Composite biochar filler, preparation method thereof and sewage treatment method

Abstract

The invention belongs to the field of water treatment, and particularly relates to a composite biochar filler, a preparation method thereof and a sewage treatment method. The composite biochar filler provided by the invention is prepared according to the following steps: a) mixing dry municipal sludge, composite minerals, kaolin and starch, then mixing with a sodium alginate solution to prepare particles, and naturally drying to obtain green body particles; b) immersing the green body particles into a calcium chloride solution, taking out the green body particles, and naturally drying the green body particles to obtain to-be-calcined particles; and c) carrying out oxygen-isolated calcination on the to-be-calcined particles to obtain the composite biochar filler. The preparation raw materials and the preparation process of the composite biochar filler are optimally designed, so that the prepared composite biochar filler has relatively high nitrogen and phosphorus adsorption capacity and stable microorganism immobilization performance, and nitrogen and phosphorus pollutants in sewage can be efficiently and stably removed.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of water treatment, and particularly relates to a composite biochar filler, a preparation method thereof and a sewage treatment method. BACKGROUND

[0002] With the increasing demand for ecological basin water pollution control, artificial wetlands have become one of the mainstream technologies for basin sewage purification due to their low cost, ecological friendliness and simple operation. In the artificial wetland system, the filler, as the core carrier for adsorbing pollutants and attaching microorganisms, directly determines the sewage treatment efficiency and long-term stability, and is a key factor affecting the purification effect of the wetland.

[0003] Biochar fillers are widely used in artificial wetlands due to their wide raw material sources (such as municipal sludge and agricultural waste) and rich pore structure. However, the existing biochar fillers still have obvious deficiencies: first, the adsorption function is single, and traditional schemes mostly use single kaolin as a binder, which can only guarantee the molding of the filler, and the adsorption capacity of ammonia nitrogen and phosphate is low, which is difficult to adapt to the demand for high-nitrogen and high-phosphorus sewage treatment; second, the stability of microbial attachment is poor, and there is a lack of special microbial fixation design, which relies on the natural biofilm formation of microorganisms in sewage, not only the biofilm formation period is long, but also the microorganisms are easy to be lost with water flow, and the biomass decays quickly in long-term operation, resulting in continuous decline of nitrogen and phosphorus removal efficiency.

[0004] To solve the above problems, it is urgent to develop a sludge biochar filler with efficient adsorption and stable biological fixation functions to improve the nitrogen and phosphorus removal efficiency and long-term stability through a synergistic mechanism. SUMMARY

[0005] Therefore, the present application aims to provide a composite biochar filler, a preparation method thereof and a sewage treatment method. The composite biochar filler provided by the present application has high nitrogen and phosphorus adsorption capacity and stable microbial fixation performance, and can efficiently and stably remove nitrogen and phosphorus pollutants in sewage.

[0006] The present application provides a preparation method of a composite biochar filler, comprising the following steps:

[0007] a) mixing municipal sludge dry material, composite mineral, kaolin and starch, then mixing with a solution of sodium alginate to form particles, and naturally drying to obtain ceramic body particles;

[0008] In step a), the composition of the composite mineral includes bentonite and sepiolite, and the mass ratio of the bentonite to the sepiolite is (1-3):1; the mass ratio of the municipal sludge dry material, the composite mineral, the kaolin, the starch and the sodium alginate is 40:(20-25):(30-35):(3-5):(0.2-2);

[0009] b) Immerse the ceramic blank particles in a calcium chloride solution, remove them, and allow them to dry naturally to obtain the particles to be calcined;

[0010] c) The particles to be calcined are subjected to oxygen-free calcination to obtain composite biochar filler.

[0011] Preferably, in step a), the particle size of the municipal sludge dry material is 10-20 mesh; the particle size of the bentonite is 80-200 mesh; the particle size of the sepiolite is 200-300 mesh; the particle size of the kaolin is 200-300 mesh; and the particle size of the starch is 200-300 mesh.

[0012] Preferably, in step a), the particle size of the ceramic blank particles is 4~8mm.

[0013] Preferably, in step b), the concentration of the calcium chloride solution is 5-20 wt%; and the immersion time is 5-20 min.

