Sludge dewatering agent and sludge dewatering method
By sequentially adding the sludge dewatering agent kit, the extracellular polymer is broken down and a magnesium ammonium phosphate crystal framework is generated, which solves the problems of high dosage of chemicals and secondary pollution in sludge dewatering, and achieves low moisture content and high efficiency dewatering.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Filing Date
- 2026-04-22
- Publication Date
- 2026-07-10
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Abstract
Description
Technical Field
[0001] This invention relates to the field of sludge treatment technology, specifically to a sludge dewatering agent and a sludge dewatering method. Background Technology
[0002] With the rapid development of the wastewater treatment industry, the treatment and disposal of excess activated sludge and anaerobic digestion sludge has become a crucial step. Sludge contains a large number of extracellular polymers, which form a highly hydrated micro-network that encapsulates a significant amount of bound water within the sludge flocs, making it difficult for conventional mechanical dewatering equipment to achieve the desired low moisture content. To improve the dewatering performance of sludge, pre-conditioning is usually required before mechanical filter press.
[0003] Current sludge conditioning processes primarily release bound water by adding chemical oxidants to break down extracellular polymers, or by adding physically inert materials such as lime and fly ash as a supporting framework to construct internal seepage channels. While adding external framework materials can solve the problem of sludge deformation under pressure and improve permeability, it significantly increases the total dry weight of the dewatered sludge cake. This increased cake volume not only raises subsequent transportation and landfill costs but also dilutes the organic matter content of the sludge itself, which is detrimental to subsequent incineration and resource utilization.
[0004] Furthermore, during the chemical oxidation process to break down extracellular polymers in sludge, the rupture of sludge cells not only releases internal water but also releases large amounts of endogenous nitrogen and phosphorus elements that were originally sealed within the cells into the liquid phase. In the subsequent filter press process, this filtrate, rich in high concentrations of free nitrogen and phosphorus, is directly returned to the upstream biological treatment system of the wastewater treatment plant. This high-concentration side-flow return liquid severely impacts the nitrogen and phosphorus removal load of the water treatment system, leading to effluent quality exceeding standards and causing secondary pollution problems.
[0005] Therefore, how to achieve efficient cell disruption of sludge extracellular polymers while reducing the amount of external inert skeleton material added to control sludge increment, and effectively fix and utilize the free nitrogen and phosphorus elements released by cell disruption, is a pressing technical problem that needs to be solved in the field of sludge treatment and dewatering. Summary of the Invention
[0006] To address the shortcomings of existing technologies, this invention provides a sludge dewatering agent and a sludge dewatering method, which solves the problems of high difficulty in breaking down extracellular polymers, high agent dosage, and high moisture content in the dewatered sludge cake in existing sludge dewatering processes. It also addresses the problem that the phosphorus and nitrogen elements rich in sludge are not effectively utilized and instead cause secondary pollution.
[0007] To address the above problems, the present invention provides the following technical solution: In a first aspect, the present invention provides a sludge dewatering agent, which adopts the following technical solution: A sludge dewatering agent is a composition kit consisting of reagents A, B, C, and D, which are packaged independently. Reagent A comprises sodium percarbonate powder and tetraacetylethylenediamine powder in a mass ratio of 3.0:1 to 4.0:1. Reagent B comprises a magnesium sulfate solution with a mass fraction of 10% to 15%. Reagent C comprises a polyferric sulfate solution with a mass fraction of 10% to 12%. Reagent D comprises a cationic polyacrylamide solution with a mass fraction of 0.1% to 0.3%.
[0008] By adopting the above technical solution, and using a kit composed of independently packaged reagents A, B, C, and D, which are added sequentially during use to initiate a cascade reaction, synergistic dehydration and in-situ generation of an inorganic framework from endogenous substances are achieved. The specific reaction process and mechanism are as follows: Sodium percarbonate in reagent A dissolves in water to form sodium carbonate and hydrogen peroxide. The hydrogen peroxide then reacts with tetraacetylethylenediamine to generate peracetic acid, which has oxidizing properties. Through the synergistic effect of peracetic acid and hydrogen peroxide, the extracellular polymeric structure of the sludge is oxidized and broken down, converting bound water into free water and releasing intracellular free phosphate and ammonia nitrogen. During this process, the carbonate ions produced by the hydrolysis of sodium percarbonate increase the pH of the system, thus providing a slightly alkaline environment for subsequent reactions. The relevant reaction equation is: 2Na₂CO₃·3H₂O₂ → 2Na₂CO₃ + 3H₂O₂.
[0009] Subsequently, under the established slightly alkaline environment, reagent B (magnesium sulfate) added dissociates into magnesium ions. These dissociated magnesium ions directly react with the free phosphate and ammonia nitrogen just released from the sludge liquid phase, crystallizing in situ to form magnesium ammonium phosphate crystals. The resulting crystals are distributed within the sludge flocs, acting as an inorganic rigid framework, which not only reduces the compressibility of the sludge but also constructs permeability channels within it. The relevant reaction formula is: Mg 2+ +NH4 + +PO4 3- +6H2O→MgNH4PO4·6H2O↓.
[0010] Next, reagent C is added, in which polyferric sulfate undergoes a hydrolysis reaction to form a polynuclear hydroxyl complex. This hydrolysis process releases hydrogen ions, which neutralize the residual alkalinity from the previous reaction, restoring the system to a neutral range. Simultaneously, thanks to the sieve-sweeping effect of polyferric sulfate, unreacted microcrystals and free phosphate ions in the system are coagulated and precipitated, preventing potential phosphorus release and wastewater pollution problems later on.
[0011] Finally, relying on the charge neutralization and adsorption bridging effect of the cationic polyacrylamide in reagent D, the skeleton and destabilized microparticles generated in the previous steps are aggregated into large flocs, thereby accelerating the solid-liquid separation process.
[0012] Preferably, the sodium percarbonate powder in reagent A has a mass fraction of 95%, and the tetraacetylethylenediamine powder has a mass fraction of 98%; the mass ratio of sodium percarbonate powder to tetraacetylethylenediamine powder in reagent A is 3.5:1.0.
[0013] By adopting the above technical solution, controlling the purity and mass ratio of oxidant and activator, a stable yield of peracetic acid can be maintained, and reagent residues can be reduced to a certain extent to prevent negative impacts on subsequent biochemical treatment units.
[0014] Preferably, the preparation method of reagent A is as follows: sodium percarbonate powder and tetraacetylethylenediamine powder are added to a double cone mixer and dry-mixed at 15 rpm for 20 min at room temperature, controlling the moisture content of the mixed powder to be ≤1.0% by mass; the preparation method of reagent B is as follows: magnesium sulfate heptahydrate is added to deionized water with a conductivity ≤5 μS / cm, stirred and dissolved at 25°C for 30 min, allowed to stand for aging for 10 min, and then filtered through a 5 μm pore size filter membrane to obtain a clear solution; the preparation method of reagent C is as follows: polyferric sulfate stock solution is diluted with deionized water, stirred slowly at 30 rpm for 15 min at 25°C, and allowed to stand for defoaming for 5 min; the preparation method of reagent D is as follows: cationic polyacrylamide particles are slowly added to a shear rate of 200 s. -1 The solution was added to a high-speed dispersion system of deionized water and stirred continuously at 30 rpm for 60 min until completely dissolved. The solution was then allowed to stand and mature for 30 min to obtain the final product.
[0015] By adopting the above technical solutions and controlling the moisture content of reagent A, the active ingredient can be prevented from absorbing moisture and becoming inactive during storage. Reagent B undergoes aging and filtration to remove insoluble impurities, preventing these impurities from interfering with subsequent crystallization purity. For reagent D, the introduction of a step-by-step dissolution process (i.e., high-speed shear dispersion combined with low-speed aging) effectively avoids the risk of polymer molecular chain breakage, enabling the agent to dissolve homogeneously and thus maintaining the bridging and flocculation activity of the macromolecular agent.
