A composite conditioner, its preparation method, and its application in sludge dewatering.

Abstract

This invention relates to the field of sludge treatment technology, specifically to a composite conditioner, its preparation method, and its application in sludge dewatering. The invention provides a composite conditioner comprising the following components: industrial solid waste, biochar, and an alkaline conditioner; the industrial solid waste includes desulfurized gypsum, fly ash, steel slag, and mineral slag. This invention simultaneously achieves efficient dewatering and harmless stabilization of sludge, resulting in significant sludge volume reduction and high safety, laying a solid foundation for subsequent resource utilization and demonstrating the dual environmental and economic advantages of treating waste with waste. This invention utilizes industrial and agricultural solid waste to synergistically construct a green conditioner, with widely available and low-cost raw materials, avoiding reliance on polymeric flocculants and high-quality chemicals, achieving waste-to-pollution treatment, promoting the high-value utilization of solid waste, and conforming to the application scenarios of solid waste resource utilization and green sludge volume reduction.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, specifically to a composite conditioner, its preparation method, and its application in sludge dewatering. Background Technology

[0002] With the continuous development of urbanization and industrialization, the production of sludge is constantly increasing, and its safe and efficient disposal has become a significant challenge in the field of environmental protection. Currently, deep dewatering of sludge is a crucial step in achieving volume reduction and subsequent resource utilization. However, the inherent characteristics of sludge, such as its stable colloidal structure, high bound water content, and complex composition, present significant technical bottlenecks in its dewatering process. Existing mainstream technologies often struggle to balance dewatering efficiency, operating costs, and environmental impact, making the development of new, highly efficient dewatering technologies an urgent need.

[0003] Focusing on the widely used but bottlenecked field of chemical conditioning and dewatering, existing technologies have significant limitations: First, traditional conditioning agents mostly rely on single components or simple physical compounds, lacking synergistic effects among components, resulting in limited dewatering efficiency. Furthermore, achieving a certain dewatering effect often requires large doses of agents, causing significant sludge volume increase, which is detrimental to subsequent resource utilization. Second, their mechanisms of action mainly focus on charge neutralization and / or flocculation, failing to construct a stable framework structure within the sludge that combines high mechanical strength with durable permeable channels. This leads to easy compaction of the filter cake and decreased permeability during high-pressure dewatering. In addition, most solutions lack sufficient ability to solidify pollutants such as heavy metals in the sludge, posing secondary environmental risks. Technologies employing high-cost special materials or complex processes are difficult to scale up due to insufficient economic viability and operability. Therefore, there is an urgent need for a novel conditioning agent that can simultaneously achieve deep dewatering, structural enhancement, and pollutant stabilization through multi-component, multi-mechanism synergy. Summary of the Invention

[0004] This invention provides a composite conditioner, its preparation method, and its application in sludge dewatering to solve the above-mentioned problems.

[0005] In a first aspect, the present invention provides a composite conditioner comprising the following components: industrial solid waste, biochar, and an alkaline conditioner; The industrial solid waste includes desulfurized gypsum, fly ash, steel slag, and mineral slag.

[0006] In one optional embodiment, the mass ratio of the industrial solid waste, biochar, and alkaline regulator is (40-60):(20-40):(10-20).

[0007] It should be noted that the industrial solid waste components, serving as the framework support and active mineral source for the conditioner, are selected from industrial by-products such as desulfurized gypsum, fly ash, steel slag, and blast furnace slag. These materials possess excellent physical structural properties, providing the necessary granular support framework during sludge dewatering, constructing a rigid sludge cake structure with good filtration performance, improving the sludge floc structure, reducing sludge specific resistance, maintaining sludge permeability during pressure filtration, providing a water passage for free water, and effectively promoting water release. Simultaneously, the active SiO2, CaO, and Al2O3 components contained within can activate gelation activity in an alkaline environment, effectively reducing the leaching risk of heavy metals in the sludge; steel slag provides an active Ca source and alkaline environment, promoting colloidal breakdown and hydration reactions; fly ash provides a spherical granular framework and pore support; the pozzolanic active components in blast furnace slag and fly ash undergo secondary hydration in the system, improving the framework density; and the Ca in desulfurized gypsum... 2+ With SO4 2- It participates in the reaction and, under the stimulation of alkaline regulators, generates ettringite needle-like crystals in situ inside the sludge colloid, enhancing the drainage channels.

