Biochar catalyst, preparation method thereof and method for catalytic decolorization of printing and dyeing wastewater

Abstract

The present invention provides a biochar catalyst, a preparation method thereof, and a method for catalytic decolorization of printing and dyeing wastewater. The biochar catalyst is obtained by using anaerobic pond sludge, ferrous sulfate, and manganese dichloride as raw materials, followed by stirring, mixing, centrifuging, calcining, and grinding. The present invention uses the biochar catalyst for catalytic oxidation decolorization, directly destroying the light-emitting group structure of dye molecules. Compared with adding decolorizing agents or iron and aluminum coagulants to conventional printing and dyeing wastewater, it does not produce a large amount of chemical sludge classified as hazardous waste. The biochar catalyst used is prepared from solid waste such as urban sludge, having the significance of resource utilization and practical application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of urban sludge treatment, and particularly to a biochar catalyst, a preparation method thereof, and a method for catalytic decolorization of printing and dyeing wastewater. Background Art

[0002] Printing and dyeing wastewater is industrial wastewater discharged in the production process of printing and dyeing enterprises. It contains dye molecules, various auxiliaries, finishing agents, etc., and has the characteristics of large discharge volume, high chroma, high COD, high toxicity, high salt content, high suspended solid concentration, complex composition, and high temperature (can reach 40 - 60 °C or higher), resulting in difficult biodegradation. There are many types of dyes in printing and dyeing wastewater, which are related to the types of printed and dyed fabrics. Dyes are further divided into disperse dyes, vat dyes, reactive dyes, direct dyes, acid dyes, etc. The reason for the chroma in printing and dyeing wastewater is that dyes have chromophoric groups and auxochromic groups such as amino groups, carboxyl groups, hydroxyl groups, and sulfonic acid groups.

[0003] Since printing and dyeing wastewater is the industry with the largest amount of wastewater generated in industrial wastewater, and it is difficult to biodegrade, it increases the difficulty of achieving the standard treatment of printing and dyeing wastewater. According to the "Technical Specification for the Treatment of Textile Dyeing and Finishing Industry Wastewater (HJ 471 - 2020)", the treatment process of printing and dyeing wastewater generally uses the coagulation - precipitation / air flotation process to achieve the purpose of decolorization. However, due to the stable chemical properties of synthetic dyes, the treatment is difficult. In addition, there are various auxiliaries and finishing agents in printing and dyeing wastewater, which are all substances such as polycyclic aromatic hydrocarbons and heavy metals (such as antimony) that are difficult to degrade, resulting in a large dosage of coagulants, high water treatment costs, a large amount of chemical sludge, and low decolorization efficiency. In recent years, many cities have determined the chemical sludge generated in the treatment of printing and dyeing wastewater as hazardous solid waste, making the problems of using coagulation decolorization more and more. Summary of the Invention

[0004] The purpose of the present invention is to provide a biochar catalyst, a preparation method thereof, and a method for catalytic decolorization of printing and dyeing wastewater. The biochar catalyst used is prepared from solid waste such as urban sludge. Compared with the conventional addition of decolorizing agents or iron and aluminum coagulants to printing and dyeing wastewater, it does not produce a large amount of chemical sludge classified as hazardous waste. For printing and dyeing wastewater with a water temperature reaching 40 - 60 °C, it is more conducive to using this biochar catalyst for catalytic reaction. Therefore, this technology has the significance of resource utilization and practical application prospects.

[0005] The present invention is achieved by the following technical solutions:

[0006] The present invention provides a preparation method of a biochar catalyst, including:

[0007] 1) Take anaerobic pond sludge, dry, grind, and sieve it to obtain dry sludge WA.

[0008] 2) Mix ferrous sulfate, manganese dichloride, and dry sludge WA, add deionized water, slowly add alkali until the pH is neutral, after mixing and stirring, heat at a constant temperature of 50 - 90 °C for 1 - 8 h, and dry to obtain TB. Ferrous sulfate : manganese dichloride : deionized water : WA = 10 - 80 (g) : 5 - 50 (g) : 30 - 80 (mL) : 15 - 55 (g);

[0009] 3) Put TB into an atmosphere furnace and pyrolyze it under nitrogen protection at 300 °C - 600 °C for 1 - 3 h to obtain TC.