[0014] Preferably, in step c), the oxygen-free calcination process includes: first calcining at 400~600℃ for 50~70min, and then raising the temperature to 900~1050℃ for calcination for 5~15min.

[0015] This invention provides a composite biochar packing material, which is prepared according to the preparation method described in the above technical solution.

[0016] This invention provides a wastewater treatment method, comprising the following steps:

[0017] Wastewater flows through the filter layer to produce effluent;

[0018] The filter layer is filled with the composite biochar packing material described in the above technical solution.

[0019] Preferably, the filter layer is also filled with ceramsite and river sand.

[0020] Preferably, the volume ratio of the composite biochar filler, ceramsite, and river sand is 1:(0.8~1.3):(0.8~1.3).

[0021] Preferably, the composite biochar filler, ceramsite, and river sand are filled in the filter layer in a layered manner, with river sand in the upper layer, composite biochar filler in the middle layer, and river sand in the lower layer; the wastewater flows in from the top of the filter layer and flows out from the bottom.

[0022] Compared with the prior art, the present invention provides a composite biochar packing material, its preparation method, and a wastewater treatment method. The composite biochar packing material provided by the present invention is prepared according to the following steps: a) municipal sludge dry material, composite minerals, kaolin and starch are mixed, and then mixed with sodium alginate solution to form granules, which are then naturally dried to obtain ceramic granules; in step a), the composite minerals include bentonite and sepiolite, and the mass ratio of bentonite to sepiolite is (1~3):1; the mass ratio of municipal sludge dry material, composite minerals, kaolin, starch and sodium alginate is 40:(20~25):(30~35):(3~5):(0.2~2); b) the ceramic granules are immersed in calcium chloride solution, taken out and naturally dried to obtain granules to be calcined; c) the granules to be calcined are subjected to oxygen-free calcination to obtain the composite biochar packing material. This invention optimizes the raw materials and preparation process of the composite biochar packing material, enabling the resulting composite biochar packing material to possess both high nitrogen and phosphorus adsorption capacity and stable microbial immobilization performance, thus achieving efficient and stable removal of nitrogen and phosphorus pollutants from wastewater. More specifically, the technical solution of this invention has at least the following advantages:

[0023] (1) Significantly improved adsorption capacity: The introduction of bentonite and sepiolite enhanced the adsorption properties of the composite biochar packing.

[0024] (2) Strong microbial immobilization stability: The introduction of sodium alginate enhances the adsorption capacity of microorganisms;

[0025] (3) High efficiency of simultaneous nitrogen and phosphorus removal: Under the synergistic effect of adsorption and biodegradation, the removal efficiency of organic matter can be increased by 20.3-30.3%, the removal efficiency of ammonia nitrogen can be increased by 16.9-42.4%, and the removal efficiency of phosphate can be increased by 20.7-28.9%;

[0026] (4) Low cost and environmentally friendly: municipal sludge is used as raw material (solid waste resource utilization). Both composite minerals and sodium alginate are low-cost materials. The preparation process does not require complicated equipment and is suitable for large-scale production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0028] Figure 1 These are COD test results of different embodiments and comparative examples provided by the present invention, wherein Figure A shows the COD test results of Examples 1 to 5, and Figure B shows the COD test results of Example 1 and Comparative Examples 1 to 3.

[0029] Figure 2 These are graphs showing the ammonia nitrogen test results of different embodiments and comparative examples provided by the present invention. Graph A shows the ammonia nitrogen test results of Examples 1 to 5, and Graph B shows the ammonia nitrogen test results of Example 1 and Comparative Examples 1 to 3.

[0030] Figure 3 These are graphs showing the phosphate test results of different embodiments and comparative examples provided by the present invention. Graph A shows the phosphate test results of Examples 1 to 5, and Graph B shows the phosphate test results of Examples 1 and Comparative Examples 1 to 3. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] This invention provides a method for preparing composite biochar packing material, comprising the following steps:

[0033] a) Mix municipal sludge dry material, composite minerals, kaolin and starch, then mix in sodium alginate solution to form granules, and dry naturally to obtain ceramic granules;

[0034] b) Immerse the ceramic blank particles in a calcium chloride solution, remove them, and allow them to dry naturally to obtain the particles to be calcined;

[0035] c) The particles to be calcined are subjected to oxygen-free calcination to obtain composite biochar filler.

