation, a composite bacterial inoculum (including Klebsiella oxytoca and Lactobacillus buchneri) is inoculated. The metabolic characteristics of these specific strains optimize the fermentation process, improve acid production efficiency, and enhance sludge treatment effectiveness. The synergistic effect of Klebsiella oxytoca and Lactobacillus buchneri can better destroy the colloidal structure of the sludge, making the organic matter in the sludge more easily accessible to microorganisms, thereby shortening the fermentation cycle. During implementation, the anaerobic fermentation temperature is preferably controlled at 30-35°C and the pH is preferably controlled at 5.5-6.5 to better ensure the fermentation effect.

[0016] As an option, modified zeolite containing magnesium ions is used to carry out adsorption reaction of clarified liquid to remove nitrogen and phosphorus components.

[0017] Modified zeolite containing magnesium ions is an existing material. This material is loaded with magnesium ions by chemical impregnation, mixing natural zeolite with a magnesium salt solution and then drying it. The resulting magnesium salt-modified zeolite contains a large amount of magnesium ions. Zeolite itself has a strong ability to remove ammonia nitrogen. The added magnesium ions can be dissolved and react with phosphate and ammonia after modification to form struvite precipitates. Therefore, the modified zeolite significantly improves its adsorption capacity for ammonia nitrogen and phosphate in the clarified liquid. The resulting struvite precipitate can be used as a slow-release fertilizer in agriculture, achieving the recycling of nitrogen and phosphorus components.

[0018] As another better option, the nitrogen and phosphorus components can be removed by adsorption reaction of the clarified liquid through unmodified zeolite and then through modified zeolite containing magnesium ions.

[0019] This method first passes through unmodified zeolite, which has a strong ammonia-nitrogen removal capacity and can effectively remove ammonia-nitrogen components from the clarified liquid. The clarified liquid is then controlled to pass through modified zeolite containing magnesium ions. The magnesium ions participate in the reaction to form struvite precipitates, which further enhances the zeolite's adsorption capacity for ammonia-nitrogen, thereby further improving ammonia-nitrogen removal efficiency and enhancing the comprehensive treatment capacity for multiple pollutants in complex water quality. This supplements the limited adsorption capacity of a single zeolite and its poor adsorption effect on some pollutants.

[0020] Furthermore, the present invention is implemented by a sludge treatment system for preparing a liquid carbon source, the sludge treatment system comprising a stirring and mixing container, a microaerobic fermentation container, an anaerobic fermentation container, an adsorption reaction device and a solution dehydration device arranged in series in sequence; a sludge feeding pipe and a soluble sugar feeding port with an on-off valve are provided at the upper end of the stirring and mixing container, and a first stirring device is provided in the stirring and mixing container; the lower end of the stirring and mixing container is connected to the microaerobic fermentation container through a sludge pipe equipped with a third sludge pump, the upper end of the microaerobic fermentation container is closed and a second stirring device is installed inside, and an air supply port is also provided at the bottom of the microaerobic fermentation container, and the air supply port is connected to the microaerobic fermentation container through a sludge pipe equipped with a third sludge pump. The air supply pipe of the switch control valve is connected to the oxygen tank; one side of the lower end of the micro-aerobic fermentation container is connected to the anaerobic fermentation container through a sludge pipe equipped with a fourth sludge pump, the upper end of the anaerobic fermentation container is closed and equipped with an acid-producing bacteria agent addition port with a switch valve, a third stirring device is installed inside the anaerobic fermentation container, and a sewage pipe with a switch valve is also installed at the lower end of the anaerobic fermentation container. The upper end of the anaerobic fermentation container is also connected to a liquid outlet pipe equipped with a first liquid pump and is connected to the upper end of the adsorption reaction device, a nitrogen and phosphorus adsorption module is provided in the adsorption reaction device, and the bottom of the adsorption reaction device is connected to the solution dehydration device through a liquid outlet pipe equipped with a second liquid pump.

[0021] In this way, when the sludge treatment system is in operation, primary sludge can be added from the sludge feeding pipe to the mixing vessel. Then, some soluble sugar is added from the soluble sugar feeding port to the mixing vessel. The carbon-nitrogen ratio in the sludge is adjusted to an appropriate range and then mixed uniformly. The mixed sludge is then pumped into the micro-aerobic fermentation vessel via a third sludge pump. The micro-aerobic fermentation vessel is supplied with oxygen from an oxygen tank and mixed uniformly before micro-aerobic fermentation, which degrades large organic molecules. After micro-aerobic fermentation, the sludge is transferred to the anaerobic fermentation vessel via a fourth sludge pump. Acidogenic bacteria such as Klebsiella oxytoca and Lactobacillus buchneri are introduced through the acidogenic bacteria feeding port at the top of the vessel for anaerobic fermentation and acid production. Anaerobic fermentation gradually decomposes complex organic matter in the sludge into small organic acids such as VFAs (fatty acids). Since organic acids are liquid, they gradually rise to the surface and clarify to form a clear liquid rich in organic acids at the top of the sludge. The clear liquid is then directed through an outlet pipe to the adsorption reaction unit. The excess sludge in the anaerobic fermentation vessel is drained through a drain pipe, achieving batch processing. The clarified liquid, rich in organic acids, undergoes nitrogen and phosphorus adsorption in the adsorption reactor. It then undergoes dehydration in a solution dehydration unit to produce a high-concentration liquid carbon source. This solution allows for the production of a liquid carbon source from primary sludge, and the resulting high-concentration liquid carbon source is free of nitrogen and phosphorus, making it convenient for wastewater carbon source supplementation.