[0008] It should be noted that the biochar component is a biochar material obtained by pyrolysis and carbonization of agricultural biomass such as rice husks and sawdust. It has characteristics such as large specific surface area and well-developed pore structure. Its surface contains carboxyl groups, hydroxyl groups and silicon-oxygen bonds, which have the ability to adsorb heavy metals and organic pollutants. It can also participate in the stability construction of the overall structure of the conditioner, which helps to form a denser and more stable floc skeleton during sludge dewatering. Through the pipeline effect and interlayer channel effect, it effectively promotes water release and sludge dewatering performance. In addition, the well-developed micropores of biochar can adsorb extracellular polymers (EPS) released by sludge under pressure, preventing EPS from clogging the drainage channels of industrial solid waste.

[0009] Under preferred conditions, the rice husk ash is prepared by calcining rice husks at 600–700℃ for 1.8–2.2 hours in a non-reactive atmosphere, followed by pulverizing. The sawdust ash is prepared by calcining sawdust at 600–700℃ for 1.8–2.2 hours in a non-reactive atmosphere, followed by pulverizing. The rice husk ash and sawdust ash are mixed at a mass ratio of (0.8–1.2):(0.8–1.2). The rice husk ash provides a rigid framework rich in amorphous SiO2 and reactive sites, while the sawdust ash provides a multi-level porous structure and surface functional groups. Together, they construct a composite structure of "framework support and pore channel drainage." Within this ratio range, the continuity and mechanical stability of the framework structure are ensured, while the connectivity and permeability of the pore structure are maintained, thereby achieving efficient water migration and multi-mechanism fixation of heavy metals in the sludge. When the ratio of any component deviates from this range, it will lead to structural imbalance, reducing dewatering performance and stabilization effect. The incineration holding time is controlled at 1.8-2.2 h to optimize its porous structure and reactivity, thereby obtaining a high content of amorphous silica and good pozzolanic activity. In one alternative embodiment, the alkalinity regulator comprises calcium oxide and calcium hydroxide; Optionally, the mass ratio of calcium oxide to calcium hydroxide is 1:(1-2).

[0010] It should be noted that the alkaline regulators, such as calcium oxide, calcium hydroxide, and magnesium oxide, are used to adjust the pH environment of the sludge-conditioner mixture system and to stimulate the reactivity of potential active mineral components in industrial solid waste, so that the conditioner can perform multiple functions such as flocculation, mineralization, and adsorption during the dewatering process. Each component has a synergistic cementing and dewatering conditioning effect, which can effectively destroy the colloidal structure of sludge, promote water leaching, improve sludge dewatering performance, and also has a certain heavy metal passivation ability.

[0011] In one optional embodiment, the mass ratio of the desulfurized gypsum, fly ash, steel slag and blast furnace slag is (20-30):(20-30):(20-30):(20-40).

[0012] It should be noted that this invention uses a multi-source solid waste (steel slag, slag, fly ash and desulfurization gypsum) in synergistic compounding with biochar and alkaline regulators. After activation by high-energy ball milling, a composite skeleton support system is cleverly constructed, which effectively improves the internal structure of sludge and highlights the synergistic integration of colloidal structure destruction and pollutant fixation. This not only improves the dewatering effect, but also has the value of heavy metal passivation, filtrate purification and sludge cake energy utilization. Steel slag is rich in active substances such as Ca and Fe, which quickly neutralize the colloidal charge of sludge, promote the aggregation of colloidal particles, destroy the colloidal structure of sludge, and build a skeletal support structure inside the sludge. The spherical microstructure of fly ash is conducive to the further formation of a spatial skeleton and reduces the specific resistance of sludge flocs. In addition, the chemical composition of slag and fly ash is mainly glassy SiO2 and Al2O3, which have potential cementing activity. Under alkaline activation, they participate in the hydration reaction, fill the pores of the skeleton formed by steel slag, and improve the structural density and mechanical stability. Desulfurization gypsum provides a sulfate environment, which can generate ettringite (AFt) in situ in the sludge system, forming a needle-like crystal structure, supporting the floc skeleton, increasing the free water removal rate, enhancing the structural stability of the sludge cake, and effectively consolidating heavy metal ions.