[0016] Secondly, the present invention provides a sludge dewatering method, which adopts the following technical solution: A sludge dewatering method using the aforementioned sludge dewatering agent, the method comprising the following sequential steps: S1. Place the sludge into the reactor, turn on the stirring device, and add the reagent A while stirring to react, thereby destroying the extracellular polymers of the sludge and releasing endogenous phosphorus and nitrogen. S2. Add reagent B to the system treated in S1, adjust the stirring speed and continue stirring to promote in-situ crystallization to form a framework; S3. Add the reagent C to the system after S2 treatment, adjust the stirring speed and continue stirring to neutralize the alkalinity of the system and coagulate and capture small crystals. S4. Add reagent D to the system treated in S3, adjust the stirring speed and stir slowly to promote the formation of flocs; S5. The sludge after S4 conditioning is pumped into a filter press for mechanical dewatering and pressure filtration, and the dewatered cake is obtained by maintaining pressure and unloading.
[0017] By adopting the above technical solution and limiting the order of reagent addition, the sludge conditioning process is essentially divided into several alternating physicochemical stages: oxidation release, in-situ skeleton formation, acid-base neutralization coagulation, and bridging maturation. This sequential control method cuts off possible side reactions between different agents, reduces ineffective consumption, and enables good synergy between chemical conditioning and subsequent physical pressure filtration separation processes.
[0018] Preferably, in S1 to S4, the effective dosage range of each reagent, based on its pure dry matter and the oven-dry sludge mass, is as follows: reagent A is 2%–6%; reagent B is 1%–3%; reagent C is 2%–6%; and reagent D is 0.1%–0.3%. More preferably, the effective dosage of each reagent is: reagent A is 4%, reagent B is 2%, reagent C is 4%, and reagent D is 0.2%.
[0019] By adopting the above technical solutions, the dosage of various agents can be limited to a specific range, which can control the consumption of agents while maintaining the effect of sludge cell disruption and skeleton formation, thereby reducing the process operating cost and limiting the increase of sludge cake.
[0020] Preferably, the specific process parameters for S1 to S4 are as follows: In S1, stirring is performed at a speed of 150–250 rpm for 15–25 min; in S2, the stirring speed is adjusted to 80–120 rpm, and stirring continues for 10–20 min; in S3, the stirring speed is adjusted to 100–200 rpm, and stirring continues for 8–12 min; in S4, the stirring speed is adjusted to 30–80 rpm, and slow stirring is performed for 3–8 min. In S5, the mechanical pressure filtration and dewatering is carried out using a plate and frame filter press, with the pressing pressure controlled at 0.8–1.2 MPa and the holding time controlled at 25–35 min.
[0021] By adopting the above technical solution, corresponding hydraulic stirring conditions were matched to the reaction rates of different stages. Specifically, the high shear force in stage S1 helps to accelerate the oxidation and cell disruption process. When entering stages S2 and S3, the reduction in rotation speed provides a suitable flow environment for crystal nucleation and particle collision and aggregation. In stage S4, the use of slow stirring is mainly to prevent the already formed flocs from breaking apart, thereby maintaining the permeability of the filter cake in the filter press process.
[0022] Preferably, in S1, the sludge is municipal residual activated sludge or high-phosphorus anaerobic digestion sludge; when the sludge is high-phosphorus anaerobic digestion sludge, the total phosphorus content based on the sludge's oven-dry weight is ≥35g / kg.
[0023] By adopting the above technical solution, the endogenous phosphorus in the sludge matrix, which is rich in phosphorus, can be directly converted into the inorganic framework required for dewatering, thereby reducing the dependence on external dewatering auxiliary materials.
[0024] This invention provides a sludge dewatering agent and a sludge dewatering method. It has the following beneficial effects: 1. This invention utilizes the reaction of sodium percarbonate and tetraacetylethylenediamine to produce peracetic acid, which disrupts the extracellular polymers of sludge, releasing the phosphate and ammonia nitrogen trapped within the sludge into the liquid phase by sequentially adding reagents A and B. Subsequently, magnesium sulfate is introduced into a slightly alkaline system, causing it to crystallize in situ with the released phosphorus and nitrogen to form magnesium ammonium phosphate inorganic particles. This process directly transforms the endogenous substances of the sludge into a rigid support structure that improves sludge dewatering performance, reduces the compressibility of the sludge, and improves its permeability. It also reduces the moisture content of the filter cake without introducing large amounts of external physical conditioners, thus controlling the total amount of sludge after dewatering.
[0025] 2. In this invention, polyferric sulfate is added as reagent C after the crystallization step. Its hydrolysis reaction consumes excess hydroxide ions in the system, restoring the slightly alkaline environment caused by the hydrolysis of sodium percarbonate to a neutral range. Simultaneously, the polynuclear complex generated by the hydrolysis of polyferric sulfate can, through coagulation, trap and precipitate tiny magnesium ammonium phosphate particles that have not fully participated in crystallization, as well as residual free phosphate ions. This combination of chemical reaction and coagulation effectively traps phosphorus in the sludge system, preventing secondary pollution caused by the return of phosphorus-rich filtrate to the upstream of the wastewater treatment system.
[0026] 3. This invention employs a modular composition and specifies the sequential addition steps of each reagent, dividing the sludge chemical conditioning process into four stages: oxidation release, in-situ crystallization, acid-base adjustment, and polymer bridging. The reaction products and environmental changes of the previous stage can directly serve as the initiation conditions for the subsequent stage. For example, the substrate released by reagent A after cell disruption and the increased alkalinity perfectly meet the crystallization requirements of reagent B. This sequential workflow avoids ineffective side reactions caused by the simultaneous mixing of different types of reagents, improving the system's utilization rate of added reagents. Attached Figure Description
[0027] Figure 1 The figure shows the test results of the nutrient release law of sludge liquid phase in the embodiments of the present invention; wherein, (a) is the evolution trend of SCOD concentration in the untreated blank group, comparative example 4 group and example 1 group during the stirring reaction process, and (b) is the cumulative dynamic change of orthophosphate concentration in the supernatant of the untreated blank group, comparative example 4 group and example 1 group. Figure 2 This is a graph showing the in-situ pH evolution of the sludge reaction system in an embodiment of the present invention. Figure 3 This is a verification diagram showing the correspondence between the determination of liquid phase materials in the reaction system and their macroscopic dehydration performance in the embodiments of the present invention; wherein, (a) is a comparison diagram of the changes in phosphorus and nitrogen concentrations in Example 1, Comparative Example 2 and Comparative Example 4 during the reaction period; (b) is a graph showing the decay of capillary water absorption time (CST) of sludge during the same period in Example 1, Comparative Example 2 and Comparative Example 4. Figure 4 This is a comparison chart of the deep dehydration efficiency and compressibility resistance characteristics of the embodiments of the present invention; wherein, (a) is a comparison chart of the sludge cake biscuit index after high pressure pressing treatment in each group; (b) is a scatter plot of the specific resistance parameter reflecting the water leakage performance of each group; (c) is a comparison chart of the compressibility coefficients of each group, which reflect the ability of sludge to resist deformation.
[0028] Figure 5 This is a graph showing the determination of water quality parameters associated with the derived filtrate after deep desalination in an embodiment of the present invention; wherein, a) is a graph showing the test results of total phosphorus concentration in the filtrate under pressure in each operation sequence; (b) is a graph showing the test results of the total residual iron dissolved in the filtrate under pressure in each operation sequence; (c) is a data fluctuation graph of the turbidity of the filtrate under each operation sequence. Detailed Implementation
[0029] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.
[0030] The municipal excess activated sludge was taken from the secondary sedimentation tank of the municipal wastewater treatment plant, with a solids content of 2.5% to 4.5%, an initial pH of 6.8 to 7.4, a total phosphorus content of 15 g / kg to 25 g / kg based on the oven-dry weight of the sludge, and a total ammonia nitrogen content of 30 g / kg to 50 g / kg based on the oven-dry weight of the sludge.
