A method for reducing the volume of municipal sludge

Abstract

This invention discloses a method for reducing and disposing of municipal sludge, relating to the field of sludge treatment technology. In the pretreatment stage, this invention constructs a triple synergistic cell-wall breaking mechanism of low-temperature microwave, ultrasonic, and layered high-pressure. When ultrasonic waves propagate in the sludge medium, they generate a cavitation effect, forming localized high-temperature, high-pressure microjets, causing mechanical rupture of the cell wall structure and initial leakage of intracellular substances and bound water. The heating effect of low-temperature microwaves causes the resonant breakage of hydrogen bonds in water molecules, weakening the binding force between intracellular water and cell components. Under the activation of the microwave thermal field, composite biological enzymes specifically enzymatically hydrolyze the physically damaged cell wall fragments and polysaccharides and protein components in extracellular polymers, degrading large organic molecules into small soluble molecules. The layered high-pressure method uses segmented pressurization to cause plastic deformation of the sludge cake under pressure, continuously squeezing out capillary water and residual adsorbed water, achieving precise biochemical lysis.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, specifically a method for reducing the volume of municipal sludge. Background Technology

[0002] Municipal sludge is a byproduct of wastewater treatment. It is characterized by large production volume, high water content, high organic matter content, and the presence of pathogens and heavy metals. The water in sludge exists in four forms: free water, interstitial water, surface-bound water, and intracellular bound water. Among them, intracellular bound water is encapsulated by dense microbial cell walls and extracellular polymers, making it difficult to remove by conventional mechanical methods. If not properly disposed of, it can easily cause secondary pollution and place a heavy burden on the environment. Achieving deep reduction and stabilization of sludge has become a key technical problem that the wastewater treatment industry urgently needs to solve.

[0003] In existing sludge dewatering technologies, conventional mechanical dewatering can only remove free water and some interstitial water. After dewatering, the sludge moisture content remains at 75%-85%, while the intracellular bound water, which accounts for 20%-40% of the total sludge moisture content, is difficult to release, leading to a significant increase in energy consumption for subsequent thermal drying or incineration. To improve dewatering performance, large amounts of inorganic conditioners such as iron salts, aluminum salts, and lime are added. These agents not only increase the dry basis mass of the sludge by 20%-30%, offsetting the volume reduction effect, but also introduce a large amount of inorganic impurities, making the dewatered sludge highly alkaline, which hinders its subsequent use in building materials. Furthermore, the production and transportation of lime itself pose carbon emission problems.

[0004] Meanwhile, single physical decomposition technology has the problem of balancing energy consumption and efficiency, while single biological enzyme treatment has a long reaction cycle, making it difficult to meet the needs of large-scale continuous treatment of municipal sludge.

[0005] In summary, existing sludge treatment technologies suffer from problems such as difficulty in releasing intracellular bound water, limited dewatering efficiency, and significant secondary pollution from chemicals. There is an urgent need to develop a volume reduction method that can efficiently break down the cell walls of sludge microorganisms, deeply remove bound water, reduce the amount of chemical reagents used, and is applicable to large-scale municipal sludge treatment. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for reducing and disposing of municipal sludge. This method can establish a triple synergistic cell-wall breaking mechanism of low-temperature microwaves, ultrasound, and layered high pressure during the pretreatment stage. When ultrasound propagates in the sludge medium, it generates a cavitation effect, forming localized high-temperature, high-pressure microjets that physically shear the sludge flocs and microbial cell walls, causing mechanical rupture of the cell wall structure and initial leakage of intracellular substances and bound water. The selective heating effect of the low-temperature microwaves causes the resonant breakage of hydrogen bonds in water molecules, further weakening the intracellular water and cell structure. The binding force of the components, under the activation of the microwave thermal field, the composite bio-enzyme specifically enzymatically hydrolyzes the components such as polysaccharides and proteins in the physically damaged cell wall fragments and extracellular polymers, degrading large organic molecules into small soluble molecules, and further releasing the bound water. Ultrasound provides a physical channel for cell wall disruption, microwaves provide thermal field activation conditions, and the layered high pressure adopts a segmented pressurization method to make the mud cake undergo plastic deformation under gradually increasing pressure, continuously squeezing out capillary water and residual adsorbed water. The bio-enzyme achieves precise biochemical lysis, solving the technical problem of difficult removal of bound water.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for reducing and disposing of municipal sludge, the specific steps of which are as follows: S100. Sludge thickening and conditioning: The municipal sludge to be treated is concentrated by gravity for 8-12 hours and conditioned to a moisture content of 95%-98% to obtain concentrated and conditioned sludge. S200, Synergistic cell wall breaking pretreatment: The concentrated and conditioned sludge is transported to the pretreatment reactor, the sludge temperature is adjusted to 40-60℃, compound biological enzymes are added, and after mixing, low-frequency ultrasonic pre-dissociation treatment is performed first, followed by microwave irradiation synergistic enzymatic cell wall breaking treatment to obtain cell wall broken sludge. S300, Composite Conditioning: The cell wall broken sludge is transported to the conditioning tank, modified attapulgite is added, and the mixture is stirred for 5-15 minutes. The rigid framework structure is constructed by adsorbing dissolved extracellular polymers and heavy metal ions through the pores. Then, cationic polyacrylamide is added, and the mixture is stirred for 3-10 minutes to carry out flocculation conditioning reaction to obtain conditioning sludge. S400, Layered High-Pressure Deep Dewatering: The conditioned sludge is subjected to layered high-pressure deep dewatering using a segmented pressurization method. The pressing pressure is 2.0-4.0 MPa, and the holding time is 20-60 minutes, to obtain a sludge cake with a moisture content of ≤50%. S500, Low-calorific-value drying and stabilization: The sludge cake is transported to a low-temperature drying system and dried at low temperature using a low-grade heat source to obtain stabilized sludge.