[0013] Secondly, the present invention also provides a method for preparing a composite conditioner, comprising the following steps: drying and mixing industrial solid waste, and adding biochar and an alkaline conditioner to obtain the composite conditioner.

[0014] In one alternative implementation, the mixing includes ball milling; Optionally, the ball mill is operated at a speed of 300-500 rpm for 20-40 minutes. It should be noted that after ball milling and activation, the composite conditioner can form a multi-level framework structure of CSH / CAH gel + AFt crystals + biochar channels in the sludge system, which significantly reduces the specific resistance of the sludge cake and increases the free water discharge rate.

[0015] In one alternative embodiment, the D50 particle size of the industrial solid waste after ball milling is less than or equal to 100µm.

[0016] Thirdly, the present invention also provides the application of the above-mentioned composite conditioner or the composite conditioner prepared by the above-mentioned preparation method in sludge dewatering.

[0017] In one optional embodiment, the application includes the following steps: mixing the composite conditioner with wet sludge in one step, adding auxiliary additives and mixing in another step, and then dewatering to obtain dewatered sludge.

[0018] In one optional embodiment, the amount of the composite conditioner added is 5wt%-10wt% of the dry weight of the sludge; In one optional embodiment, the amount of the auxiliary additive is 5wt%-10wt% of the compound conditioner; It should be noted that, depending on actual needs, auxiliary additives such as inorganic salt conditioners or inorganic polymeric flocculants can be added to promote floc formation, adjust particle size distribution, or improve dispersibility, thereby further enhancing the overall performance and applicability of the conditioner. The amount of the auxiliary additives added is 5%-9% of the composite conditioner, optionally 6%-8%.

[0019] In one alternative embodiment, the auxiliary additive includes at least one of polyferric chloride, polyferric sulfate, and polyacrylamide.

[0020] In one optional embodiment, the auxiliary additive is a compound of polyferric chloride (PAC) and polyacrylamide (PAM), wherein the amount of PAC added is 4%-5% of the compound conditioner and the amount of PAM added is 1%-2% of the compound conditioner, which is used to enhance flocculation sedimentation and improve the compressibility of filter cake.

[0021] In one optional embodiment, the mixing time is 10-20 min and the rotation speed is 200-500 r / min; In one optional embodiment, the secondary mixing time is 5-10 minutes and the temperature is 20-40°C; In one alternative embodiment, the dewatering process includes using one of a belt filter press, a plate and frame filter press, or a horizontal screw centrifuge.

[0022] The dewatering equipment can be a plate and frame filter press, which can be adapted to the continuous or intermittent dewatering operation requirements of different types of sludge. The sludge treated with the conditioner has a cake moisture content of 40% to 55%, and the concentration of heavy metal ions in the filtrate is reduced by 50% to 70% compared with untreated sludge.

[0023] In one optional embodiment, the specific application steps of the composite sludge dewatering conditioner are as follows: S1: Sludge feeding and initial conditioning agent addition.

[0024] Municipal or industrial sludge with a moisture content of 92%-98% is transported to a conditioning reactor. A composite conditioning agent containing industrial solid waste components, biochar components, and alkaline regulators is then added at a ratio of 5%-10% of the sludge's dry weight, with a preferred addition ratio of 6%-8%. This addition ratio effectively constructs a granular skeleton structure, disrupts the original colloidal floc structure in the sludge, significantly improves the sludge's dewatering performance, and simultaneously balances cost control and resource utilization efficiency.

[0025] S2: Stirring and mixing and adding auxiliary additives.

[0026] A motor-driven mechanical stirrer is used to mix the sludge at a speed of 200-500 r / min for an initial stirring time of 10-15 min. After the aforementioned conditioning agent components are fully mixed with the sludge, auxiliary additives (such as polyferric chloride, polyacrylamide, etc.) are added, and stirring continues for 5-10 min to ensure the flocculation reaction proceeds fully. The temperature of the conditioning reaction system is controlled at 20-40℃, preferably maintained at room temperature of 20-35℃ to avoid excessive energy consumption. The conditioned sludge samples can be tested for dewatering performance indicators such as capillary time to sink (CST) and sludge specific resistance (SRF) to verify the conditioning effect.

