Preparation and application of modified biochar for enhancing methanogenesis from recycled papermaking wastewater

Abstract

This invention relates to the field of environmental engineering and waste resource utilization technology, and discloses a modified biochar preparation and application for enhancing methane production from anaerobic fermentation of recycled paper mill wastewater. The modified biochar uses recycled paper mill wastewater sludge biochar as a base, which is sequentially modified by loading nano-manganese iron spinel and encapsulating polyaniline conductive polymer. The material of this invention possesses high conductivity, paramagnetism, selective adsorption, and microbial carrier functions, synergistically promoting direct interspecies electron transfer, breaking down recalcitrant organic matter, adsorbing toxic substances, and buffering system pH, thereby significantly improving methane production, rate, and system stability during anaerobic fermentation of recycled paper mill wastewater. This invention achieves "waste-to-waste treatment," providing new materials and technologies for the efficient energy recovery of recycled paper mill wastewater.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and waste resource utilization, and in particular to the preparation and application of modified biochar for enhancing the anaerobic fermentation of recycled papermaking wastewater to produce methane. Background Technology

[0002] The recycled paper industry is a major consumer of water resources and a significant contributor to pollution. Wastewater from recycled paper production is characterized by high chemical oxygen demand (COD), high suspended solids (SS), and complex composition (containing ink, adhesives, and trace amounts of heavy metals). Anaerobic biological treatment technology is widely used for this type of wastewater due to its low energy consumption and the ability to recover biomass energy (methane). However, the anaerobic treatment process for recycled paper wastewater often faces the following challenges: Low methane production efficiency: The wastewater contains a lot of recalcitrant organic matter, which limits the rate of hydrolysis and acidification, resulting in low methane yield.

[0003] Poor system stability: Inhibitory substances (such as ammonia nitrogen, trace heavy metals and chlorophenols) that may be present in the wastewater can easily inhibit the activity of methanogens, causing the accumulation of volatile fatty acids (VFA), system acidification and even collapse.

[0004] Microbial loss: Microorganisms grow slowly in anaerobic reactors and are easily lost with the effluent, affecting sludge concentration and reaction efficiency.

[0005] Biochar, as a porous carbon material, possesses characteristics such as a large specific surface area and abundant surface functional groups, making it suitable as a carrier for microorganisms and promoting interspecies electron transfer (DIET), thereby enhancing anaerobic digestion. However, ordinary biochar has strong hydrophobicity, few functional groups, and insufficient conductivity. When directly applied to the complex wastewater from recycled papermaking, its enhancing effect is limited, and it is easily contaminated by impurities in the wastewater, clogging its pores. Therefore, its promoting effect often fails to meet the ideal requirements for engineering applications.

[0006] Therefore, developing a novel biochar material that can specifically address the challenges of anaerobic fermentation in recycled papermaking wastewater, and that combines high conductivity, strong microbial loading capacity, and selective adsorption and inhibition functions, is of great significance for improving the energy conversion efficiency of papermaking wastewater. Summary of the Invention

[0007] Purpose of the invention: To address the problems of insufficient conductivity, limited functionality, and poor removal of specific inhibitors in the use of raw biochar in promoting anaerobic fermentation of recycled papermaking wastewater, this invention provides a modified biochar preparation and application for enhancing methane production in anaerobic fermentation of recycled papermaking wastewater. The aim is to significantly improve methane yield, shorten fermentation start-up time, and enhance the system's resistance to shock loads.

[0008] Technical solution: In a first aspect, the present invention provides a modified biochar for enhancing the anaerobic fermentation of recycled papermaking wastewater to produce methane. The modified biochar has a porous biochar framework loaded with nano-manganese iron spinel and is externally wrapped with a polyaniline conductive polymer film.

[0009] Furthermore, in the modified biochar, the amount of polyaniline encapsulation accounts for 5%-15% of the total mass of the modified biochar, and the loading of nano-manganese iron spinel accounts for 5%-15% of the total mass of the modified biochar; The modified biochar is porous biochar obtained by pyrolysis of carbon-containing solid waste generated during the papermaking process.