[0010] 4) Stop introducing nitrogen, introduce CO2, heat and pyrolyze TC at 600 - 800 °C for 1 - 3 h, cool, take out, grind, and obtain the biochar catalyst TD.

[0011] Preferably, in step 1), the anaerobic pond sludge is dried at 60 - 80 °C.

[0012] Preferably, in step 1), a sieve with 10 - 50 meshes is used for sieving.

[0013] Preferably, in step 3), the heating rate of the atmosphere furnace is set to 10 - 30 °C / min.

[0014] Preferably, in step 4), the introduction amount of CO2 is 300 - 500 mL / min.

[0015] Preferably, in step 4), the heating rate is increased at a rate of 30 - 50 °C / min.

[0016] The present invention also provides a biochar catalyst prepared by the above preparation method.

[0017] The present invention further provides a method for catalytic decolorization of printing and dyeing wastewater using the above biochar catalyst, including:

[0018] Add the biochar catalyst to the printing and dyeing wastewater, after staying for 2 - 30 min, add persulfate and stir.

[0019] The components of different printing and dyeing wastewaters are different, and when performing catalytic decolorization treatment, the amount of the added biochar catalyst is also different. Generally, a concentration of 0.05 - 0.5 g / L in the printing and dyeing wastewater is sufficient, and appropriate adjustment can be made during actual use. The added persulfate can be potassium persulfate or sodium persulfate, etc., and the specific type will not have a substantial impact on the catalytic effect.

[0020] When the above biochar catalyst is used for rhodamine B printing and dyeing wastewater, the mass ratio of the added persulfate to rhodamine B in the printing and dyeing wastewater is preferably 4:1 - 20:1.

[0021] The biochar catalyst prepared in this application contains C=C, C=O and oxygen-containing functional groups, presenting nanoscale crystal grains and graphite carbon structure, which contains trivalent iron and divalent iron, mainly composed of Fe3O4, FeO, FeMnOx, and a small amount of ferrosilicon, and there are metal silicate components such as K, Mn, Cu, etc. The functions of this biochar catalyst include: ① The iron in the biochar is divalent and trivalent iron metal oxides, and there are also nitrogen compounds, which promote the formation of catalytic sites; ② The C=O, graphitized structure, defect structure and a small amount of oxygen vacancies contained in the biochar can change the surface properties of the biochar and form catalytic sites; ③ The biochar catalyst can activate potassium persulfate to generate hydroxyl radicals and sulfate radicals; ④ The hydroxyl radicals and sulfate radicals destroy the luminescent groups and play a decolorization role; ⑤ The hydroxyl radicals and sulfate radicals destroy polycyclic aromatic hydrocarbon substances such as auxiliaries and degrade organic substances; ⑥ The biochar has magnetism and can be conveniently recycled and reused.

[0022] The principle of using the biochar catalyst to catalytically decolorize printing and dyeing wastewater in this application is: through the activation of persulfate by the biochar catalyst, hydroxyl radicals ·OH and SO4 ·- radicals are generated, and there are defect structures and a small amount of oxygen vacancies, which destroy the molecular structures of dye molecules and polycyclic aromatic hydrocarbon organic molecules in the printing and dyeing wastewater, thereby destroying the luminescent groups and breaking other macromolecular organic substances into small molecule substances, so as to achieve the purpose of decolorization and degradation of organic substances.

[0023] The beneficial effects of the present invention are as follows:

[0024] The biochar catalyst of the present invention is prepared by high-temperature pyrolysis of municipal sludge under the protection of nitrogen and CO2 atmospheres. Municipal sludge contains various organic substances such as polypeptide substances, phenols, as well as heavy metals, nitrogen and phosphorus, etc. Especially, the sludge contains a large amount of organic components such as proteins and polypeptides, with a high nitrogen content, and also contains polycyclic aromatic hydrocarbons and other substances. The polymerization iron and other substances contained in the sludge increase the iron content in the sludge and promote the formation of catalytic sites; the biochar catalyst has pores with a large number of micropores (pore diameters are 5-20 nm), which can diffuse dye molecules to catalytic sites and shorten the reaction time; the sludge biochar rich in Fe also activates H2O2 and realizes the efficient degradation of polycyclic aromatic hydrocarbon organic substances in printing and dyeing wastewater; compared with adding decolorants or iron and aluminum coagulants to conventional printing and dyeing wastewater, it does not produce a large amount of chemical sludge defined as hazardous waste, and has the significance of resource utilization and practical application prospects. Description of the Drawings