[0036] In the preparation method provided by this invention, in step a), the municipal sludge dry material is obtained by drying, crushing, and sieving municipal sludge; wherein, the drying method is preferably natural air drying; the natural air drying time is preferably 3-7 days. In this invention, the particle size of the municipal sludge dry material is 10-20 mesh.

[0037] In the preparation method provided by the present invention, in step a), the composite mineral comprises bentonite and sepiolite; wherein, the particle size of the bentonite is preferably 80-200 mesh; the particle size of the sepiolite is preferably 200-300 mesh; the mass ratio of the bentonite to the sepiolite is (1-3):1, specifically 1:1, 2:1 or 3:1.

[0038] In the preparation method provided by the present invention, in step a), the composite mineral is preferably prepared by mixing bentonite and sepiolite and then drying; wherein, the mixing time is preferably 5-15 min, specifically 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min or 15 min; the drying temperature is preferably 100-110℃, specifically 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃ or 110℃; the drying time is preferably 1-5 h, specifically 1 h, 2 h, 3 h, 4 h or 5 h.

[0039] In the preparation method provided by the present invention, in step a), the mass ratio of the composite mineral to municipal sludge dry material is (20~25):40, specifically 20:40, 21:40, 22:40, 23:40, 24:40 or 25:40.

[0040] In the preparation method provided by the present invention, in step a), the particle size of the kaolin is preferably 200-300 mesh.

[0041] In the preparation method provided by the present invention, in step a), the mass ratio of kaolin to municipal sludge dry material is (30~35):40, specifically 30:40, 31:40, 32:40, 33:40, 34:40 or 35:40.

[0042] In the preparation method provided by the present invention, in step a), the particle size of the starch is preferably 200-300 mesh.

[0043] In the preparation method provided by the present invention, in step a), the mass ratio of starch to municipal sludge dry material is (3~5):40, specifically 3:40, 3.5:40, 4:40, 4.5:40 or 5:40.

[0044] In the preparation method provided by the present invention, in step a), the mixing time is preferably 10-20 min, specifically 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min or 20 min.

[0045] In the preparation method provided by the present invention, in step a), the concentration of sodium alginate in the solution is preferably 1~2wt%, specifically 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, or 2wt%.

[0046] In the preparation method provided by this invention, in step a), the mass ratio of sodium alginate to municipal sludge dry material is (0.2~2):40, specifically 0.2:40, 0.3:40, 0.4:40, 0.5:40, 0.6:40, 0.7:40, 0.8:40, 0.9:40, 1:40, 1.1:40, 1.2:40, 1.3:40, 1.4:40, 1.5:40, 1.6:40, 1.7:40, 1.8:40, 1.9:40, or 2:40.

[0047] In the preparation method provided by the present invention, in step a), the moisture content of the mixture after mixing with the solution is preferably 30-35%, specifically 30%, 31%, 32%, 33%, 34% or 35%.

[0048] In the preparation method provided by the present invention, in step a), the particle size of the ceramic blank particles is preferably 4~8mm, specifically 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm or 8mm.

[0049] In the preparation method provided by the present invention, in step b), the concentration of the calcium chloride solution is preferably 5 to 20 wt%, specifically 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%.

[0050] In the preparation method provided by the present invention, in step b), the immersion temperature is preferably 10~40℃, specifically 10℃, 15℃, 20℃, 25℃ (room temperature), 30℃, 35℃ or 40℃; the immersion time is preferably 5~20min, specifically 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min or 20min.

[0051] In the preparation method provided by the present invention, in step c), the specific process of oxygen-free calcination preferably includes: calcining at 400~600℃ for 50~70min, and then raising the temperature to 900~1050℃ for calcination for 5~15min; wherein, the calcination temperature before heating can be 400℃, 450℃, 500℃, 550℃ or 600℃; the calcination time before heating can be 50min, 55min, 60min, 65min or 70min; the calcination temperature after heating can be 900℃, 950℃, 1000℃ or 1050℃; and the calcination time after heating can be 5min, 7min, 10min, 12min or 15min.