[0010] Secondly, the present invention provides a method for preparing modified biochar as described in any of the above claims, specifically comprising the following steps: S1. Raw material carbonization: Take dried recycled papermaking wastewater sludge, crush and sieve it, and then pyrolyze it at high temperature under an inert atmosphere to obtain raw biochar. S2, Manganese-iron spinel loading: The original biochar was impregnated in an iron-manganese salt solution, precipitated with alkali, aged, filtered and separated, dried, calcined under an inert atmosphere, washed and dried again to obtain an intermediate loaded with manganese-iron spinel. S3. Conductive polymer encapsulation: The intermediate is dispersed in an acidic medium, aniline monomer is added, and in-situ polymerization is carried out under the action of an oxidant. After post-treatment, modified biochar is obtained.

[0011] Furthermore, in S1, the high-temperature pyrolysis specifically involves heating to 500-700℃ at a rate of 5-10℃ / min and pyrolyzing for 1-2 hours.

[0012] Preferably, in S1, the material has been crushed and passed through a 60-100 mesh sieve.

[0013] Furthermore, in S2, the molar ratio of FeCl3 to KMnO4 in the iron-manganese salt solution is 2:1-3:1.

[0014] Preferably, in S2, the specific steps for aging after alkali precipitation are as follows: slowly add alkali solution until pH>10, and age for 6-8 hours.

[0015] Furthermore, in S2, the specific conditions for calcination are: calcination temperature of 300-400℃ and calcination time of 1-2 hours.

[0016] Furthermore, in S3, the acidic medium is hydrochloric acid; the oxidant is ammonium persulfate solution; The mass ratio of the intermediate, acidic medium, aniline monomer and oxidant is 4-5::3-4:0.5-1:1-2.

[0017] Preferably, the in-situ polymerization reaction takes 4-8 hours.

[0018] Thirdly, the present invention provides an application of modified biochar as described in any of the above claims in the anaerobic fermentation of recycled papermaking wastewater or similar wastewater containing high organic matter and inhibitors to produce methane.

[0019] Further, the specific steps are as follows: the modified biochar is added to the anaerobic fermentation system at a dosage of 3-5 g / L.

[0020] The modified biochar provided by this invention can increase the methane yield of the anaerobic fermentation system by more than 80% compared with the control group without added biochar, reduce volatile fatty acids and COD by more than 40%, and stabilize the pH at around 7.

[0021] Mechanism Explanation: The modified biochar provided by this invention uses porous biochar loaded with nano-manganese iron spinel as a framework, externally coated with a polyaniline conductive polymer film. High-temperature pyrolysis biochar possesses a large specific surface area and porous structure, serving as a "sanctuary" for microbial attachment and growth. Simultaneously, its high alkalinity effectively buffers pH fluctuations in the system, maintaining the reaction system's pH within the neutral range and enhancing microbial activity. Loading nano-manganese iron spinel onto the porous biochar endows it with paramagnetic and Fenton-like catalytic activity, enabling partial degradation of recalcitrant organic matter (such as...). The modified biochar, through multiple synergistic effects, significantly improves methane yield, shortens fermentation start-up time, and enhances the system's resistance to shock loads. Furthermore, the Fenton-like catalytic activity of nano-manganese-iron spinel initiates the further polymerization of low-molecular-weight polyaniline oligomers and unreacted aniline into polyaniline. Finally, an external polyaniline conductive polymer film is coated, forming Fe-N and Mn-N chemical bonds between polyaniline and manganese-iron spinel, significantly improving the overall conductivity of the material. This creates an efficient "electronic bridge" between electrogenic bacteria, biochar, and methanogenic bacteria. The amino and other functional groups on its surface can selectively adsorb heavy metals, chlorophenols, and other toxic inhibitors from papermaking wastewater. The modified biochar provided by this invention significantly improves methane yield, shortens fermentation start-up time, and enhances the system's resistance to shock loads through multiple synergistic functions.

[0022] Beneficial effects: Compared with the prior art, the specific beneficial effects of this invention are as follows: 1. Synergistic effect of multiple functions: The material of this invention has the functions of high conductivity, paramagnetism, selective adsorption and microbial carrier. It can synergistically promote direct interspecies electron transfer, break down recalcitrant organic matter, adsorb toxic substances and buffer the pH of the system, thereby significantly improving the methane production, rate and system stability of anaerobic fermentation of recycled papermaking wastewater.

