A method for zero-discharge treatment of printing process wastewater and waste paper

Abstract

This invention proposes for the first time a method for preparing waste paper-based adsorption filter cartridges directly from waste paper generated during the printing process. This method is applicable not only to waste books and newspapers but also to waste labels, thus solving the problem that waste labels can only be disposed of as solid waste through landfill or incineration. It is environmentally friendly and has significant social implications. The density of the waste paper-based filter cartridge is 10-40 g / cm³. 3 With a porosity of 95-99%, the adsorption capacity is significantly enhanced, and the material is reusable. Using the aforementioned filter element to treat printing wastewater, a "waste-to-waste" approach, is not only simple and safe but also environmentally friendly. The treated wastewater exhibits a 90-99% color removal rate, 70-80% COD and 75-85% BOD removal rates, and a 95-99% SS removal rate, making it suitable for use as washing water in the printing process. This achieves zero discharge of printing wastewater and waste paper, yielding unexpected results and holding significant importance for the development of the printing industry.

Description

Technical Field

[0001] This invention belongs to the field of environmental engineering industrial wastewater treatment technology, and relates to the treatment of printing wastewater and waste paper, specifically to a method for zero-discharge treatment of printing wastewater and waste paper. Background Technology

[0002] Printing wastewater is a general term for wastewater generated during the printing process, including plate-making wastewater, printing wastewater, and cleaning wastewater. It contains pollutants such as ink, adhesives, dampening solution, and paper scraps. In particular, the ink contains a large amount of metal ions (Pb). 2+ Cr 6+ The toxic unsaturated organic compounds derived from carbocyclic or heterocyclic aromatic organic compounds (such as hydroxyl, hydroxyl, and hydroxyl) result in printing wastewater with complex composition, high color, high toxicity, and poor biodegradability. Direct discharge without treatment not only poses a significant threat to human health but also causes severe environmental pollution.

[0003] Currently, the main methods used for treating printing wastewater include: 1) Coagulation and sedimentation: This is the most commonly used method, mainly using reagents such as polyacrylamide and polyaluminum chloride to settle metal ions and organic matter in the wastewater, thereby purifying the water. 2) Biological contact oxidation: This method uses strong oxidants such as Fenton's reagent to decompose organic matter in the wastewater. After anaerobic microbial fermentation, the organic matter is decomposed into gases such as methane and carbon dioxide, which are then discharged. This method can effectively remove various pollutants from the wastewater, making the treated wastewater meet discharge standards. However, the process is complex, and the treated wastewater cannot be directly reused in the printing process. Furthermore, multi-stage biological contact oxidation tanks require a large area and are costly, limiting their practical application. 3) Adsorption: This method is simple to operate, inexpensive, reusable, and does not produce secondary pollution. Currently, the adsorbents used in this method have problems such as high cost, lack of green raw materials, or poor adsorption effect. 4) Membrane bioreactor: This method separates components in wastewater through membrane treatment technology, but it is costly and has poor applicability.

[0004] Due to the complex composition and difficulty in treating printing wastewater, a single treatment method is usually insufficient, requiring multiple methods in a multi-stage process. Among these, flocculation and physical adsorption are two of the most commonly used water treatment methods. First, flocculants are used to flocculate large organic molecules and suspended solids in the wastewater, followed by physical adsorption of metal ions and other small molecules. While this method combines the advantages of both approaches and achieves good results, it still does not overcome the inherent problems of adsorbents in existing technologies.

[0005] Besides printing wastewater, a large amount of waste paper is also generated during the printing and post-processing stages. Common waste paper, such as waste newspapers, waste book paper, and waste corrugated cardboard, can be directly pulped and reused as secondary fibers in the papermaking process after simple sorting, or it can be reprocessed to produce low-value paper-based materials or foam absorbent materials. However, with the development of packaging materials, the market share of self-adhesive labels is also increasing. Because waste label paper is a special paper-based material containing adhesive and ink, it is difficult to recycle and is currently usually disposed of as solid waste through landfill or incineration.

[0006] If zero discharge of printing wastewater and waste paper can be achieved simultaneously, it will not only be environmentally friendly, but also solve the problem that restricts the development of the printing industry, and has important practical application value. However, there have been no related reports yet. Summary of the Invention

[0007] To address the problems existing in the treatment of wastewater and waste paper in the printing industry, this invention proposes for the first time a method for treating printing wastewater by directly utilizing waste paper materials generated during the printing process to prepare waste paper-based adsorption filter cartridges; and further utilizes the adsorption filter cartridges to achieve zero discharge of printing wastewater. Wastewater treated using the method described in this application can be used as washing water in the printing process; thus achieving zero discharge of printing wastewater and waste paper, yielding unexpected results and having significant implications for the development of the printing industry.

