Method for preparing sludge-based biochar, and method for mitigating membrane fouling based on sludge-based biochar catalyzing persulfate

Abstract

This application relates to the field of membrane fouling technology, specifically to a method for preparing sludge-based biochar and a method for alleviating membrane fouling by catalyzing persulfate with sludge-based biochar. The method includes: providing a first mixed liquor containing sludge-based biochar, the sludge-based biochar comprising pyrolysis products of Fe and Ca elements from sludge; providing a second mixed liquor containing organic pollutants; mixing the first and second mixed liquors, then mixing with persulfate to treat the second mixed liquor; wherein the concentration of persulfate is 0.1-10 mM, the concentration of sludge-based biochar is 0.1-0.5 g / L, and the mass ratio of persulfate to sludge-based biochar is 1:(1-1.3). The method of this application can reduce the specific filtration resistance by more than 86.6% compared to the untreated system, improve the efficiency of pollutant control, effectively alleviate membrane fouling, and simultaneously reduce sludge disposal costs.

Description

Technical Field

[0001] This application relates to the field of membrane fouling technology, specifically to a method for preparing sludge-based biochar and a method for alleviating membrane fouling by catalyzing persulfate based on sludge-based biochar. Background Technology

[0002] Ultrafiltration technology has become a major component in wastewater treatment due to its small footprint, high modularity, and ease of operation. However, membrane fouling can lead to problems such as reduced ultrafiltration membrane flux, increased energy consumption, frequent chemical cleaning, and premature aging of membrane modules. Improving hydraulic operating conditions, enhancing the membrane cleaning process, modifying the membrane surface, and adding pre-treatment can mitigate the impact of membrane fouling on membrane performance. Pre-treatment oxidation involves using strong oxidants to degrade organic pollutants in the water, altering their molecular weight distribution and hydrophilicity / hydrophobicity. Moderate oxidation can alleviate membrane fouling by breaking down organic molecules, but excessive oxidation can lead to microbial cell rupture and the release of intracellular secretions, thus exacerbating membrane fouling. Furthermore, conventional organic membranes have limited tolerance to oxidants, and long-term operation can lead to irreversible membrane damage.

[0003] Therefore, developing efficient, mild, and highly selective oxidation systems has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application provides a method for preparing sludge-based biochar and a method for alleviating membrane fouling by catalyzing persulfate based on sludge-based biochar. The above method can reduce the specific filtration resistance by more than 86.6% compared with the untreated system, improve the efficiency of pollutant control, effectively alleviate membrane fouling, and reduce sludge disposal costs.

[0005] In a first aspect, this application provides a method for mitigating membrane fouling based on sludge-based biochar catalytic persulfate, comprising: providing a first mixed liquid containing sludge-based biochar, wherein the sludge-based biochar includes pyrolysis products of Fe and Ca elements in sludge; providing a second mixed liquid containing organic pollutants; mixing the first mixed liquid and the second mixed liquid, and then mixing with persulfate, thereby treating the second mixed liquid; wherein the concentration of the persulfate is 0.1-10 mM, the concentration of the sludge-based biochar is 0.1-0.5 g / L, and the mass ratio of the persulfate to the sludge-based biochar is 1:(1-1.3).

[0006] This application uses persulfate as an oxidant, with a concentration ranging from 0.1 to 10 mM. Persulfate exhibits strong oxidizing properties under mild conditions, with a fast reaction rate, wide pH applicability, and no secondary pollution. By introducing sludge-based biochar as a catalyst into the persulfate oxidation pretreatment system, and maintaining a concentration of sludge-based biochar within the range of 0.1-0.5 g / L, the mass ratio of sulfate to sludge-based biochar is adjusted to 1:(1-1.3), allowing the sulfate and sludge-based biochar to work synergistically to construct an advanced oxidation process (AOPs) pretreatment system. This system directly utilizes the sludge pyrolysis products without the need for acid or alkali washing or metal loading, retaining the in-situ Fe / Ca active components in the sludge. Simultaneously, the C=O groups or defect sites on the surface of the sludge-based biochar serve as active centers, activating PMS to generate free radicals. · OH and SO4 ·- ) or non-free radicals ( 1 O2 species, through oxidative degradation before membrane filtration, disrupt the gel structure of pollutants, thereby controlling membrane fouling. Through the synergistic adsorption-catalytic oxidation effect of the sludge-based biochar / persulfate system, the specific filtration resistance (SFR) can be reduced by more than 86.6% compared to the untreated system, improving the efficiency of pollutant control, effectively mitigating membrane fouling, and reducing sludge disposal costs.

[0007] In some embodiments, based on the total mass of sludge-based biochar being 100%, the mass content of iron in the sludge-based biochar is 129 g / kg-132 g / kg, and the mass content of calcium is 81 g / kg-84 g / kg.

[0008] In some embodiments, in the step of mixing the first mixture and the second mixture and then mixing with persulfate to treat the second mixture, the concentration of the organic pollutant is 0.03-0.07 g / L.

[0009] In some embodiments, the step of providing a first mixture containing sludge-based biochar includes: dispersing the sludge-based biochar in deionized water, stirring at a speed of 280-320 rpm for 0.4-0.6 h, and then subjecting it to ultrasonic treatment for 0.4-0.6 h.

[0010] In some embodiments, the step of providing a second mixture containing organic contaminants includes: dispersing the organic contaminants into deionized water and stirring at a speed of 280-320 rpm for 0.8-1.2 h.

[0011] In some embodiments, the organic pollutant includes one or more of sodium alginate and proteins.

[0012] In some embodiments, the persulfate includes one or more of sodium persulfate and potassium peroxymonosulfate.