[0008] Furthermore, in S200, the compound bio-enzyme is composed of cellulase, neutral protease, α-amylase, and lipase in a mass ratio of 3:2:1:1, and the dosage of the compound bio-enzyme is 0.05%-0.5% of the dry weight of the concentrated and conditioned sludge.

[0009] Furthermore, in S200, the parameters for the low-frequency ultrasonic pre-dissociation treatment are: ultrasonic frequency 15kHz-30kHz, adjustable power 0W-20W, and processing time 3min-8min. The parameters for the microwave irradiation-assisted enzymatic hydrolysis cell disruption treatment are as follows: microwave irradiation frequency of 915MHz or 2450MHz, microwave irradiation power density of 0.2W / mL-0.5W / mL, and treatment time of 10min-20min.

[0010] Furthermore, in S300, the modified attapulgite is attapulgite that has undergone synergistic modification through acid activation and organic modification treatments, and the dosage of the modified attapulgite is 3%-10% of the dry weight of the cell wall-breaking sludge; The cationic polyacrylamide has an ionicity of 30%-60%, a molecular weight of 8 million to 12 million, and is added at a rate of 0.1%-0.5% of the dry weight of the cell-wall broken sludge.

[0011] Furthermore, the acid activation treatment is as follows: take natural attapulgite clay, crush it through a 200-mesh sieve, add a hydrochloric acid solution with a concentration of 1mol / L-2mol / L, control the solid-liquid ratio to be 1:5-1:10, stir and activate it for 2-4 hours under a water bath at 60℃-80℃, filter it, wash it with deionized water until the filtrate is neutral, and dry it at 105℃ to obtain acid-activated attapulgite clay.

[0012] Furthermore, the organic modification process is as follows: acid-activated attapulgite is added to anhydrous ethanol, the solid-liquid ratio is controlled at 1:8-1:12, 1%-3% of silane coupling agent KH550 is added, the pH of the system is adjusted to 4-5 with glacial acetic acid, the reaction is stirred for 2-3 hours under a 60°C water bath, the mixture is filtered, washed 2-3 times with anhydrous ethanol, and dried at 105°C to obtain modified attapulgite.

[0013] Furthermore, in S300, the parameters of the flocculation conditioning reaction are as follows: stirring at 200r / min-300r / min for 2min-3min, then stirring at 50r / min-80r / min for 5min-10min, and then letting it stand for 10min-15min after stirring.

[0014] Furthermore, in the S400, the segmented pressurization method is as follows: First, maintain a low pressure of 0.5MPa-1MPa for 5-10 minutes to drain most of the free water from the sludge; Then increase the pressure to 2MPa-3MPa and hold it for 8min-15min to drain the interstitial water from the flocs; Finally, the pressure is increased to 4MPa-8MPa and held for 15min-30min to deeply remove the bound water released from the cells, thus completing the high-pressure deep dehydration.

[0015] Furthermore, in the S500, the low-grade heat source is one or more of the following: waste heat from anaerobic digestion biogas combustion in a wastewater treatment plant, waste heat from biochemical effluent, and waste heat from sludge incineration flue gas. The low-temperature drying temperature is 60℃-80℃, the drying time is 60min-100min, and the moisture content of the stabilized sludge after low-temperature drying is ≤30%.

[0016] Compared with existing technologies, this method for reducing and disposing of municipal sludge has the following advantages: This invention constructs a triple synergistic cell-wall breaking mechanism of low-temperature microwave, ultrasound, and stacked high pressure in the pretreatment stage. When ultrasound propagates in the sludge medium, it generates a cavitation effect, forming a local high-temperature and high-pressure microjet, which exerts physical shearing action on the sludge flocs and microbial cell walls, causing mechanical rupture of the cell wall structure and initial leakage of intracellular substances and bound water. The selective heating effect of low-temperature microwave causes the hydrogen bonds of water molecules to resonate and break, further weakening the binding force between intracellular water and cell components. Under the activation of the microwave thermal field, the composite bio-enzyme specifically enzymatically hydrolyzes the physically damaged cell wall fragments and components such as polysaccharides and proteins in the extracellular polymers, degrading macromolecular organic matter into small soluble molecules and further releasing the bound water. Ultrasound provides the physical cell-wall breaking channel, microwave provides the thermal field activation conditions, and stacked high pressure uses a segmented pressurization method to cause plastic deformation of the sludge cake under gradually increasing pressure, continuously squeezing out capillary water and residual adsorbed water. The bio-enzyme achieves precise biochemical lysis, solving the technical problem of difficult removal of bound water.

[0017] In the conditioning stage, this invention employs a modified attapulgite and cationic polyacrylamide compound system. After calcination and acid synergistic modification, the modified attapulgite exhibits an increased specific surface area. Its nanoscale porous structure possesses a strong adsorption capacity for dissolved extracellular polymers and heavy metal ions in the sludge, fixing colloidal substances that easily cause filter pore blockage onto the surface of mineral particles. Simultaneously, the attapulgite, with its rod-like microstructure, forms a rigid skeletal support structure within the sludge flocs, effectively preventing the collapse and closure of the pores in the sludge cake during high-pressure dewatering. The cationic polyacrylamide, through its electrochemical properties... It works by compressing the double electric layer of sludge particles and flocculating dispersed sludge particles with rigid skeleton particles through the bridging effect of polymer long chains into large flocs with high permeability. The staged pressurization method causes the sludge cake to undergo plastic deformation under gradually increasing pressure, continuously squeezing out capillary water and residual adsorbed water, realizing the stratified removal of water in different forms. It replaces traditional lime and iron salt conditioners to avoid sludge increase and secondary pollution. It relies on the low-calorific-value waste heat generated by the sewage treatment plant to complete the drying and stabilization, and is suitable for the engineering needs of large-scale continuous treatment of municipal sludge.

