Method for preparing printing and dyeing wastewater purification medium from residue by using mineral-microalgae composite dyeing agent and application thereof

Abstract

The present application belongs to the technical field of printing and dyeing, and particularly relates to a method for preparing a printing and dyeing wastewater purification medium from residues by using a mineral-microalgae composite dyeing agent and application thereof. The method uses solid-liquid mixed waste produced in the preparation process of the natural mineral-microalgae composite dyeing agent as raw material, and the raw material is crushed and sieved after dewatering pretreatment, then carbonized under temperature control, and finally, a porous composite purification medium is obtained through mild activation modification. The present application first carries out resource treatment on the residues produced in the preparation of the natural mineral-microalgae composite dyeing agent, and converts the residues into a printing and dyeing wastewater purification medium. In combination with the role of the natural mineral-microalgae dyeing agent in the printing and dyeing process, the present application realizes a complete closed loop of "front-end dyeing pollution reduction-residue resource utilization-end purification pollution control", and implements the core concept of "waste is resource" of circular economy.

Description

Technical Field

[0001] This invention belongs to the field of printing and dyeing technology, specifically relating to a method for preparing a purification medium for printing and dyeing wastewater using the residue from a mineral-microalgae composite dyeing agent, and its application. Background Technology

[0002] The traditional dyeing and printing industry is a high-energy-consuming and high-emission sector. Traditional dyeing auxiliaries contain harmful components such as phosphorus, phenols, and formaldehyde. Their extensive use significantly increases wastewater BOD and COD values, and also leads to AOX pollution and eutrophication of water bodies. With the successive promulgation of policies such as the "Technical Guidelines for Green and Low-Carbon Development of the Dyeing and Printing Industry" and the "Standard Conditions for the Dyeing and Printing Industry" in China, which explicitly require enterprises to use eco-friendly auxiliaries and impose strict constraints on the biodegradability and VOCs content of auxiliaries, the dyeing and printing auxiliary industry is being forced to upgrade towards environmental protection. Therefore, the environmental friendliness of dyeing auxiliaries has become an important direction for enterprise research and development, and the preparation residues of dyeing auxiliaries are receiving increasing attention.

[0003] Chinese patent CN116514121B discloses a "method for preparing porous activated carbon by carbonization of plant dye residue coupled with activation of dyeing and printing wastewater". This method achieves a COD removal rate of up to 95% for dyeing and printing wastewater. However, the method has extremely high energy consumption and costs, making the equipment investment and operation threshold too high for small and medium-sized environmental protection enterprises. Chen Tianhu et al. published "Experimental Study on Treatment of Dyeing and Printing Wastewater with Montmorillonite-Modified Adsorbent" in *Chinese Journal of Environmental Science*, using sodium-modified and inorganic polymer-modified montmorillonite to treat dyeing and printing wastewater. The COD removal rate of red wastewater was 85% and the decolorization rate was 88%, while the COD removal rate of blue wastewater was 94% and the decolorization rate was 98%. In addition, A. Kausar et al. published a review article "Montmorillonite and modified montmorillonite as adsorbents for removal of water-soluble organic dyes" in *Inorganic Chemistry Communications* (2022, Vol. 143), which systematically summarized the research progress of montmorillonite and modified montmorillonite in adsorbing water-soluble organic dyes. Zhang Mengdi, Zhang Wei, and Yao Jiming reported in the *Journal of Textile Research* the application of natural clay minerals (diatomite, etc.) in the electrocoagulation of indigo dyeing wastewater. However, these applications used primary or chemically modified minerals as raw materials and did not address the treatment of minerals with adsorption saturation.

