Biochar capable of synchronously adsorbing nitrogen and phosphorus as well as preparation method and application of biochar

Abstract

The invention discloses nitrogen and phosphorus synchronous adsorption biochar as well as a preparation method and application thereof. Comprising the following steps: respectively crushing dewatered sludge, biogas residues and agricultural and forestry wastes, mixing, adding 0.2-1.5 mol / L of a modified metal solution in the mixing process, fully stirring and uniformly mixing, aging, and drying until the water content is less than 10%; heating to 500-800 DEG C at the speed of 5-10 DEG C / min in a nitrogen atmosphere, pyrolyzing for 1-3 hours, cooling, grinding and sieving to obtain pyrolytic carbon; and adding KOH powder, carrying out ball milling, fully and uniformly mixing, and carrying out anaerobic heating reaction at 750-900 DEG C to obtain the nitrogen and phosphorus synchronous adsorption biochar with a high BET specific surface area and a honeycomb porous structure. The preparation method disclosed by the invention is low in cost, is applied to an advanced treatment unit of a sewage treatment plant of 50,000 tons per day, is equivalent to 200 tons of compound fertilizer in annual recovery of nitrogen and phosphorus resources, and has remarkable environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the field of environmental functional materials technology, and in particular to a nitrogen and phosphorus simultaneous adsorption biochar, its preparation method and uses. Background Technology

[0002] Currently, nitrogen and phosphorus removal in wastewater treatment mainly relies on chemical precipitation and traditional adsorbents, but these methods suffer from problems such as high reagent consumption and secondary pollution. While biochar has adsorption potential, the raw materials have drawbacks such as low adsorption capacity and poor selectivity. Patent application CN112028235A discloses a method for preparing magnesium-modified biochar, but its raw materials are limited and it does not achieve simultaneous nitrogen and phosphorus adsorption. Furthermore, traditional incineration and landfill methods lead to resource waste.

[0003] Therefore, there is an urgent need to develop highly efficient adsorption materials based on the co-utilization of solid waste. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing biochar that simultaneously adsorbs nitrogen and phosphorus.

[0005] To achieve the above objectives, the present invention provides a method for preparing nitrogen and phosphorus simultaneously adsorbed biochar, characterized by comprising the following steps: (1) Raw material pretreatment: Dewatered sludge, biogas residue and agricultural and forestry waste are crushed separately and mixed in a mass ratio of (3-5):(1-2):(2-4). During the mixing process, 0.2-1.5 mol / L of modified metal solution is added. After thorough mixing, the mixture is aged and then dried until the moisture content is <10%. (2) Synergistic pyrolysis carbonization: The temperature is raised to 500-800℃ for 1-3 h under a nitrogen atmosphere at 5-10℃ / min. After cooling, the carbon is ground through a 100-mesh sieve to obtain pyrolytic carbon. (3) Pore structure construction: KOH powder and the above-obtained pyrolytic carbon are ball-milled for 1-4 hours to fully mix evenly. The mixture is then heated at 750-900℃ in an oxygen-free environment to further obtain nitrogen and phosphorus simultaneous adsorption biochar.

[0006] Furthermore, in step (1), the agricultural and forestry waste is at least one of straw, sawdust, or fruit shells, with a particle size ≤ 5 mm.

[0007] Furthermore, in step (1), the modified metal solution includes at least one of ferrous sulfate, calcium sulfate, and magnesium sulfate.

[0008] Furthermore, in step (1), the modified metal solution is added at a flow rate of 0.3-1.5 L / min, and the solid-liquid ratio is 1 kg: (0.5-1.5) L; Optional, aging time is 1-4 hours.

[0009] Furthermore, in step (3), the specific surface area of ​​the nitrogen and phosphorus simultaneous adsorption biochar is as high as 300-600 m² / g. The present invention also provides nitrogen and phosphorus simultaneous adsorption biochar prepared by the method.

