Method for improving dewatering performance of excess sludge through combination of mushroom residue-based ferromagnetic biochar and persulfate

Abstract

The invention discloses a method for improving the dewatering performance of excess sludge by combining mushroom residue-based ferromagnetic biochar with persulfate, and belongs to the technical field of solid waste treatment. The method comprises the following steps: pyrolyzing mushroom residues at a high temperature to prepare biochar, and loading iron ions on the biochar by adopting a hydrothermal method to obtain a heterogeneous catalyst of persulfate, namely the mushroom residue-based ferromagnetic biochar. The mushroom residue-based ferromagnetic biochar and persulfate are added into the excess sludge, the sludge structure can be destroyed through stirring treatment, the water content can be reduced, and the dewatering performance of the excess sludge can be improved. Compared with traditional catalysts such as transition metal ions, the mushroom residue-based ferromagnetic biochar provided by the invention is combined with persulfate as the catalyst, so that the catalyst is more environmentally friendly, efficient and stable.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste treatment, and in particular to a method for improving the dewatering performance of excess sludge by combining mushroom residue-based ferromagnetic biochar with persulfate. Background Art

[0002] With the acceleration of my country's urbanization process, the number of urban sewage treatment plants has increased sharply, and the output of sludge, a byproduct of the biological treatment process of sewage treatment plants, has also increased. It is reported that the output of residual sludge accounts for 0.3%-0.5% of the volume of sewage treatment. With the improvement of the water quality requirements for sewage treatment effluent, the sludge output of sewage treatment plants that combine conventional processes with deep treatment may increase by 0.5-1 times. Residual sludge has the dual attributes of pollution and resources. On the one hand, the sludge composition is complex, with extracellular polymers EPS as the core, containing a large amount of organic matter, bacteria, viruses, heavy metals and other pollutants; the gel-like structure of the sludge is tightly bound to a large amount of bound water, with a water content of about 98%-99%, which increases the difficulty of treatment and disposal and easily causes secondary pollution; on the other hand, the organic resources rich in sludge can achieve resource transformation if they are reasonably utilized. Therefore, the goal of sludge treatment focuses on harmlessness, resource utilization and reduction. Based on its special structural components, sludge dehydration is a key link in sludge treatment and disposal.

[0003] Studies have shown that sludge dewatering performance can be effectively improved by pre-treating sludge through physical, chemical, biological or a combination of multiple methods. Among the many current methods for improving sludge dewatering performance, the sulfate radical oxidation method in the advanced oxidation method has become a sludge pretreatment method that has attracted much attention due to its strong adaptability to sludge pH, non-corrosiveness and excellent sulfate radical oxidation ability. However, sulfate radicals are generally formed by exciting persulfate, and the decomposition rate of persulfate itself is slow, requiring the help of a catalyst to accelerate the generation of sulfate radicals. Transition metal iron ions, as an economical and efficient catalyst, can significantly improve the reaction efficiency, but high concentrations can easily lead to quenching of the oxidation reaction and excessive iron content in the sludge. Therefore, it is urgent to find new methods to solve the problems of difficult sludge dewatering and poor results in existing technologies. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving the dewatering performance of residual sludge by combining mushroom residue-based ferromagnetic biochar with persulfate, so as to solve the problems existing in the above-mentioned prior art. The present invention utilizes iron ions loaded on biochar to catalyze persulfate to produce strongly oxidizing sulfate radicals, destroy the sludge floc structure, release intracellular bound water, and achieve sludge dehydration and reduction. This method utilizes mushroom residue-based Fe-SBC to catalyze persulfate to condition sludge for the first time, thereby improving the dewatering performance of sludge, and the method is green, environmentally friendly, stable and efficient.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The invention provides a mushroom residue-based ferromagnetic biochar, which is formed by loading iron on the mushroom residue biochar by a hot water method.