[0008] The technical solution of the present invention: a method for preparing adsorption filter elements using waste printing paper, comprising the following steps:

[0009] (a) Waste printing paper is crushed and sieved to obtain pulp raw material; then, it is subjected to high-pressure homogenization to obtain a nano-sized pulp dispersion. The high-pressure homogenization process specifically involves dispersing the pulp raw material in water at a concentration of 0.1-1.0 wt%, and homogenizing at 400-1000 bar for 5-20 cycles. The waste printing paper is corrugated paper, book paper, newspaper, or label paper.

[0010] (b) Add a crosslinking agent to the pulp dispersion obtained in step (a) and stir until homogeneous to obtain a gelling system; the amount of crosslinking agent is 0.5-10% of the weight of the pulp raw material. The crosslinking agent is a silane coupling agent, citric acid, tannic acid, epichlorohydrin, or an aldehyde crosslinking agent.

[0011] (c) The gelation system obtained in step (b) is washed with excess tert-butanol and then freeze-dried to obtain a waste paper-based adsorption filter element for printing wastewater treatment. The specific operation of the tert-butanol washing is as follows: 1-2 times the volume of tert-butanol is added to the gelation system, sealed and soaked for 1-2 hours, and then the adsorption filter element material is removed; this process is repeated 2-5 times. The inventors unexpectedly discovered that by adding a tert-butanol washing step, the freeze-dried adsorption filter element can form a smaller, more uniform, loose, porous structure, effectively increasing the specific surface area of ​​the filter element and thus significantly improving its adsorption capacity. Furthermore, because tert-butanol has a high vapor pressure, it is conducive to sublimation; therefore, the tert-butanol washing step significantly reduces the freeze-drying time required for the adsorption material.

[0012] Preferably, the sieving in step (a) refers to passing the pulverized raw material through a 100-mesh sieve, and taking raw material with a mesh size greater than 100 mesh; the freeze-drying in step (c) specifically involves: pre-freezing the gel system at -20 to 10°C for 30 min to 2 h, and then freeze-drying it at -20 to -90°C, with a freeze-drying time of 20-60 min per unit volume of gel material, and a unit volume of 1 cm³. 3 .

[0013] A waste paper-based filter element for treating printing wastewater is prepared using the method described above; the density of the waste paper-based filter element is 10-40 g / cm³. 3 The porosity is 95-99%. Unlike filter cartridges in the prior art that are only used for filtration, the waste paper-based filter cartridge prepared in this application has significantly enhanced adsorption capacity and can be reused by compression, with a reuse count of no less than 20 times. Furthermore, the size and shape of the waste paper-based filter cartridge can be adjusted according to the mold size.

[0014] A method for zero-discharge treatment of printing wastewater and waste paper includes the following steps:

[0015] (1) First-stage wastewater treatment: Printing wastewater is treated by flocculation to obtain second-stage wastewater; the flocculant used is polyacrylamide or polyaluminum chloride. The dosage of polyacrylamide is 5-30 mg / L of wastewater volume, and the dosage of polyaluminum chloride is 1-20 mg / L of wastewater volume. The printing wastewater contains 30,000-50,000 mg / L of COD (chemical oxygen demand), 2,000-3,000 mg / L of BOD (biochemical oxygen demand), and 100-300 mg / L of SS (suspended solids), with a color greater than 1000 times. Compared with the original printing wastewater, the second-stage wastewater has a color removal rate of 40-60%, COD and BOD removal rates of 30-50% and 40-60% respectively, and an SS removal rate of 70-90%.

[0016] (2) Second-stage wastewater treatment: The wastewater obtained in step (1) is treated using the waste paper-based filter cartridge to obtain treated wastewater. The amount of the filter cartridge used is 5-50 mg / L relative to the second-stage wastewater. Compared with printing wastewater, the treated wastewater has a color removal rate of 90-99%, a COD and BOD removal rate of 70-80% and 75-85% respectively, and an SS removal rate of 95-99%. It can be directly reused as washing water in the printing industry, achieving zero discharge of printing wastewater and achieving unexpected results.

[0017] Moreover, this invention innovatively introduces a "waste-to-waste" process in the treatment of printing wastewater. It uses waste label paper that cannot be recycled to prepare water purification materials, which not only treats printing wastewater but also turns waste label paper into a valuable resource. This provides an efficient, low-cost, and easy-to-operate method for the comprehensive treatment of printing waste.