[0013] In some embodiments, the step of mixing the first mixture and the second mixture and then mixing them with persulfate, and treating the second mixture includes stirring at a speed of 280-320 rpm for 0.8-1.2 h.

[0014] In some embodiments, the step of mixing the first mixture and the second mixture and then mixing them with persulfate, and treating the second mixture includes adding methanol to quench the reaction.

[0015] Secondly, this application provides a method for preparing sludge-based biochar as described in the first aspect of this application, comprising: drying activated sludge to obtain dried activated sludge; pyrolyzing the dried activated sludge in an inert gas atmosphere to obtain pyrolyzed activated sludge; and grinding the pyrolyzed activated sludge to obtain sludge-based biochar.

[0016] In some embodiments, the drying temperature is 100°C-110°C.

[0017] In some embodiments, the flow rate of the inert gas is 8-12 mL / min.

[0018] In some embodiments, the pyrolysis treatment includes: heating the dried activated sludge to 500℃-900℃ at a heating rate of 4-6℃ / min, and then holding the temperature at that temperature for 1.5-2.5h.

[0019] In some embodiments, the sludge-based biochar has an average particle size of 180-200 mesh.

[0020] In some embodiments, the sludge-based biochar includes one or more of microporous, mesoporous, and macroporous structures.

[0021] In some embodiments, the specific surface area of ​​the sludge-based biochar is 40-60 m². 2 / g.

[0022] In some embodiments, based on the total mass of sludge-based biochar being 100%, the mass content of iron in the sludge-based biochar is 129 g / kg-132 g / kg, and the mass content of calcium is 81 g / kg-84 g / kg. Attached Figure Description

[0023] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0024] Figure 1a Scanning electron microscope image of commercial biochar (CB); Figure 1b Nitrogen adsorption-desorption isotherms and pore size distribution of commercial biochar. Figure 1c Scanning electron microscope image of sludge-based biochar; Figure 1d Nitrogen adsorption-desorption isotherms and pore size distribution of sludge-based biochar (SBC); Figure 2a Raman spectra of commercial biochar and sludge-based biochar; Figure 2b XRD patterns of commercial biochar and sludge-based biochar; Figure 2c This is a distribution map of iron in sludge-based biochar. Figure 2d This is a distribution map of calcium in sludge-based biochar. Figure 3a XPS spectrum of Fe element in sludge-based biochar; Figure 3b XPS spectrum of Ca in sludge-based biochar; Figure 3c XPS spectrum of Fe element in commercial biochar; Figure 3d XPS spectrum of Ca in commercial biochar; Figure 4a The images shown are scanning electron microscope (SEM) images and optical images of the contamination layer formed in Comparative Example 1. Figure 4b Example 1: Scanning electron microscope and optical images of a contamination layer formed by 0.1 g / L SBC; Figure 4c Example 2: Scanning electron microscope and optical images of a contamination layer formed by 0.2 g / L SBC; Figure 4d Example 3: Scanning electron microscope and optical images of the contamination layer formed by 0.3 g / L SBC; Figure 5a The interaction energy between the pollutant and the membrane interface in Comparative Example 1; Figure 5b Example 1: Interfacial interaction energy between 0.1 g / L SBC contaminants and the membrane interface; Figure 5c Example 2: Interfacial interaction energy between 0.2 g / L SBC contaminants and the membrane interface; Figure 5d Example 3: Interfacial interaction energy between 0.3 g / L SBC contaminants and the membrane interface; Figure 6 The water loss rate of the contaminated layers in Comparative Example 1, Example 1, Example 2, and Example 3 after heating at 60°C for 30 minutes; Figure 7 The effect of PMS on SFR in Comparative Examples 1, 2, 3 and 4; Figure 8a The changes in SFR caused by the adsorption of SBC (Comparative Example 1, Comparative Examples 5-9) and CB (Comparative Example 1, Comparative Examples 10-14); Figure 8b The study investigated the changes in SFR with increasing PMS concentration in the SBC / PMS systems of Comparative Example 5, Example 1, Example 4, Example 14 and Comparative Example 10, Comparative Example 15-17 CB / PMS systems when the biochar dosage was fixed at 0.1 g / L. Figure 9a To compare the effects of SBC dosage on SFR under the fixed PMS concentration of 0.1 mM in Examples 2 and 9-13; Figure 9b To investigate the effect of SBC dosage on SFR under the fixed PMS concentration of 1 mM in Comparative Examples 2, 1, and 5-8. Detailed Implementation

[0025] The embodiments of this application will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of this application.

[0026] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having" and any variations thereof in the specification, claims and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0027] In this application, the reference to "embodiment" means that a specific 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 mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0028] 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.

[0029] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two).

[0030] Unless otherwise stated, the test temperature for all parameters mentioned in this application is 25°C.

[0031] Ultrafiltration is a core process in water treatment, but membrane fouling caused by organic matter (such as sodium alginate, SA), especially gel layer fouling with high resistance, restricts the large-scale application of ultrafiltration. To overcome this problem, pretreatment technologies such as coagulation, adsorption, and oxidation have emerged, but high reagent consumption, operational complexity, and membrane damage risks have hindered the widespread application of pretreatment technologies.