[0031] Sodium percarbonate, CAS No. 15630-89-4, industrial grade solid dry powder, mass fraction ≥95.0%.
[0032] Tetraacetylethylenediamine, CAS No. 10543-57-4, industrial grade solid powder, mass fraction ≥98.0%.
[0033] Magnesium sulfate heptahydrate, CAS number 10034-99-8, industrial grade crystalline granules, mass fraction ≥98.0%.
[0034] Polyferric sulfate, CAS number 10028-22-5, is an inorganic polymer with the general molecular formula [Fe2(OH)]. n (SO4) m ] p It has an alkalinity of 1.0 to 1.6, a total iron mass fraction of 11.0% to 13.0%, and a liquid density of 1.35 g / cm³ at 20°C. 3 Up to 1.45 g / cm 3 .
[0035] Cationic polyacrylamide, CAS number 69418-26-4, is a linear polymer formed by the random copolymerization of acrylamide and cationic monomers, with a main chain structure of -[CH2-CH(CONH2)]. n - The side chain contains quaternary ammonium groups, the cationicity is 20 mol% to 40 mol%, and the viscosity-average molecular weight is 8.0 × 10⁻⁶. 6 g / mol up to 12.0 × 10 6 g / mol.
[0036] Preparation Example 1: This preparation example provides a method for preparing a sludge dewatering agent, comprising the following steps: Sodium percarbonate powder (95.0% by mass) and tetraacetylatedrethylenediamine powder (98.0% by mass) are added to a double cone mixer at a mass ratio of 3.0:1.0. The mixture is dry-mixed at 15 rpm for 20 min at room temperature. The moisture content of the mixed powder is ≤1.0%. The mixture is then sealed and stored in a dark place to obtain reagent A. Magnesium sulfate heptahydrate is added to deionized water with a conductivity ≤5 μS / cm and stirred at 25°C for 30 min to prepare a 10.0% magnesium sulfate solution. After standing for 10 min, the solution is filtered through a 5 μm pore size filter to obtain a clear solution to obtain reagent B. A 11.0% polyferric sulfate stock solution is diluted with deionized water and stirred slowly at 30 rpm for 15 min at 25°C. After standing for 5 min to remove foam, a 10.0% polyferric sulfate solution is obtained to obtain reagent C. Cationic polyacrylamide particles were slowly added at a shear rate of 200 s. - In a deionized water high-speed dispersion system, after the addition is complete, the mixture is stirred continuously at 30 rpm for 60 min until completely dissolved. After standing for 30 min, a cationic polyacrylamide solution with a mass fraction of 0.10% is prepared and prepared for use within 24 h to obtain reagent D.
[0037] Preparation Example 2: This preparation example provides a method for preparing a sludge dewatering agent, comprising the following steps: Sodium percarbonate powder (95.0% by mass) and tetraacetylethylenediamine powder (98.0% by mass) are added to a double cone mixer at a mass ratio of 3.5:1.0. The mixture is dry-mixed at 15 rpm for 20 min at room temperature. The moisture content of the mixed powder is ≤1.0%. The mixture is then sealed and stored in the dark to obtain reagent A. Magnesium sulfate heptahydrate is added to deionized water with a conductivity ≤5 μS / cm and stirred at 25°C for 30 min to prepare a 12.5% magnesium sulfate solution. After standing for 10 min, the solution is filtered through a 5 μm pore size filter to obtain a clear solution, which is then used to obtain reagent B. A 12.0% polyferric sulfate stock solution is diluted with deionized water and stirred slowly at 30 rpm for 15 min at 25°C. After standing for 5 min to remove foam, an 11.0% polyferric sulfate solution is obtained, which is then used to obtain reagent C. Cationic polyacrylamide particles were slowly added at a shear rate of 200 s. - In a deionized water high-speed dispersion system, after the addition is complete, the mixture is stirred continuously at 30 rpm for 60 min until completely dissolved. After standing for 30 min, a cationic polyacrylamide solution with a mass fraction of 0.20% is prepared and prepared for use within 24 h to obtain reagent D.
[0038] Preparation Example 3: This preparation example provides a method for preparing a sludge dewatering agent, comprising the following steps: Sodium percarbonate powder (95.0% by mass) and tetraacetylatedrethylenediamine powder (98.0% by mass) are added to a double cone mixer at a mass ratio of 4.0:1.0. The mixture is dry-mixed at 15 rpm for 20 min at room temperature. The moisture content of the mixed powder is ≤1.0%. The mixture is then sealed and stored in the dark to obtain reagent A. Magnesium sulfate heptahydrate is added to deionized water with a conductivity ≤5 μS / cm and stirred at 25°C for 30 min to prepare a magnesium sulfate solution with a mass fraction of 15.0%. After standing for 10 min, the solution is filtered through a 5 μm filter membrane to obtain a clear solution to obtain reagent B. A polyferric sulfate stock solution with a total iron mass fraction of 13.0% is diluted with deionized water and stirred slowly at 30 rpm for 15 min at 25°C. After standing for 5 min to remove foam, a polyferric sulfate solution with a mass fraction of 12.0% is obtained to obtain reagent C. Cationic polyacrylamide particles were slowly added at a shear rate of 200 s. - In a deionized water high-speed dispersion system, after the addition is complete, the mixture is stirred continuously at 30 rpm for 60 min until completely dissolved. After standing for 30 min, a cationic polyacrylamide solution with a mass fraction of 0.30% is prepared and prepared for use within 24 h to obtain reagent D.
[0039] Example 1: This embodiment provides a sludge dewatering method using a sludge dewatering agent, including the following steps: (1) Take municipal residual activated sludge and put it into the reactor. Turn on the stirring device and stir at a speed of 200 rpm. While stirring, add reagent A obtained in Preparation Example 2. The effective dosage of reagent A is 4.0% of the dry sludge mass. Continue stirring at a speed of 200 rpm for 20 min. (2) Add reagent B obtained in Preparation Example 2 to the above reaction system. The effective dosage of reagent B pure dry matter is 2.0% of the dry sludge mass. Adjust the stirring speed to 100 rpm and continue stirring for 15 min to promote in-situ crystallization. (3) Add reagent C obtained in Preparation Example 2 to the above reaction system. The effective dosage of reagent C in pure dry matter is 4.0% of the dry sludge mass. Adjust the stirring speed to 150 rpm and continue stirring for 10 min. (4) Add reagent D obtained in Preparation Example 2 to the above reaction system. The effective dosage of reagent D pure dry matter is 0.20% of the dry sludge mass. Adjust the stirring speed to 50 rpm and stir slowly for 5 min to promote the formation and maturation of flocs. (5) The sludge after conditioning is pumped into a plate and frame filter press and mechanically dewatered under a pressing pressure of 1.2 MPa for 30 min. The dewatered cake is then discharged.
[0040] Example 2: This embodiment provides a sludge dewatering method using a sludge dewatering agent, including the following steps: (1) Take municipal residual activated sludge and put it into the reactor. Turn on the stirring device and stir at 150 rpm. While stirring, add reagent A obtained in Preparation Example 1. The effective dosage of reagent A is 2.0% of the dry sludge mass. Continue stirring at 150 rpm for 15 min. (2) Add reagent B obtained in Preparation Example 1 to the above reaction system. The effective dosage of reagent B pure dry matter is 1.0% of the dry sludge mass. Adjust the stirring speed to 80 rpm and continue stirring for 10 min to promote in-situ crystallization. (3) Add reagent C obtained in Preparation Example 1 to the above reaction system. The effective dosage of reagent C in pure dry matter is 2.0% of the dry sludge mass. Adjust the stirring speed to 100 rpm and continue stirring for 8 min. (4) Add reagent D obtained in Preparation Example 1 to the above reaction system. The effective dosage of reagent D pure dry matter is 0.10% of the dry sludge mass. Adjust the stirring speed to 30 rpm and stir slowly for 3 min to promote the formation and maturation of flocs. (5) The sludge after conditioning is pumped into a plate and frame filter press and mechanically dewatered under a pressing pressure of 0.8 MPa for 25 min. The dewatered cake is then discharged.
