Papermaking sludge biochar and its application and method for degrading organic matter

Abstract

The present invention relates to a papermaking sludge biochar and its application and a method for degrading organic matter. The papermaking sludge biochar obtained by the present invention is obtained by pyrolysis in a N2 atmosphere at 600-1500°C, without subsequent water washing or acid washing, or physical or chemical activation again, and can be directly used to activate persulfate to degrade organic pollutants. The inherent chemical components of papermaking sludge are converted into low-valent iron species, CaO, and defect-rich graphite carbon through pyrolysis, and pyrolysis also prompts carbon materials to produce abundant oxygen vacancies, which provides abundant multi-category active sites for activating persulfate, so that it obtains excellent persulfate activation ability; when the papermaking sludge biochar is used to degrade organic matter, the pH of the water body that can be treated can be between 3-11, and the treated water body is in a neutral or alkaline state, and the waste biochar can be recycled after pyrolysis again.

Description

Technical Field

[0001] The invention relates to papermaking sludge biochar and its application and a method for degrading organic matter. Background Art

[0002] Papermaking sludge is the main solid waste of pulp and paper enterprises, containing rich organic components such as cellulose, hemicellulose and lignin. In addition, papermaking fillers CaCO3, SiO2 and iron-containing flocculants added in papermaking wastewater treatment, such as polyferric sulfate and polyferric aluminum sulfate, will also be enriched in the sludge, forming the main source of papermaking sludge mineral components. For a long time, most papermaking sludge is still treated by incineration and landfill, but the resulting environmental problems, such as occupying land, polluting groundwater, producing toxic and harmful compounds and greenhouse gases, have gradually restricted its use. With the annual increase in the amount of papermaking sludge discharged in various countries around the world, the resource disposal of papermaking sludge has become a hot issue of concern to the world. At present, pyrolysis, as an emerging sludge treatment technology, has attracted much attention due to its advantages such as high energy utilization, high degree of sludge reduction, stable solidification of heavy metals, and low secondary pollution.

[0003] With the rapid development of industrial technology, the synthesis and application of various emerging organic compounds are also on the rise. At the same time, various emerging organic pollutants are constantly detected in natural water bodies, such as pharmaceuticals and personal care products (PPCPs), endocrine disruptors (EDCs), etc. Although the content of these trace emerging pollutants in the natural environment is very low, they have an impact on human health and environmental safety that cannot be ignored. Persulfate-based advanced oxidation technology (SR-AOPs) is an important means to degrade such water pollutants. Compared with traditional H2O2-based AOPs, SO4•- produced by persulfate activation has a longer half-life than HO•. However, the heterogeneous catalysts currently used for persulfate activation either have a complicated preparation process or have high costs for the preparation of raw materials and processes. Therefore, exploring heterogeneous catalysts with high activity, low cost, and easy large-scale production is still a key issue in the field of SR-AOPs.

[0004] At present, there are relevant patents and literature reports on the research of pyrolysis biochar of municipal sludge, tannery sludge, etc. in catalyzing the degradation of antibiotics in water by persulfate, but most of the studies require additional supplementation of iron sources (ferric chloride, ferric sulfate, etc.), nitrogen sources or sulfur sources (such as urea, NH4Cl, polythiophene, thiourea, SO2, MgSO4, etc.). In addition, the introduction of persulfate in SR-AOPs will reduce the pH of the water body and cause water acidification. However, the current research on heterogeneous catalysts for preparing SR-AOPs using various biomass waste residues and industrial wastes has not effectively solved this problem. Summary of the invention

[0005] One of the purposes of the present invention is to provide a papermaking sludge biochar, which is obtained by pyrolyzing papermaking sludge under an inert atmosphere, and the obtained biochar does not require subsequent water washing or acid washing, and does not require external iron source, nitrogen source or sulfur source, etc. to become a highly active persulfate activator; the second purpose of the present invention is to apply the biochar obtained by the first purpose of the present invention to advanced oxidation technology, for activating persulfate, and providing abundant multi-category activation sites for persulfate; the third purpose of the present invention is to provide a method for degrading organic matter in sewage using the papermaking sludge biochar obtained by the first purpose of the present invention, the pH of the treated water body can be between 3-11, and the treated water body will not be acidified, and the biochar after treating the organic matter can be recycled after being pyrolyzed again.