[0052] The present invention also provides a composite biochar packing material, which is prepared according to the preparation method described in the above technical solution.

[0053] The present invention also provides a wastewater treatment method, comprising the following steps:

[0054] Wastewater flows through the filter layer to produce effluent;

[0055] The filter layer is filled with the composite biochar packing material described in the above technical solution.

[0056] In the wastewater treatment method provided by the present invention, the filter layer is preferably further filled with ceramsite and river sand; wherein, the particle size of the ceramsite is preferably 4~6mm; and the particle size of the river sand is preferably 1~2mm.

[0057] In the wastewater treatment method provided by the present invention, the preferred volume ratio of the composite biochar filler, ceramsite, and river sand in the filter layer is 1:(0.8~1.3):(0.8~1.3); wherein, the specific volume ratio of the composite biochar filler and ceramsite can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, or 1:1.3; the specific volume ratio of the composite biochar filler and river sand can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, or 1:1.3.

[0058] In the wastewater treatment method provided by this invention, the composite biochar packing material, ceramsite, and river sand are preferably packed in layers in the filter layer; wherein the upper layer is river sand, the middle layer is composite biochar packing material, and the lower layer is river sand. During wastewater treatment, the wastewater flows in from the top of the filter layer and flows out from the bottom.

[0059] In the wastewater treatment method provided by the present invention, the height of the filter layer is preferably 60~120cm, specifically 60cm, 70cm, 80cm, 90cm, 100cm, 110cm or 120cm.

[0060] For clarity, the following examples and comparative models will be used to provide a detailed description.

[0061] Example 1

[0062] This embodiment prepares a composite biochar packing material and applies it to the treatment of ecological watershed wastewater in constructed wetlands, specifically including the following steps:

[0063] S1. After the municipal sludge is naturally air-dried to constant weight, it is crushed using a crusher and passed through a 20-mesh sieve to obtain sludge dry powder. 200-mesh bentonite and 300-mesh sepiolite are mixed at a mass ratio of 2:1, dry-mixed for 10 minutes, and then placed in an oven at 105℃ for 2 hours to obtain composite minerals. Starch and kaolin are passed through a 200-mesh sieve for later use.

[0064] S2. Weigh 40 parts of dry sludge, 22 parts of composite minerals, 33 parts of kaolin, and 4 parts of starch according to the mass fraction. Mix them evenly and add a pre-prepared 1.5wt% sodium alginate solution. While adding, stir to adjust the moisture content of the material to 30-35%. Obtain round ceramic raw materials with a diameter of 4-6mm through a disc granulator.

[0065] S3. After the raw ceramic blanks obtained in step S2 are naturally dried for 24 hours, they are soaked in a 10wt% calcium chloride aqueous solution for 10 minutes, with stirring twice during the process. After that, they are naturally dried for 12 hours.

[0066] S4. Place the ceramic blank obtained in step S3 into a muffle furnace for oxygen-free calcination. First, heat the furnace to 400℃ and calcinate for 60 minutes, then continue to heat the furnace to 950℃ and calcinate for 15 minutes. Allow the furnace to cool naturally to room temperature to obtain the composite biochar filler.

[0067] S5. From bottom to top, construct a wetland by filling it with 30cm of commercial ceramsite (4-6mm particle size), 30cm of composite biochar filler (4-6mm particle size), and 30cm of river sand (1-2mm particle size). The wastewater to be treated is introduced into the constructed wetland system from top to bottom, with a hydraulic load of 40cm / d. The water quality at the outlet is monitored every 10 days for 120 consecutive days, and the concentrations of COD, ammonia nitrogen, and total phosphorus at the outlet are recorded.

[0068] Example 2

[0069] The only difference from Example 1 is that the mass ratio of bentonite to sepiolite is 1:1.

[0070] Example 3

[0071] The only difference from Example 1 is that the mass ratio of bentonite to sepiolite is 3:1.