[0041] Example 3: This embodiment provides a sludge dewatering method using a sludge dewatering agent, including the following steps: (1) Take municipal residual activated sludge into the reactor, turn on the stirring device and stir at a speed of 250 rpm. While stirring, add reagent A obtained in Preparation Example 3. The effective dosage of reagent A is 6.0% of the dry sludge mass. Continue stirring at a speed of 250 rpm for 25 min. (2) Add reagent B obtained in Preparation Example 3 to the above reaction system. The effective dosage of reagent B in pure dry matter is 3.0% of the dry sludge mass. Adjust the stirring speed to 120 rpm and continue stirring for 20 min to promote in-situ crystallization. (3) Add reagent C obtained in Preparation Example 3 to the above reaction system. The effective dosage of reagent C in pure dry matter is 6.0% of the dry sludge mass. Adjust the stirring speed to 200 rpm and continue stirring for 12 min. (4) Add reagent D obtained in Preparation Example 3 to the above reaction system. The effective dosage of reagent D pure dry matter is 0.30% of the dry sludge mass. Adjust the stirring speed to 80 rpm and stir slowly for 8 min to promote the formation and maturation of flocs. (5) The sludge after conditioning is pumped into a plate and frame filter press and mechanically dewatered under a pressing pressure of 1.2 MPa for 35 min. The dewatered cake is then discharged.
[0042] Example 4: This embodiment provides a sludge dewatering method using a sludge dewatering agent, including the following steps: (1) Take high-phosphorus anaerobic digestion sludge (solid content of 3.5%, total phosphorus content of 35 g / kg based on the dry weight of sludge, initial pH of 7.2) and put it into the reactor. Turn on the stirring device and stir at 200 rpm. While stirring, add reagent A obtained in Preparation Example 2. The effective dosage of reagent A is 4.0% of the dry weight of sludge. Continue stirring at 200 rpm for 20 min. (2) Add reagent B obtained in Preparation Example 2 to the above reaction system. The effective dosage of reagent B pure dry matter is 2.0% of the dry sludge mass. Adjust the stirring speed to 100 rpm and continue stirring for 15 min to promote in-situ crystallization. (3) Add reagent C obtained in Preparation Example 2 to the above reaction system. The effective dosage of reagent C in pure dry matter is 4.0% of the dry sludge mass. Adjust the stirring speed to 150 rpm and continue stirring for 10 min. (4) Add reagent D obtained in Preparation Example 2 to the above reaction system. The effective dosage of reagent D pure dry matter is 0.20% of the dry sludge mass. Adjust the stirring speed to 50 rpm and stir slowly for 5 min to promote the formation and maturation of flocs. (5) The sludge after conditioning is pumped into a plate and frame filter press and mechanically dewatered under a pressing pressure of 1.0 MPa for 30 min. The dewatered cake is then discharged.
[0043] Comparative Example 1: The difference from Example 1 is that reagent A (a mixture of sodium percarbonate and tetraacetylethylenediamine) was not added in step (1), while the rest were the same.
[0044] The effect of contrast is highlighted: Due to the absence of reagent A, the extracellular polymeric substances (EPS) in the sludge could not be effectively destroyed to prevent cell rupture, thus preventing the release of solid phosphorus and ammonia nitrogen from the sludge into the liquid phase. Simultaneously, the system lacked the large amount of carbonate ions generated from the hydrolysis of sodium percarbonate, failing to naturally raise the system to a weakly alkaline environment of pH 8.5-9.5. This resulted in the subsequent addition of reagent B lacking both sufficient free phosphorus and ammonia nitrogen reactants and alkalinity support, hindering the in-situ crystallization reaction to build the skeletal framework. Ultimately, this led to difficulty in releasing water from the cells, extremely poor pressure filtration dewatering, and a significantly high moisture content in the sludge cake.
[0045] Comparative Example 2: The difference from Example 1 is that reagent B (magnesium sulfate solution) was not added in step (2), but the rest are the same.
[0046] The effect of contrast is highlighted: Due to the absence of reagent B, although a large amount of free phosphorus and ammonia nitrogen were released into the system after reagent A completed the cell disruption and energy release and provided a perfectly weakly alkaline environment, the lack of a magnesium source prevented in-situ crystallization of magnesium ammonium phosphate (struvite). Therefore, the sludge failed to form hard struvite crystals, lacking a "rigid framework" for support during dewatering. This resulted in the sludge cake being easily compacted by inorganic polymers and pressing pressure, leading to compressible deformation and clogging of water channels. This severely reduced the filtration rate and overall sludge dewatering efficiency, and the filtrate often contained extremely high concentrations of free phosphorus and ammonia nitrogen.
[0047] Comparative Example 3: The difference from Example 1 is that reagent C (polyferric sulfate solution) was not added in step (3), but all other steps are the same.
[0048] The effect of contrast is highlighted: Due to the absence of reagent C, the system lacks the charge neutralization and trapping effect of inorganic polymers on fine colloids, preventing the effective aggregation of microparticles. More critically, the lack of iron ions prevents the dissipation of residual alkalinity (i.e., the inability to neutralize the high pH left by reagent A), hindering the system's gradual return to near-neutral pH. Simultaneously, unreacted residual phosphate cannot be effectively captured and fixed by iron salts, potentially leading to complex colloidal interference in the struvite generated at the front end and resulting in a high total phosphorus content in the filtrate after pressure filtration and dehydration, which easily causes secondary pollution.
[0049] Comparative Example 4: Compared with Example 1, the difference is that reagent A in step (1) is replaced with an equal effective mass of conventional hydrogen peroxide, while the rest are the same.
[0050] The effect of contrast is highlighted: While hydrogen peroxide also possesses oxidizing properties, it cannot generate carbonate ions simultaneously with hydrogen peroxide hydrolysis, unlike sodium percarbonate. Due to the lack of a pH buffer and driving force for carbonate formation, the system cannot maintain the optimal weakly alkaline environment of 8.5-9.5. Consequently, even with the addition of reagent B (magnesium sulfate), the Mg:P:N ratio within the system struggles to cross the homogeneous nucleation window to form dense struvite crystals. Because of the lack of an in-situ generated "rigid framework," the sludge is prone to plastic deformation during subsequent filtration, hindering water drainage. This results in significantly lower pressing and dewatering efficiency and sludge cake dryness compared to Example 1.
[0051] Test Example 1: Test on the energy release and nutrient release patterns of sludge cell wall disruption: This test case is mainly used to verify the degree of damage and disintegration of sludge extracellular polymeric substances (EPS) and cell wall structure under actual operating conditions, and to explore the release pattern of carbon-containing organic matter and phosphorus-containing nutrients from inside the cells through transmembrane migration into the liquid aqueous phase.
[0052] 1. Take the same batch of municipal waste activated sludge (solids content 3.0%, initial pH neutral) and divide it into three equal volumes. Define them as the untreated blank group, comparative example group 4, and example 1 group, respectively.
[0053] 2. The three sludge samples were transferred to three reactors equipped with mechanical stirring devices, and the stirring was started and kept at a constant speed of 200 rpm. No chemical reagents were added to the untreated blank group; conventional hydrogen peroxide was added to Comparative Example 4 at 4.0% of the oven-dry sludge mass; and the prepared reagent A mixture was added to Example 1 at 4.0% of the oven-dry sludge mass.
[0054] 3. After the reaction system starts timing, at 0 min, 5 min, 10 min, 15 min and 20 min of the reaction process, 50 mL of mud-water mixture is taken from 5 cm below the liquid surface of each reactor using a pipette.