[0004] Regarding the natural mineral-microalgae composite dyeing agent developed by our unit, the preparation process generates residue. This residue is essentially a solid-liquid mixture of waste, primarily originating from ultrafiltration retrieval residue and formulation sedimentation residue. Ultrafiltration retrieval residue is the solid residue from the ultrafiltration concentration step during the preparation of microalgae active extracts, rich in microalgae cell fragments, denatured protein aggregates, and polysaccharides. Formulation sedimentation residue is the sediment produced after the composite formulation step through settling or low-speed centrifugation, mainly containing unsuspended mineral microparticles, mineral-algae protein composite flocs, and small amounts of impurities. Direct discharge or landfilling of these residues would result in resource waste and secondary pollution; however, there are currently no commercially available technologies for treating such residues. Summary of the Invention

[0005] To address the problems in existing technologies, this invention provides a method for manufacturing a purification medium for dyeing and printing wastewater using residue prepared from a mineral-microalgae composite dyeing auxiliary. This method is the first to utilize the residue prepared from a natural mineral-microalgae composite dyeing auxiliary for resource recovery, transforming it into a purification medium for dyeing and printing wastewater. Combined with the role of the natural mineral-microalgae dyeing auxiliary in the dyeing and printing process, this achieves a complete closed loop of "front-end dyeing and pollution reduction - residue resource recovery - end-end purification and pollution control," embodying the core concept of the circular economy that "waste is a resource."

[0006] To achieve the above technical objectives, the technical solution of the present invention is as follows: A method for preparing a wastewater purification medium for printing and dyeing using the residue from a mineral-microalgae composite dyeing aid includes the following steps: Step 1, Residue Collection and Dehydration Pretreatment: Combine the ultrafiltration residue and the prepared sedimentation residue, and centrifuge at 4000-6000 rpm for 15-20 min for preliminary dehydration, discarding the supernatant; transfer the centrifuged precipitate to a vacuum drying oven and dry at 60-80℃ and -0.08 to -0.10 MPa until the moisture content is ≤10% (by mass), obtaining a grayish-green to grayish-brown dried residue block. The selection of low-temperature vacuum drying conditions in this step can avoid excessive denaturation and cross-linking of microalgal proteins at high temperatures, retain the integrity of active functional groups in the residue, and provide a favorable precursor structure for subsequent carbonization; Step 2, Crushing and Screening: The dried residue blocks are crushed by a pulverizer, passed through a 60-100 mesh sieve, and the sieve-passing material is collected to obtain residue powder with uniform particle size. Step 3, temperature-controlled carbonization: The residue powder is placed in a tube furnace and carbonized under a controlled temperature environment. After carbonization, it is naturally cooled to room temperature under an inert atmosphere to obtain the carbonized product. The inert protective atmosphere is nitrogen or argon with a purity ≥99.9% and a gas flow rate of 50-200 mL / min. The carbonization heating program is as follows: the temperature is increased from room temperature to 200-250℃ at a heating rate of 5-10℃ / min and held for 30-60 min (pre-carbonization stage, to remove physically adsorbed water and some volatile components); the temperature is then increased to 400-600℃ at a heating rate of 3-5℃ / min (main carbonization stage) and held for 1-3 h. The carbonization temperature in this step is controlled at 400-600℃. This temperature range is sufficient to allow microalgal proteins and polysaccharides to undergo sufficient carbonization and form a porous carbon structure containing nitrogen / oxygen functional groups. At the same time, it is lower than the thermal decomposition temperature of calcite (CaCO3, the main component of Bian stone) (about 825℃), thus preserving the integrity of the mineral skeleton. Step 4, Mild Activation Modification: The carbonized product is placed in an oxygen-containing atmosphere and activated at 200-350℃ for 0.5-2 hours. After natural cooling, a porous composite purification medium is obtained. The oxygen-containing atmosphere is air or an O2 / N2 mixture with an O2 volume fraction of 5-21%. This mild oxidation activation step increases the specific surface area by creating micropores and mesopores on the carbon material surface through partial oxidation etching. At the same time, oxygen-containing functional groups (carboxyl-COOH, hydroxyl-OH, carbonyl C=O) are introduced on the carbon surface to enhance the chemical adsorption and ion exchange capacity for dye molecules. The temperature is controlled below 350℃ to avoid excessive oxidation damage to the carbon skeleton.

