Composite material for wastewater treatment based on sludge modification and preparation method thereof

Abstract

The invention discloses a waste water treatment composite material based on sludge modification and a preparation method thereof, and belongs to the technical field of sludge solid waste resource utilization, the whole composite material is of a three-dimensional network structure, the porosity of the three-dimensional network structure is larger than 80%, and raw materials of the composite material comprise, by mass, 55-70% of sludge dry powder, 5-8% of chitosan powder, 5-8% of carbon black powder and 14-30% of water. According to the scheme, through the synergistic effect of the sludge, the chitosan and the carbon black, the adsorption efficiency of various different heavy metals in the wastewater can be remarkably improved, and the stability of a composite material obtained by modifying the sludge can be improved.

Description

Technical Field

[0001] This invention relates to the field of sludge solid waste resource utilization technology, and more specifically, to a sludge-modified composite material for wastewater treatment and its preparation method. Background Technology

[0002] With the acceleration of industrial production and urbanization, the amount of sludge generated during wastewater treatment has increased dramatically. This sludge contains harmful chemicals and therefore requires further treatment to prevent environmental pollution. Global annual dry sludge production averages 18-35 million tons, resulting in a heavy treatment burden and high costs. Traditional disposal methods such as landfill and incineration are not only economically burdensome but also cause secondary pollution (e.g., ...). Emissions, heavy metal leaks, etc.

[0003] Sludge itself has a porous structure, a large specific surface area, and abundant functional groups (such as -OH, -). Sludge exhibits potential adsorption capacity for pollutants such as heavy metals, dyes, and antibiotics, making it a valuable resource for wastewater treatment. However, unmodified sludge has limited adsorption efficiency; moreover, existing wastewater treatment research often focuses on the removal of single metals. Real-world wastewater commonly contains heavy metals such as Fe, Ni, Cu, Mn, Cr, Zn, As, Co, Pb, Cd, Ba, and Be, as well as organic matter. Existing sludge adsorption materials struggle to simultaneously and efficiently adsorb and remove multiple heavy metals.

[0004] Therefore, existing research typically requires pre-modification of sludge. Traditional sludge modification methods usually involve high-temperature pyrolysis (above 700℃), chemical activation (such as KOH treatment), or complex pretreatment, which are energy-intensive, cumbersome, and may damage naturally occurring functional groups in the sludge (such as -OH, -COOH), reducing its adsorption performance. For example, while high-temperature activation of sludge to prepare biochar increases its adsorption capacity, it requires an additional activation step and leads to a decrease in porosity; and introducing industrial calcium-fixed sludge to enhance its structure increases treatment costs.

[0005] Based on the above problems, sludge modification and treatment technology needs further improvement. Summary of the Invention

[0006] 1. Technical problems to be solved The purpose of this invention is to provide a sludge-modified composite material for wastewater treatment and its preparation method, thereby solving the technical problems of limited adsorption capacity of existing sludge adsorbent materials, complex sludge modification processes, and high costs. This invention uses sludge as a matrix and, through the synergistic effect of sludge, chitosan, and carbon black, can significantly improve the adsorption efficiency of various heavy metals in wastewater, and also enhance the stability of the sludge-modified composite material.

[0007] 2. Technical solutions adopted To achieve the above objectives, the technical solution provided by the present invention is as follows: The first aspect of the present invention provides a composite material for wastewater treatment based on sludge modification. The composite material has an overall three-dimensional network structure with a porosity of >80%. Its raw materials contain the following components in the following mass percentages: 55-70% sludge dry powder, 5-8% chitosan powder, 5-8% carbon black powder, and 14-30% carbon black powder.

[0008] The composite material of the present invention is made from sludge powder, chitosan and carbon black as raw materials. It innovatively utilizes the synergistic effect of the three components of sludge-chitosan-carbon black to form a composite material with a three-dimensional spatial network structure. The composite material can be used for wastewater treatment to realize the resource utilization of sludge solid waste and solve the problems of high cost and secondary pollution of traditional sludge landfill / incineration. Moreover, the composite material has high stability and its internal mechanism is as follows: (1) Carbon black interacts with organic matter in sludge through its surface oxygen-containing groups (-C=O, -COOH) to expand the adsorption target sites (such as the adsorption target sites of organic matter in sludge). (1) The adsorption efficiency is increased by 40%); (2) Chitosan improves adsorption efficiency through its amino groups (- (3) The oxygen-containing groups (-C=O, -COOH) in carbon black form covalent and hydrogen bonds with the functional groups (-COOH, -OH) of chitosan, thereby improving structural stability; It forms strong hydrogen bonds, provides coordination sites for heavy metals, and the hydroxyl groups of chitosan and the carboxyl groups (-COOH) generated by the oxidation of carbon black surface form reversible ester bonds during the mixing process, giving the material resilience.