[0006] The present invention is achieved through the following technical solutions:

[0007] The papermaking sludge biochar is obtained by pyrolyzing papermaking sludge in an inert atmosphere, with a pyrolysis temperature of 600-1500° C., preferably a pyrolysis temperature of 800-1500° C. The obtained papermaking sludge biochar does not require subsequent water washing or acid washing, or physical or chemical activation again, and can be directly used for pollutant degradation.

[0008] Furthermore, the papermaking sludge is papermaking primary sludge, papermaking secondary sludge or papermaking deinking sludge.

[0009] Application of paper sludge biochar in activating persulfate; in this application, the paper sludge biochar obtained after pyrolysis does not require water washing or acid washing, nor does it require the introduction of additional iron sources, nitrogen sources or sulfur sources, etc., to effectively activate persulfate in SR-AOPs.

[0010] Furthermore, the persulfate is peroxydisulfate or peroxymonosulfate, or contains both peroxydisulfate and peroxymonosulfate.

[0011] The method for degrading organic matter uses the above-mentioned papermaking sludge biochar.

[0012] Furthermore, the method for degrading organic matter using papermaking sludge biochar comprises the following steps:

[0013] (1) Papermaking sludge is directly pyrolyzed under an inert atmosphere to obtain papermaking sludge biochar.

[0014] (2) Adding the papermaking sludge biochar and persulfate from step (1) into wastewater containing organic pollutants to degrade the pollutants. The persulfate is peroxydisulfate or peroxymonosulfuric acid or contains both peroxydisulfate and peroxymonosulfate.

[0015] Furthermore, in step (2), the concentration of persulfate is 3-8 mM.

[0016] Furthermore, in step (2), the dosage of papermaking sludge biochar is 0.3-1.0 g / L, and the degradation time is 0.5-2 h.

[0017] Furthermore, the papermaking sludge biochar obtained after the degradation of organic matter in step (2) is regenerated by pyrolysis at 400-800° C. for 0.5-1 h.

[0018] Further, the organic pollutants treated include but are not limited to bisphenol A, bisphenol S, sulfamethoxazole, sulfadiazine, diclofenac sodium, tetracycline, ciprofloxacin, carbamazepine, atrazine, and 2,4-dichlorophenol.

[0019] Beneficial effects of the present invention:

[0020] The papermaking sludge biochar obtained by the present invention does not need to be subsequently washed with water or acid, or physically or chemically activated again, and can be directly used for pollutant degradation.

[0021] When the polyferric sulfate, polyferric aluminum sulfate and other flocculants in the sludge are pyrolyzed in an inert atmosphere of N2, a phase transition will occur at the temperature of the present invention, and they will be reduced to low-valent iron species, such as Fe 0 , Fe3O4, etc., which can provide metal active sites for activating persulfate without the need for an external iron source; the oxygen-containing functional groups, topological structural defects, and inherent N, S heteroatom defects on the surface of biochar also have the ability to activate persulfate without the need for external nitrogen and sulfur sources; the oxygen vacancies (O V ) can significantly improve the adsorption and activation ability of persulfate due to its abundant local electrons. The iron species, carbon defects and oxygen vacancies rich in the papermaking sludge biochar of the present invention provide abundant multi-category active sites for activating persulfate, thereby obtaining excellent persulfate activation ability.