[0055] 4. Immediately transfer the extracted mud-water mixture to a centrifuge tube and centrifuge at 4000 rpm for 10 minutes in a high-speed centrifuge. Then, extract the supernatant and pass it through a glass fiber filter membrane with a pore size of 0.45 μm to retain any small free suspended solids that have not settled in the liquid phase.
[0056] 5. The dissolved chemical oxygen demand (SCOD) concentration in the filtered supernatant was determined using the potassium dichromate digestion method, while the orthophosphate (PO4³⁺) concentration was determined using the ammonium molybdate spectrophotometric colorimetric method. - The mass concentration of -P was measured in three parallel measurements and the arithmetic mean of the data was recorded.
[0057] Table 1. Record of SCOD and orthophosphate concentrations in the supernatant of sludge from each treatment group over time:
[0058] Figure 1 This is a graph showing the test results of the nutrient release pattern in the sludge liquid phase of this invention. Figure 1 Part (a) shows the evolution trend of SCOD concentration in the untreated blank group, the four comparative groups with conventional hydrogen peroxide, and the first example group with reagent A during the stirring reaction process; Part (b) shows the concentration of orthophosphate (PO4) in the supernatant of the three corresponding systems under the same conditions. 3- The cumulative dynamic changes in the release concentration of -P.
[0059] According to the data in Table 1, under natural stirring without any chemical conditioning, the SCOD and orthophosphate concentrations in the supernatant of municipal waste activated sludge showed only small, irregular fluctuations throughout the 20-minute monitoring period. This reflects that the dense natural extracellular polymer network and the complete physical barrier of the cell membrane can effectively block the internal organic components and nutrients. Traditional advanced oxidation processes generally rely on bulk-phase forced cell disruption by hydroxyl radicals. When hydrogen peroxide was added to the system to replace the original formulation materials (corresponding to ratio 4), the SCOD in the liquid phase slowly increased to 895.6 mg / L after 20 minutes of reaction, and the release of orthophosphate was limited to the range of 61.3 mg / L. Conventional hydrogen peroxide has a limited decomposition rate under low catalysis and near-neutral conditions and insufficient penetration into the structurally solidified polysaccharide matrix, directly restricting the dissolution and desorption of sludge cell endoplasm. The Example 1 treatment group, operating under benchmark conditions, exhibited nonlinear amplified mass transfer kinetics after its unique dry compound reagent came into contact with the liquid phase. Within just 5 minutes of the reaction, free SCOD exceeded the 800 mg / L threshold, and by 20 minutes, it surpassed the 2100 mg / L limit. At this point, a large amount of gel-bound water, along with organic matter, was expelled from the cells into the liquid phase, resulting in a corresponding orthophosphate accumulation of up to 165.2 mg / L. This generational advantage in release flux stems not only from the chain segment shearing effect of peracetic acid and a series of highly reactive oxides generated after sodium percarbonate and tetraacetylethylenediamine are activated by water on the EPS polymer backbone, but also, more fundamentally, from the rapid in-situ alkalinity spike triggered by the abundant carbonate ions released by sodium percarbonate at the sludge micro-interface. The temporarily elevated pH in the liquid-phase microenvironment caused deprotonation and swelling of the tightly cross-linked peptidoglycan chains within the cell wall, which, combined with targeted bombardment by large free radical groups, led to the complete disintegration and inactivation of the cell wall and cell membrane. The concentrated emergence of free phosphate and organic nitrogen products accumulated in the supernatant by the forced release perfectly matches the material conservation logic of the system's transition from a homogeneous colloid to a heterogeneous system. The phosphate components released in the suspension at high concentrations happen to constitute the necessary precursor resources for subsequent combination with magnesium-iron-based agents to form a stable struvite hard crystalline layer, completely eliminating the process obstacle of loose mesh structure caused by the lack of reaction substrate when simply adding inorganic salts for conditioning in the past.
[0060] Test Example 2: In-situ pH self-evolution and buffering capacity test of the reaction system: This test is used to examine the spontaneous regulatory ability of the conditioner on the hydrochemical microenvironment of the sludge system at different addition stages, and to verify whether each reactant can achieve the entire process of alkalinity enhancement, nucleation, and neutralization without relying on external acid-base regulators.
[0061] 1. Municipal residual activated sludge samples from the same period were obtained as test objects. The original natural temperature and initial pH of about 7.1 were maintained. The samples were divided into three portions with fixed volume and placed in a reactor equipped with an online pH monitoring probe and a digital display speed control stirrer. These three groups were labeled as Test Group 1 of Example, Test Group 3 of Comparative Example, and Test Group 4 of Comparative Example.
[0062] 2. Start the mixer and set the speed. Add reagent A obtained from the preparation example to the corresponding preparation group in Example 1 and Comparative Example 3, and add an equal proportion of conventional hydrogen peroxide to the comparative example 4, and record the pH measured potential data from 0 to 20 minutes.
[0063] 3. Adjust the rotation speed to enter the reaction cycle of step (2). Input the corresponding preparation example or comparative example reagent B into the three systems respectively and continue the reaction for 15 min. Record the pH reading at fixed intervals and observe the consumption of free base caused by the nucleation reaction.
[0064] 4. Proceed to step (3) Reagent C addition stage. Polyferric sulfate solution was injected into Example 1 group and Comparative Example 4 group, while no solution was added to Comparative Example 3 group. The reaction continued for 10 minutes, and the pH adjustment range of the system was monitored.
[0065] 5. All three groups were injected with cationic polyacrylamide and stirred gently for 5 minutes until the liquid phase data no longer showed a trend of change, at which point recording was terminated. The online probe stored data at specific reaction nodes to obtain a table of average values for each group's continuous time series.
[0066] Table 2. Record of in-situ pH monitoring data in the liquid phase throughout the entire sludge conditioning process:
[0067] Figure 2 This is an observation curve of the in-situ pH evolution law of the sludge reaction system of the present invention. The figure systematically records the benchmark comparison curve of Example 1 group under the complete process procedure, Comparative Example 3 group is used to indicate the deviation pattern in the case of missing iron salt coagulant, and Comparative Example 4 group is used to characterize the environment in which effective water quality parameters cannot be constructed after single hydrogen peroxide cell disruption.
[0068] According to the data in Table 2, the initial potential of the sludge samples entering the reactor site remained stable in the neutral range. In Example 1, after the introduction of the prepared sodium percarbonate and tetraacetylethylenediamine components during the conditioning initiation stage, the pH detected in the liquid phase showed a steep increase in a short period of time, entering the region of 8.6 to 9.2 within 20 minutes. During this stage, the free carbonate ions released during the hydrolysis of the reagents formed a locally high-concentration alkaline buffer zone at the extracellular polymer breakdown interface. Observation of Comparative Example 4, which used a hydrogen peroxide system, revealed that due to the lack of an alkali release pathway and the weakly acidic nature of hydrogen peroxide itself, the liquid phase gradually acidified and dropped to around 6.5. In actual production, this directly deprives the chemical potential support required for subsequent free components to induce in-situ struvite crystallization. Conventional engineering projects often require the forced addition of caustic alkali solution dosing pumps for passive compensation in response to this phenomenon, increasing the energy consumption of the process. This invention utilizes the highly dissociated salt structure generated by the reaction of the reagents to self-construct the micro-chemical microenvironment. With the introduction of reagent B, some hydroxide ions are consumed to meet the crystallization requirements, as evidenced by a very slight decrease in pH after 25 minutes in Example 1. This type of artificially constructed, highly reactive weakly alkaline space presents objective engineering risks of equipment corrosion and excessive liquid phase concentration at the reaction end. How to restore the treatment system to a suitable discharge state is a key control point in the entire process.