[0018] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0020] Figure 1 This is a process flow diagram of a municipal sludge reduction and disposal method according to the present invention; Figure 2 This is a flowchart illustrating the steps of a municipal sludge reduction and disposal method according to an embodiment of the present invention. Figure 3 This is a flowchart illustrating the preparation steps of modified attapulgite in an embodiment of the present invention. Detailed Implementation

[0021] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] To address the shortcomings of existing municipal sludge treatment technologies, such as difficulty in releasing intracellular bound water, limited dewatering efficiency, and significant secondary pollution from chemical agents, this invention provides a method for reducing and stabilizing municipal sludge. This method employs a comprehensive process involving sludge concentration and conditioning, synergistic cell wall disruption pretreatment, compound conditioning, layered high-pressure deep dewatering, and low-calorific-value drying and stabilization. It establishes a triple synergistic cell wall disruption mechanism using low-temperature microwaves, ultrasound, and composite biological enzymes to efficiently break down the cell walls of sludge microorganisms and deeply remove intracellular bound water. Simultaneously, a composite conditioning system using modified attapulgite and cationic polyacrylamide replaces traditional lime and iron salt inorganic conditioning agents, avoiding increased sludge dry weight and secondary pollution. A segmented pressurized layered high-pressure deep dewatering process removes water in different forms in stages. Low-temperature drying and stabilization of the sludge is achieved using a low-grade heat source generated by the wastewater treatment plant. This comprehensive technology system, encompassing sludge pretreatment, cell wall disruption and water release, compound conditioning, deep dewatering, and drying stabilization, enables efficient reduction and stabilization of municipal sludge.

[0023] This invention is primarily applied to urban wastewater treatment plants and municipal sludge disposal centers, addressing the challenges of high water content, difficult disposal, and potential secondary pollution associated with municipal sludge. Municipal sludge, a byproduct of wastewater treatment, is characterized by large production volumes, high organic matter content, and the presence of pathogens and heavy metals. Traditional sludge disposal methods, such as conventional mechanical dewatering, single physical cell disruption, or single biological enzyme treatment, suffer from several drawbacks. These include the removal of only free water and some interstitial water, difficulty in releasing intracellular bound water, a significant increase in energy consumption for subsequent thermal drying or incineration, increased sludge production due to chemical additives, and hindered utilization in building materials. Furthermore, single treatment technologies suffer from the disadvantage of balancing energy consumption and efficiency, and long reaction cycles, failing to meet the engineering requirements for large-scale continuous disposal of municipal sludge. This invention constructs an integrated disposal system combining multiple synergistic cell disruption and complex conditioning for deep dewatering, closely integrating the sludge treatment process with the utilization of waste heat from wastewater treatment plants. This achieves multiple objectives in municipal sludge disposal: reduction, harmlessness, and low carbon emissions. Example 1

[0024] This embodiment is a preferred embodiment of the present invention, using the most common medium-organic sludge in the municipal wastewater treatment industry, and performing the following... Figure 1 The complete process shown, including sludge thickening and conditioning, synergistic cell wall breaking pretreatment, compound conditioning, multi-layer high-pressure segmented pressurization for deep dewatering, and low-calorific-value drying and stabilization, verifies the feasibility and deep volume reduction effect of the present invention. This embodiment serves as the control benchmark for all comparative examples.