[0018] The beneficial effects of this invention are:

[0019] (1) This invention provides a process for zero discharge of printing wastewater and waste paper. It innovatively proposes to use printing waste paper to treat printing wastewater, “using waste to treat waste”. The process is not only simple, but also safe and environmentally friendly, providing a new method for the comprehensive treatment of printing waste.

[0020] (2) The method for preparing waste paper-based adsorbent materials using waste paper described in this invention is applicable not only to waste books and newspapers, but also to waste label paper, thereby solving the problem that waste label paper can only be disposed of as solid waste through landfill or incineration. It is environmentally friendly and has important social significance.

[0021] (3) The treatment method in this invention combines a first stage of flocculation for wastewater treatment and a second stage of adsorption treatment using the waste paper-based adsorption filter described in this application. This ensures that the treated wastewater meets the requirements for washing water in the printing industry, thereby achieving zero discharge of printing wastewater and waste paper. It has broad application prospects in the field of printing waste treatment. Attached Figure Description

[0022] Appendix Figure 1 This is a photograph of the actual printing wastewater from Example 1.

[0023] Appendix Figure 2 It is the waste corrugated paper-based adsorption filter material used in Example 1.

[0024] Appendix Figure 3 The color change of the wastewater before and after filtration in Example 1 is shown.

[0025] Appendix Figure 4 It is the waste label paper used in Example 5.

[0026] Appendix Figure 5 It is the waste label paper-based adsorption filter material obtained in Example 5.

[0027] Appendix Figure 6 This is the filtration process of the waste label paper-based adsorption filter cartridge in Example 5.

[0028] Appendix Figure 7 The color changes of the wastewater before and after filtration in Example 5 are shown.

[0029] Appendix Figure 8 This is a scanning electron microscope image of the waste label paper-based adsorption filter prepared in Example 5.

[0030] Appendix Figure 9 This is a scanning electron microscope image of the waste label paper-based adsorption filter prepared in Comparative Example 5. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments.

[0032] The following description, through specific implementation examples and accompanying drawings, does not imply that the present invention is limited to these examples.

[0033] Example 1: Waste paper-based filter cartridges prepared from waste corrugated paper for printing wastewater treatment

[0034] (1) The mixed wastewater from printing plate making and ink roller washing is treated by flocculation. Figure 1 The wastewater was tested and found to contain 30,000 mg / L of COD (Chemical Oxygen Demand), 2,000 mg / L of BOD (Biochemical Oxygen Demand), and 100 mg / L of SS (Suspended Solids), with a color greater than 1000 times. Polyacrylamide was used as the flocculant at a dosage of 30 mg / L of wastewater volume. After flocculation, the color removal rate was 60%, the COD and BOD removal rates were 50% and 60%, respectively, and the SS removal rate was 90%.

[0035] (2) Waste corrugated paper from printing was crushed and sieved to obtain pulp raw material with a mesh size greater than 100. The pulp raw material was dispersed in water at a concentration of 0.1%, and a nano-sized pulp dispersion was obtained by high-pressure homogenization (400 bar, 5 cycles). 2% formaldehyde (relative to the pulp raw material) was added to the pulp dispersion and mixed evenly to obtain a gelation system. 1 times the volume of tert-butanol was added to the gelation system, and after sealing and soaking for 1 hour, the adsorption filter material was removed; this was repeated 5 times. The gel filter was pre-frozen at -20℃ for 30 min, and then freeze-dried at -20℃ for 60 min / cm³ of gel material volume. 3 To obtain waste paper-based adsorption filter cartridges ( Figure 2 ).

[0036] (3) 50 mg / L (relative to the volume of wastewater) of filter material was used to filter the second stage of wastewater. After filtration, the color removal rate of the wastewater was 99%, the COD and BOD removal rates were 80% and 85% respectively, and the SS removal rate was 99%. The adsorbed wastewater can be directly reused as washing water. Figure 3 The filter cartridge can still achieve the same effect in terms of color removal rate and other indicators after being repeated 20 times.

[0037] Example 2: Waste paper-based filter cartridges prepared from waste book and magazine paper for printing wastewater treatment

[0038] (1) Flocculation treatment was used to treat the mixed wastewater from printing plate making and ink roller washing. The wastewater was found to contain 50,000 mg / L of COD (Chemical Oxygen Demand), 3,000 mg / L of BOD (Biochemical Oxygen Demand), and 300 mg / L of SS (Suspended Solids), with a color greater than 1000 times. Polyaluminum chloride was used as the flocculant at a dosage of 20 mg / L of the wastewater volume. After flocculation, the color removal rate was 50%, the COD and BOD removal rates were 40% and 50% respectively, and the SS removal rate was 90%.