[0069] The monitoring chromatograms showed a dramatic divergence in the terminal responses of different systems after reagent C was introduced at 35 minutes. In Example 1, due to the hydrolysis and dissociation of the ferric bridging bonds in polyferric sulfate, a large number of coordinating protons were released, directly neutralizing the remaining free alkali in the early stage, resulting in a sharp drop in the curve, which returned to around 6.8 during the conditioning and maturation stage. In Comparative Example 3, which did not have the iron salt system, the final pH remained at a highly alkaline state above 8.8. From an engineering perspective, this mechanism, which utilizes inorganic polymer coagulants to both neutralize and capture impurities and simultaneously act as an acid-base counterbalancing agent throughout the process, eliminates the risk of the crystallization network being impacted by strong acids and bases. The final pH degradation is completed through the hydrolysis of metal ions, and the water quality of the final precipitated dehydrated cake aquifer and the effluent from the stripped pipe all meet the influent load requirements of the plant's internal and external treatment structures.
[0070] Test Example 3: Liquid Phase Phosphorus and Nitrogen Consumption and In-situ Crystallization Macroscopic Dehydration Response Test: This test is based on the mass evolution mechanism within the chemical system. By tracking the difference in concentration consumption of key phosphorus and nitrogen ions in the liquid phase before and after the crystallization reaction, as well as the change in sludge capillary water absorption time, it demonstrates the formation process of the inorganic framework and its direct intervention effect on physical dewatering performance without relying on microscopic characterization instruments.
[0071] 1. Collect the sludge mixture from the same batch of municipal dewatering equipment, bring it to a constant volume, and measure and record the original capillary time of water absorption (CST) of the raw sludge. Divide the sludge into three equal test samples, designated as Test Group 1 (Example 1), Test Group 2 (without magnesium source for crystallization), and Test Group 4 (with pretreatment to replace the chemical for cell disruption).
[0072] 2. Place the three test groups in a stirred reactor and start the stirring speed at 200 rpm. Mix the Example 1 group and the Comparative Example 2 group at a ratio of 4.0% by oven-dry weight and add the mixed powder reagent A prepared in the previous step. Add hydrogen peroxide stock solution to the Comparative Example 4 group in an equal ratio. Maintain the initial cell wall disruption reaction for 20 min to prepare and collect the liquid phase precursor.
[0073] 3. After the cell disruption stage, stop the machine for 30 seconds and take the first intermediate node sample. Extract a portion of the mud-water mixture to determine the current CST value, and perform high-speed centrifugation and 0.45μm membrane processing on the sampled phase to obtain the supernatant sample to be tested. Measure the mass concentration of free orthophosphate and ammonia nitrogen at this time.
[0074] 4. Resume stirring and reduce the speed to 100 rpm. Add the pre-prepared magnesium sulfate solution reagent B to Example 1 and Comparative Example 4 to initiate the crystallization induction stage. In Comparative Example 2, only constant speed stirring is maintained for the same amount of time without introducing external reagents. The reaction duration is 15 min.
[0075] 5. At the end of the crystallization induction period, a second endpoint sampling and measurement was performed. Each group of materials was processed according to the same centrifugation and membrane treatment procedure, and the residual orthophosphate and ammonia nitrogen concentrations of the final supernatant were measured. At the same time, the final CST of the entire sludge sample was measured and recorded.
[0076] Table 3. Test data on liquid phase ion dissipation and capillary water absorption time response during the crystallization and dehydration stage:
[0077] Figure 3 This is a verification diagram showing the correspondence between the determination of liquid phase materials in the reaction system of this invention and their macroscopic dehydration performance. Figure 3 The subplot (a) shows the characteristics of the depletion of the liquid sediment concentration. The solid line represents the sharp drop in phosphorus and nitrogen concentrations in Example 1 at a specific reaction cycle node. In contrast, the dashed line representing Comparative Example 2 and the dotted line representing Comparative Example 4 show no change in trend. Subplot (b) tracks and depicts the measured decay state of the sludge capillary filtration barrier parameter CST that occurred simultaneously in the three test groups.
[0078] According to the data in Table 3, after reagent A completed the pre-treatment stage of disrupting cell structure, the liquid phase of the system in Example 1 accumulated 151.6 mg / L of orthophosphate and 78.5 mg / L of free ammonia nitrogen. This large amount of free colloidal substances mixed with intracellular macromolecular fragments, increasing the viscosity of the suspension and causing the measured sludge CST to spike to 126 s. This indicated a more severe tendency for water binding compared to the original sludge state, and even viscous clumping could be observed on the liquid surface during on-site sampling. Subsequent treatment demonstrated the ability of the reaction components to reconstruct the water quality. Once the pre-mixed magnesium salts were introduced into the sludge-water environment with pH support, the triggered ion dissipation effect was extremely sharp. The absolute phosphorus consumption in the test supernatant reached 113.4 mg / L, while the simultaneous nitrogen reduction remained stable in the range of 52.4 mg / L, translating to a molar ratio of reacted substances that remained stable within the range of approximately 0.98. This ratio closely follows the theoretical metric standard of phosphorus and nitrogen ratios required for the formation of orthorhombic struvite, confirming that the exact destination of free nutrients is to combine and form a solid-phase inorganic crystalline complex.
[0079] What kind of interference does this phase deflection based on the crystallization and solidification of dissolved substances cause to the final performance of the project? A clear judgment can be made from the deviation of macroscopic parameters. With the precipitation of liquid ions, the CST index of Example 1 group simultaneously plummeted to 32s, exceeding the natural filtration baseline of the un-introduced raw mud. Comparative Example 2, lacking a magnesium source, could not promote phosphorus and nitrogen precipitation, and the system stagnated in a state of excess colloid, with the measured CST remaining in the inferior range of 118s, unable to break through. Comparative Example 4, which used conventional hydrogen peroxide to intervene in the destructive process, experienced a slight decrease in concentration after the addition of magnesium salts, but was limited by the inability to construct a local weakly alkaline environment in the early stages, resulting in a severe barrier to co-precipitation conversion. The study of the correlation results of these widely different indicators confirms that the magnesium microcrystals generated in situ directly participate in and interfere with the establishment of the physical structure of sludge before dewatering. A large number of small, rigid, hard particles are essentially replaced by the traditional high-compression ratio organic mesh in the dewatering filter press, thus opening up hydrophobic gaps that are not squeezed and closed for the discharge of filtered water.
[0080] Test Example 4: Comparative Test of Dewatering Efficiency and Compressibility of Mud Cake: This test aims to examine the influence of the microstructure of the material induced by the synergistic effect of the components on the macroscopic dewatering parameters of the sludge, and to verify the ability of the filter cake to resist deformation and blockage of the water passage by applying external mechanical pressure.
[0081] 1. Raw sludge from the municipal dewatering machine room's sludge storage tank was extracted during the same period, and its initial moisture content was measured to be 97.8%. The obtained sludge was divided into five equal parts, which were designated as the test group of Example 1 and the test groups of Comparative Examples 1 to 4, respectively.
[0082] 2. Perform the above five groups of mud samples independently according to the corresponding dosing procedures. Example 1 group followed the full reagent dosing process; Comparative Example 1 intervened by missing reagent A; Comparative Example 2 skipped the reagent B introduction step; Comparative Example 3 omitted reagent C addition; Comparative Example 4 used full amount of hydrogen peroxide to replace the original process reagent A (i.e., the mixture of sodium percarbonate and tetraacetylethylenediamine). Stop stirring after all the set reaction and curing periods were completed.
[0083] 3. Extract 100 mL of each processed sludge-water mixture sample and transfer it into a Buchner funnel lined with qualitative filter paper. Perform vacuum filtration at a constant vacuum of 0.05 MPa, simultaneously recording the volume of filtrate precipitated at each time point using a graduated cylinder and stopwatch, and calculate the corresponding sludge specific resistance (SRF) value.
[0084] 4. Adjust the vacuum setting valve of the filtration system, and measure and record the filter specific resistance parameters under pressure gradients of 0.02MPa, 0.04MPa, 0.06MPa and 0.08MPa respectively. Extract the specific resistance data measured under different pressure bands and perform logarithmic linear fitting to obtain the macroscopic compressibility coefficient used to characterize the rigidity of the sludge skeleton.