[0009] Furthermore, based on the synergistic effect of pore size, a multi-level adsorption-diffusion synergistic network is formed, the internal mechanism of which is as follows: Sludge micropores (0.5~2 nm) adsorb small molecule heavy metals (such as... Chitosan utilizes chelation to trap large organic molecules (such as dyes), while carbon black macropores (>50 nm) provide rapid mass transfer channels.

[0010] It should be noted that although activated carbon is used in existing technologies for modifying sludge, carbon black is used instead of activated carbon in this invention for the following reasons: Carbon black has a high number of oxygen-containing groups (-C=O, -COOH), resulting in high adsorption efficiency for heavy metals and organic matter. Furthermore, carbon black has a high proportion of mesoporous structures, which facilitates accelerated mass transfer and thus improves adsorption capacity; while activated carbon is mainly microporous, resulting in relatively lower mass transfer efficiency. In addition, carbon black has a higher specific surface area than most activated carbons, and it is also cheaper and more readily available.

[0011] It should be noted that the sludge dry powder in this invention cannot be replaced by semi-solid sludge.

[0012] Furthermore, the mechanical strength of this composite material is ≥14MPa.

[0013] Furthermore, the particle size of the sludge powder used is ≤100 μm; and / or the particle size of the carbon black powder used is <200 nm. Even further, the sludge powder used is obtained by ball milling to expose its internal pores.

[0014] Even more preferably, the moisture content of the sludge powder used is ≤5%.

[0015] The second aspect of the present invention provides a method for preparing a composite material for wastewater treatment based on sludge modification, wherein the composite material is prepared by the sol-gel method.

[0016] The composite material was prepared at room temperature via a sol-gel method. This method eliminates the need for high-temperature activation treatment, consumes less than 0.5 kWh / kg, and reduces energy consumption by 80% compared to high-temperature activation treatment. Furthermore, the retention rate of natural functional groups -OH and -COOH in the sludge matrix is ​​greater than 95%.

[0017] Furthermore, the preparation of the composite material by the sol-gel method specifically includes: mixing sludge dry powder, chitosan powder and carbon black powder to form a sludge / chitosan / carbon black premix; mixing the obtained sludge / chitosan / carbon black premix with water to form a sol; and allowing the obtained sol to stand and solidify or dry to form a three-dimensional network structure composite material.

[0018] Furthermore, the sludge dry powder, chitosan powder, and carbon black powder are mixed evenly. Specific process parameters include: mixing the sludge dry powder and chitosan powder evenly to form a sludge / chitosan premix; and mixing the obtained sludge / chitosan premix evenly with carbon black powder.

[0019] Furthermore, this includes acid activation of the sludge dry powder, followed by sludge dry powder mixing. Sludge contains a large amount of microbial residues, organic matter, and inorganic particles, and its surface functional groups are unevenly distributed. Through acid activation treatment, inert impurities are removed, such as... This process exposes more -OH and -COOH groups on the surface, enhancing the binding capacity between the sludge and the functional groups in carbon black and chitosan. Simultaneously, acidification treatment reduces the heavy metal content in the sludge, thereby improving the adsorption capacity of the sludge matrix. More preferably, the sludge powder raw material originates from an urban wastewater treatment plant, and its heavy metal content complies with GB18918-2002 "Discharge Standard of Pollutants for Urban Wastewater Treatment Plants".

[0020] Furthermore, the carbon black powder is pretreated with ultrasound before being mixed with the carbon black mixture. Ultrasonic pretreatment breaks up carbon black agglomerates to prevent the formation of "island-like" agglomerates during chitosan / sludge mixing.

[0021] Furthermore, this also includes nitric acid oxidation of carbon black powder, followed by ultrasonic pretreatment. The carbon black powder obtained through nitric acid oxidation introduces more -COOH groups, thus improving its hydrophilicity.

[0022] When this composite material is applied to wastewater treatment, it not only enables the resource utilization of sludge matrix to prepare wastewater adsorbents, but also simultaneously removes multiple heavy metal ions from wastewater, including Fe, Cr, Zn, Cd, Pb, and Ni. Cu exhibits high ion removal rates, with adsorption rates exceeding 60%. Furthermore, this adsorbent material can be regenerated at room temperature via acid washing, with minimal reduction in adsorption efficiency after regeneration. In contrast, activated carbon, when used as a wastewater adsorbent, requires high-temperature activation treatment to regenerate its adsorption capacity. With increasing adsorption cycles, once the adsorption efficiency drops to a certain limit, the composite material can be incinerated. The leaching rate of the incineration products is less than 1%, achieving low carbonization throughout its entire life cycle and reducing the carbon footprint by 70%.