[0072] Example 4

[0073] The only difference from Example 2 is that the concentration of the sodium alginate solution is 1 wt%.

[0074] Example 5

[0075] The only difference from Example 2 is that the concentration of sodium alginate is 2 wt%.

[0076] Comparative Example 1

[0077] This comparative example demonstrates the preparation of a composite biochar packing material without the addition of bentonite, sepiolite, and sodium alginate, and its application in constructed wetlands for treating ecological watershed wastewater. The specific steps include:

[0078] S1. After the municipal sludge is naturally air-dried to constant weight, it is crushed using a crusher and passed through a 20-mesh sieve to obtain sludge dry powder; starch and kaolin are passed through a 200-mesh sieve for later use.

[0079] S2. Weigh 40 parts of dry sludge, 55 parts of kaolin, and 4 parts of starch according to the mass ratio. Mix them evenly and add distilled water to dissolve them. While adding the water, stir to adjust the moisture content of the material to 30-35%. Use a disc granulator to obtain round ceramic raw materials with a diameter of 4-6 mm.

[0080] S3. Place the ceramic blank raw material obtained in step S2 into a muffle furnace for oxygen-free calcination. First, heat the furnace to 400℃ and calcine for 60 minutes, then continue to heat the furnace to 950℃ and calcine for 15 minutes. Allow the furnace to cool naturally to room temperature to obtain the composite biochar filler.

[0081] S4. From bottom to top, construct a wetland by filling it with 30cm of commercial ceramsite (4-6mm particle size), 30cm of composite biochar filler (4-6mm particle size), and 30cm of river sand (1-2mm particle size). The wastewater to be treated is introduced into the constructed wetland system from top to bottom, with a hydraulic load of 40cm / d. The water quality at the outlet is monitored every 3 days for 120 consecutive days, and the concentrations of COD, ammonia nitrogen, and total phosphorus at the outlet are recorded.

[0082] Comparative Example 2

[0083] Compared with Examples 2 and 4-5, the only difference is that distilled water is used instead of sodium alginate solution in step S2.

[0084] Comparative Example 3

[0085] Compared with Examples 1-3, the only difference is that instead of adding a mixed mineral made of bentonite and sepiolite, the mixed mineral is replaced with an equal mass fraction of kaolin, with kaolin as the binder.

[0086] Performance Evaluation

[0087] The concentration of ammonia nitrogen in the water sample was determined by Nessler's reagent spectrophotometry (GB7479-87);

[0088] Total phosphorus (TP) was determined using a Lianhua multi-parameter water quality analyzer (5B-6C);

[0089] The concentration of COD was determined by the potassium dichromate method (GB11914-89);

[0090] Removal rate (%) = [(Influent concentration - Effluent concentration) / Influent concentration] × 100%;

[0091] The concentrations of ammonia nitrogen, total phosphorus, and COD were tested for Examples 1-5 and Comparative Examples 1-3, respectively, and the results are as follows:

[0092] The test results are listed in Table 1:

[0093] Table 1

[0094]

[0095] (1) The specific test results of COD are as follows: Figure 1 As shown:

[0096] Compared to Comparative Example 1, without the addition of composite minerals and sodium alginate, the COD removal rate was 29.7%–67.1%. In Examples 1–5, the addition of different proportions of bentonite-sepiolite composite minerals and different proportions of sodium alginate enhanced the removal effect on organic matter. Among them, the best effect on organic matter removal was achieved when the ratio of bentonite-sepiolite was 2:1 and the sodium alginate content was 1.5 wt%, with a COD removal rate of 50%–97.4%, an improvement of 20.3%–30.3%.

[0097] Compared to Comparative Example 2, which added compound minerals but not sodium alginate, and Comparative Example 3, which added sodium alginate but not compound minerals, the COD degradation rate in Example 1 was significantly higher than that in Comparative Examples 2 and 3, indicating that there is a synergistic effect between compound minerals and sodium alginate.