[0039] (2) Waste printed books and periodicals were crushed and sieved to obtain pulp raw material with a mesh size greater than 100. The pulp raw material was dispersed in water at a concentration of 0.5%, and a nano-sized pulp dispersion was obtained by high-pressure homogenization (1000 bar, 10 cycles). 10% tannic acid (relative to the pulp raw material) was added to the pulp dispersion and mixed evenly to obtain a gelation system. According to the volume ratio, 2 times the amount of tert-butanol was added to the gelation system, and after sealing and soaking for 2 hours, the adsorption filter material was taken out; this was repeated twice. The gel filter was pre-frozen at -10℃ for 1 hour, and then freeze-dried at -50℃ for 40 min / cm³ relative to the volume of the gel material. 3 To obtain waste paper-based adsorption filter cartridges.

[0040] (3) Use filter material with a concentration of 40 mg / L (relative to the volume of wastewater) for filtering the second stage of wastewater. Figure 4 After filtration, the wastewater achieved a 98% removal rate for color, 70% for COD, 75% for BOD, and 95% for SS. The adsorbed wastewater can be directly reused as washing water. Figure 5 The filter cartridge can still achieve the same effect in terms of color removal rate and other indicators after being repeated 20 times.

[0041] Example 3: Using waste newspapers to prepare waste paper-based filter cartridges for printing wastewater treatment

[0042] (1) Flocculation treatment was used to treat the mixed wastewater from printing plate making and ink roller washing. The wastewater was found to contain 35,000 mg / L of COD (Chemical Oxygen Demand), 2,500 mg / L of BOD (Biochemical Oxygen Demand), and 200 mg / L of SS (Suspended Solids), with a color greater than 1000 times. Polyacrylamide was used as the flocculant at a dosage of 5 mg / L of the wastewater volume. After flocculation, the color removal rate was 40%, the COD and BOD removal rates were 30% and 40% respectively, and the SS removal rate was 70%.

[0043] (2) Waste newspapers were crushed and sieved to obtain pulp raw material with a mesh size greater than 100. The pulp raw material was dispersed in water at a concentration of 1%, and a nano-sized pulp dispersion was obtained by high-pressure homogenization (500 bar, 20 cycles). 0.5% epichlorohydrin (relative to the pulp raw material) was added to the pulp dispersion and mixed evenly to obtain a gelation system. 1.5 times the volume of tert-butanol was added to the gelation system, and the mixture was sealed and soaked for 2 hours. The adsorption filter material was then removed; this process was repeated 4 times. The gel filter was pre-frozen at 10°C for 2 hours and then freeze-dried at -90°C for 20 min / cm³ of gel material volume. 3 , and obtain waste paper-based adsorption filter cartridges. (3) Take 5 mg / L (relative to the volume of wastewater) of filter cartridge material for filtering the second stage of wastewater. After filtration, the color removal rate of the wastewater is 90%, the COD and BOD removal rates are 72% and 79% respectively, and the SS removal rate is 95%. The adsorbed wastewater can be directly reused as washing water. After the filter cartridge is repeated 20 times, the color removal rate and other indicators can still achieve the same effect.

[0044] Example 4: Waste paper-based filter cartridges prepared from waste corrugated paper for printing wastewater treatment

[0045] (1) Flocculation was used to treat the mixed wastewater from printing plate making and ink roller washing. The wastewater was found to contain 40,000 mg / L of COD (Chemical Oxygen Demand), 2,200 mg / L of BOD (Biochemical Oxygen Demand), and 150 mg / L of SS (Suspended Solids), with a color greater than 1000 times. Polyaluminum chloride was used as the flocculant at a dosage of 1 mg / L of the wastewater volume. After flocculation, the color removal rate was 43%, the COD and BOD removal rates were 35% and 44%, respectively, and the SS removal rate was 75%.

[0046] (2) Waste corrugated paper from printing was crushed and sieved to obtain pulp raw material with a mesh size greater than 100. The pulp raw material was dispersed in water at a concentration of 0.8%, and a nano-sized pulp dispersion was obtained by high-pressure homogenization (800 bar, 15 cycles). 5% silane coupling agent (relative to the pulp raw material) was added to the pulp dispersion and mixed evenly to obtain a gelation system. According to the volume ratio, 2 times tert-butanol was added to the gelation system, and after sealing and soaking for 1.5 h, the adsorption filter material was taken out; this was repeated 3 times. The gel filter was pre-frozen at 0℃ for 1 h, and then freeze-dried at -80℃ for 30 min / cm³ relative to the volume of the gel material. 3 To obtain waste paper-based adsorption filter cartridges.