[0027] S3: Dehydration treatment.

[0028] The conditioned sludge is sent to a dewatering device for mechanical dewatering. The device is any one of a belt filter press, a plate and frame filter press, or a horizontal screw centrifuge. The plate and frame filter press preferably has a dewatering pressure of 1-2 MPa and a filtration time of 30-60 min. Finally, a dry sludge filter cake with a moisture content of 40%-55%, preferably not higher than 50%, is obtained, which helps in subsequent resource utilization.

[0029] S4: Filtrate recovery and detection and sludge cake resource utilization.

[0030] The filtrate generated during the dehydration process is collected and its heavy metal ion concentration and other pollutants are tested. It should meet the discharge limit requirements of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) to ensure the safety of discharge or reuse. The resulting filter cake can be used for the preparation of cement clinker, building bricks and other materials as needed to achieve the goal of synergistic treatment of sludge reduction, harmlessness and resource utilization.

[0031] Under optimal conditions, this composite conditioner has the following effects: it can effectively reduce the moisture content of sludge from 92%-98% to 40%-50%; the concentrations of heavy metals such as Cd, Cr, Cu, Pb, and Zn in the filtrate are all lower than the maximum allowable emission concentrations of Class I pollutants; the preparation process is simple to operate and has relatively low energy consumption; the sludge cake after filtration is suitable for subsequent incineration, building material preparation, or safe landfill treatment.

[0032] The technical solution of this invention has the following advantages: 1. This invention provides a composite conditioner comprising the following components: industrial solid waste, biochar, and an alkaline conditioner; wherein the industrial solid waste includes desulfurized gypsum, fly ash, steel slag, and mineral slag. The composite conditioner provided by this invention significantly improves the filtration characteristics of sludge through the synergistic effect of the rigid framework constructed by the industrial solid waste and the porous network formed by the biochar, greatly reducing dewatering resistance and enabling the sludge cake to achieve deep dewatering after pressure filtration, with a dense and well-formed structure. Simultaneously, under the activation environment of the alkaline conditioner, the active components undergo a gelation and solidification reaction, synergizing with the adsorption function of the biochar to effectively stabilize heavy metals, ensuring that the concentrations of various heavy metal ions in the filtrate are far below the national emission standard limits, greatly reducing environmental risks. This technology simultaneously achieves efficient dewatering and harmless stabilization of sludge, resulting in significant sludge reduction and high safety after treatment, laying a solid foundation for subsequent resource utilization and demonstrating the dual environmental and economic advantages of waste-to-waste treatment. Among these, steel slag in industrial solid waste provides an active calcium source and an alkaline environment, promoting colloid breakdown and hydration; fly ash provides a spherical skeleton and pore support; the pozzolanic active components in slag and fly ash undergo secondary hydration, improving the density of the skeleton; and the Ca in desulfurization gypsum... 2+ With SO4 2- It participates in the reaction, forming needle-like crystals of ettringite, which enhances the drainage channels; This invention utilizes industrial and agricultural solid waste to collaboratively construct a green conditioner. The raw materials are widely available and inexpensive, avoiding dependence on polymeric flocculants and high-quality chemicals. It achieves pollution control through waste, promotes the high-value utilization of solid waste, and is in line with the application scenarios of solid waste resource utilization and green sludge reduction.

[0033] 2. This invention introduces mechanical ball milling into the preparation process of dewatering conditioners for multi-source solid waste sludge. The operating conditions are mild and the process is simple, requiring no strict pH and temperature control. It achieves synergistic activation of functional components, microstructure regulation, and phase boundary reaction control, realizing the transformation of traditional fly ash / slag and other "filler aggregates" into "highly active synergistic conditioners." In addition, this invention prepares composite conditioners through mechanical ball milling, which significantly improves the mineral reactivity and surface energy, achieves controllable particle size, and adjusts the pore structure. This facilitates the formation of reasonable pore and channel structures in the sludge system, which is conducive to water migration and more uniform particle distribution. This enhances the stability of the floc structure and the compressibility of the filter cake during the filter press process.