[0023] 2. “Waste-to-waste” and targeted design: Using sludge or waste residue generated in the papermaking process as raw materials, which are rich in lignin, the prepared biochar has more aromatic structures and achieves stronger conductivity; the modification scheme is designed to target the unique inhibitors and fermentation bottlenecks of recycled papermaking wastewater, which is highly targeted.

[0024] 3. Significant effects: The material of this invention can simultaneously enhance the effects from four dimensions: "substrate pretreatment", "electron transfer enhancement", "microbial protection" and "toxicity mitigation", thereby achieving the comprehensive goals of significantly increasing methane production, accelerating system start-up and enhancing operational stability in engineering applications. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope image of the modified biochar (PANI@MnFe2O4 / BC) prepared in Example 1. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the embodiments.

[0027] Example 1: Properties and Application Effects of Different Biochar Materials

[0028] Dry recycled papermaking wastewater sludge was taken, crushed and passed through a 100-mesh sieve, and then pyrolyzed at 500℃ for 1.5 hours under nitrogen protection at a temperature of 10℃ / min to obtain raw biochar (BC).

[0029] 10g of BC was immersed in a solution containing 0.5 mol / L FeCl3 and sonicated for 1 hour. Then, 2 mol / L NaOH was added dropwise with stirring until the pH reached 11. After aging for 8 hours, the mixture was filtered and separated, dried at 60℃, calcined at 350℃ in nitrogen for 1 hour, washed with deionized water, and dried at 60℃ to obtain Fe3O4 / BC.

[0030] 10g of BC was immersed in a solution containing 0.5 mol / L FeCl3 and 0.2 mol / L KMnO4. After sonication for 1 hour, 2 mol / L NaOH was added dropwise with stirring until the pH reached 11. After aging for 8 hours, the mixture was filtered and separated, dried at 60℃, calcined at 350℃ in nitrogen for 1 hour, washed with deionized water, and dried at 60℃ to obtain MnFe2O4 / BC.

[0031] 5 g of Fe3O4 / BC was dispersed in 100 mL of 1M HCl, and 0.5 mL of aniline monomer was added. After stirring in an ice bath for 30 minutes, 20 mL of aqueous solution containing 1.14 g of ammonium persulfate was added dropwise, and the reaction was allowed to proceed for 6 hours. The product was filtered, washed with water, and dried under vacuum at 60 °C to obtain polyaniline-coated modified biochar (PANI@Fe3O4 / BC).

[0032] 5 g of MnFe2O4 / BC was dispersed in 100 mL of 1 M HCl, and 0.5 mL of aniline monomer was added. After stirring in an ice bath for 30 minutes, 20 mL of aqueous solution containing 1.14 g of ammonium persulfate was added dropwise, and the reaction was allowed to proceed for 6 hours. The product was filtered, washed with water, and dried under vacuum at 60 °C to obtain polyaniline-coated modified biochar (PANI@MnFe2O4 / BC).

[0033] The properties of the prepared materials were analyzed, and the results are shown in Table 1. Overall, PANI@MnFe2O4 / BC outperforms other materials in terms of pH, electron transport capacity, specific surface area, and saturation magnetization.

[0034]

[0035] In addition, simulated recycled papermaking wastewater with a chemical oxygen demand (COD) concentration of 5000 mg / L was prepared as the fermentation substrate. Four sets of parallel anaerobic fermentation flasks were set up: Control group: No materials added; Experimental group 1: BC was added at a dosage of 5 g / L; Experimental group 2: Fe3O4 / BC was added at a dosage of 5 g / L; Experimental group 3: Add MnFe2O4 / BC, dosage 5 g / L; Experimental group 4: PANI@Fe3O4 / BC was added at a dosage of 5 g / L; Experimental group 5: PANI@MnFe2O4 / BC was added at a dosage of 5 g / L.

[0036] Batch fermentation was carried out under mesophilic conditions at 35℃. The results in Table 2 show that experimental group 5 (PANI@MnFe2O4 / BC) had the best performance. During the 20-day fermentation period, the cumulative methane yield was increased by more than 85% compared with the control group, the pH of the system was stable at around 7.14, and there was no serious accumulation of volatile fatty acids and COD.