[0047] (3) A filter material with a concentration of 30 mg / L (relative to the volume of wastewater) was used to filter the second stage of wastewater. After filtration, the color removal rate of the wastewater was 95%, the COD and BOD removal rates were 79% and 80%, respectively, and the SS removal rate was 97%. The adsorbed wastewater can be directly reused as washing water. After the filter material was repeated 20 times, the color removal rate and other indicators still achieved the same effect.

[0048] Example 5: Preparation of waste paper-based filter cartridges from waste label paper for printing wastewater treatment

[0049] (1) Flocculation treatment was used to treat the mixed wastewater from printing plate making and ink roller washing. The wastewater was found to contain 45,000 mg / L of COD (Chemical Oxygen Demand), 2,800 mg / L of BOD (Biochemical Oxygen Demand), and 200 mg / L of SS (Suspended Solids), with a color greater than 1000 times. Polyacrylamide was used as the flocculant at a dosage of 20 mg / L of the wastewater volume. After flocculation, the color removal rate was 55%, the COD and BOD removal rates were 44% and 53%, respectively, and the SS removal rate was 84%.

[0050] (2) Waste label paper from printing was crushed and sieved to obtain pulp raw material with a mesh size greater than 100. The pulp raw material was dispersed in water at a concentration of 0.6%, and a nano-sized pulp dispersion was obtained by high-pressure homogenization (900 bar, 5 cycles). 1% glutaraldehyde (relative to the pulp raw material) was added to the pulp dispersion and mixed evenly to obtain a gelation system. According to the volume ratio, 1 part tert-butanol was added to the gelation system, sealed and soaked for 2 hours, and then the adsorption filter material was taken out; this was repeated 4 times. The gel filter was pre-frozen at -20℃ for 2 hours, and then freeze-dried at -60℃ for 50 min / cm³ relative to the volume of the gel material. 3 To obtain waste paper-based adsorption filter cartridges.

[0051] (3) Use filter material with a concentration of 10 mg / L (relative to the volume of wastewater) for filtering the second stage of wastewater. Figure 6After filtration, the color removal rate of the wastewater was 92%. Figure 7 The COD and BOD removal rates are 70% and 75%, respectively, and the SS removal rate is 96%. The adsorbed wastewater can be directly reused as washing water. After the filter element is repeated 20 times, the color removal rate and other indicators still achieve the same effect.

[0052] Example 6: Preparation of waste paper-based filter cartridges from waste label paper for printing wastewater treatment

[0053] (1) Flocculation was used to treat the mixed wastewater from printing plate making and ink roller washing. Testing revealed that the wastewater contained 30,000 mg / L of COD (Chemical Oxygen Demand), 2,000 mg / L of BOD (Biochemical Oxygen Demand), and 100 mg / L of SS (Suspended Solids), with a color greater than 1000 times. Polyaluminum chloride was used as the flocculant at a dosage of 10 mg / L of the wastewater volume. After flocculation, the color removal rate was 51%, the COD and BOD removal rates were 43% and 50%, respectively, and the SS removal rate was 88%.

[0054] (2) Waste label paper from printing was crushed and sieved to obtain pulp raw material with a mesh size greater than 100. The pulp raw material was dispersed in water at a concentration of 0.1%, and a nano-sized pulp dispersion was obtained by high-pressure homogenization (400 bar, 20 cycles). 8% citric acid crosslinking agent (relative to the pulp raw material) was added to the pulp dispersion and mixed evenly to obtain a gelation system. According to the volume ratio, 2 times tert-butanol was added to the gelation system, and after sealing and soaking for 1 hour, the adsorption filter material was taken out; this was repeated 5 times. The gel filter was pre-frozen at -10℃ for 1 hour, and then freeze-dried at -80℃ for 30 min / cm³ relative to the volume of the gel material. 3 To obtain waste paper-based adsorption filter cartridges.

[0055] (3) A filter material with a concentration of 20 mg / L (relative to the volume of wastewater) was used to filter the second stage of wastewater. After filtration, the color removal rate of the wastewater was 94%, the COD and BOD removal rates were 75% and 77% respectively, and the SS removal rate was 98%. The adsorbed wastewater can be directly reused as washing water. After the filter material was repeated 20 times, the color removal rate and other indicators still achieved the same effect.