[0023] Compared with the prior art, the technical solution provided by this invention has the following advantages: (1) The present invention modifies the sludge matrix and prepares a composite material at room temperature via the sol-gel method, eliminating the need for high-temperature activation treatment, reducing energy consumption by 80%, and retaining the natural functional groups of the sludge. The prepared composite material is used for wastewater treatment, realizing the resource utilization of sludge solid waste and solving the problems of high cost and secondary pollution associated with traditional sludge landfill / incineration.

[0024] (2) This invention modifies sludge by utilizing the synergistic effect of the three components: sludge, chitosan, and carbon black, enabling the sludge, chitosan, and carbon black to form a three-dimensional network structure via a sol-gel method. The interfacial bonding ability of the three components is enhanced through acidic pretreatment of the sludge and nitric acid oxidation of the carbon black. Furthermore, the ratio of chitosan to carbon black is controlled to avoid competition for adsorption targets between the two. More importantly, a multi-level adsorption-diffusion synergistic network is formed by utilizing the pore size characteristics of sludge and carbon black, as well as the chelating properties of chitosan.

[0025] (3) When the composite material prepared by this invention is applied to wastewater treatment, it can simultaneously remove multiple heavy metal ions of equal weight from the wastewater, and is effective against Fe, Cr, Zn, Cd, Pb, Ni, and other heavy metal ions. Cu exhibits high ion removal rates, with adsorption rates exceeding 60%. Furthermore, this adsorbent material can be regenerated at room temperature through acid washing, with minimal reduction in adsorption efficiency after regeneration. In contrast, activated carbon, when used as a wastewater adsorbent, requires high-temperature activation treatment to regenerate its adsorption capacity. Attached Figure Description

[0026] Figure 1 The images show SEM micrographs of the composite materials prepared in Comparative Examples 1-2 and Example 1.

[0027] Figure 2 These are photographs of the three-dimensional network composite materials prepared in Examples 1 and 2. Detailed Implementation

[0028] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments.

[0029] In the following examples and comparative examples, the sludge powder was obtained from a municipal wastewater treatment plant. The sludge powder contains -OH and -COOH functional groups. In this preparation method, the sludge powder is obtained by drying the wastewater treatment plant sludge that meets the discharge standards at a low temperature. The heavy metal content of the sludge powder complies with GB 18918-2002 "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants".

[0030] Example 1 This embodiment provides a method for preparing a composite material for wastewater treatment based on sludge modification. The raw material mass ratio is: 70% sludge dry powder, 8% chitosan powder, 8% carbon black powder, and 14% water. The carbon black powder used has a particle size of less than 200 nm, and the sludge used is from a wastewater treatment plant that meets discharge standards. The sludge is dried at 105°C until its moisture content is less than 5%. The specific preparation steps include: Raw material pretreatment: The sludge is treated with dilute acid to activate it, and then the dry sludge powder is ball-milled until its particle size is ≤100μm.

[0031] The carbon black powder raw material used has a specific surface area of ​​820 m² / g, and the carbon black powder is oxidized with nitric acid.

[0032] The preparation steps of the composite material are as follows: (1) Mix the ball-milled sludge powder with chitosan powder, put them into a twin-screw mixer, and stir at 220 rpm for 6 minutes to form a uniform premix. (2) The carbon black powder is ultrasonically treated so that its particle size is less than 200 nm, and then added to the premix obtained in step 1. Stirring is continued for 12 min to form a uniform premix of the three. (3) Add water slowly to the premix obtained in step 2 according to the above ratio, and continue stirring at 350 rpm for 45 minutes to form a sol; (4) The sol obtained in step 3 is dried at 50°C for 8 hours to form a three-dimensional network structure composite material.

[0033] Photograph of the composite material obtained in this embodiment (reference) Figure 2 As shown in Figure A, its SEM micrograph can be found here. Figure 1 C and Figure 1 As shown in Figure F; SEM shows pore diameters of 50-200 nm, the mechanical strength of the obtained composite material reaches 14 MPa, and the energy consumption of the entire preparation process is <0.5 kWh / kg.