[0032] Based on sulfate free radicals (SO4) •- The persulfate advanced oxidation process has become a research hotspot in environmental remediation and water treatment in recent years. Although persulfate has a high standard electrode potential (E0), it is still a promising area of ​​research. 0 = 1.82~2.01V), but under normal temperature and pressure conditions, its oxidation rate of complex organic pollutants in wastewater is relatively slow. The performance of the persulfate system is determined by the activity of the catalyst and its regulation of reactive oxygen species, requiring catalytic activation. Common activation methods mainly include physical activation (such as thermal activation, ultraviolet activation, and ultrasonic activation) and chemical catalytic activation (such as transition metal ion activation and carbon-based material activation). Carbon-based materials (such as activated carbon, biochar, and carbon nanotubes) have attracted widespread attention as efficient and environmentally friendly non-metallic activators due to their porous structure, abundant oxygen-containing functional groups, and good electron conductivity. However, the preparation cost of activated carbon and carbon nanotubes is high, and the large-scale application of carbon nanotubes is limited by complex purification processes. Biochar, with properties and structure comparable to other carbon materials, plays a certain value in the field of catalytic activation due to its low cost, efficiency, and sustainability.

[0033] A common approach to mitigating organic fouling (such as sodium alginate SA) in ultrafiltration membranes is to use commercial wood / nutshell biochar (CB) as a catalyst. However, untreated commercial biochar has very low porosity and extremely limited surface active sites, which is detrimental to the utilization of adsorption and catalytic sites. Therefore, untreated commercial biochar often fails to meet the requirements of industrial-grade ultrafiltration pretreatment. To improve catalytic efficiency, related technologies typically require exogenous doping. Through equal-volume impregnation, electrochemical deposition, or co-precipitation, transition metals such as iron (Fe), cobalt (Co), and manganese (Mn) are forcibly loaded onto the carbon surface, or heteroatoms such as nitrogen (N), sulfur (S), and phosphorus (P) are introduced to alter the electron cloud distribution of the carbon skeleton, forming highly efficient active sites. Although related technologies attempt to improve the catalytic performance of commercial activated carbon by loading transition metals or doping with non-metals, the cumbersome modification process, expensive raw material consumption, and potential risk of metal oxide loss limit their large-scale application in water treatment.

[0034] Therefore, developing low-cost, environmentally friendly catalysts holds the potential to alleviate membrane fouling through persulfate pretreatment.

[0035] In view of this, this application provides a method for mitigating membrane fouling by catalytic persulfate based on sludge-based biochar, comprising: A first mixed liquor containing sludge-based biochar is provided, wherein the sludge-based biochar comprises pyrolysis products of Fe and Ca elements in sludge; Provide a second mixture containing organic contaminants; The first mixture and the second mixture are mixed, and then mixed with persulfate to treat the second mixture. The concentration of persulfate is 0.1-10 mM, the concentration of sludge-based biochar is 0.1-0.5 g / L, and the mass ratio of persulfate to sludge-based biochar is 1:(1-1.3).

[0036] This application uses persulfate as an oxidant, with a concentration ranging from 0.1 to 10 mM. Persulfate exhibits strong oxidizing properties under mild conditions, with a fast reaction rate, wide pH applicability, and no secondary pollution. By introducing sludge-based biochar as a catalyst into the persulfate oxidation pretreatment system, and maintaining a concentration of sludge-based biochar within the range of 0.1-0.5 g / L, the mass ratio of sulfate to sludge-based biochar is adjusted to 1:(1-1.3), allowing the sulfate and sludge-based biochar to work synergistically to construct an advanced oxidation process (AOPs) pretreatment system. This system directly utilizes the sludge pyrolysis products without the need for acid or alkali washing or metal loading, retaining the in-situ Fe / Ca active components in the sludge. Simultaneously, the C=O groups or defect sites on the surface of the sludge-based biochar serve as active centers, activating PMS to generate free radicals.· OH and SO4 ·- ) or non-free radicals ( 1 O2 species, through oxidative degradation before membrane filtration, disrupt the gel structure of pollutants, thereby controlling membrane fouling. Through the synergistic adsorption-catalytic oxidation effect of the sludge-based biochar / persulfate system, the specific filtration resistance (SFR) can be reduced by more than 86.6% compared to the untreated system, improving the efficiency of controlling membrane pollutants, effectively alleviating membrane fouling, and reducing sludge disposal costs.

[0037] The method for mitigating membrane fouling based on sludge-based biochar catalysis of persulfate in this application has strong universality and can effectively address high concentrations of biological macromolecular fouling, with a membrane fouling control efficiency of over 86.6%.

[0038] In some embodiments, the solvent for the first mixed solution may be deionized water.

[0039] In some embodiments, the solvent for the second mixed solution may be deionized water.

[0040] In some embodiments, the mass ratio of the persulfate to the sludge-based biochar is 1:(1-1.3).

[0041] In some embodiments, in the step of mixing the first mixture and the second mixture, and then mixing with persulfate to treat the second mixture: the concentration of the persulfate is 0.1-10 mM, for example, it can be 0.1 mM, 0.2 mM, 0.3 mM, 0.4 mM, 0.5 mM, 0.6 mM, 0.7 mM, 0.8 mM, 0.9 mM, 1 mM, 2 mM, 3 mM, 4 mM, 5 mM, 6 mM, 7 mM, 8 mM, 9 mM, 10 mM, or any range of two of the above values.

[0042] In some embodiments, in the step of mixing the first mixture and the second mixture, and then mixing with persulfate to treat the second mixture, the concentration of the sludge-based biochar is 0.1-0.5 g / L, for example, it can be 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, or any range of two of the above values.

[0043] In some embodiments, based on the total mass of sludge-based biochar being 100%, the mass content of iron in the sludge-based biochar is 129 g / kg-132 g / kg, and the mass content of calcium is 81 g / kg-84 g / kg.

[0044] The mass content of iron and calcium in sludge-based biochar is within the above range. Iron can act as a catalyst for Fenton-like reactions, activating persulfate and generating free radicals to degrade pollutants. Calcium strengthens the bridging effect, thereby "anchoring" pollutants to the biochar.