[0010] The present invention also provides an application of the nitrogen and phosphorus simultaneous adsorption biochar prepared by the method in wastewater treatment.

[0011] Furthermore, nitrogen and phosphorus simultaneous adsorption biochar was added to nitrogen and phosphorus-containing wastewater at a dosage of 0.5-10 g / L, the pH was adjusted to 6-8, and the adsorption time was 2-6 h. The present invention also provides a method for preparing biochar slow-release fertilizer, characterized in that biochar after adsorbing nitrogen and phosphorus is mixed with humic acid and bentonite in a mass ratio of (5-7):(2-3):(1-2) and granulated, and then dried at 60-80℃ to obtain biochar slow-release fertilizer.

[0012] The modified solution described in this invention is mainly used to enhance the nitrogen and phosphorus adsorption and removal capacity of subsequent materials, increase the reactive sites of the materials, and achieve a certain catalytic effect during the thermal reaction. When the concentration of the modified metal solution is 0.2-1.5 mol / L, the flow rate is 0.3-1.5 L / min, and the solid-liquid ratio is 1 kg:(0.5-1.5) L, the prepared biochar has the highest number of reactive sites and the best adsorption effect. The flow rate mainly controls the uniformity of the material loading.

[0013] Drying to a moisture content of <10% is mainly based on the need for self-heating during pyrolysis. Excessive moisture content would increase the energy consumption of subsequent thermochemical reactions.

[0014] The heating rate of 5-10℃ / min, pyrolysis temperature of 500-800℃, and pyrolysis time of 1-3 h in step (2) of this invention can better realize the porous structure of biochar and its ability to remove nitrogen and phosphorus. The specific surface area of ​​the pyrolyzed char reaches a more ideal result at 500-800℃. If the temperature is too low, the raw materials cannot be fully pyrolyzed and the reaction of modified metal ions cannot be guaranteed. If the temperature is too high, the pores will collapse, which will reduce the specific surface area. The heating rate and time can take into account both the properties of the pyrolyzed material and its economy. The 100-mesh sieve is used to match the spherical graphite in step (3). If it is too fine, it will increase the difficulty of sieving. If it is too coarse, it will increase the ball milling time.

[0015] This invention incorporates KOH powder, which reacts with carbon to achieve a porous structure in the material. Ball milling enables thorough mixing of pyrolytic carbon and KOH and promotes surface modification.

[0016] The nitrogen and phosphorus simultaneous adsorption biochar prepared by the present invention has a honeycomb porous structure as shown by scanning electron microscopy, with a BET specific surface area of ​​521-578 m² / g.

[0017] This invention has established a pilot production line with a capacity of 200 tons / year. The production cost of nitrogen and phosphorus simultaneous adsorption biochar is approximately RMB 1200 / ton, which is 60% lower than that of commercial activated carbon. Applied to the deep treatment unit of a 50,000-ton / day wastewater treatment plant, it recovers nitrogen and phosphorus resources equivalent to 200 tons of compound fertilizer annually, demonstrating significant environmental and economic benefits. Attached Figure Description

[0018] Figure 1 These are morphological and particle characterization diagrams of metal-supported co-thermolysis modified biochar.

[0019] Figure 2 This refers to the surface morphology of biochar after the porous structure is constructed.

[0020] Figure 3 This refers to the effect of biochar in removing nitrogen and phosphorus. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0022] Example 1: Preparation of Nitrogen and Phosphorus Simultaneous Adsorption Biochar (1) Raw material pretreatment: municipal dewatered sludge (from sewage treatment plant, with a moisture content of 40%), kitchen waste biogas residue and wheat straw were mixed in a mass ratio of 4:1.5:3. During the mixing process, 0.2 mol / L modified metal solution was added at a flow rate of 1L / min to make the solid-liquid ratio 1kg:1L. After thorough mixing, the mixture was aged for 4 hours and then dried until the moisture content was <10%.