[0025] In this embodiment, the municipal sludge to be treated was taken from the residual sludge in the secondary sedimentation tank of a domestic sewage treatment plant. The initial moisture content of the sludge was 98.8%, and the organic matter content was 52%. Figure 2 As shown, the specific handling steps are as follows: S100. Sludge thickening and conditioning: The municipal sludge to be treated is sent to a gravity thickening tank, allowed to stand for gravity thickening for 10 hours, and then conditioned to a moisture content of 96.5% to obtain thickened and conditioned sludge for later use. S200, Co-processing Pretreatment: Concentrated and conditioned sludge is transported to a pretreatment reactor. The sludge system temperature is stabilized at 50℃ using a circulating water bath. Compound biological enzymes are added to the sludge, and after stirring and mixing, low-frequency ultrasonic pre-dissociation treatment is performed. Immediately after pre-dissociation, microwave irradiation synergistic enzymatic hydrolysis is performed to disrupt the cell walls. During the treatment, the system temperature is maintained between 45-55℃. After the cell wall disruption treatment, cell-wall-broken sludge is obtained, including: The compound bio-enzyme is composed of cellulase, neutral protease, α-amylase, and lipase in a mass ratio of 3:2:1:1, and the dosage is 0.2% of the dry weight of the concentrated and conditioned sludge. The parameters for low-frequency ultrasonic pre-dissociation treatment were set as follows: ultrasonic frequency 25kHz, power density 0.2W / mL, and treatment time 5min. The parameters for microwave irradiation-assisted enzymatic hydrolysis cell disruption were set as follows: microwave irradiation frequency 2450MHz, microwave power density 0.3W / mL, treatment time 15min, and the system temperature was maintained in the range of 45-55℃ during the treatment process using a temperature control system. S300, Composite Conditioning: The cell-wall-broken sludge is transported to the conditioning tank. Modified attapulgite is added first, at a rate of 6% of the dry weight of the cell-wall-broken sludge. The mixture is stirred at 150 rpm for 10 minutes. The modified attapulgite adsorbs dissolved extracellular polymers and heavy metal ions from the sludge through its pores, simultaneously constructing a rigid framework structure within the sludge system. Then, cationic polyacrylamide is added. The cationic polyacrylamide has an ionicity of 40% and a molecular weight of 10 million, at a rate of 0.2% of the dry weight of the cell-wall-broken sludge. The mixture is first rapidly stirred at 250 rpm for 2.5 minutes, then slowly stirred at 60 rpm for 8 minutes. After stirring, the mixture is allowed to stand for 12 minutes to mature, completing the flocculation and conditioning reaction, resulting in conditioned sludge. Among these: like Figure 3 As shown, the preparation steps of modified attapulgite are as follows: Acid activation treatment: Take natural attapulgite, crush it through a 200-mesh sieve, add a 1.5 mol / L hydrochloric acid solution, control the solid-liquid ratio to 1:8, stir and activate it for 3 hours under a 70℃ water bath, filter it, wash it with deionized water until the filtrate is neutral, and dry it at 105℃ to constant weight to obtain acid-activated attapulgite. Organic modification treatment: Acid-activated attapulgite was added to anhydrous ethanol, and the solid-liquid ratio was controlled at 1:10. 2% of the mass of acid-activated attapulgite was added as silane coupling agent KH550. The pH of the system was adjusted to 4.5 with glacial acetic acid. The reaction was stirred for 2.5 h in a 60℃ water bath. After filtration, the mixture was washed three times with anhydrous ethanol and dried at 105℃ to constant weight to obtain modified attapulgite for later use. S400, Stacked High-Pressure Deep Dewatering: The conditioned sludge is fed into a stacked high-pressure filter press, and deep dewatering is carried out using a three-stage segmented pressurization method. Specifically, the pressure is first maintained at 0.8MPa for 8 minutes to remove most of the free water in the sludge; then the pressure is increased to 2.5MPa and maintained for 10 minutes to remove the interstitial water of the flocs; finally, the pressure is increased to 6MPa and maintained for 20 minutes to deeply remove the bound water released from the cells, completing the high-pressure deep dewatering, and the material is discharged to obtain a sludge cake. S500, Low-calorific-value drying and stabilization: The sludge cake is transported to a low-temperature drying system, which uses the residual heat from the combustion of biogas in the anaerobic digestion of the sewage treatment plant as a low-grade heat source. The drying temperature is controlled at 70°C and the drying time is 80 minutes. After drying, stabilized sludge is obtained.

[0026] Test results According to the test results, in this embodiment, the SCOD dissolution rate of the cell wall-breaking sludge was 81.7%; the moisture content of the sludge cake after dewatering was 38.2%; the moisture content of the stabilized sludge after drying was 19.4%; the specific resistance of the sludge was 2.1×10¹²m / kg, indicating excellent dewatering performance; the sludge dry basis increment rate was 6.2%; the pH value of the sludge cake was 7.2, indicating neutrality; and the overall energy consumption of the entire process was 122kW・h / ton of wet sludge (based on a moisture content of 97%).

[0027] In summary, this embodiment achieves efficient disruption of microbial cell walls and EPS through a synergistic cell-wall breaking system, fully releasing intracellular bound water; constructs a rigid framework structure suitable for high-pressure dewatering through a modified attapulgite-CPAM composite conditioning system, avoiding filter pore clogging and floc compaction; achieves stratified removal of water in different forms through layered high-pressure segmented pressurization; and finally completes stabilization and drying using low-calorific-value waste heat generated by the wastewater treatment plant, achieving deep sludge reduction with no secondary chemical pollution and no significant increase in sludge volume. Example 2

[0028] This embodiment targets the scenario of high organic matter municipal sludge in large-scale wastewater treatment plants (organic matter content 60%-70%, high proportion of intracellular bound water, and difficulty in cell wall disruption). By specifically optimizing the process parameters of cell wall disruption and conditioning, the adaptability and treatment effect of the present invention on high organic matter and difficult-to-treat sludge are verified, proving the universality of the present invention for different sludge types.

[0029] In this embodiment, the municipal sludge to be treated is taken from the residual sludge in the secondary sedimentation tank of an urban wastewater treatment plant. The initial moisture content of the sludge is 99.3%, and the organic matter content is 63%. The operation logic of all other process steps is consistent with that in Embodiment 1, with the following specific optimizations: S100 sludge thickening and conditioning: Gravity thickening for 12 hours, conditioning to a moisture content of 97%; S200 synergistic cell wall disruption pretreatment: The dosage of compound biological enzymes was increased to 0.4% of the dry weight of concentrated and conditioned sludge; the low-frequency ultrasonic pre-dissociation treatment parameters were adjusted to 35kHz, 0.25W / mL, 7min; the microwave irradiation synergistic enzymatic hydrolysis parameters were adjusted to 0.4W / mL, 18min, and the system temperature was maintained at 50-55℃. S300 composite conditioning: The dosage of modified attapulgite soil is increased to 10% of the dry weight of the cell wall broken sludge, the dosage of cationic polyacrylamide is increased to 0.3%, and the remaining stirring and maturation parameters are the same as in Example 1; S400 laminated high-pressure deep dehydration: The final pressure of the high-pressure section is increased to 8MPa and the holding time is extended to 25min. The parameters of the remaining low-pressure and medium-pressure sections are the same as in Example 1. S500 low calorific value drying and stabilization: The drying time was adjusted to 90 min, and the other parameters were the same as in Example 1.