[0045] In some embodiments, in the step of mixing the first mixture and the second mixture, and then mixing with persulfate to treat the second mixture, the concentration of the organic pollutant is 0.03-0.07 g / L, for example, it can be 0.03 g / L, 0.04 g / L, 0.05 g / L, 0.06 g / L, 0.07 g / L, or any range of two of the above values.

[0046] In some embodiments, the step of providing a first mixture containing sludge-based biochar includes: dispersing the sludge-based biochar in deionized water, stirring at 280-320 rpm for 0.4-0.6 h, and then subjecting it to ultrasonic treatment for 0.4-0.6 h. This allows the sludge-based biochar to be uniformly dispersed in the deionized water.

[0047] In some embodiments, the step of providing a second mixture containing organic contaminants includes: dispersing the organic contaminants into deionized water and stirring at a speed of 280-320 rpm for 0.8-1.2 h.

[0048] In some embodiments, the organic pollutant includes one or more of sodium alginate and proteins.

[0049] In some embodiments, the first mixture and the second mixture are mixed, and then mixed with persulfate. The step of treating the second mixture includes stirring at a speed of 280-320 rpm for 0.8-1.2 hours. This allows the sludge-based biochar, organic pollutants, and persulfate to come into sufficient contact and undergo an effective reaction.

[0050] In some embodiments, the step of mixing the first mixture and the second mixture, and then mixing them with persulfate, and treating the second mixture includes adding methanol to quench the reaction. Adding excess methanol can effectively quench free radicals and terminate the reaction. In the embodiments of this application, the amount of methanol added only needs to be in excess relative to the above reaction, for example, it can be 3 mL, 4 mL, 5 mL, 6 mL, or 7 mL.

[0051] Sludge-based biochar Methods for preparing sludge-based biochar include: The activated sludge is dried to obtain dried activated sludge. The dried activated sludge was pyrolyzed in an inert gas atmosphere to obtain pyrolyzed activated sludge. The pyrolyzed activated sludge was ground to obtain sludge-based biochar.

[0052] To improve the dewatering performance of sludge, wastewater treatment plants typically add iron salts (such as FeCl3 or Fe2(SO4)3) as flocculants. The metal ions in these iron salts destabilize and flocculate colloidal particles through charge neutralization and double-layer compression, ultimately leaving them in the sludge as hydroxides or mineral salts. Simultaneously, the sludge itself also accumulates transition metals (Fe, Ca, Zn, Mn, etc.) from the raw water. During pyrolysis, these metals are converted in situ into stable metal oxides or elements, giving the sludge-based biochar the catalytic activity to activate persulfate without the need for additional metal loading.

[0053] Furthermore, sludge-based biochar retains a large number of oxygen-containing functional groups on its surface. These groups can directly participate in catalytic reactions via electron transfer and enhance pollutant adsorption through electrostatic interactions and hydrogen bonding. Pyrolysis can improve the graphitization degree of sludge-based biochar and expose its active sites. Pyrolytic sludge can achieve "waste-to-waste treatment" while obtaining high-performance carbon-based functional materials, thus reducing environmental risks such as pathogen load and heavy metal pollution to a certain extent.

[0054] In some embodiments, the drying process can be carried out in a tube furnace.

[0055] In some embodiments, the sludge described above can be obtained through municipal wastewater treatment.

[0056] In some embodiments, the drying temperature is 100℃-110℃, for example, it can be 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃, 110℃, or any range of two of the above values.

[0057] In some embodiments, the flow rate of the inert gas is 8-12 mL / min, for example, it can be 8 mL / min, 9 mL / min, 10 mL / min, 11 mL / min, 12 mL / min, or any range of two of the above values.

[0058] In some embodiments, the inert gas may be nitrogen.

[0059] In some embodiments, the pyrolysis treatment includes: heating the dried activated sludge to 500℃-900℃ at a heating rate of 4-6℃ / min, and then holding the temperature at that temperature for 1.5-2.5h.

[0060] It should be noted that the pyrolyzed activated sludge needs to be cooled to room temperature before grinding.

[0061] In some embodiments, the average particle size of the sludge-based biochar is 180-200 mesh, for example, it can be 180 mesh, 185 mesh, 190 mesh, 195 mesh, 200 mesh, or any range of two of the above values.

[0062] Sludge-based biochar possesses a rich porous structure. In some embodiments, the sludge-based biochar includes one or more of microporous, mesoporous, and macroporous structures. The interweaving of organic and inorganic components in sludge results in a multi-level pore structure of micropores, mesopores, and macropores in the sludge-based biochar after pyrolysis. This structure not only provides capture sites for large molecular pollutants but also facilitates the transfer of active substances during the reaction process.

[0063] In some embodiments, the specific surface area of ​​the sludge-based biochar is 40-60 m². 2 / g, for example, can be 40m 2 / g、45m 2 / g, 50m 2 / g、55m 2 / g、60m 2 / g, or a range consisting of any two of the above values.

[0064] In some embodiments, based on the total mass of sludge-based biochar being 100%, the mass content of iron in the sludge-based biochar is 129 g / kg-132 g / kg, and the mass content of calcium is 81 g / kg-84 g / kg.

[0065] Example The following embodiments describe the contents of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0066] Commercial biochar (CB, purchased from Henan Dongtai Charcoal Industry Technology Co., Ltd.) Example 1 (1) Preparation of sludge-based biochar After drying in an oven at 105℃, the sludge was placed in a tube furnace and pyrolyzed under continuous nitrogen flow (10.0 mL / min). During pyrolysis, the tube furnace was heated to 800℃ at a rate of 5℃ / min and then held at this temperature for 2 hours. After the sample was allowed to cool naturally to room temperature in a nitrogen atmosphere, the resulting solid product was ground, passed through a 200-mesh sieve, and finally stored in a sealed container labeled as sludge-based biochar for later use. Based on a total mass of 100%, the iron content in the sludge-based biochar was 130.238 g / kg, and the calcium content was 81.77 g / kg.