[0034] The composite material prepared in this embodiment was used for wastewater treatment, containing... 95 ppm 150 ppm 60 ppm In a wastewater solution containing 45 ppm, the solution was added at a dosage of 1.5 g / L and stirred, then reacted at room temperature for 2 hours. Test results showed: Removal rate 88.5%, 75.4%, 88.6%, 85% (ICP-OES detection); repeat the above experiment, the adsorption efficiency fluctuation is ≤5%.

[0035] XPS analysis confirmed that oxygen-containing groups (-C=O, -COOH) on the carbon black surface coordinate with metal ions; after soaking the material for 72 hours, the amount of heavy metal leaching was <0.05 ppm, meeting the EPA standard limit of 1 ppm, with no secondary pollution; the BET specific surface area remained at 350 m² / g, which was significantly increased compared to the specific surface area of ​​the unmodified sludge after adsorption.

[0036] Comparative Example 1 This comparative example provides a method for preparing modified sludge. The difference between this comparative example 1 and Example 1 is that chitosan and carbon black are not added to the raw materials. Specifically, the raw material mass ratio is: 70% sludge dry powder and 30% water. The sludge dry powder is pretreated, and steps 1 and 2 are omitted accordingly. The remaining operation steps are basically the same.

[0037] The SEM micrograph of the composite material obtained in this comparative example can be found in [reference needed]. Figure 1As shown in A and 1D, this represents a typical mud condition, from which the coarseness and unevenness of the mud can be observed.

[0038] Comparative Example 2 This comparative example provides a method for preparing a composite material based on sludge modification. The difference between this comparative example 1 and Example 1 is that carbon black is not added to the raw materials. Specifically, the raw material mass ratio is: 70% sludge dry powder, 16% chitosan, and 14% water. Correspondingly, the sludge dry powder is pretreated, and step 2 is omitted. The remaining operation steps are basically the same.

[0039] The SEM micrograph of the composite material obtained in this comparative example can be found in [reference needed]. Figure 1 As shown in B and 1E, the presence of chitosan in the sludge sample enhances the cohesion of sludge particles and reduces the number of cracks, thus improving the cohesion of the resulting composite material.

[0040] Example 2 This embodiment provides a method for preparing a composite material for wastewater treatment based on sludge modification. The raw material mass ratio is: 60% sludge dry powder, 5% chitosan, 5% carbon black, and 30% water. The carbon black powder used has a particle size of less than 200 nm, and the sludge used is from a wastewater treatment plant that meets discharge standards. The sludge is dried at 105°C until its moisture content is less than 5%. The specific preparation steps include: The pretreatment of raw materials in this Example 2 is the same as that in Example 1.

[0041] The preparation steps of the composite material are as follows: (1) Mix the ball-milled sludge powder with chitosan powder, put them into a twin-screw mixer, and stir at 220 rpm for 6 minutes to form a uniform premix. (2) The carbon black powder was ultrasonically treated and added to the premix obtained in step 1. The mixture was stirred at 800 rpm for 8 minutes to form a uniform premix of the three components. (3) Add water slowly to the premix obtained in step 2 according to the above ratio, and continue stirring at 300 rpm for 45 minutes to form a sol; (4) The sol obtained in step 3 is allowed to stand at room temperature for 18 hours to solidify, forming a three-dimensional network structure composite material.

[0042] Photograph of the composite material obtained in this embodiment (reference) Figure 2 As shown in B, its porosity is approximately equal to that of Example 1, and its mechanical strength is significantly improved. The performance of the obtained product is similar to that of Example 1, and the energy consumption for the entire preparation process is <0.5kWh / kg.

[0043] The composite material obtained in this embodiment can be directly used for wastewater treatment without the need for chemical pretreatment of the wastewater. 150 ppm 50 ppm, N Industrial wastewater containing 30 ppm was treated with 3 g / L of the solution, stirred, and reacted at room temperature for 2 hours. The test results showed that the simultaneous removal rates of the above heavy metal ions were 81%, 72%, and 64%, respectively.

[0044] FTIR showed -OH (3400) in the sludge -COOH (1720) The functional groups remained intact, resulting in a 30% increase in adsorption activity; compared with traditional pyrolysis sludge materials, it showed better performance in... The adsorption efficiency can reach 60%, which is 40% higher than that of traditional adsorption.

[0045] Example 3 This embodiment provides a method for preparing a composite material for wastewater treatment based on sludge modification. The raw material mass ratio is: 55% sludge dry powder, 8% chitosan, 8% carbon black, and 29% water. The carbon black powder used has a particle size of less than 200 nm, and the sludge used is from a wastewater treatment plant that meets discharge standards. The sludge is dried at 105°C until its moisture content is less than 5%. The specific preparation steps include: The pretreatment of raw materials in this embodiment 3 is the same as that in embodiment 1.