[0007] The porous composite purification medium has the following characteristics: Specific surface area (BET method): 100-350 m² / g; Total pore volume (BJH method): 0.15-0.50 cm³ / g; Pore ​​structure: A hierarchical pore structure with micropores (<2 nm), mesopores (2-50 nm) and macropores (>50 nm), wherein mesopores account for ≥40%; Surface functional groups (XPS and FT-IR characterization): rich in oxygen-containing functional groups (CO, C=O, OC=O) and nitrogen-containing functional groups (pyridine-N, pyrrole-N, graphite-N), with a total nitrogen content (elemental analysis) of 1.5%-6.0%; Phase composition (XRD characterization): contains diffraction peaks of calcite (CaCO3) and / or quartz (SiO2) crystals (from Bianstone mineral components), as well as broad diffuse peaks of amorphous carbon; Morphological characteristics (SEM characterization): The surface is rough, with micropores and cracks distributed throughout. Mineral particles are embedded in the porous carbon matrix to form a composite microstructure of "mineral core-carbon shell" or "carbon-encased mineral".

[0008] The application method of the porous composite purification medium is to make the porous composite purification medium into a modular "purification core". The specific method is to fill the purification medium into a porous mesh bag or fixed bed module, with a medium filling density of 0.3-0.6 g / cm³, and then embed the purification core modularly into an existing dyeing and printing wastewater treatment device.

[0009] The operating parameters of the purification core are as follows: Water temperature: 15-45℃; pH: 5.0-9.0; Hydraulic retention time (HRT): 2-6 hours; Operating mode: continuous stream or sequential batch.

[0010] Under the above operating conditions, the purification core prepared by the porous composite purification medium can achieve the following purification effects: COD reduction rate ≥80% (potassium dichromate method, GB 11914-89); total nitrogen (TN) reduction rate, of which ammonia nitrogen removal efficiency ≥90% (Nessler's reagent method, HJ 535-2009); color removal rate ≥85% (dilution ratio method, GB 11903-89); the effluent quality is better than the direct discharge limit of the "Water Pollutant Discharge Standard for Textile Dyeing and Finishing Industry" (GB 4287-2012).

[0011] The regeneration method for the porous composite purification medium is as follows: after the purification medium is saturated (the COD removal rate of the effluent drops to below 50% of the initial value), its adsorption capacity can be restored through simple thermal regeneration. The regeneration method involves removing the saturated purification medium from the purification core and heating it in air at 300-400℃ for 1-2 hours to restore more than 80% of the initial adsorption capacity. The regeneration cycle is no less than 5 times. The exhaust gas generated during the regeneration process is treated by an activated carbon adsorption device before being discharged in compliance with standards. Waste medium whose adsorption capacity drops to below 60% of the initial value after 5 cycles can be pulverized and used as building material raw material for final disposal, without generating secondary solid waste.

[0012] As can be seen from the above description, the present invention has the following advantages: 1. This invention is the first to treat the residue from the preparation of natural mineral-microalgae composite dyeing auxiliaries in a resource-based manner and transform it into a purification medium for dyeing and printing wastewater. Combined with the role of natural mineral-microalgae dyeing auxiliaries in the dyeing and printing process, it realizes a complete closed loop of "front-end dyeing and pollution reduction - residue resource utilization - end-end purification and pollution control", and implements the core concept of circular economy that "waste is a resource".

[0013] 2. The carbonization temperature of this invention is controlled at 400-600℃ and the activation temperature is at 200-350℃, which can reduce energy consumption by 40-60%. At the same time, this invention uses waste as raw material, so the raw material cost is almost zero. The comprehensive purification cost of the prepared porous composite purification medium can be reduced to less than 0.38 yuan / ton of water, which is 40%-65% lower than the cost of traditional deep treatment of dyeing and printing wastewater (0.65-1.10 yuan / ton).

[0014] 3. The raw material of this invention is the residue of a natural mineral-microalgae dyeing agent. The naturally coexisting Bianstone mineral powder and microalgae-derived carbon in the residue form an in-situ "mineral framework-carbon matrix" composite material during carbonization, eliminating the need for additional chemical activators (KOH, ZnCl2, etc.) or external carbon / nitrogen sources. The porous framework and surface hydroxyl groups (-OH) provided by the mineral powder synergistically adsorb the nitrogen-containing functional groups (pyridine-N, pyrrole-N) of the algae-derived biochar, resulting in a dye adsorption capacity superior to that of simple mineral adsorbents or biochar. This natural "pre-composite" advantage is unattainable through physical mixing in existing technologies.