[0034] 3. This invention has a wide range of applications, requiring no multi-step drug preparation or additional equipment modification. It is directly compatible with mainstream filter press equipment such as belt filter press and plate and frame filter press, and has good prospects for industrial application. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 This is a process flow diagram of Experimental Example 1 of the present invention. Detailed Implementation

[0037] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having” and any variations thereof in the text of this application are intended to cover non-exclusive inclusion.

[0039] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers from a to b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥ 2, it is equivalent to disclosing that the parameter can be, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0040] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone.

[0041] In the description of the embodiments of this application, the term "at least one" refers to one or more (including two).

[0042] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0043] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0044] The rice husk ash used in the following examples was prepared by burning rice husks at 650°C for 2 hours under a nitrogen atmosphere and then crushing them. The sawdust ash used in the following examples was prepared by burning sawdust at 650°C for 2 hours under a nitrogen atmosphere, followed by pulverization.

[0045] Example 1 This embodiment provides a method for preparing a compound conditioner, and the specific steps and parameter settings are as follows: Desulfurized gypsum, fly ash, steel slag, and blast furnace slag were dried and pretreated in a mass ratio of 30:20:25:25, and then mixed by mechanical ball milling (400 r / min, 30 min) to obtain an industrial solid waste mixture. Biochar (rice husk ash and wood ash in a mass ratio of 1:1) and an alkaline conditioner (calcium oxide and calcium hydroxide in a mass ratio of 1:2) were then added to obtain the composite conditioner. The mass ratio of the industrial solid waste, biochar, and alkaline regulator is 48:28:18.

[0046] Example 2 This embodiment provides a method for preparing a compound conditioner, and the specific steps and parameter settings are as follows: Desulfurized gypsum, fly ash, steel slag, and blast furnace slag in a mass ratio of 15:25:20:40 were dried and pretreated before being mixed by mechanical ball milling (400 r / min, 30 min) to obtain an industrial solid waste mixture. Biochar (rice husk ash and wood ash in a mass ratio of 1:1) and an alkaline conditioner (calcium oxide and calcium hydroxide in a mass ratio of 1:1) were then added to obtain the composite conditioner. The mass ratio of the industrial solid waste, biochar, and alkaline regulator is 40:30:24.

[0047] Example 3 This embodiment provides a method for preparing a compound conditioner, and the specific steps and parameter settings are as follows: Desulfurized gypsum, fly ash, steel slag, and blast furnace slag were dried and pretreated in a mass ratio of 15:25:20:40, and then mixed by mechanical ball milling (400 r / min, 30 min) to obtain an industrial solid waste mixture. Biochar (rice husk ash and wood ash in a mass ratio of 1:1) and an alkaline conditioner (calcium oxide and calcium hydroxide in a mass ratio of 1:1) were then added to obtain the composite conditioner. The mass ratio of the industrial solid waste, biochar, and alkaline regulator is 54:24:16.

[0048] Example 4 This embodiment provides a method for preparing a compound conditioner, and the specific steps and parameter settings are as follows: Desulfurized gypsum, fly ash, steel slag, and blast furnace slag were dried and pretreated in a mass ratio of 20:30:20:40, and then mixed by mechanical ball milling (300 r / min, 40 min) to obtain an industrial solid waste mixture. Biochar (rice husk ash and wood ash in a mass ratio of 1:1) and an alkaline conditioner (calcium oxide and calcium hydroxide in a mass ratio of 1:1) were then added to obtain the composite conditioner. The mass ratio of the industrial solid waste, biochar, and alkaline regulator is 60:20:20.

[0049] Example 5 This embodiment provides a method for preparing a compound conditioner, and the specific steps and parameter settings are as follows: Desulfurized gypsum, fly ash, steel slag, and blast furnace slag were dried and pretreated in a mass ratio of 30:20:30:20, and then mixed by mechanical ball milling (500 r / min, 20 min) to obtain an industrial solid waste mixture. Biochar (rice husk ash and wood ash in a mass ratio of 1:1) and an alkaline conditioner (calcium oxide and calcium hydroxide in a mass ratio of 1:2) were then added to obtain the composite conditioner. The mass ratio of the industrial solid waste, biochar, and alkaline regulator is 40:40:10.