[0037]

[0038] Example 2: Preparation and application effects of biochar materials prepared at different pyrolysis temperatures Dry recycled paper mill wastewater sludge was pulverized and passed through a 100-mesh sieve. Under nitrogen protection, it was pyrolyzed at 300℃, 400℃, 500℃, 600℃, and 700℃ for 1.5 hours at a rate of 10℃ / min to obtain raw biochar at different pyrolysis temperatures. 10g of each raw biochar at different pyrolysis temperatures was impregnated in solutions containing 0.5 mol / L FeCl3 and 0.2 mol / L KMnO4. After sonication for 1 hour, 2 mol / L NaOH was added dropwise with stirring until the pH reached 11. After aging for 8 hours, the mixture was filtered, dried at 60℃, calcined at 350℃ for 1 hour under nitrogen, washed with deionized water, and dried at 60℃ to obtain MnFe2O4 / BC intermediates at different pyrolysis temperatures.

[0039] 5g of MnFe2O4 / BC at different pyrolysis temperatures were dispersed in 100mL of 1M HCl, and 0.5mL of aniline monomer was added. The mixture was stirred in an ice bath for 30 minutes. 20mL of an aqueous solution containing 1.14g of ammonium persulfate was added dropwise, and the reaction was allowed to proceed for 6 hours. The product was filtered, washed with water, and dried under vacuum at 60℃ to obtain polyaniline-coated modified biochar (the polyaniline-coated modified biochar obtained by pyrolysis at 300℃, 400℃, 500℃, 600℃, and 700℃ were designated as PANI@MnFe2O4 / BC-300, PANI@MnFe2O4 / BC-400, PANI@MnFe2O4 / BC-500, PANI@MnFe2O4 / BC-600, and PANI@MnFe2O4 / BC-700, respectively).

[0040] Simulated recycled papermaking wastewater with a chemical oxygen demand (COD) concentration of 5000 mg / L was prepared as the fermentation substrate. Four sets of parallel anaerobic fermentation flasks were set up: Control group: No materials added; Experimental group 1: Add the material prepared in Example 2 - PANI@MnFe2O4 / BC-300, at a dosage of 3 g / L; Experimental group 2: Add the material prepared in Example 2 - PANI@MnFe2O4 / BC-400, at a dosage of 3 g / L; Experimental group 3: Add PANI@MnFe2O4 / BC-500 prepared in Example 2 at a dosage of 3 g / L.

[0041] Experimental group 4: Add PANI@MnFe2O4 / BC-600 prepared in Example 2 at a dosage of 3 g / L.

[0042] Experimental group 5: Add PANI@MnFe2O4 / BC-700 prepared in Example 2 at a dosage of 3 g / L.

[0043] Batch fermentation was carried out under mesophilic conditions at 35℃. The results in Table 3 show that, compared with the control, the biochar material prepared at 500-700℃ increased the cumulative methane yield by more than 82.2% during the 20-day fermentation cycle, stabilized the pH of the system between 6.91 and 7.04, and significantly reduced volatile fatty acids and COD, but the differences between treatments were not significant.

[0044]

[0045] Example 3: Application effects of different dosages Dry recycled paper mill wastewater sludge was pulverized and passed through a 100-mesh sieve. Then, under nitrogen protection, it was pyrolyzed at 500℃ for 1.5 hours at a rate of 10℃ / min to obtain raw biochar (BC). 10g of BC was impregnated in a solution containing 0.5 mol / L FeCl3 and 0.2 mol / L KMnO4. After sonication for 1 hour, 2 mol / L NaOH was added dropwise with stirring until the pH reached 11. After aging for 8 hours, the mixture was filtered, dried at 60℃, calcined at 350℃ for 1 hour under nitrogen, washed with deionized water, and dried at 60℃ to obtain the MnFe2O4 / BC intermediate.