[0015] 4. This invention utilizes a porous composite purification medium to support a modular purification core, which can be directly embedded into an enterprise's existing wastewater treatment device (shallow flotation / aeration device) without requiring production shutdowns or additional civil engineering work, achieving "zero-threshold" wastewater upgrading for small and medium-sized printing and dyeing enterprises. The number of modules in the purification core can be flexibly configured according to water quality and quantity, supporting plug-and-play operation.

[0016] 5. This invention implements the principles of green chemistry and circular economy throughout the entire cycle, from raw materials (dyeing agent residue, waste), preparation (medium and low temperature carbonization + mild activation, no chemical activator), use (normal temperature and pressure operation, modular embedding), regeneration (simple thermal regeneration, ≥5 cycles) to final disposal (brick making raw materials, no secondary solid waste generated). Detailed Implementation

[0017] The present invention will be described in detail with reference to the embodiments, but the claims of the present invention are not intended to limit the scope of the invention.

[0018] A method for preparing a wastewater purification medium for printing and dyeing using the residue from a mineral-microalgae composite dyeing aid includes the following steps: Step 1, Residue Collection and Dehydration Pretreatment: Combine the ultrafiltration residue and the prepared sedimentation residue, and centrifuge at 4000-6000 rpm for 15-20 min for preliminary dehydration, discarding the supernatant; transfer the centrifuged precipitate to a vacuum drying oven and dry it at 60-80℃ and -0.08 to -0.10 MPa until the moisture content is ≤10% (by mass), obtaining a gray-green to gray-brown dry residue block; Step 2, Crushing and Screening: The dried residue blocks are crushed by a pulverizer, passed through a 60-100 mesh sieve, and the sieve-passing material is collected to obtain residue powder with uniform particle size. Step 3, temperature-controlled carbonization: The residue powder is placed in a tube furnace and carbonized under a controlled temperature environment. After carbonization, it is naturally cooled to room temperature under an inert atmosphere to obtain the carbonized product. The inert protective atmosphere is nitrogen or argon with a purity ≥99.9% and a gas flow rate of 50-200 mL / min. The carbonization heating program is as follows: the temperature is increased from room temperature to 200-250℃ at a heating rate of 5-10℃ / min and held for 30-60 min (pre-carbonization stage, to remove physically adsorbed water and some volatile components); the temperature is then increased to 400-600℃ at a heating rate of 3-5℃ / min (main carbonization stage) and held for 1-3 h. Step 4, mild activation modification: The carbonized product is placed in an oxygen-containing atmosphere and activated at 200-350℃ for 0.5-2h. After natural cooling, a porous composite purification medium is obtained; the oxygen-containing atmosphere is air or an O2 / N2 mixture with an O2 volume fraction of 5-21%.

[0019] The following examples use the optimal solution as an example: Example

[0020] A method for preparing a purification medium using Bianstone-Chlorella dyeing agent residue includes the following steps: Step 1, Residue Collection: The ultrafiltration residue and the prepared sedimentation residue from the preparation of the natural mineral-microalgae composite dyeing agent are collected together. The ultrafiltration residue is a dark green, viscous slurry (solid content approximately 8.5 wt%, crude protein content 42.3%, crude polysaccharide content 18.6%); the prepared sedimentation residue is a grayish-green mud (solid content approximately 22.3 wt%, mineral components (calcite + quartz) content approximately 65%). The two residues are combined at a wet weight ratio of 1:1. Step 2, Dehydration Pretreatment: Combine the residues and centrifuge at 5000 rpm for 15 min (Xiangyi H1850 centrifuge, 6×500mL rotor), discarding the supernatant. Transfer the centrifuged precipitate to a vacuum drying oven (Shanghai Yiheng DZF-6050) and dry at 70℃ and -0.095 MPa for 24 h until the moisture content is 8.5%, yielding 523g of gray-green dried residue.