[0056] Comparative Example 1: Waste paper-based filter cartridges not cleaned with tert-butanol

[0057] Unlike Example 1, in this example, the gel system obtained by adding the crosslinking agent and mixing evenly in step (2) is directly freeze-dried without undergoing a tert-butanol washing step. Following the freeze-drying method of Example 1, the gel system was pre-frozen at -20°C for 30 minutes, but it could not be completely frozen and could not be placed in the freeze dryer. Therefore, the pre-freezing time was extended to 2 hours. Then, the gel system was freeze-dried at -20°C, with a freeze-drying time relative to the gel material volume of 24 h / cm³. 3 Compared to the lyophilization time of the gel after washing with tert-butanol in Example 1 (60 min / cm),... 3 The time was extended by 24 times. Finally, the obtained filter element was used to filter two stages of wastewater using the same process to verify the wastewater treatment effect.

[0058] The treated wastewater achieved a 70% removal rate for color, 60% for COD, 66% for BOD, and 92% for SS. Due to the extremely low removal rates of color and COD, the adsorbed wastewater cannot be directly reused, and secondary reuse offers virtually no further removal of pollutants.

[0059] Comparative Example 2: Waste paper-based filter cartridges not cleaned with tert-butanol

[0060] Unlike Example 1, in this example, the gel system obtained by adding the crosslinking agent and mixing evenly in step (2) is directly freeze-dried without undergoing a tert-butanol washing step. Following the freeze-drying method of Example 2, the gel system was pre-frozen at -10°C for 1 hour, but it could not be completely frozen and could not be placed in the freeze dryer. Therefore, the pre-freezing time was extended to 3 hours. Then, the gel system was freeze-dried at -50°C, with a freeze-drying time of 8 hours / cm³ relative to the gel material volume. 3 Compared to the lyophilization time of the gel after washing with tert-butanol in Example 2 (40 min / cm),... 3 The time was extended by 12 times. Finally, the obtained filter element was used to filter two stages of wastewater using the same process to verify the wastewater treatment effect.

[0061] The treated wastewater achieved a color removal rate of 55%, a COD and BOD removal rate of 43% and 54%, respectively, and a SS removal rate of 91%. Due to the extremely low removal rates of color and COD, the adsorbed wastewater cannot be directly reused, and secondary reuse offers virtually no further removal of pollutants.

[0062] Comparative Example 3: Waste paper-based filter cartridges not cleaned with tert-butanol

[0063] Unlike Example 3, in this example, the gel system obtained by adding the crosslinking agent and mixing evenly in step (2) is directly freeze-dried without undergoing a tert-butanol washing step. Following the freeze-drying method of Example 3, the gel system was pre-frozen at 10°C for 2 hours, but it could not be frozen and therefore could not be placed in the freeze dryer. Therefore, the pre-freezing conditions were adjusted to -20°C for 2 hours. Then, the gel system was freeze-dried at -90°C for 5 hours per cm³ of gel material volume. 3 Compared to the lyophilization time of the gel after washing with tert-butanol in Example 3 (20 min / cm),... 3 The time was extended by 15 times. Finally, the obtained filter element was used to filter two stages of wastewater using the same process to verify the wastewater treatment effect.

[0064] The treated wastewater achieved a color removal rate of 60%, a COD and BOD removal rate of 45% and 60%, respectively, and a SS removal rate of 75%. Due to the extremely low removal rates of color and COD, the adsorbed wastewater cannot be directly reused, and secondary reuse offers virtually no further removal of pollutants.

[0065] Comparative Example 4: Waste paper-based filter cartridges not cleaned with tert-butanol

[0066] Unlike Example 4, in this example, the gel system obtained by adding the crosslinking agent and mixing evenly in step (2) is directly freeze-dried without undergoing a tert-butanol washing step. Following the freeze-drying method of Example 4, the gel system was pre-frozen at 0°C for 1 hour, but it could not freeze and could not be placed in the freeze dryer. Therefore, the pre-freezing conditions were adjusted to -20°C for 2 hours. Then, the gel system was freeze-dried at -80°C, with a freeze-drying time of 7 hours / cm³ relative to the gel material volume. 3 Compared to the lyophilization time of the gel after washing with tert-butanol in Example 4 (30 min / cm),... 3 The time was extended by 14 times. Finally, the obtained filter element was used to filter two stages of wastewater using the same process to verify the wastewater treatment effect.

[0067] The treated wastewater achieved a color removal rate of 63%, a COD and BOD removal rate of 50% and 55%, respectively, and a SS removal rate of 80%. Due to the extremely low removal rates of color and COD, the adsorbed wastewater cannot be directly reused, and secondary reuse offers virtually no further removal of pollutants.