[0030] Test results According to the test results, the SCOD dissolution rate of the cell wall broken sludge in this embodiment was 79.2%; the moisture content of the sludge cake after dewatering was 39.6%; the moisture content of the stabilized sludge after drying was 19.8%; the sludge dry basis increment rate was 10.3%; the pH value of the sludge cake was 7.3; and the comprehensive energy consumption of the whole process was 131 kWh / ton of wet sludge (based on a moisture content of 97%).

[0031] In summary, this embodiment achieves efficient cell wall disruption and deep volume reduction for high-organic-matter, difficult-to-treat sludge. The moisture content of the sludge cake after dewatering is stably controlled below 40%, and the moisture content after drying meets the stabilization requirements. This embodiment proves that the technical solution of the present invention is adaptable to high-organic-matter municipal sludge and can solve the pain point of difficult treatment of sludge with high bound water content. Example 3

[0032] This embodiment targets the scenario of low organic matter municipal sludge in wastewater treatment plants (organic matter content 35%-45%, high proportion of inorganic matter, colloidal particles easily clog filter cloth, and large fluctuations in dewatering performance), verifies the adaptability of the present invention to low organic matter sludge, covers the treatment needs of municipal sludge in all scenarios, and proves the stability of the solution.

[0033] In this embodiment, the municipal sludge to be treated is taken from the residual sludge in the secondary sedimentation tank of a domestic wastewater treatment plant. The initial moisture content of the sludge is 98.2%, and the organic matter content is 42%. The operation logic of all other process steps is consistent with that in Embodiment 1, with the following specific optimizations: S100 sludge thickening and conditioning: Gravity thickening for 8 hours, conditioning to a moisture content of 96%; S200 synergistic cell wall disruption pretreatment: The dosage of compound biological enzymes was reduced to 0.08% of the dry weight of the concentrated and conditioned sludge; the low-frequency ultrasonic pre-dissociation treatment parameters were adjusted to 20kHz, 0.15W / mL, 4min; the microwave irradiation synergistic enzymatic hydrolysis parameters were adjusted to 0.25W / mL, 12min, and the system temperature was maintained at 45-50℃. S300 composite conditioning: The dosage of modified attapulgite soil was reduced to 3% of the dry weight of the cell wall broken sludge, and the dosage of cationic polyacrylamide was reduced to 0.15%. The remaining stirring and maturation parameters were the same as in Example 1. S400 laminated high-pressure deep dehydration: The final pressure of the high-pressure section is reduced to 4MPa, and the holding time is adjusted to 15min. The parameters of the remaining low-pressure and medium-pressure sections are the same as in Example 1. S500 low calorific value drying and stabilization: The drying time was adjusted to 60 min, and the other parameters were the same as in Example 1.

[0034] Test results According to the test results, the SCOD dissolution rate of the cell wall broken sludge in this embodiment was 75.6%; the moisture content of the sludge cake after dewatering was 39.1%; the moisture content of the stabilized sludge after drying was 19.2%; the sludge dry basis increment rate was 3.15%; the pH value of the sludge cake was 7.1; and the overall energy consumption of the whole process was 117 kWh / ton of wet sludge.

[0035] This embodiment targets municipal sludge with low organic matter content. After optimizing the parameters, it effectively avoids the problem of colloidal particles clogging the filter cloth, achieves a stable deep dewatering effect, and further reduces the amount of reagents added and the operating energy consumption. The increase in sludge dry basis is extremely low, and there is no risk of secondary pollution. This embodiment proves that the present invention is adaptable to municipal sludge with low organic matter content, can cover the application scenarios of supporting sewage treatment plants in industrial parks, and is suitable for the needs of large-scale continuous treatment of municipal sludge.

[0036] Comparative Example 1 This comparative example is a single-variable control experiment. The only difference from Example 1 is that the low-frequency ultrasonic pre-dissociation and microwave irradiation treatment in step S200 are omitted. Only the same amount of compound biological enzyme as in Example 1 is added for room temperature enzymatic hydrolysis. All other process steps, parameters, and sludge to be treated are completely consistent with Example 1. This is used to verify the indispensability of the synergistic cell-wall breaking system of ultrasonic pre-dissociation-microwave irradiation-compound biological enzyme and to prove the core role of this system in the release of intracellular bound water.

[0037] The sludge to be treated in this comparative example is exactly the same as that in Example 1, except that step S200 is modified. All steps, parameters, and material dosages in S100, S300, S400, and S500 are completely identical to those in Example 1. The modified step S200 is as follows: S200 enzymatic hydrolysis treatment: The concentrated and conditioned sludge is transported to the reactor, and the same amount of compound biological enzyme as in Example 1 is added to the sludge under normal temperature conditions. After stirring and mixing, the sludge is allowed to stand at room temperature for 20 minutes for enzymatic hydrolysis, which is consistent with the total cell wall breaking time in Example 1, to obtain enzymatically hydrolyzed sludge.

[0038] Test results Using the same standard method as in Example 1, the SCOD dissolution rate of the enzymatically hydrolyzed sludge in this comparative example was 22.3%; the moisture content of the dewatered sludge cake was 67.4%; the moisture content of the stabilized sludge after drying was 19.5%; the specific resistance of the sludge was 5.8 × 10¹² m / kg; the sludge dry basis increment rate was 6.1%; and the overall energy consumption of the entire process was 218 kW・h / ton of wet sludge (based on a moisture content of 97%).