[0007] Preferably, the method for preparing mushroom residue-based ferromagnetic biochar comprises the following steps:

[0008] Pyrolyzing mushroom residue at a high temperature of 500-800°C to obtain mushroom residue-based biochar;

[0009] Grinding and sieving the mushroom residue-based biochar, and performing ultrasonic cleaning with water;

[0010] The washed mushroom residue-based biochar is mixed with a ferrous ion solution and heated to react, so that iron is loaded on the mushroom residue-based biochar, and then washed with an organic solvent to obtain the mushroom residue-based ferromagnetic biochar.

[0011] Preferably, the ultrasonic cleaning conditions are: temperature of 35-40° C., and cleaning time of 10-15 min.

[0012] Preferably, the ferrous ion solution includes ferrous sulfate heptahydrate solution or ferrous chloride solution with a concentration of 0.2-0.4 mol / L; and / or the mixed heating reaction conditions are: heating at 150-200° C. for 6-10 h; and / or the organic solvent includes methanol or ethanol.

[0013] The present invention also provides the use of the mushroom residue-based ferromagnetic biochar combined with persulfate in the preparation of a sludge dehydration catalyst.

[0014] The present invention also provides a method for improving the dewatering performance of excess sludge based on mushroom residue-based ferromagnetic biochar combined with persulfate, comprising the steps of adding the mushroom residue-based ferromagnetic biochar and persulfate to the excess sludge and stirring evenly to reduce the moisture content of the excess sludge.

[0015] Preferably, the concentration of the persulfate is 75 mmol / L-125 mmol / L, and the persulfate includes potassium persulfate, sodium persulfate or ammonium persulfate.

[0016] Preferably, the volume ratio of the residual sludge to the mushroom residue-based ferromagnetic biochar is (40-50):1.

[0017] Preferably, the stirring method includes aeration or mechanical stirring, the stirring time is 10-20 min, and the stirring speed is 100-200 rpm.

[0018] The present invention also provides a sludge dehydration catalyst, comprising the mushroom residue-based ferromagnetic biochar and persulfate, wherein the persulfate comprises potassium persulfate, sodium persulfate or ammonium persulfate.

[0019] The present invention discloses the following technical effects:

[0020] (1) The present invention uses mushroom residue to prepare biochar loaded with metal ions as a catalyst carrier, wherein the mushroom residue is a waste generated during mushroom cultivation in the agricultural production process, and the output is huge. Using it as a persulfate catalyst carrier to condition sludge plays a role in treating waste with waste.

[0021] (2) The present invention uses mushroom residue-based ferromagnetic biochar as a persulfate catalyst to condition sludge, which is more environmentally friendly, efficient and stable than traditional transition metal ion catalysts.

[0022] (3) In addition to catalyzing persulfate, the mushroom residue-based ferromagnetic biochar of the present invention can itself be used as a fuel with a higher calorific value. When the sludge is incinerated, the mushroom residue-based ferromagnetic biochar can provide calorific value for the incineration of the sludge, which will reduce the original energy usage during the incineration of the sludge.

[0023] (4) The present invention is the first to use mushroom residue-based ferromagnetic biochar to improve sludge dewatering performance, which can effectively improve sludge dewatering performance, reduce sludge moisture content, and improve sludge filter cake filtration performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 SEM images of mushroom residue-based biochar characterization;

[0026] Figure 2 This is the SEM image of mushroom residue-based ferromagnetic biochar;

[0027] Figure 3 This is a graph showing the change in the content of iron ions in the aqueous solution of the iron ion leaching experiment in Example 1;

[0028] Figure 4 The graphs showing the changes in WC, SRF, CST and SCOD of the sludge supernatant in the treatment of excess sludge using ferromagnetic biochar based on mushroom residues prepared with ferrous ions.