[0022] Furthermore, it also includes a sludge dewatering device, the sludge outlet of the sludge dewatering device is connected to the stirring and mixing container through a sludge feeding pipe, a second sludge pump is installed on the sludge feeding pipe, and the sludge inlet of the sludge dewatering device is connected to a primary sludge storage tank through a sludge feeding pipe equipped with a first sludge pump.

[0023] This is because the moisture content of primary sludge is generally 95-98%. Too high a moisture content is not conducive to subsequent fermentation treatment. Therefore, the primary sludge is first dehydrated to adjust and reduce the moisture content to a certain extent, so as to improve the effect of subsequent treatment.

[0024] Furthermore, a floating liquid outlet device is installed at the upper end of the anaerobic fermentation container and is connected to the liquid outlet pipe. The liquid outlet device includes a float. A downward inverted conical liquid suction port is provided at the lower end of the float. A liquid outlet is opened at the upper end of the float and is communicated with the liquid suction port. The liquid outlet is connected upward to a hose with a movable margin and is connected to the liquid outlet pipe at the upper end of the anaerobic fermentation container. A lifting rope is also provided upward from the middle part of the upper end of the float, and the upper end of the lifting rope is wound around a wire drum of a winch installed on the end panel of the upper end of the anaerobic fermentation container.

[0025] In this way, when the anaerobic fermentation vessel is stirring and undergoing anaerobic fermentation, the winch is controlled to lift the float so that it does not interfere with the stirring and fermentation process of the sludge. When the anaerobic fermentation process is completed and clarified liquid is generated at the top of the sludge, the winch is controlled again to lower the float so that it drops to the surface of the clarified liquid. At this time, the clarified liquid generated at the top of the anaerobic fermentation vessel can be pumped away through the liquid outlet pipe, minimizing the disturbance of the sludge below.

[0026] Furthermore, a telescopic adjustment rod is respectively provided downwardly around the lower surface of the float, and a horizontal baffle is provided at the lower end of each telescopic adjustment rod.

[0027] As the clarified liquid is gradually drawn away, the liquid level drops, and the float follows it down until the baffle falls onto the upper surface of the settled sludge below and is blocked. At this point, the float stops sinking, preventing the sludge from being drawn away. A small amount of remaining clarified liquid is discharged along with the sludge. The distance between the baffle and the float can be adjusted using a telescopic lever to prevent excess clarified liquid from remaining. This device maximizes the removal of clarified liquid while minimizing sludge disturbance.

[0028] Furthermore, an observation window made of glass is vertically arranged on the side wall of the anaerobic fermentation container, so that the progress of the anaerobic fermentation can be judged by observing the height of the output of the clarified liquid in real time, and the liquid output can be processed in time.

[0029] Furthermore, the nitrogen and phosphorus adsorption module includes a zeolite material layer, a modified zeolite material layer and a physical adsorption material layer arranged in sequence from top to bottom, the modified zeolite material layer is filled with modified zeolite obtained by modification with ammonia ions and magnesium ions, and the physical adsorption material layer is activated carbon or phosphorus removal resin.

[0030] In this way, the clarified liquid first passes through the upper layer of unmodified zeolite material, which can first remove part of the ammonia nitrogen by adsorption. The pH of the upper water body is usually close to neutral, which is conducive to the zeolite's absorption of NH4 + At the same time, some cation competitors are removed. The water then passes through the middle layer of modified zeolite with high magnesium content. At this time, the ammonia nitrogen concentration in the water is reduced, the competition is weakened, and the cations released by the upper zeolite exchange (such as Na + ) will slightly raise the pH (especially when using Na-type zeolite), facilitating the dissolution of magnesium ions and their reaction with phosphates to form precipitates (such as struvite). The water then passes through the activated carbon or phosphorus removal resin below, capturing any trace pollutants that penetrate and better ensuring the effluent quality.