[0025] Figure 1 Electron microscope photograph of the biochar catalyst prepared in Example 1 of the present invention. Detailed Description of the Invention

[0026] To more clearly illustrate the present invention, the following further elaborates on the present invention in conjunction with embodiments. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0027] The main process of the present invention for catalytic decolorization of printing and dyeing wastewater using a biochar catalyst is as follows:

[0028] I. Preparation of the biochar catalyst

[0029] 1) Take anaerobic pond sludge, dry it at 60 - 80 °C, grind it, and sieve it through a 10 - 50 mesh sieve to obtain dry sludge WA.

[0030] 2) Mix ferrous sulfate, manganese dichloride, and dry sludge WA, add deionized water, slowly add alkali until the pH is neutral, mix and stir, then heat at a constant temperature of 50 - 90 °C for 1 - 8 h, and dry to obtain TB. Ferrous sulfate: manganese dichloride: deionized water: WA = 10 - 80 (g): 5 - 50 (g): 30 - 80 (mL): 15 - 55 (g);

[0031] 3) Put TB into an atmosphere furnace, pyrolyze it under nitrogen protection at a heating rate of 10 - 30 °C / min at 300 °C - 600 °C for 1 - 3 h to obtain TC.

[0032] 4) Stop introducing nitrogen, introduce CO2 (introduction rate 300 - 500 mL / min), heat TC at a heating rate of 30 - 50 °C / min to 600 - 800 °C and pyrolyze for 1 - 3 h, cool, take out, grind, and obtain the biochar catalyst TD.

[0033] II. Catalytic decolorization of printing and dyeing wastewater

[0034] During operation, add the biochar catalyst to the printing and dyeing wastewater. After staying for 2 - 30 min, add persulfate and stir. Activate the persulfate through the catalyst to generate hydroxyl radicals ·OH and SO4 ·- radicals, and there are defective structures and a small amount of oxygen vacancies, which destroy the molecular structures of dye molecules and polycyclic aromatic hydrocarbon organic molecules in the printing and dyeing wastewater, thereby destroying the luminescent groups and breaking other macromolecular organic substances into small molecular substances, so as to achieve the purpose of decolorization and degradation of organic substances.

[0035] The printing and dyeing wastewater is generally at 40 - 60 °C, which is just conducive to the catalytic reaction. Just add the biochar catalyst directly without the need for additional cooling. Of course, this catalytic reaction can also be carried out at room temperature. In the present invention, "room temperature" can be 20 - 25 degrees.

[0036] Example 1

[0037] 1) Take the anaerobic pond sludge, dry it at 60 °C, grind it, and sieve it through a 50-mesh sieve to obtain dry sludge WA.

[0038] 2) Mix 32 g of ferrous sulfate, 8 g of manganese dichloride, and 30 g of dry sludge WA, add 60 mL of deionized water, slowly add alkali until the pH is neutral, after mixing and stirring, heat it at a constant temperature of 80 °C for 5 h, and dry it to obtain TB.

[0039] 3) Put TB into an atmosphere furnace, pyrolyze it at a heating rate of 20 °C / min under nitrogen protection at 500 °C for 2 h to obtain TC.

[0040] 4) Stop introducing nitrogen, introduce CO2 at a flow rate of 400 mL / min, heat up to 700 °C at a heating rate of 40 °C / min and pyrolyze TC for 2 h, cool it, take it out, and grind it to obtain the biochar catalyst TD-1.

[0041] The electron microscope photograph is shown in Figure 1 , it can be seen that the biochar catalyst prepared by the present invention has pores with a large number of micropores (pore diameters are between 5 and 20 nm), which can diffuse dye molecules to catalytic sites and shorten the reaction time.

[0042] 5) Select rhodamine B dye as a representative and prepare wastewater with rhodamine B at 20 mg / L. To investigate the catalytic decolorization effect under adverse conditions, this implementation process is still carried out at normal temperature (room temperature 20 °C) and normal pressure. Add 0.15 g of the biochar catalyst TD-1 to 1 L of wastewater, mix for 2 min, adjust the pH to 4.0 - 7.0 with dilute sulfuric acid, add 85 mg of potassium persulfate, and stir at normal temperature and pressure for 40 min. The detection results before and after the treatment of the printing and dyeing wastewater are shown in Table 1.