[0029] Figure 5 This is a graph showing the changes in WC, SRF, CST and SCOD of the sludge supernatant in the treatment of residual sludge using mushroom residue-based ferromagnetic biochar loaded with trivalent iron ions. DETAILED DESCRIPTION

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terms described in the present invention are only for describing a particular embodiment and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0032] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0033] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0034] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0035] The preparation of Fe-SBC and its dehydration principle of the present invention are as follows: biochar is prepared by high-temperature pyrolysis of mushroom residue under micro-aerobic conditions, and iron ions are loaded on the biochar by a hydrothermal method to obtain a heterogeneous catalyst for persulfate, namely Fe-SBC. The mushroom residue-based biochar used can evenly load iron and effectively improve the stability of the sulfate catalytic process; the obtained magnetic biochar catalyst can efficiently excite sulfate radicals, and has the ability to oxidize sludge organic matter, destroy sludge floc structure, release bound water, and improve sludge dehydration performance; the iron ions loaded on the biochar are relatively stable, and in the process of catalyzing persulfate, the iron ions on the biochar will not be leached or will be rarely leached, and at the same time, the iron ions are evenly loaded on the biochar, and the process of catalyzing persulfate will be more stable. The method produces a new type of green, environmentally friendly, economical and efficient persulfate catalyst. For the first time, this catalyst is used to catalyze persulfate to produce sulfate radicals, which can effectively destroy the sludge structure and improve the dehydration performance of the sludge.

[0036] The raw material of the iron-loaded biochar of the present invention is the waste generated after the cultivation of edible mushrooms - mushroom residue, such as: Pleurotus eryngii residue, Pleurotus ostreatus residue, Lentinus edodes residue, Flammulina velutipes residue, etc. The present invention is described by taking Pleurotus eryngii residue as an example.

[0037] Example 1 Preparation of mushroom residue-based ferromagnetic biochar

[0038] (1) Pretreatment of mushroom residue: screening the obtained mushroom residue, removing impurities, and drying;

[0039] (2) Preparation of mushroom residue-based biochar: The dried mushroom residue was wrapped with double-layer aluminum foil and placed in a muffle furnace for pyrolysis at 600 °C to prepare mushroom residue-based biochar;

[0040] (3) Grind the pyrolyzed mushroom residue-based biochar and pass it through a 100-mesh sieve. Then, put the sieved biochar into a beaker and put it into an ultrasonic cleaning machine for ultrasonic cleaning (the time is set to 10 min and the temperature is 40°C). After ultrasonic cleaning, heat and stir in a water bath. If turbidity floats up, replace the water and stir until the supernatant is clear.

[0041] (4) Iron loading: The iron was loaded by hydrothermal method. The cleaned mushroom residue biochar was placed in the reactor lining, and then water and ferrous sulfate heptahydrate (concentration of 0.3 mol / L) were added. The reactor was heated in an oven at 180°C for 8 hours. The high temperature and high pressure in the reactor made the iron evenly loaded on the biochar surface. The iron stuck on the mushroom residue-based iron-loaded biochar was washed away with 99% methanol. The preparation of the mushroom residue-based iron-loaded biochar was completed and named Fe-SBC.

[0042] The prepared mushroom residue-based biochar and Fe-SBC were characterized, and their SEM images are shown in Figure 1 and Figure 2 The results showed that iron ions were uniformly loaded on the mushroom residue biochar.

[0043] Example 2 Preparation of mushroom residue-based ferromagnetic biochar

[0044] (1) Pretreatment of mushroom residue: screening the obtained mushroom residue, removing impurities, and drying;

[0045] (2) Preparation of mushroom residue-based biochar: The dried mushroom residue was wrapped with double-layer aluminum foil and placed in a muffle furnace for pyrolysis at 500 °C to prepare mushroom residue-based biochar;

[0046] (3) Grind the pyrolyzed mushroom residue-based biochar and pass it through a 100-mesh sieve. Then, put the sieved biochar into a beaker and put it into an ultrasonic cleaning machine for ultrasonic cleaning (the time is set to 15 min and the temperature is 35°C). After ultrasonic cleaning, heat and stir in a water bath. If turbidity floats up, replace the water and stir until the supernatant is clear.

[0047] (4) Iron loading: The iron was loaded by hydrothermal method. The cleaned mushroom residue biochar was placed in the reactor lining, and then water and ferrous chloride (concentration of 0.2 mol / L) were added. The reactor was placed in a 150°C oven and heated for 10 h. The iron was evenly loaded on the biochar surface after high temperature and high pressure in the reactor. The iron stuck on the mushroom residue-based iron-loaded biochar was washed away with 99% methanol. The preparation of mushroom residue-based iron-loaded biochar was completed and named Fe-SBC.