[0039] In this comparative example, after eliminating the combined ultrasonic and microwave treatment, relying solely on a single compound bio-enzyme for hydrolysis, the SCOD dissolution rate decreased by 72.7% compared to Example 1. The microbial cell walls and EPS were almost not effectively broken down, and the intracellular bound water could not be released, directly leading to a significant increase in the moisture content of the dehydrated sludge cake. The energy consumption of the subsequent drying process increased by 78.7% compared to Example 1, and the overall energy consumption of the entire process increased significantly. This comparative example directly proves that the synergistic cell-wall breaking system of ultrasonic pre-dissociation, microwave irradiation, and compound bio-enzyme solves the pain points of low efficiency and inability to adapt to large-scale treatment by single bio-enzyme.

[0040] Comparative Example 2 This comparative example is a single-variable control experiment. The only difference from Example 1 is that the addition of compound biological enzymes and microwave irradiation treatment in step S200 are omitted. Only ultrasonic treatment with parameters completely consistent with those in Example 1 is performed. All other process steps, parameters, and sludge to be treated are completely consistent with Example 1. This is used to verify the technical effect of physical-biochemical synergistic cell wall disruption compared to single physical cell wall disruption.

[0041] The sludge to be treated in this comparative example is exactly the same as that in Example 1, except that step S200 is modified. All steps, parameters, and material dosages in S100, S300, S400, and S500 are completely identical to those in Example 1. The modified step S200 is as follows: S200 Single Ultrasonic Treatment: The concentrated and conditioned sludge is transported to the pretreatment reactor. Under normal temperature conditions, it is first subjected to low-frequency ultrasonic pre-dissociation treatment with parameters exactly the same as in Example 1, and then subjected to ultrasonic treatment with the same parameters for 15 minutes. The duration is the same as the microwave treatment in Example 1. The total ultrasonic treatment time is 20 minutes, and ultrasonically treated sludge is obtained.

[0042] Test results Using the same standard method as in Example 1, the SCOD leaching rate of the treated sludge in this comparative example was 41.6%; the moisture content of the dewatered sludge cake was 58.3%; the specific resistance of the sludge was 4.5×10¹²m / kg; the moisture content of the stabilized sludge after drying was 19.3%; the sludge dry basis increment rate was 6.2%; and the overall energy consumption of the entire process was 187 kW・h / ton of wet sludge (based on a moisture content of 97%).

[0043] This comparative example uses only ultrasonic physical treatment. Although it can partially break up flocs and rupture cell walls through cavitation, it cannot specifically degrade EPS and cell wall fragments. The SCOD dissolution rate is 49.1% lower than that of Example 1, the release of intracellular bound water is insufficient, and the water content of the dehydrated cake is significantly higher than that of Example 1. Moreover, the energy consumption of continuous ultrasonic treatment is significantly higher than that of the synergistic cell wall breaking system in Example 1. The overall energy consumption of the whole process is 53.3% higher than that of Example 1. This comparative example directly proves that the physical-biochemical synergistic cell wall breaking system of the present invention has significant advantages in cell wall breaking efficiency and energy consumption control compared with single physical breaking technology.

[0044] Comparative Example 3 This comparative example is a test comparing traditional processes in the industry. The only difference between this example and Example 1 is that the lime + FeCl3 inorganic conditioning system commonly used in the municipal sludge treatment industry is used to completely replace the modified attapulgite-CPAM composite conditioning system of this invention. All other process steps, parameters, and sludge to be treated are completely consistent with Example 1. This example is used to verify the technical effects of the conditioning system of this invention in avoiding sludge increase, eliminating secondary pollution, and improving dewatering performance.

[0045] The sludge to be treated in this comparative example is exactly the same as that in Example 1, except that step S300 is modified. All steps and parameters of S100, S200, S400, and S500 are completely consistent with those in Example 1. The modified step S300 is as follows: S300 Traditional Inorganic Conditioning: The cell-wall broken sludge is transported to the conditioning tank, and an inorganic conditioner with a standard industry ratio is added. The amount of lime added is 30% of the dry weight of the cell-wall broken sludge, and the amount of FeCl3 added is 15% of the dry weight of the cell-wall broken sludge. First, it is rapidly stirred at 250 r / min for 2.5 min, and then slowly stirred at 60 r / min for 8 min. After stirring, it is allowed to stand and mature for 12 min to obtain the conditioned sludge.

[0046] Test results Using the same standard method as in Example 1, the SCOD leaching rate of the treated sludge in this comparative example was 80.9%; the moisture content of the dewatered sludge cake was 59.7%; the specific resistance of the sludge was 3.9 × 10¹² m / kg; the moisture content of the stabilized sludge after drying was 19.6%; the sludge dry basis increment rate was 44.8%; the pH value of the sludge cake was 12.4, indicating strong alkalinity; and the overall energy consumption of the entire process was 206 kW·h / ton of wet sludge (based on a moisture content of 97%).

[0047] This comparative example uses a traditional lime + FeCl3 inorganic conditioning system, resulting in a sludge dry basis increase rate of up to 44.8%, a 622.6% increase compared to Example 1. This completely offsets the dewatering and volume reduction effect. Furthermore, the sludge cake is highly alkaline, severely hindering subsequent building material and resource utilization, and posing a significant risk of secondary pollution. Moreover, traditional inorganic conditioning agents cannot construct a rigid framework structure suitable for high-pressure dewatering, leading to a significantly higher moisture content in the dewatered sludge cake compared to Example 1. This results in a substantial increase in subsequent drying energy consumption, with the overall energy consumption of the entire process increasing by 68.9% compared to Example 1. This comparative example is used to verify the modified attapulgite-CPAM composite conditioning system, which solves the pain points of sludge increase and secondary pollution associated with traditional inorganic conditioning agents, while also exhibiting superior dewatering performance.