[0067] (2) A method for mitigating membrane fouling by catalyzing persulfate based on sludge-based biochar Disperse the sludge-based biochar in 80 mL of deionized water and stir thoroughly at 300 rpm for 0.5 h on a magnetic stirrer, then continue sonication for 0.5 h to ensure uniform dispersion of the sludge-based biochar and obtain the first mixture.

[0068] Add 20 mL of sodium alginate stock solution to 98 mL of deionized water and stir thoroughly at 300 rpm for 1 hour to obtain the second mixture.

[0069] Add the second mixture to the first mixture, and immediately add 2 mL of potassium persulfate stock solution (100 mM). Stir continuously at 300 rpm for 1 hour to ensure sufficient contact between the sludge-based biochar, sodium alginate and potassium persulfate, so that an effective reaction can occur.

[0070] At the end of the reaction, 5 mL of excess methanol was added to the system to effectively quench the free radicals and terminate the reaction.

[0071] The concentration of sodium alginate was 0.05 g / L, the concentration of persulfate was 1 mM, and the concentration of sludge-based biochar was 0.1 g / L.

[0072] Test section (1) Morphology of sludge-based biochar and commercial biochar The morphology of sludge-based biochar and commercial biochar was observed using scanning electron microscopy.

[0073] (2) Determination of specific filtration resistance Specific filtration resistance (SFR) is a core parameter for evaluating the degree of membrane fouling, used to quantify the filtration resistance caused by a unit mass of contaminants. Comparing changes in membrane fouling before and after treatment using SFR provides reliable conclusions. A decrease in SFR indicates reduced membrane fouling, while an increase indicates increased fouling. This application uses a dead-end filtration device to measure SFR, consisting of a nitrogen cylinder, an ultrafiltration cup, and an electronic balance. The experimental transmembrane pressure difference was 0.06 MPa, and the effective membrane area was 0.00332 m². 2 The flux was recorded by monitoring changes in the mass of the filtrate in real time using an electronic balance. Based on the filtration data, the SFR was calculated using a formula:

[0074] in, K The slope representing the linear relationship between filtration time and volume-time ratio. µ Cs represents the dynamic viscosity of the permeate (Pa·s), and Cs represents the concentration of contaminants (kg·m³). -3 ), ΔP Represents constant transmembrane pressure (kPa) and Am Represents membrane area (m²) 2 ).

[0075] (3) Analysis of thermodynamic parameters (interfacial energy, chemical potential) The degree of membrane fouling mitigation was quantified using the XDLVO and Flory-Huggins models.

[0076] Example 2 Except that the concentration of persulfate was 1 mM and the concentration of sludge-based biochar was 0.2 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0077] Example 3 Except that the concentration of persulfate was 1 mM and the concentration of sludge-based biochar was 0.3 g / L, the rest of the method for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar was the same as in Example 1.

[0078] As shown in Figure 4(ad), in Example 1, the fouling layer remained highly cross-linked and appeared even denser, leading to a further increase in SFR. In Example 2, the cross-linked network underwent partial degradation, resulting in defects throughout the fouling layer. However, due to the remaining cross-linked structure, the degree of mitigation of membrane fouling was relatively limited. In Example 3, the cross-linked network structure exhibited high instability, manifested as widespread structural collapse and the formation of a loose, porous filter cake layer. This morphological transformation was directly related to the significant reduction in SFR, indicating that membrane fouling was substantially alleviated. With the increase of SBC dosage, the fouling layer structure underwent a gradual evolution, transforming from an initial dense, low-permeability state to a high-permeability porous structure. This reflects a dynamic balance between adsorption and catalytic oxidation, and this balance is influenced by different dosage ratios, thus determining the competitive or synergistic effects between the two.

[0079] The adhesion behavior of pollutants on membrane surfaces is usually analyzed and predicted using the XDLVO theory. According to this theory, the total interaction energy between pollutants and the membrane surface is influenced by the synergistic effects of van der Waals forces (LW), electrostatic double-layer forces (EL), and acid-base interactions (AB).

[0080] This application uses the total interaction energy at the minimum separation distance (h = 0.158 nm) to measure contaminant adhesion. A more negative value indicates a stronger attraction, making it easier for contaminants to deposit on the membrane surface. A higher value indicates a stronger repulsion, which is more conducive to inhibiting the adhesion of the fouling layer on the membrane surface. As shown in Figure 5 (ad), compared to the control group, when the SBC dosage is 0.1 g / L, the interaction energy becomes more negative, meaning that the adhesion of contaminants to the membrane surface is enhanced, resulting in a dense fouling layer. Simultaneously, the SFR also slightly increases. As the SBC dosage increases to 0.2 g / L, the interaction energy increases from -24.43 × 10⁻⁶. 7 KT becomes -9.14×10 7 KT indicates a decrease in adhesion, resulting in a loose fouling layer, consistent with the lower SFR observed in the experiment. At 0.3 g / L, the interaction energy changes from attractive to repulsive. The amount of contaminant adhering is significantly reduced, forming a porous, weakly adhesive filter cake layer, thus greatly mitigating membrane fouling. Therefore, the dose-dependent change in the interfacial interaction between contaminants and the membrane surface is the main reason for the non-monotonic increasing membrane fouling behavior observed in the SBC / PMS system. From the thermodynamic perspective of interfacial interactions, the influence of catalyst dosage on contaminant adhesion, and consequently on the fouling layer structure and final membrane filtration performance, is systematically elucidated.