[0048] The mushroom residue-based biochar and Fe-SBC prepared above were characterized, and the results were the same as those in Example 1, showing that iron ions were uniformly loaded on the mushroom residue biochar.

[0049] Example 3 Preparation of mushroom residue-based ferromagnetic biochar

[0050] (1) Pretreatment of mushroom residue: screening the obtained mushroom residue, removing impurities, and drying;

[0051] (2) Preparation of mushroom residue-based biochar: The dried mushroom residue was wrapped with double-layer aluminum foil and placed in a muffle furnace for pyrolysis at 800 °C to prepare mushroom residue-based biochar;

[0052] (3) Grind the pyrolyzed mushroom residue-based biochar and pass it through a 100-mesh sieve. Then, put the sieved biochar into a beaker and put it into an ultrasonic cleaning machine for ultrasonic cleaning (the time is set to 12 minutes and the temperature is 38°C). After ultrasonic cleaning, heat and stir in a water bath. If turbidity floats up, replace the water and stir until the supernatant is clear.

[0053] (4) Iron loading: The iron was loaded by hydrothermal method. The cleaned mushroom residue biochar was placed in the reactor lining, and then water and ferrous sulfate heptahydrate or ferrous chloride (concentration of 0.4 mol / L) were added. The reactor was placed in a 200°C oven and heated for 6 hours. After impregnation-drying-calcination, the iron was evenly loaded on the biochar surface. The iron stuck on the mushroom residue-based iron-loaded biochar was washed away with 99.5% ethanol. The preparation of the mushroom residue-based iron-loaded biochar was completed and named Fe-SBC.

[0054] The mushroom residue-based biochar and Fe-SBC prepared above were characterized, and the results were the same as those in Example 1, showing that iron ions were uniformly loaded on the mushroom residue biochar.

[0055] Example 4

[0056] Take an appropriate amount of the mushroom residue-based ferromagnetic biochar prepared in Example 1 and put it into a beaker filled with 500 mL of ultrapure water. Place the beaker on a magnetic stirrer and stir. Measure the total iron concentration in the water in the beaker every 5 minutes. Figure 3 It can be seen that the iron ion concentration is no more than 0.3 mg / L, which meets the effluent quality requirements of the sewage treatment plant.

[0057] In addition, it was also verified that the mushroom residue-based ferromagnetic biochar prepared in other embodiments also meets the effluent quality requirements of the sewage treatment plant.

[0058] Example 5

[0059] (1) Five 250 mL beakers were filled with 200 mL of sludge from a concentration tank with a water content of 97.3% and a TS of 20,000 mg / L. Potassium persulfate of 75, 85, 95, 105, 115, and 125 mmol / L was added, respectively. Then, 2 mg / g TS of mushroom residue-based ferromagnetic biochar (density 1.5 g / cm2) prepared in Example 1 was added. 3 ), stirring with a six-joint stirrer for 20 min at a speed of 200 r / min;

[0060] (2) After the reaction, 50 mL of the sludge after reaction was taken, centrifuged, and the water content (WC) was measured. The supernatant was taken for the determination of dissolved organic matter (SCOD). 110 mL of the sludge after reaction was taken for the determination of sludge specific resistance (SRF) and capillary water absorption time (CST) (see Figure 4 ).

[0061] from Figure 4 It can be seen that under the optimal potassium persulfate dosage conditions, the sludge moisture content decreased from 97.3% of the original sludge to 72.9%, and the sludge resistance decreased from 1.2×10 12 m / kg decreased to 8.2×10 11m / kg, the SCOD content of the sludge supernatant increased from 300.98 mg / L of the original sludge to 570 mg / L, and the sludge capillary absorption time decreased from 21 s of the original sludge to 12.3 s.