[0022] The papermaking sludge biochar obtained by the present invention contains alkaline components such as CaO, which greatly increases the zero charge point of the biochar (pH pzc >10), which can play a self-buffering role on acidic water bodies, and the water bodies will not become acidic. The SR-AOPs process is always carried out under neutral or alkaline conditions, thus avoiding the need for secondary treatment of purified water bodies.

[0023] After the activated sludge biochar obtained by the present invention is regenerated by pyrolysis, the activation ability of persulfate can be restored to the level of fresh biochar. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the XRD diagram of the papermaking sludge biochar of the present invention;

[0025] Figure 2is the Raman graph of the papermaking sludge biochar of the present invention;

[0026] Figure 3 is the EPR diagram of the papermaking sludge biochar of the present invention;

[0027] Figure 4 Changes in wastewater pH during pollutant degradation at different initial pH values. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and beneficial effects of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention. Example 1

[0029] Preparation method of papermaking sludge biochar, and method of using the same to degrade organic matter

[0030] The paper sludge was pyrolyzed at 400-1500 °C (from room temperature to 600-1500 °C at a heating rate of 5 °C / min) under an inert atmosphere for 1.5 h, and then cooled to obtain paper sludge biochar (labeled as PSBC-T, T refers to the pyrolysis temperature).

[0031] When the flocculants such as polyferric sulfate and polyferric aluminum sulfate in the sludge are pyrolyzed in an inert atmosphere of N2, they will undergo a phase transition and be reduced to low-valent iron species, such as Fe under the action of pyrolysis gas H2, CO and other components. 0 , Fe3O4, etc., which can provide metal active sites for activating persulfate without the need for external iron sources. The oxygen-containing functional groups, topological structural defects and inherent N, S heteroatom defects on the surface of biochar also have the ability to activate persulfate, without the need for external nitrogen and sulfur sources.

[0032] Attached Figure 1 The XRD spectra of paper sludge biochar obtained at different pyrolysis temperatures are shown. When the pyrolysis temperature is 600 °C, the decomposition degree of CaCO3 in paper sludge is poor, and there is a very strong CaCO3 diffraction signal in the biochar. When the pyrolysis temperature is increased to 800 °C, the CaCO3 diffraction signal disappears completely, and the diffraction peaks of the new phases CaO and CaS appear. At the same time, magnetite and Fe 0 When the pyrolysis temperature continues to rise to 950 ℃, part of the C dissolves in the Fe 0And react with it to form well-crystalline Fe3C. When the pyrolysis temperature is increased to 1500 ℃, Fe3C quickly decomposes into graphite carbon and fine Fe particles, which can be judged as the disappearance of the Fe3C diffraction peak. Overall, the iron species inherent in papermaking sludge itself is converted into low-valent Fe during pyrolysis. 0 , Fe3O4 and other phases can provide rich metal activation sites for activating persulfate.

[0033] Attached Figure 2 The Raman spectra of papermaking sludge biochar obtained at different pyrolysis temperatures are shown. It can be seen from the figure that the Raman spectra of papermaking sludge biochar can be deconvoluted into four characteristic peaks, which are highly ordered sp 2 Graphitic carbon (G band) (1578-1598 cm -1 ), characteristic band of defective and disordered graphite (D1 band) (1330-1343 cm -1 ), amorphous carbon (1471-1533 cm -1 ) and the D4 band (1247–1286 cm -1 ), which indicates that the obtained papermaking sludge biochar contains defective graphite carbon. Defects such as serrated edges, topological vacancies, and doped atoms (N, S) on graphite carbon can interfere with or even destroy the periodic structure of the crystal, leading to the rearrangement of carbon atom electrons around the defects, increasing the degree of delocalization of confined π electrons, and thus breaking the sp 2 The -C network is inert and provides active sites for the activation of persulfate.

[0034] Attached Figure 3 Solid EPR spectra of biochar obtained at different pyrolysis temperatures. In the figure, the strong asymmetric signal at the g=2.003 position indicates that there are abundant oxygen vacancies in the biochar. Oxygen vacancies can significantly enhance the adsorption and activation ability of persulfate because of their abundant local electrons.