[0081] The filtration behavior of contaminants on the membrane surface is typically analyzed and predicted using the Flory-Huggins theory. Numerous studies have shown that the surface filtration rate (SFR) of the gel layer is generally several orders of magnitude higher than that of the filter cake layer, indicating that it plays a major role in membrane fouling. Since the gel layer is composed of a dense, highly hydrated polymer network with almost no or very few physical pores, its filtration behavior is essentially determined by the release of bound water from the polymer matrix to the free aqueous phase. The Flory-Huggins lattice theory attributes the thermodynamic nature of SFR to the significant chemical potential difference between bound and free water within the gel layer, meaning that continuous filtration must overcome a substantial energy barrier. Furthermore, the magnitude of this chemical potential difference is related to the microstructure of the gel layer; even small structural changes can significantly affect filtration characteristics. Therefore, an additional transmembrane pressure differential is required to maintain water permeation within the gel layer.

[0082] After heating at 60°C for 30 minutes in 0.1 g / L SBC and 1 mM PMS, the moisture loss of the fouling layer was slightly reduced. Combined with Flory-Huggins theory and SEM images, this reveals a more compact structure and tighter cross-linking, which may lead to a decrease in the Flory-Huggins interaction parameters (…). χ ) higher. With χ The increase in the saturation increases the chemical potential difference between the gel layer and the permeable layer. This raises the energy barrier for water release, resulting in a higher SFR. Figure 6 It can be seen that when the SBC concentration is 0.2 g / L, the water loss reaches 75%, indicating that the cross-linked network is partially destroyed and the water-binding capacity is reduced. While reducing the chemical potential difference, it also promotes water release and lowers the SFR. At 0.3 g / L SBC, the water loss is the greatest, reaching 92%, forming a loose and porous filter cake structure. The water-binding capacity is very low, thus the SFR is significantly reduced. The results show that the non-monotonic increasing membrane fouling behavior of the SBC / PMS system is related to changes in water-binding capacity and the microstructure of the fouling layer. From the perspective of interfacial thermodynamics, integrating XDLVO and Flory-Huggins analyses, the non-monotonic membrane fouling behavior of the SBC / PMS system is demonstrated, highlighting the influence of adhesion energy and chemical potential difference on the membrane fouling process.

[0083] Example 4 Except that the concentration of persulfate was 0.1 mM and the concentration of sludge-based biochar was 0.1 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0084] Example 5 Except that the concentration of persulfate was 1 mM and the concentration of sludge-based biochar was 0.2 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0085] Example 6 Except that the concentration of persulfate was 1 mM and the concentration of sludge-based biochar was 0.3 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0086] Example 7 Except that the concentration of persulfate was 1 mM and the concentration of sludge-based biochar was 0.4 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0087] Example 8 Except that the concentration of persulfate was 1 mM and the concentration of sludge-based biochar was 0.5 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0088] Example 9 Except that the concentration of persulfate was 0.1 mM and the concentration of sludge-based biochar was 0.5 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0089] Example 10 Except that the concentration of persulfate was 0.1 mM and the concentration of sludge-based biochar was 1 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0090] Example 11 Except that the concentration of persulfate was 0.1 mM and the concentration of sludge-based biochar was 2 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0091] Example 12 Except that the concentration of persulfate was 0.1 mM and the concentration of sludge-based biochar was 4 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0092] Example 13 Except that the concentration of persulfate was 0.1 mM and the concentration of sludge-based biochar was 8 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0093] Example 14 Except that the concentration of persulfate was 10 mM and the concentration of sludge-based biochar was 0.1 g / L, the other methods for mitigating membrane fouling by catalyzing persulfate with sludge-based biochar were the same as in Example 1.

[0094] Figure 9aThe effect of SBC dosage on SFR at 0.1 mM PMS was demonstrated. As the SBC dosage increased from 0 to 8 g / L, the SFR initially increased and then decreased. Nevertheless, at an SBC dosage of 8 g / L, the SFR remained as high as 2.49 × 10⁻⁶. 15 m·kg -1 The membrane fouling was not effectively alleviated even at a much higher concentration than in the SA group. This is because the 0.1 mM PMS concentration is limited by reactant concentration; even with a sufficiently high SBC dosage, the system still cannot generate enough reactive oxygen species (ROS) to degrade pollutants. Therefore, a more effective strategy is to increase the PMS concentration to 1 mM and then optimize the SBC dosage accordingly to achieve a balance between cost-effectiveness and performance. Figure 9b It can be seen that at a concentration of 1 mM PMS, the effect of SBC dosage on SFR is more significant than at lower concentrations. In the low dosage range (0-0.1 g / L), SFR shows a slight upward trend, indicating that the limited catalytic active sites prevent reactive oxygen species (ROS) from effectively disrupting the pollutant structure, thus exacerbating membrane fouling. However, when SBC increases to 0.2 g / L, SFR decreases by 22.6%. Further increasing to 0.3 g / L, SFR drops to 2.49 × 10⁻⁶. 15 m·kg -1 Compared to the SA group, the reduction was as high as 86.6%. When the dosage was greater than 0.3 g / L, the SFR remained basically unchanged, which is a typical saturation effect in heterogeneous catalytic systems. This indicates that when the SBC dosage reaches a certain level, the ROS generated in the system can deeply degrade SA, thereby significantly reducing membrane fouling. It is worth noting that under mild conditions of 0.3 g / L SBC and 1 mM PMS, this system showed better inhibition of membrane fouling than traditional pretreatment processes such as coagulation, demonstrating a more economical and environmentally friendly new approach.