[0023] (2) Synergistic pyrolysis carbonization: Under a nitrogen atmosphere, the temperature was increased to 650℃ at 8℃ / min for 2 h, and the product was ground through a 100-mesh sieve to obtain pyrolytic carbon. Results are shown in […]. Figure 1 In the image, A is a scanning electron microscope (SEM) image of the modified pyrolytic carbon, and B is a transmission electron microscope (TEM) image of the modified pyrolytic carbon. (3) Pore structure construction: KOH powder and the above-obtained pyrolytic carbon are ball-milled for 1 hour to mix thoroughly and uniformly. The mixture is then heated at 750-900℃ in an oxygen-free environment to further obtain nitrogen and phosphorus simultaneous adsorption biochar.

[0024] Scanning electron microscopy shows that nitrogen and phosphorus are simultaneously adsorbed by biochar, forming a honeycomb-like porous structure (see...). Figure 2 BET has a specific surface area of ​​578 m² / g.

[0025] Example 2: Preparation of biochar with simultaneous nitrogen and phosphorus adsorption (1) Raw material pretreatment: Take municipal dewatered sludge (from sewage treatment plant, with a moisture content of 50%), kitchen waste residue and wood chips and mix them in a mass ratio of 3:1:4. During the mixing process, add 1.0 mol / L modified metal solution at a flow rate of 1L / min to make the solid-liquid ratio 1kg:1L. After thorough mixing, age the mixture for 1 hour and then dry it until the moisture content is <10%.

[0026] (2) Synergistic pyrolysis carbonization: Under a nitrogen atmosphere, the temperature is increased to 50℃ at 5℃ / min for 3 h, and the product is ground through a 100-mesh sieve to obtain pyrolytic carbon.

[0027] (3) Pore structure construction: KOH powder and the above-obtained pyrolytic carbon are ball-milled for 1 hour to mix thoroughly and uniformly. The mixture is then heated at 750-900℃ in an oxygen-free environment to further obtain nitrogen and phosphorus simultaneous adsorption biochar. Scanning electron microscopy revealed that nitrogen and phosphorus were simultaneously adsorbed into biochar, forming a honeycomb porous structure with a BET specific surface area of ​​536 m² / g.

[0028] Example 3: Preparation of biochar with simultaneous nitrogen and phosphorus adsorption (1) Raw material pretreatment: Take municipal dewatered sludge (from sewage treatment plant, with a water content of 60%), kitchen waste residue, and fruit shells and mix them in a mass ratio of 5:2:2. During the mixing process, add 1.5 mol / L modified metal solution at a flow rate of 1L / min to make the solid-liquid ratio 1kg:1L. After thorough mixing, age the mixture for 3 hours and then dry it until the water content is <10%.

[0029] (2) Synergistic pyrolysis carbonization: Under a nitrogen atmosphere, the temperature is increased to 800℃ at 10℃ / min for 1 h, and the product is ground through a 100-mesh sieve to obtain pyrolytic carbon.

[0030] (3) Pore structure construction: KOH powder and the above-obtained pyrolytic carbon were ball-milled for 3 hours to mix thoroughly and uniformly. The mixture was then heated at 750-900℃ in an oxygen-free environment to further obtain nitrogen and phosphorus simultaneous adsorption biochar. Scanning electron microscopy revealed that nitrogen and phosphorus were simultaneously adsorbed into biochar, forming a honeycomb porous structure with a BET specific surface area of ​​569 m² / g.

[0031] Example 4 Adsorption Performance Test Experiment Adsorption performance test: Secondary effluent from a wastewater treatment plant (NH4⁺-N 15 mg / L, PO4³⁻-P 5 mg / L) was taken, pH adjusted to 7.0, and 0.5 g / L, 1 g / L, 5 g / L, and 10 g / L of the nitrogen and phosphorus simultaneous adsorption biochar obtained in Example 1 were added respectively. The results are shown in the figure. Figure 3 After 4 hours of shaking adsorption, the removal capacities were measured to be 145.6 mg / g, 146.7 mg / g, 145.8 mg / g, 144.8 mg / g % (removal capacity for N) and 167.2 mg / g, 168.3 mg / g, 168.9 mg / g, 168.6 mg / g (removal capacity for P).