[0031] Furthermore, the modified zeolite is prepared by the following preparation method steps: 1) First, clean the zeolite with deionized water to remove surface impurities; 2) Then, immerse the zeolite in a 1 mol / L NH4Cl solution and stir with shaking for more than half an hour to allow the ammonium ions to fully enter the zeolite pores; 3) After the reaction is complete, remove the zeolite and immerse it in a MgCl2 solution greater than 1 mol / L (the solid-liquid ratio can be controlled to 1:10). Oscillate for a period of time (12 hours at 80°C) to allow for sufficient magnesium ion exchange reaction and complete loading. 4) After the loading reaction is completed, the zeolite is removed and washed with deionized water until neutral to remove unreacted magnesium salts, ammonium salts and other impurities; 5) Finally, the sample was dried at 45°C and then calcined at 550°C for 2 hours to remove organic matter and stabilize the structure, thereby producing a modified zeolite containing magnesium ions; Like this, by above-mentioned preparation step, first zeolite is cleaned with deionized water, removes surface impurities, ensures the efficient carrying out of subsequent reaction.Then, zeolite is immersed in the NH4Cl solution greater than 1 mol / L, and is shaken and stirred for more than half an hour so that amine ions fully enter the zeolite pores; Because some ammonium ions can produce displacement with some cations in zeolite, form adsorption reaction, therefore the amine ions entering the zeolite pores will produce reaction and then first block the pore channel of zeolite material.Then zeolite is placed in MgCl2 solution, and oscillation treatment is carried out for a period of time so that magnesium ions can replace the sodium ions or other cations in zeolite to complete load; Now because zeolite pore is blocked by the ammonium radical ion of reaction, most of magnesium ions are combined in the position protruding outside the zeolite pore for load reaction, and more active sites of magnesium ions are formed at the protruding position outside the zeolite. After the reaction is completed, the precipitate is taken out and washed with deionized water until it is neutral. Since the binding affinity between ammonium ions and zeolite is much lower than that of magnesium ions, most of the ammonium ions will be flushed away during washing, exposing the pores inside the zeolite to improve the adsorption capacity of the modified zeolite material. At the same time, a small amount of ammonia will remain attached to the pores, forming a small amount of NH4 + The adsorption active sites can adjust the ionic strength and charge balance of the local microenvironment and promote the reaction effect between magnesium ions and phosphates; specifically, the NH4 + Active sites can supplement magnesium ion active sites. During subsequent adsorption treatment, some free magnesium ions can enter the pores and then react with phosphate ions to form struvite precipitates, thereby improving the overall adsorption of nitrogen and phosphorus components in water. Finally, the zeolite is dried at 45°C and then calcined at 550°C for 2 hours to remove organic matter and stabilize the structure, thereby producing magnesium salt-modified zeolite. The calcination process removes organic impurities from the zeolite surface and pores, while stabilizing the zeolite's crystal structure, improving its stability and durability in practical applications.

[0032] Compared with the conventional magnesium-modified zeolite that is loaded by directly soaking the zeolite in a magnesium salt solution, the modified zeolite in this way avoids blockage during the magnesium loading reaction and ensures that the modified zeolite still maintains a relatively large porosity. The magnesium ion load is combined with the protruding position outside the pore, which can better adsorb the ammonia nitrogen and phosphate components in the water body when the water body passes through and react to form struvite precipitation. The zeolite itself maintains a relatively large porosity to improve physical adsorption and promote chemical reactions. At the same time, the small amount of ammonium ions loaded inside the pores can also form a supplement to the reactive sites, which is more conducive to combining with phosphate to complete the precipitation reaction. Therefore, compared with conventional magnesium-modified zeolite, the removal effect of the modified zeolite on nitrogen and phosphorus components in water bodies is greatly improved.

[0033] Furthermore, the solution dehydration device includes a container, a container-shaped frame body is arranged inside the container, and the outer surface of the frame body is covered with a layer of ultrafiltration membrane. The pore size of the ultrafiltration membrane is larger than water molecules and smaller than organic acid molecules (about 50nm). The frame body is provided with a liquid extraction tube and connected to the container body, and a third liquid pump is installed on the liquid extraction tube.

[0034] This allows the third liquid pump to generate pressure, pumping water through the ultrafiltration membrane, leaving behind a highly concentrated organic acid solution, effectively achieving solution dehydration. Ultimately, a high-purity liquid carbon source with a VFA ≥ 8000 mg / L and a COD:N:P ≥ 200:5:1 can be obtained.

[0035] The present invention has the following advantages. 1. Improved carbon source yield: VFA concentration reaches 8000-12000 mg / L (3-4 times higher than the traditional method). 2. Cost reduction: Using molasses / fruit and vegetable waste liquid instead of pure carbon source, the raw material cost is saved by more than 40%. 3. Nitrogen and phosphorus recovery: Modified zeolite can be used as a slow-release fertilizer after adsorption (adsorption rate NH4 + >85%, PO4 3- >90%). 4. Stable process: Segmented oxygen control avoids acidification inhibition and shortens the fermentation cycle to 3 days.

[0036] In summary, the present invention can realize the recycling and utilization of primary sludge, and has the advantages of high fatty acid yield and high recycling efficiency of biomass resources in sludge. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the process steps of the present invention.

[0038] Figure 2 This is a schematic structural diagram of the sludge treatment system used in the present invention.

[0039] Figure 3 for Figure 2 Schematic diagram of the structure of the separate floating liquid discharge device. DETAILED DESCRIPTION

[0040] The present invention will be further described below with reference to specific embodiments and the accompanying drawings.