[0035] In summary, the iron species, carbon defects and oxygen vacancies rich in paper sludge biochar provide abundant multi-category active sites for activating persulfate, thereby obtaining excellent persulfate activation ability.

[0036] The obtained papermaking sludge biochar is used to directly degrade organic matter without any treatment, specifically:

[0037] In 100 mL of 20 mg / L bisphenol A solution (no need to adjust pH), 0.4 g / L of papermaking sludge biochar was added and pre-adsorbed for 60 min under magnetic stirring. Then 5-8 mM PDS (peroxydisulfate) was added and reacted for 60-120 min before the degradation rate of bisphenol A was detected. The specific results are shown in Table 1.

[0038] Table 1 Degradation efficiency of bisphenol A at different pyrolysis temperatures of paper sludge

[0039] Example 2

[0040] Preparation method of papermaking sludge biochar, and method of using the same to degrade organic matter

[0041] Papermaking sludge was pyrolyzed at 950 °C (heating rate of 5 °C / min from room temperature to 950 °C) in N2 atmosphere for 1.5 h, and activated sludge biochar was obtained after cooling.

[0042] The obtained papermaking sludge biochar is used to directly degrade organic matter without any treatment, specifically:

[0043] 0.1 M HCl or 0.1 M NaOH was added to 100 mL of 20 mg / L bisphenol A solution to adjust its pH to 3.0-11.0, and then 0.4 g / L biochar was added and pre-adsorbed for 60 min under magnetic stirring. After the pre-adsorption, the liquid phase pH was 9.7-11.2. Then 5 mM PDS was added. After 60 min of reaction, bisphenol A had a good degradation effect. After the reaction, the liquid phase pH was 7.3-10.3. The specific results are shown in Table 2. The change process of the liquid phase pH during adsorption and oxidation is shown in the attached figure. Figure 4 shown.

[0044] Table 2 Degradation of bisphenol A at different initial pH

[0045]

[0046] Generally, due to the hydrolysis of persulfate, the pH of water will decrease when persulfate is added to water. For example, when 0.12 g PDS is added to 100 mL of 20 mg / L bisphenol A solution and magnetically stirred for 60 min, the pH of the bisphenol A solution drops from the initial 7.0 to 5.02. However, the papermaking sludge obtained in the present invention contains alkaline components such as CaO, which greatly increases the zero charge point of biochar (pH pzc >10), when degrading organic pollutants, the SR-AOPs process is always carried out under neutral or alkaline conditions. After adding persulfate, the pH value of the water body is still neutral or alkaline, and the water body will not become acidic, thus avoiding the need for secondary treatment of the purified water body. Example 3

[0047] Preparation method of papermaking sludge biochar, and method of using the same to degrade organic matter

[0048] Papermaking sludge was pyrolyzed at 950 °C (heating rate of 5 °C / min from room temperature to the specified temperature) in a N2 atmosphere for 1.5 h, and activated sludge biochar was obtained after cooling.

[0049] The obtained papermaking sludge biochar is used to directly degrade organic matter without any treatment, specifically:

[0050] 0.3-1.0 g / L biochar was added to 100 mL of 20 mg / L bisphenol A solution (no pH adjustment required) and pre-adsorbed for 60 min under magnetic stirring. Then 3-8 mM PDS was added and reacted for 30-120 min. The degradation rate of bisphenol A was higher than 95%. The specific results are shown in Table 3.

[0051] Table 3 Degradation efficiency of bisphenol A under different process parameters

[0052] Example 4

[0053] Preparation method of papermaking sludge biochar, and method of using the same to degrade organic matter

[0054] Papermaking sludge was pyrolyzed at 950 °C (heating rate of 5 °C / min from room temperature to the specified temperature) in a N2 atmosphere for 1.5 h, and activated sludge biochar was obtained after cooling.