[0032] Example 5 Application Experiment Fertilizer application: The adsorption-saturated biochar (i.e., the biochar after the adsorption performance test in Example 4) was mixed with humic acid and bentonite in a mass ratio of 6:2.5:1.5. 5 wt% starch binder was added to granulate (particle size 3-5 mm). After drying at 75℃, the total nitrogen and phosphorus contents were measured to be 4.8% and 3.2%, respectively. The total nutrient content was ≥8%, and the cumulative release rate after 28 days was <50% (pot soil experiment, comparing nitrogen and phosphorus contents before and after).

[0033] Industrial application This technology has been put into operation as a pilot production line with a capacity of 200 tons / year. The production cost of biochar is approximately RMB 1,200 / ton, which is 60% lower than that of commercial activated carbon. It has been applied to the deep treatment unit of a 50,000-ton / day wastewater treatment plant, and the annual recovery of nitrogen and phosphorus resources is equivalent to 200 tons of compound fertilizer, demonstrating significant environmental and economic benefits.

[0034] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing nitrogen and phosphorus simultaneously adsorbed biochar, characterized in that, Includes the following steps: (1) Raw material pretreatment: Dewatered sludge, biogas residue and agricultural and forestry waste are crushed separately and mixed in a mass ratio of (3-5):(1-2):(2-4). During the mixing process, 0.2-1.5 mol / L of modified metal solution is added. After thorough mixing, the mixture is aged and then dried until the moisture content is <10%. (2) Synergistic pyrolysis carbonization: The temperature is raised to 500-800℃ for 1-3 h under a nitrogen atmosphere at 5-10℃ / min. After cooling, the carbon is ground through a 100-mesh sieve to obtain pyrolytic carbon. (3) Pore structure construction: KOH powder and the above-obtained pyrolytic carbon are ball-milled for 1-4 hours to fully mix evenly. The mixture is then heated at 750-900℃ in an oxygen-free environment to further obtain nitrogen and phosphorus simultaneous adsorption biochar.

2. The preparation method according to claim 1, characterized in that, In step (1), the agricultural and forestry waste is at least one of straw, sawdust or fruit shells, with a particle size ≤ 5 mm.

3. The preparation method according to claim 1, characterized in that, In step (1), the modified metal solution includes at least one of ferrous sulfate, calcium sulfate, and magnesium sulfate.

4. The preparation method according to claim 1, characterized in that, In step (1), the modified metal solution is added at a flow rate of 0.3-1.5 L / min, and the solid-liquid ratio is 1 kg: (0.5-1.5) L; Optional, aging time is 1-4 hours.

5. The preparation method according to claim 1, characterized in that, In step (3), the specific surface area of ​​the nitrogen and phosphorus synchronous adsorption biochar is as high as 300-600 m² / g.

6. The nitrogen and phosphorus simultaneous adsorption biochar prepared by any one of the methods described in claims 1-5.

7. The application of nitrogen and phosphorus simultaneous adsorption biochar prepared by any one of claims 1-5 in wastewater treatment.

8. The application as described in claim 7, characterized in that, Nitrogen and phosphorus simultaneous adsorption biochar was added to nitrogen and phosphorus-containing wastewater at a dosage of 0.5-10 g / L, the pH was adjusted to 6-8, and the adsorption time was 2-6 h.

9. A method for preparing biochar slow-release fertilizer, characterized in that, The nitrogen and phosphorus biochar that has been adsorbed in claim 8 is mixed with humic acid and bentonite in a mass ratio of (5-7):(2-3):(1-2), granulated, and dried at 60-80℃ to obtain biochar slow-release fertilizer.

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