[0041] Best embodiment: See Figure 1 A method for preparing a high-concentration liquid carbon source based on the fermentation of primary sludge is characterized in that the primary sludge is added with soluble sugar to form a mixture with a C / N ratio of 15-25:1, and then subjected to microaerobic fermentation and anaerobic fermentation in sequence. The clarified liquid is taken and the nitrogen and phosphorus components are removed by adsorption reaction, and then dehydrated to obtain a high-concentration liquid carbon source.

[0042] In this way, soluble sugar is first added in the present method to adjust the appropriate carbon-nitrogen ratio of the sludge, thereby better providing a suitable nutrient ratio for subsequent fermentation microorganisms, accelerating the rate of subsequent organic matter decomposition, and ensuring the effect and efficiency of the fermentation process. During fermentation, microaerobic fermentation is first performed to rapidly degrade macromolecular organic matter, and then converted into fatty acids through anaerobic fermentation. After a large amount of liquid fatty acids are generated, they are clarified to the upper layer together with the water in the sludge. The clarified liquid is then taken and subjected to an adsorption reaction to remove nitrogen and phosphorus components, thereby avoiding the introduction of a large amount of nitrogen and phosphorus to cause pollution when the carbon source is used for sewage treatment. The liquid after the nitrogen and phosphorus components are then dehydrated through an ultrafiltration membrane to obtain a high-concentration liquid carbon source. Therefore, it has a higher fatty acid yield and a faster treatment conversion rate.

[0043] During implementation, sludge and waste molasses are mixed at a C / N ratio of 15-25:1 to ensure even distribution of the materials, reduce localized concentration fluctuations, and thus improve the reaction conversion rate. Microorganisms decompose organic matter requiring appropriate carbon and nitrogen sources to build their cell structures and carry out metabolic activities. A C / N ratio within the 15-25:1 range provides the microorganisms with an optimal nutrient ratio, promoting their growth and reproduction. During subsequent sludge fermentation, a suitable C / N ratio accelerates the decomposition of organic matter, making the fermentation process more efficient. Using molasses / fruit and vegetable wastewater instead of pure carbon sources can save over 40% in raw material costs.

[0044] In this embodiment, the primary sludge used is sludge with a moisture content of 90-92%. If the moisture content is too high, it will be detrimental to the subsequent fermentation process and reduce the treatment efficiency. If the moisture content is too low, the sludge fluidity may deteriorate, which is not conducive to the transfer and connection between the various treatment steps.

[0045] In this embodiment, the soluble sugar is industrial waste honey (sugar factory waste) or fruit and vegetable processing waste liquid. In this way, industrial waste can be better utilized to supplement soluble sugars, achieving the effect of turning waste into treasure.

[0046] In this example, the sludge oxygen content during microaerobic fermentation is controlled to a DO of 0.2-0.5 mg / L. This effectively promotes the rapid degradation of large organic molecules by facultative bacteria (such as Bacillus). This microaerobic environment simultaneously promotes the synergistic effects of aerobic, facultative, and some anaerobic microorganisms. This environment allows aerobic and facultative anaerobic bacteria to utilize trace amounts of oxygen to degrade small organic molecules, while simultaneously eliminating the toxic effects of organic acids and oxygen on methanogens, thereby achieving efficient organic degradation. The microaerobic fermentation time is generally controlled to approximately 24 hours, preferably to allow for the complete degradation of large organic molecules.

[0047] In this embodiment, during anaerobic fermentation, an acid-producing composite bacterial agent is added to assist the fermentation, and the acid-producing composite bacterial agent includes Klebsiella oxytoca and Lactobacillus buchneri.

[0048] In this way, microaerobic fermentation is followed by anaerobic treatment. Through the metabolic activity of anaerobic microorganisms, the complex organic matter in the sludge is gradually broken down into small-molecule organic acids such as VFAs. During fermentation, a composite bacterial inoculum (including Klebsiella oxytoca and Lactobacillus buchneri) is inoculated. The metabolic characteristics of these specific strains optimize the fermentation process, improve acid production efficiency, and enhance sludge treatment effectiveness. The synergistic effect of Klebsiella oxytoca and Lactobacillus buchneri can better destroy the colloidal structure of the sludge, making the organic matter in the sludge more easily accessible to microorganisms, thereby shortening the fermentation cycle. During implementation, the anaerobic fermentation temperature is preferably controlled at 30-35°C and the pH is preferably controlled at 5.5-6.5 to better ensure the fermentation effect.

[0049] As another embodiment, modified zeolite containing magnesium ions may also be used to perform adsorption reaction on the clarified liquid to remove nitrogen and phosphorus components.

[0050] Modified zeolite containing magnesium ions is an existing material. This material is loaded with magnesium ions by chemical impregnation, mixing natural zeolite with a magnesium salt solution and then drying it. The resulting magnesium salt-modified zeolite contains a large amount of magnesium ions. Zeolite itself has a strong ability to remove ammonia nitrogen. The added magnesium ions can be dissolved and react with phosphate and ammonia after modification to form struvite precipitates. Therefore, the modified zeolite significantly improves its adsorption capacity for ammonia nitrogen and phosphate in the clarified liquid. The resulting struvite precipitate can be used as a slow-release fertilizer in agriculture, achieving the recycling of nitrogen and phosphorus components.