[0062] Example 6

[0063] In the preparation process of biochar loaded with iron, ferrous iron is used to load biochar, but Fe 3+ It is worth exploring whether the catalytic effect is better when loaded on biochar. Therefore, ferrous sulfate heptahydrate was replaced with ferric chloride. Other operations were the same as in Example 1 to obtain Fe-SBC loaded with trivalent iron. Dehydration experiments were carried out under the same conditions. The results are as follows: Figure 5 As shown. Figure 5 and Figure 4 By comparison, it can be seen that the effect of Fe-SBC made from ferric chloride in catalyzing persulfate conditioning of sludge is weaker than that of Fe-SBC made from ferrous sulfate heptahydrate in catalyzing persulfate conditioning of sludge.

[0064] In summary, in order to solve the problems of difficult sludge dehydration and poor dehydration effect, the present invention uses mushroom residue to prepare biochar loaded with metal ions as a catalyst carrier, that is, mushroom residue-based loaded ferromagnetic biochar Fe-SBC, and a heterogeneous catalyst comes into being. The catalyst cleverly loads iron ions evenly on mushroom residue biochar, which not only ensures the stability of the catalytic process, but also avoids the free release of iron ions, reducing the secondary pollution of sludge. In addition, mushroom residue, as an agricultural waste, is resource-utilized in this way, and its biochar can also provide additional calorific value in sludge incineration treatment, further improving the overall treatment efficiency and environmental benefits. The present invention uses Fe-SBC as a catalyst to catalyze persulfate to improve the sludge dehydration performance. It is an innovative and promising method that effectively integrates the goals of harmlessness, resource utilization and reduction of sludge treatment, and promotes the sustainable development of sludge treatment technology.

[0065] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A mushroom residue-based ferromagnetic biochar, characterized in that: The method is to load iron onto mushroom residue biochar using a hot water method.

2. The mushroom residue-based ferromagnetic biochar according to claim 1, characterized in that: The method for preparing mushroom residue-based ferromagnetic biochar comprises the following steps: Pyrolyzing mushroom residue at a high temperature of 500-800°C to obtain mushroom residue-based biochar; Grinding and sieving the mushroom residue-based biochar, and performing ultrasonic cleaning with water; The washed mushroom residue-based biochar is mixed with a ferrous ion solution and heated to react, so that iron is loaded on the mushroom residue-based biochar, and then washed with an organic solvent to obtain the mushroom residue-based ferromagnetic biochar.

3. The mushroom residue-based ferromagnetic biochar according to claim 2, characterized in that: The ultrasonic cleaning conditions are: temperature of 35-40° C., and cleaning time of 10-15 min.

4. The mushroom residue-based ferromagnetic biochar according to claim 2, characterized in that: The ferrous ion solution includes ferrous sulfate heptahydrate solution or ferrous chloride solution with a concentration of 0.2-0.4 mol / L; and / or the mixed heating reaction conditions are: heating at 150-200° C. for 6-10 hours; and / or the organic solvent includes methanol or ethanol.

5. Use of the mushroom residue-based ferromagnetic biochar as described in any one of claims 1 to 4 in combination with persulfate in the preparation of a sludge dehydration catalyst.

6. A method for improving the dewatering performance of excess sludge based on mushroom residue-based ferromagnetic biochar combined with persulfate, characterized in that: The method comprises the steps of adding the mushroom residue-based ferromagnetic biochar and persulfate described in any one of claims 1 to 4 into the residual sludge, and stirring evenly to reduce the moisture content of the residual sludge.

7. The method according to claim 6, characterized in that The concentration of the persulfate is 75 mmol / L-125 mmol / L, and the persulfate includes potassium persulfate, sodium persulfate or ammonium persulfate.

8. The method according to claim 6, characterized in that The volume ratio of the residual sludge to the mushroom residue-based ferromagnetic biochar is (40-50):

1.

9. The method according to claim 6, characterized in that The stirring method includes aeration or mechanical stirring, the stirring time is 10-20 minutes, and the stirring speed is 100-200 rpm.

10. A sludge dehydration catalyst, characterized in that: It comprises the mushroom residue-based ferromagnetic biochar according to any one of claims 1 to 4 and persulfate, wherein the persulfate comprises potassium persulfate, sodium persulfate or ammonium persulfate.

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