[0098] (2) The specific test results of ammonia nitrogen are as follows: Figure 2 As shown:

[0099] Compared to Comparative Example 1, the ammonia nitrogen removal rate was 18.2%–53.7% without the addition of the composite mineral and sodium alginate. In Examples 1–5, the addition of different proportions of bentonite-sepiolite composite mineral and different proportions of sodium alginate enhanced the removal effect on organic matter. Among them, the ammonia nitrogen removal effect was the best when the bentonite-sepiolite ratio was 2:1 and the sodium alginate content was 1.5 wt%, ranging from 35.1% to 96.1%, which was an improvement of 16.9%–42.4%.

[0100] Compared to Comparative Example 2, which added compound minerals but not sodium alginate, and Comparative Example 3, which added sodium alginate but not compound minerals, the ammonia nitrogen removal rate in Example 1 was significantly higher than that in Comparative Examples 2 and 3, indicating that there is a synergistic effect between compound minerals and sodium alginate.

[0101] (3) The specific test results for phosphate are as follows: Figure 3 As shown:

[0102] Compared to Comparative Example 1, the phosphate removal rate was 54.2%–76.5% without the addition of the composite mineral and sodium alginate. In Examples 1–5, the addition of different proportions of bentonite-sepiolite composite mineral and different proportions of sodium alginate enhanced the removal effect on organic matter. Among them, the phosphate removal effect was best when the ratio of bentonite-sepiolite was 2:1 and the sodium alginate content was 1.5%, ranging from 83.1% to 97.2%, which was an improvement of 20.7%–28.9%.

[0103] Compared to Comparative Example 2, which added composite minerals but not sodium alginate, and Comparative Example 3, which added sodium alginate but not composite minerals, the phosphate removal rate in Example 1 was significantly higher than that in Comparative Examples 2 and 3, indicating that composite minerals and sodium alginate have a synergistic effect in the removal of phosphates by composite biochar packing.

[0104] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of preparing a composite biochar packing material, characterized by, The method comprises the following steps: a) mixing municipal sludge dry material, composite mineral, kaolin and starch, then mixing into a solution of sodium alginate to form granules, and naturally drying to obtain green body granules; In step a), the composite mineral comprises bentonite and sepiolite, and the mass ratio of the bentonite to the sepiolite is (1-3):1; the mass ratio of the municipal sludge dry material, the composite mineral, the kaolin, the starch and the sodium alginate is 40:(20-25):(30-35):(3-5):(0.2-2); b) immersing the green body granules into a calcium chloride solution, and naturally drying after taking out to obtain to-be-calcined granules; c) oxygen-isolation calcining the to-be-calcined granules to obtain composite biochar filler.

2. The production method according to claim 1, characterized by, In step a), the particle size of the municipal sludge dry material is 10-20 mesh; the particle size of the bentonite is 80-200 mesh; the particle size of the sepiolite is 200-300 mesh; the particle size of the kaolin is 200-300 mesh; and the particle size of the starch is 200-300 mesh.

3. The preparation method according to claim 1, characterized in that, In step a), the particle size of the green body granules is 4-8 mm.

4. The method of claim 1, wherein, In step b), the concentration of the calcium chloride solution is 5-20 wt%; and the immersion time is 5-20 min.

5. The preparation method according to claim 1, characterized in that, In step c), the oxygen-isolation calcining process comprises: first calcining at 400-600℃ for 50-70 min, and then calcining at 900-1050℃ for 5-15 min.

6. A composite biochar packing, characterized in that, The method is prepared according to any one of claims 1-5.

7. A method of sewage treatment, characterised in that, The method comprises the following steps: The wastewater flows through the filter layer to obtain effluent; The filter layer is filled with the composite biochar filler according to claim 6.

8. The method of sewage treatment according to claim 7, characterized in that, The filter layer is further filled with ceramsite and river sand.

9. The method of sewage treatment according to claim 8, characterized in that, The volume ratio of the composite biochar filler, the ceramsite and the river sand is 1:(0.8-1.3):(0.8-1.3).

10. The method of sewage treatment according to claim 8, characterized in that, The composite biochar filler, the ceramsite and the river sand are layered in the filter layer, the upper layer is river sand, the middle layer is the composite biochar filler, and the lower layer is river sand; and the wastewater flows into the filter layer from the top and flows out from the bottom.

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