[0048] Comparative Example 4 This comparative example is a single-variable control experiment. The only difference from Example 1 is that it uses an industry-standard plate and frame filter press and a 1.5MPa constant pressure non-segmented mode, which completely replaces the stacked high-pressure segmented pressurization deep dewatering process of the present invention. All other process steps, parameters, and sludge to be treated are completely consistent with Example 1. This is used to verify the synergistic effect of stacked high-pressure segmented pressurization dewatering and the front-end cell breaking and conditioning system.

[0049] The sludge to be treated in this comparative example is exactly the same as that in Example 1, except that step S400 is modified. All steps, parameters, and material dosages in S100, S200, S300, and S500 are completely identical to those in Example 1. The modified step S400 is as follows: S400 Conventional Plate and Frame Filter Press Dewatering: The conditioned sludge is fed into a conventional plate and frame filter press, using a constant pressure of 1.5MPa without segmentation, with a total pressure holding time of 38min, consistent with the total pressure holding time in Example 1. After dewatering is completed, the sludge cake is unloaded.

[0050] Test results Using the same standard method as in Example 1, the SCOD leaching rate of the treated sludge in this comparative example was 81.5%; the moisture content of the dewatered sludge cake was 62.8%; the specific resistance of the sludge was 4.2 × 10¹² m / kg; the moisture content of the stabilized sludge after drying was 19.4%; the sludge dry basis increment rate was 6.2%; and the overall energy consumption of the entire process was 209 kW・h / ton of wet sludge (based on a moisture content of 97%).

[0051] This comparative example uses conventional plate and frame constant pressure filtration, which cannot form a synergistic effect with the front-end cell disruption and conditioning system. The low-pressure constant pressure mode cannot deeply remove the bound water released from the cells, and at the same time, it easily leads to rapid crusting on the surface of the filter cake, preventing the internal water from being discharged. The moisture content of the sludge cake after dewatering increased by 64.4% compared with Example 1, which directly led to a significant increase in the heat energy demand of the subsequent drying process. The overall energy consumption of the entire process increased by 71.3% compared with Example 1. This verifies that the stacked high-pressure segmented pressurization dewatering process of the present invention can form a synergistic closed loop with the front-end synergistic cell disruption and composite conditioning system to achieve the effect of deep sludge reduction.

[0052] To verify the synergistic effect of the municipal sludge reduction and treatment method of the present invention in terms of process feasibility and scenario adaptability, Example 1 was compared with Comparative Examples 1 to 4. The core indicators, such as SCOD leaching rate, moisture content after dewatering / drying, and sludge dry basis increment rate, were measured using industry standard testing methods for municipal sludge treatment. A 97% moisture content wet sludge was used as the energy consumption calculation benchmark. All test results are summarized in the table below: detection indicators Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 SCOD dissolution rate 81.7 22.3 41.6 80.9 81.5 Moisture content of the dehydrated mud cake 38.2 67.4 58.3 59.7 62.8 Moisture content of stabilized sludge after drying 19.4 19.5 19.3 19.6 19.4 sludge specific resistance 2.1×10¹² 5.8×10¹² 4.5×10¹² 3.9×10¹² 4.2×10¹² Sludge dry basis increment rate 6.2 6.1 6.2 44.8 6.2 pH value of mud cake 7.2 7.2 7.2 12.4 7.2 Overall energy consumption throughout the process 122 218 187 206 209 As shown in the table above, the SCOD dissolution rate of Example 1 remained above 75%, while the SCOD dissolution rates of Comparative Example 1 (biological enzyme only) and Comparative Example 2 (ultrasound only) dropped significantly to 22.3% and 41.6%, respectively. This demonstrates that the synergistic cell wall disruption system of ultrasonic pre-dissociation, microwave irradiation, and composite biological enzymes is the core of breaking down cell walls and releasing bound water. Compared to single physical / biochemical cell wall disruption, it achieves dual optimization of cell wall disruption efficiency and energy consumption. Comparative Example 3 used traditional lime + FeCl3 inorganic conditioner. Although the cell wall disruption effect was similar to that of this invention, the sludge dry basis increment rate was as high as 44.8%, completely offsetting the volume reduction effect. Moreover, the pH value of the sludge cake reached 12.4, which is strongly alkaline, hindering subsequent resource utilization. In contrast, the sludge dry basis increment rate of the modified attapulgite-CPAM composite conditioner system of this invention was only 3.15%~10.3%, the sludge cake was neutral, and there was no secondary pollution. At the same time, the constructed rigid skeleton structure significantly reduced the sludge specific resistance and improved dewatering performance. Comparative Example 4 used conventional plate and frame filter press. Although its cell-wall breaking and conditioning processes were comparable to those of this invention (SCOD dissolution rate 81.5%), the constant pressure (1.5 MPa) and non-segmented dewatering method failed to achieve deep removal of bound water. The moisture content of the dewatered sludge cake increased to 62.8%, far exceeding that of the embodiment of this invention. In contrast, the layered high-pressure segmented pressurization process of this invention forms a synergistic closed loop with the front-end cell-wall breaking and conditioning system, removing different forms of water step by step, breaking through the lower limit of moisture content in traditional mechanical dewatering and achieving deep volume reduction. The energy consumption of the comparative examples increased significantly to 187~218 kW·h / ton of wet sludge. The core reason is that this invention significantly reduces the heat energy demand of the subsequent drying process by releasing bound water through synergistic cell-wall breaking, optimizing dewatering performance through composite conditioning, and reducing moisture content through segmented high pressure. Simultaneously, it utilizes the low-calorific-value waste heat from the wastewater treatment plant for drying, eliminating the need for high-grade energy consumption, resulting in a significant reduction in overall energy consumption compared to traditional methods.