[0021] Step 3, Crushing and Screening: The dried residue blocks are crushed for 30 seconds × 3 times (with intermittent cooling) using a high-speed universal crusher (FW-200, Tianjin Tester), and then passed through an 80-mesh standard sieve. The sieve-underfill material is collected to obtain 486g of residue powder (screening yield 92.9%). Step 4, Temperature-Controlled Carbonization: Weigh 100g of the residue powder and spread it evenly in a corundum boat (material layer thickness approximately 15mm). Place the boat in a tube furnace (Hefei Kejing GSL-1500X, quartz tube Φ60mm). Under a nitrogen atmosphere (purity 99.999%, flow rate 100 mL / min), the temperature is increased from room temperature to 220℃ at 8℃ / min and held for 45 min (pre-carbonization stage); then the temperature is increased to 500℃ at 3℃ / min (main carbonization stage) and held for 2 h. After carbonization, the furnace is naturally cooled to room temperature under a nitrogen atmosphere (approximately 4 h), and the black carbonized product is obtained (yield approximately 38.5%, i.e., 38.5g). Step 5, mild activation modification: The carbonized product is placed in a muffle furnace (Shanghai Yiheng SX2-4-10NP), heated to 280℃ at 5℃ / min in air atmosphere, held for 1h, and naturally cooled to room temperature to obtain porous composite purification medium PM-1 (yield of about 88.2%, i.e. 34.0g, relative to the total yield of residue powder of about 34.0%). Example

[0022] A purification medium was prepared using montmorillonite-spirulina composite dyeing agent residue. The residue was used as raw material, and the residue collection and pretreatment were the same as in Example 1. The dehydrated residue had a moisture content of 7.8%. The carbonization temperature was adjusted to a nitrogen atmosphere, increased to 200℃ at 6℃ / min and held for 30 min, then increased to 600℃ at 3℃ / min and held for 1.5 h. Activation conditions: air atmosphere, held at 250℃ for 1.5 h. The resulting purification medium was PM-2. Example

[0023] A purification medium was prepared using montmorillonite-spirulina dyeing agent residue. The residue from the preparation of an attapulgite-purpureus composite dyeing agent was used as raw material. The residue collection, pretreatment, and carbonization were the same as in Example 1, except that the carbonization temperature was 500℃ / 2h; the activation conditions were adjusted to: O2 / N2 mixed gas (O2 volume fraction 10%), held at 300℃ for 0.5h. The resulting purification medium was PM-3.

[0024] Comparative Example 1 Comparative Example 1 uses carbonized products that have not undergone activation treatment; that is, The carbonized product obtained in Example 1 (carbonized at 500℃ for 2h) was used directly as adsorbent material CM-1 without any activation treatment.

[0025] Comparative Example 2 Comparative Example 2 used commercially available activated carbon, specifically commercially available wood powder activated carbon (200 mesh, iodine value ≥900 mg / g, methylene blue adsorption value ≥120 mg / g), as the reference adsorbent AC.

[0026] Comparative Example 3 Comparative Example 3 used natural montmorillonite ore powder and commercially available sodium-based montmorillonite (200 mesh) without any chemical modification treatment as the reference adsorbent material MMT.

[0027] Performance testing The following performance tests were conducted using the products of Examples 1-3 and Comparative Examples 1-3 as test samples.

[0028] Specific surface area and pore structure: Micromeritics ASAP 2460 fully automated specific surface area and porosity analyzer (USA), N2 adsorption-desorption method, 77K. Samples were pre-degassed under vacuum at 150℃ for 6 h. Specific surface area was calculated using the BET equation (P / P0 = 0.05–0.30), total pore volume was calculated using the BJH desorption branch, and micropore volume was calculated using the t-plot method.

[0029] X-ray diffraction (XRD): Bruker D8 Advance X-ray diffractometer (Germany), Cu Kα radiation (λ=0.15418 nm), tube voltage 40kV, tube current 40mA, scanning range 2θ=5°-80°, step size 0.02°, scanning speed 4° / min.