[0085] 5. Collect the wet initial cake from each group after basic filtration, transfer it to a specially designed small mechanical closed filter press, apply a full mechanical pressing load of 1.2 MPa equivalent to the standard working conditions of an industrial plate and frame filter press, and maintain the pressure for 30 minutes. After depressurization, peel off the final cake, place it in a 105℃ automatic forced-air constant temperature oven to dry to constant weight, weigh and calculate the final moisture content.
[0086] Table 4. Results of Depth Dewatering Performance and Macroscopic Compressibility of Mud Cake:
[0087] Figure 4 This is a comparison chart verifying the deep dehydration efficiency and compressibility resistance characteristics of this invention. Figure 4 It includes three test subclasses arranged in a vertical array. (a) Part records the range of mud cake biscuit index obtained after high pressure pressing at the end of each working condition; (b) Part shows the scatter trend of the specific resistance parameter reflecting the smoothness of water leakage in the low pressure domain; (c) Part depicts the deviation of the coefficient reflecting the system's resistance to deformation calculated from different gradient pressure differences. The horizontal axis region is juxtaposed with all of Example 1 and the sequences of Comparative Examples 1 to 4.
[0088] According to the data in Table 4, the fluid state constructed by different process combinations directly interfered with the output quality of the subsequent mechanical dewatering process. The pretreatment group containing the dewatering reagent A was fed into the pressing tank without breaking the biochemical cell wall protection mechanism, resulting in most of the adsorbed water and intracellular water being shielded within the solid-phase coating system. The measured sludge specific resistance remained at 15.63 × 10⁻⁶. 12 The water content of the sludge cake obtained under a high m / kg concentration and a strong pressure of 1.2 MPa remained at 82.1%. In actual engineering operations, when encountering such poorly broken-cell sludge, even if the operator forcibly increases the feed pump pressure of the filter press, the result is only a layer of gelatinous wet sludge adhering to the filter cloth surface. In contrast to this inaction, Comparative Example 2 used sufficient cell-breaking material but intentionally withheld magnesium-based agents. The exposed organic gel macromolecules lost the opportunity to react and form crystalline supports. Due to the lack of hard mineral particle support in the system, the macroscopic compressibility coefficient measured during the filtration stage reached 0.96. This high compressibility characteristic reveals that the flexible sludge clumps will immediately undergo inelastic collapse and volume shrinkage when subjected to ballast stress. The original gaps and channels existing between the loose flocs are tightly blocked by the adhesive substances generated by these compression deformations, blocking the channels for the internally expelled fluid to flow out, causing its water content to remain hovering in the ineffective deep-deposition range of 75.6%.
[0089] Example 1's integrated intervention approach provides a distinctly different model of material stress resistance mechanics. Struvite particles, derived from crystalline deposits in the sludge, are extensively embedded in the three-dimensional framework constructed from residual extracellular polymers, along with the consumption of free phosphorus and nitrogen. This robust framework effectively dilutes and bears the load transmitted from the pressurized panel, causing the compressibility coefficient of the entire sludge system to plummet to a low of 0.54. The robust, non-collapse-prone particle gaps ensure continuous and unobstructed outward leakage of the filter press filtrate during periods of heavy load, resulting in a near-extreme SRF value of 1.18 × 10⁻⁶. 12 The moisture content of the dry sludge cake after dewatering was as low as 57.3%, with a concentration of m / kg. Solutions that replaced or reduced auxiliary agents also showed limitations. Comparative Example 4, which used hydrogen peroxide forcibly to replace the sludge, failed to successfully drive the spontaneous construction of an alkaline reaction tank and thus failed to complete the shell construction as scheduled. Not only was the moisture content of the dewatered sludge high, but the sludge cake also exhibited severe compaction symptoms similar to Comparative Example 2. Comparative Example 3, which removed iron salts during the final stage of coagulation, showed some moderate improvement in filtration, maintaining some compressibility of the sludge cake. However, some tiny colloidal particles scattered within the system did not receive multiple charge neutralization and encapsulation from the iron-based macromolecules, thus penetrating the filter and remaining in the filter channel, increasing liquid phase resistance. This approach, which uses the construction of an inorganic crystalline skeleton with deformation resistance to counteract the external pressure and lock-in effect, fundamentally eliminates the engineering deadlock of the traditional treatment model where the sludge layer becomes increasingly less viscous under pressure.
[0090] Test Example 5: Comparative Test of Filtration Liquid Water Quality and Secondary Pollution Control: This test is used to track the residual pollution load in the liquid phase precipitated after sludge undergoes high-intensity mechanical dewatering, and to analyze the closed-loop interception efficiency of the coagulation and sedimentation system in the reaction network for pollutants based on water quality test data.
[0091] 1. Collect the seepage filtrate from the lower inlet of each station in Test Example 4 where the mechanical closed-loop filter press dewatering operation was completed. Transfer the discrete reflux water samples extracted from Test Group 1 of Example 1 and Test Groups 1 to 4 of Comparative Examples to PTFE sampling bottles that have been pre-acid-washed and rinsed with deionized water for storage.
[0092] 2. Let the dark-colored filtrate in the sampling bottle stand for 5 minutes to simulate the hydraulic retention stage of the buffer tank in actual factory operation. Then, use a glass pipette to slowly extract the coarse water sample in the middle layer of the container that has not been vigorously stirred and transfer it into a cuvette. Measure and record the average turbidity of the high-pressure dewatering water of the current group using a portable turbidimeter.
[0093] 3. Take another 10 mL of the filtrate sample from each of the above groups after standing and dispense it into a dedicated digestion tube. Add potassium persulfate oxidant to each tube, seal it, and place it in a high-pressure digester. Digest it continuously at 120℃ for 30 min to ensure that the suspended particles and inorganic and some organic compounds containing phosphorus and iron in the filtrate are completely reversed into free monomeric ions.
[0094] 4. After the digestion tubes have cooled to room temperature, quantitative colorimetric analysis of total phosphorus (TP) concentration in each group of solutions is performed using ammonium molybdate spectrophotometry. The absorbance parameters at specific wavelengths are recorded and converted into standard mass concentrations.
[0095] 5. Take another portion of the untreated filter press liquid, filter it through filter paper to remove large pieces of suspended residue, add hydroxylamine hydrochloride solution to completely reduce the residual ferric iron in the liquid phase to ferrous iron, then add o-phenanthroline colorimetric reagent and buffer salt to mask interference, and send it into a visible light spectrophotometer to measure absorbance to assess the residual amount of free total iron in the system.
[0096] Table 5. Core Measurement Record of Water Quality Status of Pressed Filtrate from Each Treatment System:
[0097] Figure 5 This is a graph showing the water quality parameters associated with the derived filtrate after deep desalination treatment according to the present invention. Figure 5The aqueous phase data is extracted from top to bottom into three perspectives: (a) Figure reflects the total phosphorus enrichment scale inside the water sample discharged to the downstream sewage collection network after dewatering and pressure filtration; (b) Figure calculates the total iron dissolved in the same batch of water; (c) Figure depicts the data fluctuation of fluid turbidity, a physical scale that intuitively measures the clarification of the filtered material, with each broken line scatter point anchored on the horizontal axis node of different operation sequences depicted at the bottom.