[0050] Comparative Example 1 This comparative example provides a method for preparing a composite conditioner, which differs from Example 1 only in that desulfurized gypsum, steel slag, and blast furnace slag are replaced with an equal mass of fly ash. The rest is the same as in Example 1.

[0051] Comparative Example 2 This comparative example provides a method for preparing a composite conditioner, which differs from Example 1 only in that: no biochar is added, and the mass ratio of the industrial solid waste to the alkaline conditioner is 48:18. The rest is the same as in Example 1.

[0052] Comparative Example 3 This comparative example provides a method for preparing a composite conditioner, which differs from Example 1 only in that: no alkaline conditioner is added, and the mass ratio of the industrial solid waste to biochar is 48:28. The rest is the same as in Example 1.

[0053] Comparative Example 4 This comparative example provides a method for preparing a composite conditioner, the only difference from Example 1 is that the slag is replaced with an equal mass of fly ash; The rest is the same as in Example 1.

[0054] Comparative Example 5 This comparative example provides a method for preparing a composite conditioner, which differs from Example 1 only in that the desulfurized gypsum is replaced with an equal mass of fly ash; The rest is the same as in Example 1.

[0055] Comparative Example 6 This comparative example provides a method for preparing a composite conditioner, which differs from Example 1 only in that steel slag is replaced with an equal mass of fly ash; The rest is the same as in Example 1.

[0056] Experimental Example 1 The composite conditioners prepared in Examples 1-5 and Comparative Examples 1-6 were applied to sludge dewatering, such as... Figure 1 As shown, it includes the following steps: S1: Sludge feeding and compound conditioner addition: The sludge (95% moisture content) is pumped to the conditioning reactor (500 L volume, 316L stainless steel) using a screw pump, and the composite conditioning agent is added at a dosage of 7 wt% of the dry weight of the sludge to form a mixed system. The sludge used was tested according to CJ / T 221-200 "Test Methods for Sludge from Urban Wastewater Treatment Plants", and the specific data are shown in Table 1. Table 1. Basic properties of raw sludge

[0057] S2: Mixing and Adding of Auxiliary Additives: Turn on the stirring system and mix the above mixture once at a speed of 300 r / min (mechanical stirring) for 12 min; Subsequently, auxiliary additives (polyferric chloride and cationic polyacrylamide in a mass ratio of 4:2) were added at a dosage of 6 wt% of the above-mentioned composite conditioning agent, and stirring was continued for 8 minutes. During the stirring process, the system temperature was controlled at room temperature (25°C) to obtain the sample to be tested.

[0058] S3: Dehydration treatment: The sludge that has completed the conditioning reaction is transported through pipelines to a plate and frame filter press for mechanical dewatering. The dewatering pressure is set at 1.6 MPa and the filtration time is controlled at 45 min to obtain dry sludge filter cake.

[0059] The moisture content of the dried mud filter cake was determined using a moisture meter (MB23, Ohaus). The sludge dewatering characteristics include the following tests: (1) pH of the filtrate: The filtrate produced during sludge dewatering was collected, and the pH of the filtrate was determined using a pH meter (FE20, Metoletolido). (2) Content of heavy metal ions Cd, Cr, Cu, Pb, and Zn: The sludge that has completed the conditioning reaction was first filtered through a 0.22-micron filter membrane, and the supernatant was taken. Then, the concentration of heavy metal ions in the supernatant was measured using ICP-OES (Avio 200, PerkinElmer). (3) Capillary absorption time CST: The sludge that has completed the conditioning reaction was placed in an 80 mm diameter stainless steel funnel lined with filter paper and the CST of the sludge that has completed the conditioning reaction was measured using a CST meter (Triton 304MCST sludge capillary water absorption time meter from the UK). (4) Sludge specific resistance (SRF): 100 mL of the sludge after the conditioning reaction was completed was poured into a 90 mm diameter Buchner funnel lined with filter paper. The mixture was continuously filtered under a pressure of 0.06 MPa for 10 min. The volume of the filtrate in the graduated cylinder was recorded every 10 s. The specific calculation formula is as follows: ; in, P Filtering pressure (in Pa); A Filter area (Buchner funnel cross-sectional area) (unit: m²) 2 ); The viscosity of the filtrate is expressed in Pa·s. The dry mass of filter cake solids per unit volume of filtrate (in kg / m³) 3 ),according to Calculations show that, where The solids content (%) is based on the original sludge. The solid content (%) of the dewatered cake base.