[0043] Table 1 Variation of the decolorization rate of TD-1-catalyzed wastewater with reaction time at different pH values (unit: %)

[0044] Reaction time (min) pH = 4.0 pH = 7.0 0 0.0 0.0 5 45.2 34.2 10 60.2 52.7 15 74.5 68.1 20 85.6 82.2 25 89.7 84.7 30 92.2 87.0

[0045] Example 2

[0046] 1) Take the anaerobic pond sludge, dry it at 80 °C, grind it, and sieve it through a 30-mesh sieve to obtain dry sludge WA.

[0047] 2) Mix 32 g of ferrous sulfate, 8 g of manganese dichloride, and 30 g of dry sludge WA, add 80 mL of deionized water, slowly add alkali until the pH is neutral, after mixing and stirring, heat it at a constant temperature of 90 °C for 1 h, and dry it to obtain TB.

[0048] 3) Put TB into an atmosphere furnace, pyrolyze it at a heating rate of 30 °C / min under nitrogen protection at 600 °C for 1 h to obtain TC.

[0049] 4) Stop introducing nitrogen gas, introduce CO2 at a flow rate of 300 mL / min, heat it up to 800 °C at a heating rate of 50 °C / min for pyrolysis of TC for 3 h, cool it down, take it out, and grind it to obtain the biochar catalyst TD-2.

[0050] 5) Select rhodamine B dye as the representative of azo dyes, prepare wastewater with rhodamine B at 20 mg / L, control the wastewater temperature at 40 °C, and operate under atmospheric pressure. Add 0.2 g of the biochar catalyst TD-2 to 1 L of printing and dyeing wastewater, mix for 2 min, then adjust the pH to 4.0 - 9.0 with dilute sulfuric acid or sodium hydroxide solution, add 80 mg of potassium persulfate, and stir for 30 min under atmospheric pressure. The test results before and after the treatment of the printing and dyeing wastewater are shown in Table 2.

[0051] Table 2 Variation of the decolorization rate of TD-2-catalyzed rhodamine B wastewater with reaction time at different pH values (%)

[0052] Reaction time (min) pH = 4.2 pH = 7.2 pH = 9.0 0 0.0 0.0 0.0 5 46.2 28.9 15.3 10 60.2 42.6 32.8 15 72.4 59.7 43.5 20 77.5 68.9 57.1 25 86.1 78.4 62.5 30 88.0 79.8 68.9

[0053] Example 3

[0054] 1) Take the anaerobic pond sludge, dry it at 80 °C, grind it, and sieve it through a 30-mesh sieve to obtain the dry sludge WA.

[0055] 2) Mix 10 g of ferrous sulfate, 5 g of manganese dichloride, and 15 g of the dry sludge WA, add 80 mL of deionized water, slowly add alkali until the pH is neutral, mix and stir, then heat it at a constant temperature of 90 °C for 1 h, and dry it to obtain TB.

[0056] 3) Put TB into the atmosphere furnace, heat it up at a heating rate of 10 °C / min, and pyrolyze it at 300 °C under nitrogen protection for 3 h to obtain TC.

[0057] 4) Stop introducing nitrogen gas, introduce CO2 at a flow rate of 500 mL / min, heat it up to 600 °C at a heating rate of 30 °C / min for pyrolysis of TC for 1 h, cool it down, take it out, and grind it to obtain the biochar catalyst TD-3.

[0058] 5) Select rhodamine B dye as the representative of azo dyes, prepare wastewater with rhodamine B at 20 mg / L. The wastewater temperature is at room temperature (20 °C), and operate under atmospheric pressure. Add 0.05 g of the biochar catalyst TD-3 to 1 L of printing and dyeing wastewater, mix for 2 min, then adjust the pH to 4.0 - 9.0 with dilute sulfuric acid or sodium hydroxide solution, add 80 mg of potassium persulfate, and stir for 30 min under normal temperature and atmospheric pressure. The test results before and after the treatment of the printing and dyeing wastewater are shown in Table 3.