[0046] 5 g of MnFe2O4 / BC was dispersed in 100 mL of 1 M HCl, and 0.5 mL of aniline monomer was added. The mixture was stirred in an ice bath for 30 minutes. 20 mL of an aqueous solution containing 1.14 g of ammonium persulfate was added dropwise, and the reaction was allowed to proceed for 6 hours. The product was filtered, washed with water, and dried under vacuum at 60 °C to obtain polyaniline-coated modified biochar (PANI@MnFe2O4 / BC).

[0047] Simulated papermaking wastewater with a chemical oxygen demand (COD) concentration of 5000 mg / L was prepared as the fermentation substrate. Four sets of parallel anaerobic fermentation flasks were set up: Control group: No materials added; Experimental group 1: Add the material prepared in Example 3 - PANI@MnFe2O4 / BC, at a dosage of 1 g / L; Experimental group 2: Add the material prepared in Example 3 - PANI@MnFe2O4 / BC, at a dosage of 3 g / L; Experimental group 3: Add the material prepared in Example 3 - PANI@MnFe2O4 / BC, at a dosage of 5 g / L.

[0048] Experimental group 4: Add the material prepared in Example 3 - PANI@MnFe2O4 / BC, at a dosage of 7.5 g / L.

[0049] Experimental group 5: Add PANI@MnFe2O4 / BC, the material prepared in Example 3, at a dosage of 10 g / L.

[0050] Batch fermentation was conducted under mesophilic conditions at 35℃. Table 4 shows that when the biochar dosage was higher than 3-10 g / L, the cumulative methane yield increased by more than 81.0% over a 20-day fermentation period, the system pH stabilized between 6.84 and 7.06, and volatile fatty acids and COD significantly decreased, although there were no significant differences between treatments. Therefore, considering cost, a dosage of 3-5 g / L is recommended.

[0051]

[0052] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A modified biochar for enhancing the anaerobic fermentation of recycled papermaking wastewater to produce methane, characterized in that: The modified biochar uses porous biochar loaded with nano-manganese iron spinel as a framework and is wrapped with a polyaniline conductive polymer film.

2. The modified biochar according to claim 1, characterized in that: In the modified biochar, the amount of polyaniline encapsulation accounts for 5%-15% of the total mass of the modified biochar, and the loading of nano-manganese iron spinel accounts for 5%-15% of the total mass of the modified biochar; The modified biochar is porous biochar obtained by pyrolysis of carbon-containing solid waste generated during the papermaking process.

3. The method for preparing modified biochar according to any one of claims 1-2, characterized in that, Specifically, the following steps are included: S1. Raw material carbonization: Take dried recycled papermaking wastewater sludge, crush and sieve it, and then pyrolyze it at high temperature under an inert atmosphere to obtain raw biochar. S2, Manganese-iron spinel loading: The original biochar was impregnated in an iron-manganese salt solution, precipitated with alkali, aged, filtered and separated, dried, calcined under an inert atmosphere, washed and dried again to obtain an intermediate loaded with manganese-iron spinel. S3. Conductive polymer encapsulation: The intermediate is dispersed in an acidic medium, aniline monomer is added, and in-situ polymerization is carried out under the action of an oxidant. After post-treatment, modified biochar is obtained.

4. The method for preparing modified biochar according to claim 3, characterized in that: In S1, the high-temperature pyrolysis specifically involves heating at 5-10℃ / min to 500-700℃ for 1-2 hours.

5. The method for preparing modified biochar according to claim 3, characterized in that: In S2, the molar ratio of FeCl3 to KMnO4 in the iron-manganese salt solution is 2:1-3:

1.

6. The method for preparing modified biochar according to claim 3, characterized in that: In S2, the specific conditions for calcination are: calcination temperature of 300-400℃ and calcination time of 1-2 hours.

7. The method for preparing modified biochar according to claim 3, characterized in that: In S3, the acidic medium is hydrochloric acid; the oxidant is ammonium persulfate solution. The mass ratio of the intermediate, acidic medium, aniline monomer and oxidant is 4-5:3-4:0.5-1:1-2.

8. The application of the modified biochar according to any one of claims 1-2 in the anaerobic fermentation of recycled papermaking wastewater or similar wastewater with high organic matter and containing inhibitors to produce methane.

9. The application according to claim 8, characterized in that, The specific steps are as follows: the modified biochar is added to the anaerobic fermentation system at a dosage of 3-5 g / L.

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