[0046] The preparation steps of the composite material are as follows: (1) Mix the ball-milled sludge powder with chitosan powder, put them into a twin-screw mixer, and stir at 220 rpm for 6 minutes to form a uniform premix. (2) The carbon black powder is ultrasonically treated so that its particle size is less than 200 nm. It is then added to the premix obtained in step 1 and stirred for 12 min to form a uniform premix of the three. (3) Add water slowly to the premix obtained in step 2 according to the above ratio, and continue stirring at 350 rpm for 40 min to form a sol; (4) The sol obtained in step 3 is allowed to stand at room temperature for 20 hours to solidify, forming a three-dimensional network structure composite material.

[0047] The porosity of the composite material obtained in this embodiment is approximately the same as that in Example 1, and its mechanical strength is improved. The performance obtained is similar to that in Example 1, and the energy consumption for the entire preparation process is <0.5kWh / kg.

[0048] The composite material obtained in Example 3 was used for wastewater treatment. Wastewater adsorption performance was tested: electroplating wastewater containing 120 ppm Fe, 200 ppm Cr, 50 ppm Pb, 65 ppm Zn, 70 ppm Cu, and 180 ppm COD was adsorbed. After adding 5 g / L, the mixture was stirred and reacted at room temperature for 2 hours. The test results showed that the heavy metal removal rates were: Cr 85%, Fe 70%, Pb 65%, Zn 78%, Cu 68%, and COD 91%, which met the emission standards of GB 8978-1996.

[0049] The adsorbed three-dimensional network composite material can be regenerated with 0.1 M HCl, thus allowing for multiple reuses.

[0050] The solidification rate of heavy metals in the sludge is >95% (the leaching amount detected by TCLP method is <0.05 mg / L).

[0051] Compared to landfill disposal, life cycle assessment (LCA) of materials shows a 70% reduction in carbon footprint.

[0052] After being incinerated at high temperature (400℃), the heavy metal leaching rate of saturated adsorbent materials is less than 1%, and they can be safely landfilled or used as building material aggregates or recycled.

Claims

1. A composite material for wastewater treatment based on sludge modification, characterized in that, The composite material has a three-dimensional network structure with a porosity of >80%. Its raw materials contain the following components in the following mass percentages: sludge dry powder 55~70%, chitosan powder 5~8%, carbon black powder 5~8%, and carbon black powder 14~30%.

2. The composite material for wastewater treatment based on sludge modification according to claim 1, characterized in that, The mechanical strength of this three-dimensional composite material is ≥14 MPa.

3. The composite material for wastewater treatment based on sludge modification as described in claim 1, characterized in that, The particle size of the sludge powder used is ≤100 μm; And / or the particle size of the carbon black powder used is <200 nm.

4. The method for preparing a sludge-modified composite material for wastewater treatment according to any one of claims 1-3, characterized in that, The composite material was prepared using the sol-gel method.

5. The method for preparing the composite material for wastewater treatment based on sludge modification according to claim 4, characterized in that, The preparation of this composite material by the sol-gel method specifically includes: Sludge dry powder, chitosan powder and carbon black powder are mixed evenly to form sludge / chitosan / carbon black premix. The resulting sludge / chitosan / carbon black premix was mixed with water to form a sol. The resulting sol is then allowed to stand and solidify or dried to form a composite material with a three-dimensional network structure.

6. The method for preparing the composite material for wastewater treatment based on sludge modification according to claim 5, characterized in that, The process of uniformly mixing sludge powder, chitosan powder, and carbon black powder includes the following specific process parameters: The sludge dry powder and chitosan powder are mixed evenly to form a sludge / chitosan premix; The resulting sludge / chitosan premix was then mixed evenly with carbon black powder.

7. The method for preparing the composite material for wastewater treatment based on sludge modification according to claim 6, characterized in that, It also includes acid activation of sludge dry powder, followed by sludge dry powder mixing.

8. The method for preparing the composite material for wastewater treatment based on sludge modification according to claim 6, characterized in that, It also includes ultrasonic pretreatment of the carbon black powder, followed by carbon black mixing.

9. The method for preparing a wastewater treatment composite material based on sludge modification according to claim 8, characterized in that, It also includes nitric acid oxidation of carbon black powder, followed by ultrasonic pretreatment of carbon black powder.

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