[0055] The obtained papermaking sludge biochar is used to directly degrade organic matter without any treatment, specifically:

[0056] 0.4 g / L biochar was added to 100 mL of 20 mg / L organic pollutants (no pH adjustment required) and pre-adsorbed for 60 min under magnetic stirring. Then 5 mM PDS was added and reacted for 120 min. The specific results of the degradation rate of each pollutant are shown in Table 4.

[0057] Table 4 Degradation efficiency of different pollutants

[0058] Example 5

[0059] Preparation method of papermaking sludge biochar, and method of using the same to degrade organic matter

[0060] Papermaking sludge was pyrolyzed at 800 °C (heating rate of 10 °C / min from room temperature to the specified temperature) in a N2 atmosphere for 2 h, and activated sludge biochar was obtained after cooling.

[0061] The obtained papermaking sludge biochar is used to directly degrade organic matter without any treatment, specifically:

[0062] 0.3 g / L biochar was added to 100 mL of 20 mg / L tetracycline solution (no pH adjustment required) and pre-adsorbed for 60 min under magnetic stirring. Then 5 mM PMS was added and the degradation rate of tetracycline was 98.8% after 60 min of reaction. Example 6

[0063] Preparation method of papermaking sludge biochar, and method of using the same to degrade organic matter

[0064] Papermaking sludge was pyrolyzed at 950 °C (heating rate of 5 °C / min from room temperature to the specified temperature) in a N2 atmosphere for 1 h, and activated sludge biochar was obtained after cooling.

[0065] The obtained papermaking sludge biochar is used to directly degrade organic matter without any treatment, specifically:

[0066] 0.4 g / L biochar was added to 100 mL of 20 mg / L bisphenol A solution (under natural pH) and pre-adsorbed for 60 min under magnetic stirring. Then 5 mM PMS was added and after 60 min of reaction, the degradation rate of bisphenol A was 99.1%. Example 7

[0067] Preparation method of papermaking sludge biochar, and method of using the same to degrade organic matter

[0068] Waste biochar that has been used 3-4 times is heated to 500 ℃ (heating rate of 10 ℃ / min from room temperature to the specified temperature) and carbonized again for 1 h in N2 atmosphere, and then cooled to obtain regenerated activated sludge biochar.

[0069] The obtained papermaking sludge biochar is used to directly degrade organic matter without any treatment, specifically:

[0070] 0.4 g / L biochar was added to 100 mL of 20 mg / L bisphenol A solution (no pH adjustment required) and pre-adsorbed for 60 min under magnetic stirring. Then 5 mM PMS was added and after 60 min of reaction, the degradation rate of bisphenol A was 98.7%.

[0071] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A papermaking sludge biochar, characterized in that: The papermaking sludge biochar is obtained by pyrolyzing papermaking sludge in an inert atmosphere at a pyrolysis temperature of 950-1500° C. The papermaking sludge contains CaCO 3 , and the papermaking sludge contains polyferric sulfate and polyferric aluminum sulfate.

2. The use of papermaking sludge biochar in activating persulfate according to claim 1, characterized in that: The persulfate is peroxydisulfate or peroxymonosulfate or contains both peroxydisulfate and peroxymonosulfate.

3. The method for degrading organic matter using papermaking sludge biochar as claimed in claim 1, characterized in that: Papermaking sludge biochar and persulfate are added to wastewater containing organic pollutants to degrade the pollutants; the concentration of persulfate is 3-8 mM; the dosage of papermaking sludge biochar is 0.3-1.0 g / L, and the degradation time is 0.5-2 h.

4. The method according to claim 3, characterized in that The persulfate is peroxydisulfate or peroxymonosulfate or contains both peroxydisulfate and peroxymonosulfate.

5. The method according to claim 3 or 4, characterized in that The paper sludge biochar after degrading organic matter is regenerated by pyrolysis at 400-800°C for 0.5-1 h in an inert atmosphere.

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