[0030] Fourier transform infrared spectroscopy (FT-IR): Thermo Scientific Nicolet iS50 FT-IR spectrometer (USA), KBr pellet method, scanning range 4000-400 cm⁻¹, resolution 2 cm⁻¹, 32 scans.

[0031] X-ray photoelectron spectroscopy (XPS): Thermo Scientific K-Alpha XPS spectrometer (USA), Al Kα X-ray source (1486.6 eV), analysis area 400 μm diameter, full spectrum pass energy 200 eV, high-resolution narrow spectrum pass energy 50 eV.

[0032] Scanning electron microscope (SEM): JEOL JSM-IT800 field emission scanning electron microscope (Japan), accelerating voltage 5-15kV, sample sputtering with gold (Pt, 30s).

[0033] Table 1. Structural characterization data of the purification media in Examples 1-3 and Comparative Examples 1-3 Note: EA = Elemental Analysis; XPS N1s peak fitting was performed using Avantage software, pyridine-N (398.6±0.3 eV), pyrrole-N (400.1±0.3 eV), graphite-N (401.2±0.3 eV); "-" indicates that the material does not contain this type of component or is not applicable.

[0034] The data in Table 1 show that: (a) After carbonization and activation treatment, the BET specific surface area of ​​Examples 1-3 (PM-1 to PM-3) was 215-312 m² / g, which was significantly higher than that of the unactivated CM-1 (142 m² / g), confirming the promoting effect of mild oxygen activation on pore development; (b) The mesoporous content of PM-1 to PM-3 was ≥59.5%, showing hierarchical pore characteristics, which is beneficial to the mass transfer and adsorption of dye macromolecules; (c) XPS analysis confirmed that the PM series materials contained multiple nitrogen-containing functional groups such as pyridine-N, pyrrole-N and graphite-N (endogenous nitrogen doping from microalgal proteins), and these nitrogen-containing sites provided Lewis base sites in dye adsorption; (d) XRD results showed that the materials contained both mineral crystal diffraction peaks and broad diffuse peaks of amorphous carbon (2θ≈25°), confirming the formation of the "mineral-carbon" composite structure.

[0035] Application Examples 1. Preparation of Simulated Dyeing and Printing Wastewater: Based on the water quality characteristics of typical reactive dyeing wastewater for cotton fabrics, simulated dyeing and printing wastewater was prepared. The main water quality indicators are as follows: CODcr: 856 mg / L; Total Nitrogen (TN): 42.5 mg / L; Ammonia Nitrogen (NH3-N): 28.3 mg / L; Color (dilution method): 320 times; pH: 7.8; Conductivity: 3560 μS / cm. The dye composition was a mixture of Reactive Red 3BS (60%), Reactive Yellow 3RS (25%), and Reactive Blue 19 (15%).

[0036] 2. Adsorption test conditions: Weigh 1.0 g of each sample from Examples 1-3 and Comparative Examples 2-3, and add 200 mL of simulated dyeing and printing wastewater (solid-liquid ratio 1:200). Incubate at 25℃ with a constant temperature shaking chamber at 150 rpm for 4 h (simulating HRT). After adsorption, filter through a 0.45 μm microporous membrane. Determine the CODcr, TN, NH3-N, and color of the filtrate. Perform three replicates for each experiment and take the average value.

[0037] Table 2 Comparison of the purification effects of the products in Examples 1-3 and Comparative Examples 2-3 on simulated dyeing and printing wastewater Note: The values ​​in parentheses represent the removal rates (%) for each indicator. GB 4287-2012 specifies the direct discharge limits for water pollutants from the textile dyeing and finishing industry.

[0038] As can be seen from the data in Table 2, Examples 1-3 showed excellent purification effects in the adsorption test of simulated dyeing and printing wastewater, and showed excellent removal rates in terms of CODcr, TN, NH3-N and color. However, Comparative Examples 2 and 3 had some defects and could not achieve good purification effects.