[0051] In this embodiment, the nitrogen and phosphorus components are removed by adsorption reaction of the clarified liquid by first passing it through unmodified zeolite and then passing it through modified zeolite containing magnesium ions.

[0052] This method first passes through unmodified zeolite, which has a strong ammonia-nitrogen removal capacity and can effectively remove ammonia-nitrogen components from the clarified liquid. The clarified liquid is then controlled to pass through modified zeolite containing magnesium ions. The magnesium ions participate in the reaction to form struvite precipitates, which further enhances the zeolite's adsorption capacity for ammonia-nitrogen, thereby further improving ammonia-nitrogen removal efficiency and enhancing the comprehensive treatment capacity for multiple pollutants in complex water quality. This supplements the limited adsorption capacity of a single zeolite and its poor adsorption effect on some pollutants.

[0053] More specifically, in this embodiment, a sludge treatment system for preparing a liquid carbon source is used. Figure 2-3 As shown, the sludge treatment system includes a stirring and mixing container 1, a micro-aerobic fermentation container 2, an anaerobic fermentation container 3, an adsorption reaction device 4 and a solution dehydration device 5 arranged in series in sequence; the upper end of the stirring and mixing container 1 is provided with a sludge feeding pipe and a soluble sugar feeding port 6 with a switch valve, and a first stirring device 7 is provided in the stirring and mixing container 1; the lower end of the stirring and mixing container 1 is connected to the micro-aerobic fermentation container 2 through a sludge pipe equipped with a third sludge pump 8, the upper end of the micro-aerobic fermentation container 2 is closed and a second stirring device 9 is installed inside, and an air supply port is also opened at the bottom of the micro-aerobic fermentation container 2, which is connected to the oxygen tank 10 through an air supply pipe with a switch control valve. The lower end of the micro-aerobic fermentation container 2 is connected to the anaerobic fermentation container 3 through a sludge pipe equipped with a fourth sludge pump 11. The upper end of the anaerobic fermentation container 3 is closed and equipped with an acid-producing bacteria agent addition port 12 with a switch valve. A third stirring device 13 is installed inside the anaerobic fermentation container 3. A sewage pipe 14 with a switch valve is also installed at the lower end of the anaerobic fermentation container. The upper end of the anaerobic fermentation container 3 is also connected to a liquid outlet pipe equipped with a first liquid pump 15 and is connected to the upper end of the adsorption reaction device 4. A nitrogen and phosphorus adsorption module is provided in the adsorption reaction device 4. The bottom of the adsorption reaction device is connected to the solution dehydration device 5 through a liquid outlet pipe equipped with a second liquid pump 16.

[0054] In this way, when the sludge treatment system is in operation, primary sludge can be added from the sludge feeding pipe to the mixing vessel. Then, some soluble sugar is added from the soluble sugar feeding port to the mixing vessel. The carbon-nitrogen ratio in the sludge is adjusted to an appropriate range and then mixed uniformly. The mixed sludge is then pumped into the micro-aerobic fermentation vessel via a third sludge pump. The micro-aerobic fermentation vessel is supplied with oxygen from an oxygen tank and mixed uniformly before micro-aerobic fermentation, which degrades large organic molecules. After micro-aerobic fermentation, the sludge is transferred to the anaerobic fermentation vessel via a fourth sludge pump. Acidogenic bacteria such as Klebsiella oxytoca and Lactobacillus buchneri are introduced through the acidogenic bacteria feeding port at the top of the vessel for anaerobic fermentation and acid production. Anaerobic fermentation gradually decomposes complex organic matter in the sludge into small organic acids such as VFAs (fatty acids). Since organic acids are liquid, they gradually rise to the surface and clarify to form a clear liquid rich in organic acids at the top of the sludge. The clear liquid is then directed through an outlet pipe to the adsorption reaction unit. The remaining sludge in the anaerobic fermentation container is emptied through the sewage pipe to achieve batch sequential treatment. The clarified liquid rich in organic acids passes through the nitrogen and phosphorus adsorption module in the adsorption reaction device to complete the nitrogen and phosphorus adsorption treatment. It is then dehydrated through the solution dehydration device to obtain a high-concentration liquid carbon source. In this way, this solution can complete the preparation of the liquid carbon source for primary sludge, and the obtained high-concentration liquid carbon source removes the nitrogen and phosphorus components, which is convenient for sewage carbon source supplementation. During implementation, a safety exhaust valve and an exhaust pipe are also provided at the top of each container to discharge the generated fermentation gas to ensure air pressure safety.