[0068] Comparative Example 5: Waste paper-based filter cartridges not cleaned with tert-butanol

[0069] Unlike Example 5, in this example, the gel system obtained by adding the crosslinking agent and mixing it evenly in step (2) is directly freeze-dried without undergoing a tert-butanol washing step. Following the freeze-drying method of Example 5, the system is pre-frozen at -20°C for 2 hours, and then freeze-dried at -60°C for 9 hours per cm³ of gel material volume.3 Compared to the lyophilization time of the gel after washing with tert-butanol in Example 5 (50 min / cm),... 3 The time was extended by 10.8 times. Finally, the obtained filter element was used to filter two stages of wastewater using the same process to verify the wastewater treatment effect.

[0070] The treated wastewater achieved a color removal rate of 65%, a COD removal rate of 60%, a BOD removal rate of 65%, and a SS removal rate of 90%. Due to the extremely low removal rates of color and COD, the adsorbed wastewater cannot be directly reused, and secondary reuse offers virtually no further removal of pollutants.

[0071] Comparative Example 6: Waste paper-based filter cartridges not cleaned with tert-butanol

[0072] Unlike Example 6, in this example, the gel system obtained by adding the crosslinking agent and mixing evenly in step (2) is directly freeze-dried without undergoing a tert-butanol washing step. Following the freeze-drying method of Example 6, the gel system was pre-frozen at -10°C for 1 hour, but it could not be completely frozen and could not be placed in the freeze dryer. Therefore, the pre-freezing time was extended to 3 hours. Then, the gel system was freeze-dried at -80°C, with a freeze-drying time of 7 hours / cm³ relative to the volume of the gel material. 3 Compared to the lyophilization time of the gel after washing with tert-butanol in Example 6 (30 min / cm),... 3 The time was extended by 14 times. Finally, the obtained filter element was used to filter two stages of wastewater using the same process to verify the wastewater treatment effect.

[0073] The treated wastewater achieved a 70% removal rate for color, 55% for COD, 64% for BOD, and 92% for SS. Due to the extremely low removal rates of color and COD, the adsorbed wastewater cannot be directly reused, and secondary reuse offers virtually no further removal of pollutants.

[0074] Example 7: Characterization of waste paper-based filter cartridges prepared in Examples 1-6 and Comparative Examples 1-6

[0075] 1. The density and porosity of the waste paper-based filter cartridges prepared in Examples 1-6 and Comparative Examples 1-6 were characterized, and the results are detailed in Table 1. The methods for detecting density and porosity are as follows:

[0076] After placing the filter element sample in an environment with a relative humidity of 50% and a temperature of 25ºC for 12 hours, the density (ρ) and porosity (P) of the filter element were calculated by equations (1) and (2), respectively.

[0077] (1)

[0078] (2)

[0079] In the formula, m and v are the mass and volume of the filter element, respectively, and ρ0 is the density of wood fiber (1.5 g / cm³). 3 ).

[0080] 2. Scanning electron microscopy (SEM) was used to examine the waste paper-based filter cartridges prepared in Examples 1-6 and Comparative Examples 1-6. The waste paper-based filter cartridges prepared in Examples 1-6 showed similar structures, as did the waste paper-based filter cartridges prepared in Comparative Examples 1-6. Example 5 and Comparative Example 5 will be used as examples for illustration. Figure 8 It can be seen that the waste paper-based filter element prepared in Example 5 contains a large number of uniformly distributed nanopores with an average diameter of 300 nm. Figure 9 The results show that the internal pore size of the waste paper-based filter element prepared in Comparative Example 5 is not uniform, and the average pore size reaches 1 μm, which is much larger than that of the waste paper-based filter element prepared in Example 5.

[0081] Table 1. Performance parameters and adsorption effects of waste paper-based filter cartridges prepared in Examples 1-6 and Comparative Examples 1-6

[0082]

[0083] As shown in Table 1, the density of the adsorption filter cartridges prepared in Examples 1-6 is 10-40 g / cm³. 3 The porosity is 95-99%; while the density of the adsorption filter elements prepared in comparative examples 1-6 is 12-44 g / cm³. 3 The porosity is 92-95%. More importantly, according to the one-to-one comparison results, the density of waste paper-based filter cartridges without the tert-butanol cleaning step increased by 2-5 g / cm³ compared to waste paper-based filter cartridges with the tert-butanol cleaning step. 3 The porosity decreased by 2-4%. Combined with scanning electron microscopy results, it was found that the gel material contained a large number of uniformly distributed nanopores, and the average diameter of the pores was much smaller than that of the comparative example. This indicates that by adding a tert-butanol washing step, the freeze-dried adsorption filter element can form a smaller, more uniform, loose, porous structure, effectively increasing the specific surface area of ​​the filter element and thus significantly improving its adsorption capacity.