[0059] Table 3 Variation of the decolorization rate of TD-3-catalyzed rhodamine B wastewater with reaction time at different pH values (%)

[0060] Reaction time (min) pH = 4.0 pH = 7.1 pH = 8.8 0 0.0 0.0 0.0 5 11.8 10.1 7.7 10 25.2 15.0 10.7 15 32.4 19.5 14.3 20 39.0 22.3 15.8 25 47.7 28.6 20.7 30 49.6 32.5 21.9

[0061] Example 4

[0062] 1) Take the anaerobic sludge, dry it at 70 °C, grind it, and sieve it through a 10-mesh sieve to obtain dry sludge WA.

[0063] 2) Mix 80 g of ferrous sulfate, 50 g of manganese dichloride, and 55 g of dry sludge WA, add 30 mL of deionized water, slowly add alkali until the pH is neutral, mix and stir, then heat at a constant temperature of 50 °C for 8 h, and dry to obtain TB.

[0064] 3) Put TB into an atmosphere furnace, pyrolyze it at a heating rate of 20 °C / min under nitrogen protection at 500 °C for 2 h to obtain TC.

[0065] 4) Stop introducing nitrogen, introduce CO2 at a flow rate of 400 mL / min, heat up to 700 °C at a heating rate of 40 °C / min and pyrolyze TC for 2 h, cool, take out, grind, and obtain the biochar catalyst TD-4.

[0066] 5) Take 1 L of wastewater from a knitted fabric printing and dyeing factory, with an initial chromaticity of 560 times, an initial pH of 9.3, a water temperature of 40 °C, and the wastewater is navy blue. Under normal pressure, add 0.5 g of the biochar catalyst TD-4 to the wastewater, mix evenly for 5 min, adjust the pH to 3.0 - 4.0 with dilute sulfuric acid, add 380 mg of potassium persulfate, and stir for 60 min under normal pressure to complete the treatment of the printing and dyeing wastewater. The test results before and after the treatment of the printing and dyeing wastewater are shown in Table 4.

[0067] Table 4 Variation of the decolorization rate of TD-4 catalyzing printing and dyeing wastewater with reaction time at different pH values (%)

[0068] Reaction time (min) pH = 4.0 pH = 9.3 0 0.0 0.0 10 48.3 35.2 20 68.0 54.9 30 82.5 62.9 40 86.4 70.4 50 90.2 81.7 60 91.6 83.0

[0069] In the above examples, in Examples 1 - 3, the biochar catalyst prepared by this application was used to catalytically decolorize the wastewater with a rhodamine B concentration of 20 mg / L. The decolorization rates of different examples showed certain differences mainly due to different catalyst dosages, but it can be seen that each example had the effect of catalytic decolorization. In Example 4, the biochar catalyst prepared by this application was directly added to the wastewater of a certain knitted fabric printing and dyeing factory with a water temperature of 40 °C, and a relatively high decolorization rate could still be achieved, confirming that this invention has high practical application value.

[0070] Obviously, the above embodiments of the present invention are merely examples for more clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for catalytic decolorization of printing and dyeing wastewater by a biochar catalyst, comprising: Add the biochar catalyst to the printing and dyeing wastewater. After staying for 2 to 30 minutes, add persulfate and stir. The preparation method of the biochar catalyst includes: 1) Take the anaerobic sludge, dry, grind, and sieve it to obtain dry sludge WA; the anaerobic sludge is dried at 60 to 80 °C; 2) Mix ferrous sulfate, manganese dichloride, and dry sludge WA, add deionized water, slowly add alkali until the pH is neutral, mix and stir, then heat at a constant temperature of 50 to 90 °C for 1 to 8 hours, and dry to obtain TB. The ratio of ferrous sulfate: manganese dichloride: deionized water: dry sludge WA = 10 to 80 g: 5 - 50 g: 30 to 80 mL: 15 - 55 g; 3) Put TB into an atmosphere furnace and pyrolyze it under nitrogen protection at 300 °C to 600 °C for 1 to 3 hours to obtain TC; 4) Stop introducing nitrogen, introduce CO2, the flow rate of CO2 is 300 to 500 mL / min, heat up to 600 to 800 °C and pyrolyze TC for 1 to 3 hours, cool, take out, grind, and obtain the biochar catalyst TD.

2. The method according to claim 1, characterized in that, In step 1), sieve with a 10 - 50 mesh sieve.

3. The method according to claim 1, wherein In step 3), the heating rate of the atmosphere furnace is set to 10 to 30 °C / min.

4. The method according to claim 1, characterized in that In step 4), heat up at a heating rate of 30 to 50 °C / min.

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