[0039] 3. Verification using actual dyeing and printing wastewater: Actual reactive dyeing mixed wastewater (CODcr 1250 mg / L, TN 58.3 mg / L, NH3-N 35.6 mg / L, color 500 times, pH 8.2) from a dyeing and printing enterprise in Shaoxing, Zhejiang Province was treated with PM-1 continuous flow fixed bed (Φ50mm×300mm, packing volume 120g, packing density 0.45g / cm³, HRT=4h) for 72h. The effluent quality was measured every 12h. The results showed that during 72 hours of continuous operation, the average removal rates of CODcr, TN, NH3-N, and color in the effluent were 83.5% ± 2.8%, 88.7% ± 3.2%, 90.5% ± 2.5%, and 87.2% ± 3.6%, respectively. The effluent quality was consistently better than the indirect discharge limit of GB 4287-2012, and the effluent quality in the first 48 hours met the direct discharge limit requirements.

[0040] Regeneration performance test The PM-1 (Example 1) that had been saturated with adsorption (with effluent CODcr reduced to 48.5% of the initial value) was removed from the purification core and regenerated by heating at 350°C for 1.5 hours in air. The regenerated PM-1 was then subjected to adsorption experiments again (under the same conditions as in Application Example 2), with 5 cycles. Simultaneously, commercial activated carbon AC (Comparative Example 2) was used as a control for adsorption-regeneration under the same conditions.

[0041] Table 3 Comparison of 5 regeneration cycle performance between Example 1 and Comparative Example 2 Note: Adsorption capacity recovery rate (%) = (COD removal rate after regeneration ÷ initial COD removal rate) × 100%. Regeneration conditions: air atmosphere, 350℃, 1.5h.

[0042] As can be seen from the data in Table 3: (a) After 5 regeneration cycles, the adsorption capacity recovery rate of PM-1 remained at 84.5%, which was significantly better than that of commercial activated carbon AC (which only recovered 20.9% after 5 cycles); (b) The adsorption capacity of AC decreased sharply with the number of regeneration cycles, mainly because the microporous structure of activated carbon is prone to pore collapse and ablation during high-temperature oxidation regeneration, while the Bianstone mineral skeleton in PM-1 provides structural rigidity, effectively inhibiting the pore collapse of the carbon matrix; (c) The COD removal rate of PM-1 after the 5th regeneration (71.8%) was still higher than that of AC after the 1st regeneration (76.2%), which fully demonstrated the advantages of the mineral-carbon composite structure in terms of regeneration durability; (d) The waste PM-1 after 5 regeneration cycles can be crushed (passed through a 100-mesh sieve) and then mixed into brick-making raw materials (mixing ratio 5%-10%) to achieve final harmless disposal.

[0043] Regarding the purification cost of the purification medium, taking Example 1 (PM-1) as an example, a comprehensive purification cost calculation is performed. Based on a total yield of 34.0% from residual powder to purification medium PM-1, approximately 2.94 tons of auxiliary dye residue (dry basis) are required to produce 1 ton of purification medium. The residue is waste (zero cost). The carbonization process consumes approximately 850 kWh / ton of medium (including heating and insulation in the tubular furnace, actual measurement), and the activation process consumes approximately 180 kWh / ton of medium (muffle furnace). Assuming an industrial electricity price of 0.65 yuan / kWh, the energy cost is approximately 669 yuan / ton of medium. Equipment depreciation and labor costs are approximately 200 yuan / ton of medium. The comprehensive preparation cost is approximately 869 yuan / ton of medium.

[0044] Based on the calculation that each ton of media can treat approximately 500-800 tons of dyeing and printing wastewater (continuous operation for 6 months until the first regeneration under HRT 2-6h conditions), the media consumption cost is approximately 1.09-1.74 yuan / ton of water. Considering a lifespan of 5 regeneration cycles, the total water treatment capacity of the media over its entire life cycle is approximately 2500-4000 tons / ton of media, and the total purification cost over its entire life cycle is approximately 0.22-0.35 yuan / ton of water. This represents a 40%-85% reduction compared to the cost of traditional deep treatment of dyeing and printing wastewater (approximately 1.2-2.5 yuan / ton of water for the Fenton process and approximately 0.65-1.10 yuan / ton of water for activated carbon adsorption).