[0084] Furthermore, the adsorption filter cartridges prepared in Examples 1-6, when used to treat secondary wastewater, achieved color removal rates of 90-99%, COD removal rates of 70-80%, BOD removal rates of 75-85%, and SS removal rates of 95-99%, meeting the standards for washing water in the printing industry and allowing for direct recycling. In contrast, the adsorption filter cartridges prepared in Comparative Examples 1-6, when used to treat secondary wastewater, achieved color removal rates of 55-70%, COD removal rates of 43-60%, BOD removal rates of 54-66%, and SS removal rates of 75-92%. This indicates that the waste paper-based filter cartridges using the tert-butanol cleaning step significantly improve adsorption efficiency compared to those without. This is because the tert-butanol cleaning step optimizes the pore structure of the filter cartridge, increasing its specific surface area.

Claims

1. A method for preparing adsorption filter elements using waste printing paper, characterized in that: Includes the following steps: (a) Printing waste paper is crushed and sieved to obtain pulp raw material; then it is homogenized under high pressure to obtain nano-sized pulp dispersion. (b) Add a crosslinking agent to the pulp dispersion obtained in step (a), stir until homogeneous, and obtain a gelling system; the amount of the crosslinking agent is 0.5-10 wt% of the weight of the pulp raw material; (c) The gelation system obtained in step (b) is cleaned with excess tert-butanol and then freeze-dried to obtain a waste paper-based adsorption filter element for printing wastewater treatment. The specific operation of the tert-butanol cleaning is as follows: add 1-2 times the volume of tert-butanol to the gelation system, seal and soak for 1-2 hours, and then take out the adsorption filter element material. Repeat 2-5 times.

2. The method for preparing an adsorption filter element according to claim 1, characterized in that: The specific operation of the high-pressure homogenization process in step (a) is as follows: the pulp raw material is dispersed in water and homogenized under high pressure of 400-1000 bar for 5-20 times; the concentration of the pulp raw material in water is 0.1-1.0 wt%.

3. The method for preparing an adsorption filter element according to claim 2, characterized in that: The crosslinking agent mentioned in step (b) is a silane coupling agent, citric acid, tannic acid, epichlorohydrin, or an aldehyde crosslinking agent.

4. The method for preparing an adsorption filter element according to any one of claims 1-3, characterized in that: The sieving mentioned in step (a) refers to passing the pulverized raw material through a 100-mesh sieve and taking raw material with a mesh size greater than 100 mesh; the freeze-drying mentioned in step (c) specifically refers to: pre-freezing the gel system at -20 to 10℃ for 0.5-2h, and then freeze-drying at -20 to -90℃, with a freeze-drying time of 20-60min per unit volume of gel.

5. The method for preparing an adsorption filter element according to claim 4, characterized in that: The waste printing paper mentioned above is corrugated paper, book paper, newspaper, or label paper.

6. A waste paper-based filter element for treating printing wastewater, characterized in that: The waste paper-based filter element is prepared by the method according to any one of claims 1-5; the density of the filter element is 10-40 g / cm³. 3 The porosity is 95-99%.

7. A method for zero-discharge treatment of printing wastewater and waste paper, characterized in that: Includes the following steps: (1) First stage wastewater treatment: The printing wastewater is treated by flocculation to obtain second stage wastewater; (2) Second-stage wastewater treatment: The wastewater obtained in step (1) of the waste paper-based filter cartridge as described in claim 6 is treated to obtain the treated wastewater, which is then directly reused as washing water in the printing industry.

8. The method for zero-discharge treatment of printing wastewater and waste paper according to claim 7, characterized in that: In step (2), the amount of filter cartridge used is 5-50 mg / L relative to the second stage of wastewater.

9. The method for zero-discharge treatment of printing wastewater and waste paper according to claim 8, characterized in that: The flocculant used in step (1) is polyacrylamide or polyaluminum chloride; wherein, the amount of polyacrylamide is 5-30 mg / L of wastewater volume, and the amount of polyaluminum chloride is 1-20 mg / L of wastewater volume; the COD content of the printing wastewater is 30000-50000 mg / L, the BOD content is 2000-3000 mg / L, the SS content is 100-300 mg / L, and the color is greater than 1000 times.

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