[0060] b The slope of the experimental curve, in s / m. 6 Based on the recorded filtrate volume at different times t (s) V (m) 3 ),by t / V The vertical axis is , V Plotting the x-axis yields a straight line; its slope is . b .

[0061] The specific test results are shown in the table below: Table 2 Performance test data of the sample to be tested

[0062] Table 3 Moisture content of dry mud filter cake

[0063] Table 4 Filtrate composition analysis data

[0064] After conditioning with this composite sludge dewatering conditioner, the pH of the filtrate showed a gentle increase and stabilized in the weakly alkaline range, which is conducive to the fixation of heavy metals in the form of hydroxides or stable complexes / precipitates, thereby significantly reducing their leaching concentration in the filtrate. Compared with the control group, the concentrations of heavy metals such as Cd, Cr, Cu, Pb, and Zn in the filtrate treated with the composite conditioner of this invention were significantly reduced, indicating that heavy metals did not migrate with the filtrate during the conditioning process, effectively avoiding secondary water phase pollution. Combined with Ca-Al-Si-SO4 2- Through synergistic hydration reactions, heavy metals are immobilized within the sludge cake framework via multiple mechanisms, including lattice embedding, precipitation, and adsorption, reducing the risk of migration and release during subsequent treatment. Existing conditioners primarily aim to improve sludge cake dewatering performance, typically focusing only on changes in the total amount of heavy metals in the sludge cake while neglecting the environmental risks of heavy metal migration into the filtrate during the conditioning process. This invention demonstrates its ability to immobilize heavy metals from an engineering safety perspective by detecting changes in heavy metal concentration in the filtrate.

[0065] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A composite conditioning agent characterized in that, The composite conditioner comprises the following components: industrial solid waste, biochar, and alkaline regulator. The industrial solid waste comprises desulfurization gypsum, fly ash, steel slag, and slag.

2. The complex conditioning agent of claim 1, wherein, The mass ratio of the industrial solid waste, biochar, and alkaline regulator is (40-60):(20-40):(10-20).

3. The complex conditioning agent according to claim 1 or 2, characterized in that, The mass ratio of the desulfurization gypsum, fly ash, steel slag, and slag is (20-30):(20-30):(20-30):(20-40).

4. The complex conditioning agent according to any of claims 1 to 3, characterized in that, The alkaline regulator comprises calcium oxide and calcium hydroxide. Optionally, the mass ratio of the calcium oxide and calcium hydroxide is 1:(1-2).

5. A method of preparing the complex conditioning agent according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: drying the industrial solid waste, mixing the dried industrial solid waste, adding biochar and alkaline regulator to obtain the composite conditioner.

6. The production method according to claim 5, wherein The mixing comprises ball milling. Optionally, the rotation speed of the ball milling is 300-500 rpm, and the time is 20-40 min.

7. The composite conditioner of any one of claims 1-4 or the composite conditioner prepared by the method of any one of claims 5-6 is applied in sludge dewatering.

8. Use according to claim 7, characterized in that, The application comprises the following steps: mixing the composite conditioner with wet sludge once, adding auxiliary additive to mix again, performing dewatering treatment to obtain dewatered sludge.

9. Use according to claim 8, characterized in that, The addition amount of the composite conditioner is 5wt%-10wt% of the dry weight of the sludge. And / or, the addition amount of the auxiliary additive is 5wt%-10wt% of the composite conditioner. And / or, the auxiliary additive comprises at least one of polymeric ferric chloride, polymeric ferric sulfate, and polyacrylamide.

10. Use according to claim 8, characterized in that, The time of the first mixing is 10-20 min, and the rotation speed is 200-500 r / min. And / or, the time of the second mixing is 5-10 min, and the temperature is 20-40℃. And / or, the dewatering treatment comprises using one of a belt filter press, a plate-and-frame filter press, and a horizontal screw centrifuge.

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