[0098] According to the data in Table 5, the filter press water squeezed out after high-pressure delayed dewatering of municipal sludge often carries an extremely high concentration of dissolved pollutants. If this reflux liquid, which has a high tendency to cause blackening and odor, is directly returned to the upstream structures of the wastewater treatment plant, it is very likely to cause systemic exceedances of influent water quality and interfere with the biochemical operation of activated sludge. Examining the performance of Comparative Example 2 in this stage, due to the lack of necessary reagent components in the system to form a crystal framework and participate in physical precipitation, the massive amount of intracellular contents and nutrients strongly released by the upstream chemical oxidation and cell wall disruption can only be mixed in the liquid phase in a free dissolved form, resulting in a high-risk load of 136.52 mg / L in the filter press effluent. The traditional hydrogen peroxide reagent used in Comparative Example 4 is limited by the low-order reaction rate in the normal, slightly neutral sludge microenvironment, and cannot provide the necessary hydroxide ion ratio source for the formation of various metal crystal nuclei. Most of the phosphate ions that fail to form anhydrous heavy minerals also leak into the filtrate system, as evidenced by the total phosphorus data in the aqueous phase still exceeding the upper limit of 62.81 mg / L. While the struvite microcrystals induced in specific areas of the system certainly solidify a considerable proportion of the derived inorganic macromolecules, which actuator is responsible for the final interception and closure of the large number of dispersed micro / nano-scale crystalline particles and the broken, inactive, and unagglomerated EPS flocs? The extremely abnormal turbidity indicators in Comparative Example 3 directly reveal a missing link in the underlying operational logic. The treatment group, which lacked the intervention of end-of-pipe polymerized iron salts for overall coordination, showed extremely turbid water samples with a concentration as high as 285.6 NTU, accompanied by a suspended sludge phase. The free and tiny colloidal total phosphorus in the water that was not trapped overflowed with this turbid water flow and rebounded to the warning level of 45.28 mg / L.
[0099] The formulation of the fully constructed pharmaceutical preparations implemented in Example 1 seamlessly fills the gaps in the defense against outward diffusion of microscopic matter at the detachment end. During the conditioning and maturation stage, the inorganic polymeric iron salt introduced into the system utilizes metal-coordinated protons to complete the overall acid-base neutralization and degradation of the liquid pool. Simultaneously, a large number of accompanying polynuclear phase iron-based hydroxyl complexes rapidly undergo hydrolysis and copolymerization reactions within the macroscopic liquid flow space. These ferrite three-dimensional cross-linked networks carrying high positive charge density act like dense, contractile traps, not only subjecting microscale inorganic crystal particles and scattered suspended matter to forced electrical compression and bridging sweeping, but also locking the extremely small amounts of dissolved phosphorus remaining from previous reaction stages that have not yet been fully incorporated into the lattice voids within the large, tough floc core by forming insoluble iron phosphate precipitates. Protected by this comprehensive solid-liquid stripping effect, the total phosphorus in the filter press effluent of Example 1 was ultimately suppressed to a minimum value of 2.34 mg / L, and the turbidity of the discharged fluid plummeted to 18.2 NTU, a level suitable for floor flushing and reuse. Simultaneously, the concentration of volatile iron detected at the liquid end remained stable within the safety margin of 1.52 mg / L, confirming that the externally pumped metal reagent had undergone a complete phase transition, transforming into multiphase solid sediment and detaching from the dewatering mother liquor along with the sludge cake. This closed-loop operation effectively prevented secondary pollution from derived heavy metals. This simultaneous improvement of both water and land-based indicators completely changed the previously unbalanced discharge characteristics of similar desludge equipment.
[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A sludge dewatering agent, characterized in that, The sludge dewatering agent is a composition kit consisting of reagents A, B, C, and D, which are packaged independently. The reagent A contains sodium percarbonate powder and tetraacetylethylenediamine powder in a mass ratio of 3.0:1 to 4.0:
1. The reagent A is used to oxidize and break down the sludge to release endogenous available phosphorus and nitrogen, and to use the hydrolysis products to provide a slightly alkaline environment for the subsequent system. The reagent B contains a magnesium sulfate solution with a mass fraction of 10% to 15%. The reagent B is used to generate struvite inorganic rigid crystalline framework in situ under the slightly alkaline environment by utilizing the released endogenous phosphorus and nitrogen. The reagent C contains a 10%–12% polyferric sulfate solution. The reagent C is used to neutralize the slightly alkaline environment of the preceding reaction by producing acid through hydrolysis, and to coagulate and trap unreacted microcrystals and free phosphorus in the system. The reagent D contains a cationic polyacrylamide solution with a mass fraction of 0.1% to 0.3%, and the reagent D is used to promote the formation and maturation of flocs in the sludge system.
2. The sludge dewatering agent according to claim 1, characterized in that, The mass fraction of sodium percarbonate powder in reagent A is 95%, and the mass fraction of tetraacetylethylenediamine powder is 98%. Preferably, the mass ratio of sodium percarbonate powder to tetraacetylethylenediamine powder in reagent A is 3.5:1.
0.
3. The sludge dewatering agent according to claim 1, characterized in that, Reagents A, B, and C are prepared by the following method: The preparation method of reagent A is as follows: sodium percarbonate powder and tetraacetylethylenediamine powder are added to a double cone mixer and dry-mixed at 15 rpm for 20 min at room temperature, controlling the moisture content of the mixed powder to be ≤1.0% by mass. The preparation method of reagent B is as follows: magnesium sulfate heptahydrate is added to deionized water with a conductivity of ≤5μS / cm, stirred and dissolved at 25℃ for 30min, allowed to stand and age for 10min, and then filtered through a filter membrane with a pore size of 5μm to obtain a clear solution. The preparation method of reagent C is as follows: dilute the polyferric sulfate stock solution with deionized water, stir slowly at 30 rpm for 15 min at 25℃, and let stand for 5 min to remove foam.
4. The sludge dewatering agent according to claim 1, characterized in that, The reagent D is prepared by the following method: Cationic polyacrylamide particles were slowly added at a shear rate of 200 s. -1 The solution was added to a high-speed dispersion system of deionized water and stirred continuously at 30 rpm for 60 min until completely dissolved. The solution was then allowed to stand and mature for 30 min to obtain the final product.
5. A sludge dewatering method, characterized in that, Using the sludge dewatering agent as described in any one of claims 1-4, the method comprises the following sequential steps: S1. Place the sludge into the reactor, turn on the stirring device, and add the reagent A while stirring to react, thereby destroying the extracellular polymers of the sludge and releasing endogenous phosphorus and nitrogen. S2. Add reagent B to the system treated in S1, adjust the stirring speed and continue stirring to promote in-situ crystallization to form a framework; S3. Add the reagent C to the system after S2 treatment, adjust the stirring speed and continue stirring to neutralize the alkalinity of the system and coagulate and capture small crystals. S4. Add reagent D to the system treated in S3, adjust the stirring speed and stir slowly to promote the formation of flocs; S5. The sludge after S4 conditioning is pumped into a filter press for mechanical dewatering and pressure filtration, and the dewatered cake is obtained by maintaining pressure and unloading.
6. The sludge dewatering method according to claim 5, characterized in that, For S1 to S4, the effective dosage range of each reagent based on its pure dry matter and the oven-dry sludge mass is as follows: Reagent A: 2%–6%; Reagent B: 1%–3%; Reagent C: 2%–6%; The reagent D is 0.1% to 0.3%.
7. The sludge dewatering method according to claim 5, characterized in that, The preferred effective dosage of each reagent is: 4% for reagent A, 2% for reagent B, 4% for reagent C, and 0.2% for reagent D.
8. A sludge dewatering method according to claim 5, characterized in that, The specific process parameters for S1 to S4 are as follows: In S1, stir at a speed of 150-250 rpm for 15-25 minutes; In S2, adjust the stirring speed to 80-120 rpm and continue stirring for 10-20 minutes. In S3, adjust the stirring speed to 100-200 rpm and continue stirring for 8-12 minutes; In S4, adjust the stirring speed to 30-80 rpm and stir gently for 3-8 minutes.
9. A sludge dewatering method according to claim 5, characterized in that, In S5, the mechanical pressure filtration and dewatering is carried out using a plate and frame filter press, with the pressing pressure controlled at 0.8 to 1.2 MPa and the holding time controlled at 25 to 35 min.
10. A sludge dewatering method according to claim 5, characterized in that, In S1, the sludge is municipal surplus activated sludge or high-phosphorus anaerobic digestion sludge; When the sludge is high-phosphorus anaerobic digestion sludge, the total phosphorus content based on the oven-dry weight of the sludge is ≥35g / kg.