[0045] It is understood that the above detailed description of the present invention is for illustrative purposes only and is not intended to limit the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effects; as long as the usage requirements are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a purification medium for dyeing and printing wastewater using residue from a mineral-microalgae composite dyeing aid, characterized in that: Includes the following steps: Step 1, Residue Collection and Dehydration Pretreatment: Combine the ultrafiltration residue and the prepared sedimentation residue, and centrifuge at 4000-6000 rpm for 15-20 min for preliminary dehydration, discarding the supernatant; transfer the centrifuged precipitate to a vacuum drying oven and dry it at 60-80℃ and -0.08 to -0.10 MPa until the moisture content is ≤10% (by mass), obtaining a gray-green to gray-brown dry residue block; Step 2, Crushing and Screening: The dried residue blocks are crushed by a pulverizer, passed through a 60-100 mesh sieve, and the sieve-passing material is collected to obtain residue powder with uniform particle size. Step 3, temperature-controlled carbonization: The residue powder is placed in a tube furnace and carbonized under a temperature-controlled program in an inert protective atmosphere. After carbonization, it is naturally cooled to room temperature in an inert atmosphere to obtain the carbonized product. Step 4, mild activation modification: The carbonized product is placed in an oxygen-containing atmosphere and activated at 200-350℃ for 0.5-2 hours. After natural cooling, a porous composite purification medium is obtained.

2. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 1, characterized in that: The inert protective atmosphere in step 3 is nitrogen or argon with a purity ≥99.9% and a gas flow rate of 50-200 mL / min.

3. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 1, characterized in that: The carbonization heating program in step 3 is as follows: heat from room temperature to 200-250℃ at a heating rate of 5-10℃ / min, hold for 30-60 min; continue heating to 400-600℃ at a heating rate of 3-5℃ / min, hold for 1-3 h.

4. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 1, characterized in that: The oxygen-containing atmosphere in step 4 is air or an O2 / N2 mixture with an O2 volume fraction of 5-21%.

5. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 1, characterized in that: The porous composite purification medium has the following characteristics: Specific surface area: 100-350 m² / g; Total pore volume: 0.15-0.50 cm³ / g; Pore ​​structure: A hierarchical pore structure with micropores, mesopores and macropores, wherein mesopores account for ≥40%; Surface functional groups: rich in oxygen-containing and nitrogen-containing functional groups, with a total nitrogen content of 1.5%-6.0%; Phase composition: Contains diffraction peaks of calcite and / or quartz crystals, as well as broad diffuse peaks of amorphous carbon; Morphological characteristics: The surface is rough, with micropores and cracks. Mineral particles are embedded in the porous carbon matrix to form a composite microstructure of "mineral core-carbon shell" or "carbon-encased mineral".

6. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 1, characterized in that: The application method of the porous composite purification medium is to make the porous composite purification medium into a modular "purification core". The specific method is to fill the purification medium into a porous mesh bag or fixed bed module with a medium filling density of 0.3-0.6 g / cm³, and then embed the purification core modularly into an existing dyeing and printing wastewater treatment device.

7. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 6, characterized in that: The operating parameters of the purification core are as follows: Water temperature: 15-45℃; pH: 5.0-9.0; Hydraulic retention time: 2-6 hours; Operating mode: continuous stream or sequential batch.

8. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 1, characterized in that: The regeneration method of the porous composite purification medium is that after the purification medium is saturated, it can be restored to its adsorption capacity through simple thermal regeneration. The regeneration method is to take the saturated purification medium out of the purification core and heat it in an air atmosphere at 300-400℃ for 1-2 hours to restore more than 80% of the initial adsorption capacity.

9. The method for preparing a dyeing and printing wastewater purification medium using the residue from a mineral-microalgae composite dyeing aid according to claim 8, characterized in that: The porous composite purification medium undergoes at least 5 regeneration cycles.

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