[0095] Comparative Example 1 Except for the absence of persulfate and activated sludge, the methods for mitigating membrane fouling are the same as in Example 1.

[0096] Comparative Example 2 The concentration of persulfate (potassium peroxymonosulfate) was 0.1 mM, and no activated sludge was used. The other methods for mitigating membrane fouling were the same as in Example 1.

[0097] Comparative Example 3 The concentration of persulfate (potassium peroxymonosulfate) was 1 mM, and no activated sludge was used. The other methods for mitigating membrane fouling were the same as in Example 1.

[0098] Comparative Example 4 The concentration of persulfate (potassium peroxymonosulfate) was 10 mM, and no activated sludge was used. The other methods for mitigating membrane fouling were the same as in Example 1.

[0099] from Figure 7 It can be seen that the SFR exhibits a significant non-monotonic increasing trend with increasing PMS concentration. Without PMS, the SFR of SA is 1.77 × 10⁻⁶. 14 m·kg -1 When PMS concentrations of 0.1 and 1 mM were added to the system, membrane fouling was not alleviated. Instead, the lack of effective catalytic activation led to the potential aggregation of SA molecules, exacerbating the compactness of the gel layer and causing the SFR to increase to 2.47 × 10⁻⁶ at the 1 mM concentration. 15 m·kg -1 The SFR was approximately 83.7% higher than that of the single-pollutant system. Only when the PMS concentration was significantly increased to 10 mM did the SFR plummet to 2.47 × 10⁻⁶. 13 m·kg -1 Compared to the single-pollutant system, the SFR was reduced by approximately 86.0%, significantly mitigating membrane fouling and demonstrating the destructive effect of high-dose oxidants on the fouled layer. This result strongly suggests that relying solely on PMS to regulate polysaccharide membrane fouling within the conventional low-dose range has significant limitations and a high risk of further deterioration.

[0100] Comparative Example 5 Except that the concentration of sludge-based biochar is 0.1 g / L and persulfate is not used, the other methods for mitigating membrane fouling are the same as in Example 1.

[0101] Comparative Example 6 Except that the concentration of sludge-based biochar is 0.2 g / L and persulfate is not used, the other methods for mitigating membrane fouling are the same as in Example 1.

[0102] Comparative Example 7 Except that the concentration of sludge-based biochar is 0.3 g / L and persulfate is not used, the other methods for mitigating membrane fouling are the same as in Example 1.

[0103] Comparative Example 8 Except that the concentration of sludge-based biochar is 0.4 g / L and persulfate is not used, the other methods for mitigating membrane fouling are the same as in Example 1.

[0104] Comparative Example 9 Except that the concentration of sludge-based biochar is 0.5 g / L and persulfate is not used, the other methods for mitigating membrane fouling are the same as in Example 1.

[0105] Comparative Example 10 Except that the concentration of commercial biochar was 0.1 g / L and persulfate was not used, the other methods for mitigating membrane fouling were the same as in Example 1.

[0106] Comparative Example 11 Except that the concentration of commercial biochar was 0.2 g / L and persulfate was not used, the other methods for mitigating membrane fouling were the same as in Example 1.

[0107] Comparative Example 12 Except that the concentration of commercial biochar was 0.3 g / L and persulfate was not used, the other methods for mitigating membrane fouling were the same as in Example 1.

[0108] Comparative Example 13 Except that the concentration of commercial biochar was 0.4 g / L and persulfate was not used, the other methods for mitigating membrane fouling were the same as in Example 1.

[0109] Comparative Example 14 Except that the concentration of commercial biochar was 0.5 g / L and persulfate was not used, the other methods for mitigating membrane fouling were the same as in Example 1.

[0110] Figure 8 (ab) shows a comparison of the control effects after adding sludge-based biochar (SBC) and commercial biochar (CB). Figure 8a The response of SFR to different doses of SBC and CB was studied. As the SBC dose increased from 0 to 0.1 g / L, the SFR initially increased, then stabilized relatively at 1.22 × 10⁻⁶ g / L from 0.1 to 0.5 g / L. 15 Up to 1.97×10 15 m·kg -1 In contrast, the addition of CB resulted in a linear increase in SFR across the entire concentration range (from 4.57 × 10⁻⁶). 14 Up to 1.89×10 15 m·kg -1 The results showed that, without the addition of the oxidant persulfate, both SBC and CB alone exacerbated membrane fouling. This phenomenon is likely due to the large number of adsorption sites on the biochar surface, which promotes the aggregation of sodium alginate molecules, forming a dense gel layer with a high SFR. However, the modes by which SBC and CB exacerbate membrane fouling differ significantly, directly reflecting the differences in their physicochemical properties.

[0111] Comparative Example 15 Except for the concentration of commercial biochar being 0.1 g / L and the concentration of persulfate (potassium peroxymonosulfate) being 0.1 mM, the other methods for mitigating membrane fouling are the same as in Example 1.

[0112] Comparative Example 16 Except for the concentration of commercial biochar being 0.1 g / L and the concentration of persulfate (potassium peroxymonosulfate) being 1 mM, the methods for mitigating membrane fouling were the same as in Example 1.

[0113] Comparative Example 17 Except that the concentration of commercial biochar was 0.1 g / L and the concentration of persulfate (potassium peroxymonosulfate) was 10 mM, the other methods for mitigating membrane fouling were the same as in Example 1.