[0055] The sludge dewatering device 17 is also included. The sludge outlet of the sludge dewatering device 17 is connected to the mixing container 1 via a sludge feeding pipe. A second sludge pump 18 is installed on the sludge feeding pipe. The sludge inlet of the sludge dewatering device is connected to a primary sludge storage tank 20 via a sludge feeding pipe equipped with a first sludge pump 19. The structure of the sludge dewatering device 17 itself is conventional and will not be described in detail here.

[0056] This is because the moisture content of primary sludge is generally 95-98%. Too high a moisture content is not conducive to subsequent fermentation treatment. Therefore, the primary sludge is first dehydrated to adjust and reduce the moisture content to a certain extent, so as to improve the effect of subsequent treatment.

[0057] Among them, the upper end of the anaerobic fermentation container 3 is also equipped with a floating liquid discharge device connected to the liquid discharge pipe, and the liquid discharge device includes a float 21, and the lower end of the float 21 is provided with a downward inverted cone-shaped liquid suction port 22, and the upper end of the float 21 is provided with a liquid discharge port and the liquid suction port. The liquid discharge port is upwardly connected to a hose 23 with a movable margin and is connected to the liquid discharge pipe at the upper end of the anaerobic fermentation container 3. A lifting rope 24 is also upwardly provided at the middle part of the upper end of the float 21, and the upper end of the lifting rope 24 is wound around a wire drum of a winch 26 installed on the end panel 25 of the upper end of the anaerobic fermentation container.

[0058] In this way, when the anaerobic fermentation vessel is stirring and undergoing anaerobic fermentation, the winch is controlled to lift the float so that it does not interfere with the stirring and fermentation process of the sludge. When the anaerobic fermentation process is completed and clarified liquid is generated at the top of the sludge, the winch is controlled again to lower the float so that it drops to the surface of the clarified liquid. At this time, the clarified liquid generated at the top of the anaerobic fermentation vessel can be pumped away through the liquid outlet pipe, minimizing the disturbance of the sludge below.

[0059] A telescopic adjustment rod 27 is provided downwardly around the lower surface of the float 21 , and a horizontal baffle 28 is provided at the lower end of each telescopic adjustment rod 27 .

[0060] As the clarified liquid is gradually drawn away, the liquid level drops, and the float follows it down until the baffle falls onto the upper surface of the settled sludge below and is blocked. At this point, the float stops sinking, preventing the sludge from being drawn away. A small amount of remaining clarified liquid is discharged along with the sludge. The distance between the baffle and the float can be adjusted using a telescopic adjustment rod to prevent excess clarified liquid from remaining. This device maximizes clarified liquid removal while minimizing sludge disturbance. The telescopic adjustment rod utilizes a screw-on stud and a threaded sleeve for telescopic adjustment, resulting in a simple structure and convenient and reliable adjustment.

[0061] During implementation, a layer of filter paper is further provided at the lower end of the liquid suction port to better prevent sludge from being sucked in.

[0062] Wherein, an observation window made of glass material is vertically arranged on the side wall of the anaerobic fermentation container 3. In this way, the progress of the anaerobic fermentation can be judged by observing the output height of the clarified liquid in real time, and the liquid discharge can be processed in time.

[0063] Among them, the nitrogen and phosphorus adsorption module includes a zeolite material layer 41, a modified zeolite material layer 42 and a physical adsorption material layer 43 arranged in sequence from top to bottom. The modified zeolite material layer 42 is filled with modified zeolite obtained by modification with ammonia ions and magnesium ions, and the physical adsorption material layer 43 is activated carbon or phosphorus removal resin.

[0064] In this way, the clarified liquid first passes through the upper layer of unmodified zeolite material, which can first remove part of the ammonia nitrogen by adsorption. The pH of the upper water body is usually close to neutral, which is conducive to the zeolite's absorption of NH4 + At the same time, some cation competitors are removed. The water then passes through the middle layer of modified zeolite with high magnesium content. At this time, the ammonia nitrogen concentration in the water is reduced, the competition is weakened, and the cations released by the upper zeolite exchange (such as Na + ) will slightly raise the pH (especially when using Na-type zeolite), facilitating the dissolution of magnesium ions and their reaction with phosphates to form precipitates (such as struvite). The water then passes through the activated carbon or phosphorus removal resin below, capturing any trace pollutants that penetrate and better ensuring the effluent quality.