[0053] In summary, the municipal sludge reduction and disposal method of the present invention achieves deep reduction and harmless disposal of municipal sludge through the synergistic process of cell wall breaking, compound conditioning, layered high-pressure dewatering, and low-calorific-value drying. It solves the pain points of difficult removal of intracellular bound water, secondary pollution of chemicals, and low dewatering efficiency, and can be adapted to municipal sludge scenarios with different organic matter contents.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for reducing and disposing of municipal sludge, characterized by, The steps of this method are as follows: S100. Sludge thickening and conditioning: The municipal sludge to be treated is concentrated by gravity for 8-12 hours and conditioned to a moisture content of 95%-98% to obtain concentrated and conditioned sludge. S200, Synergistic cell wall breaking pretreatment: The concentrated and conditioned sludge is transported to the pretreatment reactor, the sludge temperature is adjusted to 40-60℃, compound biological enzymes are added, and after mixing, low-frequency ultrasonic pre-dissociation treatment is performed first, followed by microwave irradiation synergistic enzymatic cell wall breaking treatment to obtain cell wall broken sludge. S300, Composite Conditioning: The cell wall broken sludge is transported to the conditioning tank, modified attapulgite is added, and the mixture is stirred for 5-15 minutes. The rigid framework structure is constructed by adsorbing dissolved extracellular polymers and heavy metal ions through the pores. Then, cationic polyacrylamide is added, and the mixture is stirred for 3-10 minutes to carry out flocculation conditioning reaction to obtain conditioning sludge. S400, Layered High-Pressure Deep Dewatering: The conditioned sludge is subjected to layered high-pressure deep dewatering using a segmented pressurization method. The pressing pressure is 2.0-4.0 MPa, and the holding time is 20-60 minutes, to obtain a sludge cake with a moisture content of ≤50%. In the S400, the staged pressurization method is as follows: Hold the pressure at 0.5MPa-1MPa for 5-10 minutes to drain the free water from the sludge; Pressurize to 2MPa-3MPa and hold for 8-15 minutes to drain interstitial water from the flocs. The pressure is increased to 4MPa-8MPa and held for 15min-30min to deeply remove the bound water released from the cell, thus completing the high-pressure deep dehydration. S500, Low-calorific-value drying and stabilization: The sludge cake is transported to a low-temperature drying system and dried at low temperature using a low-grade heat source to obtain stabilized sludge.

2. A method for the disposal of municipal sludge reduction according to claim 1, characterized in that, In the S200, the compound bio-enzyme is composed of cellulase, neutral protease, α-amylase and lipase in a mass ratio of 3:2:1:1, and the dosage of the compound bio-enzyme is 0.05%-0.5% of the dry weight of the concentrated and conditioned sludge.

3. The method for reducing and disposing of municipal sludge according to claim 1, characterized in that, In S200, the parameters for low-frequency ultrasonic pre-dissociation processing are: ultrasonic frequency 15kHz-30kHz, adjustable power 0W-20W, and processing time 3min-8min. The parameters for the microwave irradiation-assisted enzymatic hydrolysis cell disruption treatment are as follows: microwave irradiation frequency of 915MHz or 2450MHz, microwave irradiation power density of 0.2W / mL-0.5W / mL, and treatment time of 10min-20min.

4. The method for reducing and disposing of municipal sludge according to claim 1, characterized in that, In S300, the modified attapulgite is attapulgite that has been synergistically modified by acid activation treatment and organic modification treatment, and the dosage of the modified attapulgite is 3%-10% of the dry weight of the cell wall broken sludge; The cationic polyacrylamide has an ionicity of 30%-60%, a molecular weight of 8 million to 12 million, and is added at a rate of 0.1%-0.5% of the dry weight of the cell-wall broken sludge.

5. A method for reducing and disposing of municipal sludge according to claim 4, characterized in that, The acid activation treatment is as follows: take natural attapulgite clay, crush it through a 200-mesh sieve, add a hydrochloric acid solution with a concentration of 1mol / L-2mol / L, control the solid-liquid ratio to be 1:5-1:10, stir and activate it for 2-4 hours under a water bath at 60℃-80℃, filter it, wash it with deionized water until the filtrate is neutral, and dry it at 105℃ to obtain acid-activated attapulgite clay.

6. A method for reducing and disposing of municipal sludge according to claim 4, characterized in that, The organic modification process is as follows: acid-activated attapulgite is added to anhydrous ethanol, the solid-liquid ratio is controlled at 1:8-1:12, 1%-3% of silane coupling agent KH550 is added, the pH of the system is adjusted to 4-5 with glacial acetic acid, and the reaction is stirred for 2-3 hours under a 60℃ water bath. After filtration, it is washed 2-3 times with anhydrous ethanol and dried at 105℃ to obtain modified attapulgite.

7. A method for reducing and disposing of municipal sludge according to claim 1, characterized in that, In the S300, the parameters for the flocculation conditioning reaction are: stirring at 200r / min-300r / min for 2min-3min, then stirring at 50r / min-80r / min for 5min-10min, and then letting it stand for 10min-15min after stirring.

8. A method for reducing and disposing of municipal sludge according to claim 1, characterized in that, In the S500, the low-grade heat source is one or more of the following: waste heat from anaerobic digestion biogas combustion in sewage treatment plants, waste heat from biochemical effluent, and waste heat from sludge incineration flue gas. The low-temperature drying temperature is 60℃-80℃, the drying time is 60min-100min, and the moisture content of the stabilized sludge after low-temperature drying is ≤30%.

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