[0114] Figure 8b The non-monotonic increase in SFR with increasing PMS concentration is presented for the SBC / PMS and CB / PMS systems at a fixed biochar dosage of 0.1 g / L. In the SBC / PMS system, as PMS increases from 0 to 0.1 mM, the SFR increases from 1.77 × 10⁻⁶ mM. 14 Increased to 5.71 × 10 14 m·kg -1 This indicates that initial membrane fouling was aggravated; when PMS was increased to 1 mM, the SFR was 2.22 × 10⁻⁶. 14 m·kg -1 Although the SFR is higher than that of the single-pollutant system, it is still lower than the SFR of the single 1 mM PMS system (2.47 × 10⁻⁶). 15 m·kg -1 The reduction rate was as high as 91.0%, indicating that SBC has excellent PMS activation ability. When PMS was increased to 10 mM, the SFR decreased to 8.27 × 10⁻⁶. 12 m·kg -1 A 95.4% reduction indicates a significant mitigation of membrane fouling. Notably, throughout the entire PMS range, the SFR value of the SBC / PMS system was consistently lower than that of the CB / PMS system, highlighting the superior PMS catalytic activation ability of SBC compared to CB. While the SBC / PMS system can greatly alleviate membrane fouling at a concentration of 10 mM, from a practical perspective, using high doses of PMS may increase costs and environmental issues. A more sustainable strategy is to reduce the PMS concentration while increasing the SBC dosage, thereby maintaining sufficient oxidation capacity and effectively controlling membrane fouling through a combined adsorption-oxidation mechanism.

[0115] As shown in Figures 1 (ad), 2 (ad), and 3 (ad), compared to commercial biochar, sludge-based biochar possesses abundant mesoporous and macroporous structures and a higher degree of defects, which is beneficial for the diffusion of macromolecular pollutants and the exposure of catalytic sites. Naturally embedded Fe²⁺ ions in sludge-based biochar... + / Fe³ + The redox cycle generates reactive oxygen species, Ca² +Auxiliary charge neutralization and bridging. Following the combined effects of oxidative degradation and metal ion coordination, the physicochemical interactions of pollutants are reshaped. Reactive oxygen species disrupt the skeletal structure of organic matter, Fe... 3+ / Ca 2+ The coordination of the pollutants causes their structure to recombine, and together these two processes drive changes in the microstructure of the pollutant layer. The recombination process forms a porous, hydrophilic filter cake layer with low water-binding capacity, which weakens interfacial adhesion and greatly reduces specific filtration resistance.

[0116] The above embodiments are merely illustrative of the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for mitigating membrane fouling by catalyzing persulfate based on sludge-based biochar, characterized in that, include: A first mixed liquor containing sludge-based biochar is provided, wherein the sludge-based biochar comprises pyrolysis products of Fe and Ca elements in sludge; Provide a second mixture containing organic contaminants; The first mixture and the second mixture are mixed, and then mixed with persulfate to treat the second mixture. The concentration of persulfate is 0.1-10 mM, the concentration of sludge-based biochar is 0.1-0.5 g / L, and the mass ratio of persulfate to sludge-based biochar is 1:(1-1.3).

2. The method according to claim 1, characterized in that, Based on a total mass of 100% for sludge-based biochar, the iron content in the sludge-based biochar is 129 g / kg-132 g / kg, and the calcium content is 81 g / kg-84 g / kg.

3. The method according to claim 1, characterized in that, In the step of treating the second mixture by mixing the first mixture and the second mixture and then mixing it with persulfate, the concentration of the organic pollutant is 0.03-0.07 g / L.

4. The method according to claim 1, characterized in that, The steps for providing a first mixed liquor containing sludge-based biochar include: Sludge-based biochar is dispersed in deionized water and stirred at 280-320 rpm for 0.4-0.6 hours, followed by ultrasonic treatment for 0.4-0.6 hours.

5. The method according to claim 1, characterized in that, The steps of providing a second mixture containing organic contaminants include: Disperse organic pollutants into deionized water and stir at 280-320 rpm for 0.8-1.2 h; and / or, The organic pollutants include one or more of sodium alginate and proteins; and / or, The persulfate includes one or more of sodium persulfate and potassium peroxymonosulfate.

6. The method according to claim 1, characterized in that, The steps of mixing the first mixture and the second mixture, and then mixing them with persulfate, and treating the second mixture include stirring at a speed of 280-320 rpm for 0.8-1.2 hours.

7. The method according to claim 1, characterized in that, The steps of mixing the first mixture and the second mixture, and then mixing them with persulfate, and treating the second mixture include adding methanol to quench the reaction.

8. A method for preparing sludge-based biochar according to any one of claims 1-7, characterized in that, include: The activated sludge is dried to obtain dried activated sludge. The dried activated sludge was pyrolyzed in an inert gas atmosphere to obtain pyrolyzed activated sludge. The pyrolyzed activated sludge was ground to obtain sludge-based biochar.

9. The preparation method according to claim 8, characterized in that, The drying process is performed at a temperature of 100℃-110℃; and / or, The flow rate of the inert gas is 8-12 mL / min; and / or, The pyrolysis treatment includes: heating the dried activated sludge to 500℃-900℃ at a heating rate of 4-6℃ / min, and then holding the temperature at that temperature for 1.5-2.5h.

10. The preparation method according to claim 8, characterized in that, The average particle size of the sludge-based biochar is 180-200 mesh; and / or, The sludge-based biochar comprises one or more of microporous, mesoporous, and macroporous structures; and / or The specific surface area of ​​the sludge-based biochar is 40-60 m². 2 / g; and / or, Based on a total mass of 100% for sludge-based biochar, the iron content in the sludge-based biochar is 129 g / kg-132 g / kg, and the calcium content is 81 g / kg-84 g / kg.

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