[0065] Furthermore, the modified zeolite is prepared by the following preparation method steps: 1) First, clean the zeolite with deionized water to remove surface impurities; 2) Then, immerse the zeolite in a 1 mol / L NH4Cl solution and stir with shaking for more than half an hour to allow the ammonium ions to fully enter the zeolite pores; 3) After the reaction is complete, remove the zeolite and immerse it in a MgCl2 solution greater than 1 mol / L (the solid-liquid ratio can be controlled to 1:10). Oscillate for a period of time (12 hours at 80°C) to allow for sufficient magnesium ion exchange reaction and complete loading. 4) After the loading reaction is completed, the zeolite is removed and washed with deionized water until neutral to remove unreacted magnesium salts, ammonium salts and other impurities; 5) Finally, the sample was dried at 45°C and then calcined at 550°C for 2 hours to remove organic matter and stabilize the structure, thereby producing a modified zeolite containing magnesium ions; Like this, by above-mentioned preparation step, first zeolite is cleaned with deionized water, removes surface impurities, ensures the efficient carrying out of subsequent reaction.Then, zeolite is immersed in the NH4Cl solution greater than 1 mol / L, and is shaken and stirred for more than half an hour so that amine ions fully enter the zeolite pores; Because some ammonium ions can produce displacement with some cations in zeolite, form adsorption reaction, therefore the amine ions entering the zeolite pores will produce reaction and then first block the pore channel of zeolite material.Then zeolite is placed in MgCl2 solution, and oscillation treatment is carried out for a period of time so that magnesium ions can replace the sodium ions or other cations in zeolite to complete load; Now because zeolite pore is blocked by the ammonium radical ion of reaction, most of magnesium ions are combined in the position protruding outside the zeolite pore for load reaction, and more active sites of magnesium ions are formed at the protruding position outside the zeolite. After the reaction is completed, the precipitate is taken out and washed with deionized water until it is neutral. Since the binding affinity between ammonium ions and zeolite is much lower than that of magnesium ions, most of the ammonium ions will be flushed away during washing, exposing the pores inside the zeolite to improve the adsorption capacity of the modified zeolite material. At the same time, a small amount of ammonia will remain attached to the pores, forming a small amount of NH4 + The adsorption active sites can adjust the ionic strength and charge balance of the local microenvironment and promote the reaction effect between magnesium ions and phosphates; specifically, the NH4 +Active sites can supplement magnesium ion active sites. During subsequent adsorption treatment, some free magnesium ions can enter the pores and then react with phosphate ions to form struvite precipitates, thereby improving the overall adsorption of nitrogen and phosphorus components in water. Finally, the zeolite is dried at 45°C and then calcined at 550°C for 2 hours to remove organic matter and stabilize the structure, thereby producing magnesium salt-modified zeolite. The calcination process removes organic impurities from the zeolite surface and pores, while stabilizing the zeolite's crystal structure, improving its stability and durability in practical applications.

[0066] Therefore, compared with the conventional magnesium-modified zeolite that is loaded by directly soaking the zeolite in a magnesium salt solution, the modified zeolite in this way avoids blockage during the magnesium loading reaction and ensures that the modified zeolite still maintains a relatively large porosity. The magnesium ion load is combined with the protruding position outside the pore, which can better adsorb the ammonia nitrogen and phosphate components in the water body when the water body passes through, and react to form struvite precipitation. The zeolite itself maintains a relatively large porosity to improve physical adsorption and promote chemical reactions. At the same time, the small amount of ammonium ions loaded inside the pores can also form a supplement to the reactive sites, which is more conducive to combining with phosphate to complete the precipitation reaction. Therefore, compared with conventional magnesium-modified zeolite, the removal effect of the modified zeolite on nitrogen and phosphorus components in water bodies is greatly improved.

[0067] Among them, the solution dehydration device 5 includes a container, a container-shaped frame body 51 is arranged inside the container, and the outer surface of the frame body 51 is covered with a layer of ultrafiltration membrane. The pore size of the ultrafiltration membrane is larger than water molecules and smaller than organic acid molecules (about 50nm). The frame body 51 is provided with a liquid extraction pipe and connected to the container, and a third liquid pump 52 is installed on the liquid extraction pipe.

[0068] This allows the third liquid pump to generate pressure, pumping water through the ultrafiltration membrane, leaving behind a highly concentrated organic acid solution, effectively achieving solution dehydration. Ultimately, a high-purity liquid carbon source with a VFA ≥ 8000 mg / L and a COD:N:P ≥ 200:5:1 can be obtained.

[0069] The present invention has the following advantages. 1. Improved carbon source yield: VFA concentration reaches 8000-12000 mg / L (3-4 times higher than the traditional method). 2. Cost reduction: Using molasses / fruit and vegetable waste liquid instead of pure carbon source, the raw material cost is saved by more than 40%. 3. Nitrogen and phosphorus recovery: Modified zeolite can be used as a slow-release fertilizer after adsorption (adsorption rate NH4 + >85%, PO4 3- >90%). 4. Stable process: Segmented oxygen control avoids acidification inhibition and shortens the fermentation cycle to 3 days.

Claims

1. A method for preparing a high-concentration liquid carbon source based on primary sludge fermentation, characterized in that: The primary sludge is added with soluble sugar to prepare a mixture with a C / N ratio of 15-25:

1. After microaerobic fermentation and anaerobic fermentation, the clarified liquid is taken to remove nitrogen and phosphorus components through adsorption reaction, and then dehydrated to obtain a high-concentration liquid carbon source.

2. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 1, characterized in that: The primary sludge is sludge with a moisture content of 90-92%.

3. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 1, characterized in that: The soluble sugar is industrial waste honey or fruit and vegetable processing waste liquid.

4. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 1, characterized in that: During the microaerobic fermentation, the sludge oxygen content is controlled to be DO 0.2-0.5 mg / L.

5. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 1, characterized in that: During anaerobic fermentation, an acid-producing composite bacterial agent is added to assist the fermentation, wherein the acid-producing composite bacterial agent includes Klebsiella acidophilus and Lactobacillus buchneri.

6. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 1, characterized in that: Modified zeolite containing magnesium ions is used to remove nitrogen and phosphorus components by adsorption reaction of clarified liquid; Alternatively, the nitrogen and phosphorus components can be removed by adsorption reaction of the clarified liquid by first passing it through unmodified zeolite and then through modified zeolite containing magnesium ions.

7. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 1, characterized in that: The method is implemented by a sludge treatment system for preparing a liquid carbon source, the sludge treatment system comprising a stirring and mixing container, a microaerobic fermentation container, an anaerobic fermentation container, an adsorption reaction device and a solution dehydration device arranged in series in sequence; a sludge feeding pipeline and a soluble sugar feeding port with a switch valve are provided at the upper end of the stirring and mixing container, a first stirring device is provided in the stirring and mixing container; the lower end of the stirring and mixing container is connected to the microaerobic fermentation container through a sludge pipeline equipped with a third sludge pump, the upper end of the microaerobic fermentation container is closed and a second stirring device is installed inside, an air supply port is also provided at the bottom of the microaerobic fermentation container, and the air supply port is controlled by a switch. The valve-controlled air supply pipe is connected to the oxygen tank; one side of the lower end of the micro-aerobic fermentation container is connected to the anaerobic fermentation container through a sludge pipe equipped with a fourth sludge pump, the upper end of the anaerobic fermentation container is closed and equipped with an acid-producing bacteria agent addition port with a switch valve, a third stirring device is installed inside the anaerobic fermentation container, and a sewage pipe with a switch valve is also installed at the lower end of the anaerobic fermentation container. The upper end of the anaerobic fermentation container is also connected to a liquid outlet pipe equipped with a first liquid pump and is connected to the upper end of the adsorption reaction device, a nitrogen and phosphorus adsorption module is provided in the adsorption reaction device, and the bottom of the adsorption reaction device is connected to the solution dehydration device through a liquid outlet pipe equipped with a second liquid pump.

8. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 7, characterized in that: It also includes a sludge dewatering device, the sludge outlet of the sludge dewatering device is connected to the stirring and mixing container through a sludge feeding pipe, a second sludge pump is installed on the sludge feeding pipe, and the sludge inlet of the sludge dewatering device is connected to a primary sludge storage tank through a sludge feeding pipe equipped with a first sludge pump.

9. A method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 7, wherein a liquid discharge device is further installed at the upper end of the anaerobic fermentation container and is connected to the liquid discharge pipe, the liquid discharge device includes a float, the lower end of the float is provided with a downward inverted conical liquid suction port, the upper end of the float is provided with a liquid discharge port and is connected to the liquid suction port, the liquid discharge port is upwardly connected to a hose with a movable margin and is connected to the liquid discharge pipe at the upper end of the anaerobic fermentation container, the middle part of the upper end of the float is further provided with a lifting rope, the upper end of the lifting rope is connected to a winch installed on the upper end panel of the anaerobic fermentation container; A telescopic adjustment rod is provided downwardly around the lower surface of the float, and a horizontal baffle is provided at the lower end of each telescopic adjustment rod; An observation window made of glass material is vertically arranged on the side wall of the anaerobic fermentation container.

10. The method for preparing a high-concentration liquid carbon source based on primary sludge fermentation according to claim 7, characterized in that: The nitrogen and phosphorus adsorption module includes a zeolite material layer, a modified zeolite material layer and a physical adsorption material layer arranged in sequence from top to bottom. The modified zeolite material layer is filled with modified zeolite obtained by modification with ammonia ions and magnesium ions. The physical adsorption material layer is activated carbon or phosphorus removal resin. The modified zeolite is prepared by the following preparation method steps: 1) First, clean the zeolite with deionized water to remove surface impurities; 2) Then, immerse the zeolite in a 1 mol / L NH4Cl solution and stir with shaking for more than half an hour to allow the ammonium ions to fully enter the zeolite pores; 3) After the reaction is complete, remove the zeolite and soak it in a MgCl2 solution greater than 1 mol / L. Oscillate it for a period of time to allow the magnesium ions to fully exchange and react to complete the loading. 4) After the loading reaction is completed, the zeolite is removed and washed with deionized water until neutral to remove unreacted magnesium salts, ammonium salts and other impurities; 5) Finally, the sample was dried at 45°C and then calcined at 550°C for 2 hours to remove organic matter and stabilize the structure, thereby producing a modified zeolite containing magnesium ions; The solution dehydration device includes a container, a container-shaped frame body is arranged inside the container, and the outer surface of the frame body is covered with an ultrafiltration membrane. The pore size of the ultrafiltration membrane is larger than water molecules and smaller than organic acid molecules. The frame body is provided with a liquid extraction pipe and connected to the outside of the container, and a third liquid pump is installed on the liquid extraction pipe.

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