Rural sewage treatment process

Abstract

The invention provides a rural sewage treatment process. The rural sewage treatment process comprises the steps of pretreatment, coagulating sedimentation, efficient adsorption, temporary storage of pond water, bottom mud cleaning, bottom mud improvement and ecological restoration. In the efficient adsorption step, by adding a composite adsorbent composed of cellulose-graphene aerogel, a pectin-based heavy metal chelating agent and a charcoal-based nitrogen and phosphorus trapping agent in a specific proportion, synergistic removal of various pollutants such as COD, NH3-N, TP and heavy metal is achieved, and the limitation of a single function is broken through. According to organic matters, ammonia nitrogen, total phosphorus and heavy metals, main pollution types in the sewage are covered, one-stop treatment is realized, the requirement of a multi-stage treatment process is reduced, and the treatment cost is reduced. In the bottom mud improvement step, a bottom mud improver composed of a composite microbial agent and calcium oxide-bentonite-bone glue composite particles in a specific proportion is added, so that multi-target treatment of COD, NH3-N and TP is achieved, and then bottom mud remediation is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a rural sewage treatment process. Background Art

[0002] The most common source of rural wastewater is pond wastewater, which primarily stems from a combination of domestic sewage, agricultural non-point source pollution, and livestock and poultry wastewater. Due to the lack of a comprehensive sewage collection system in rural areas, domestic sewage and agricultural runoff often enter ponds through surface runoff or direct dumping. High-concentration organic wastewater, such as feces and urine, from livestock and poultry farming is also easily discharged into water bodies through untreated discharge. Furthermore, the lack of rainwater and sewage diversion facilities allows rainwater to wash surface pollutants into ponds, further exacerbating pollution. Rural sewage has the following characteristics: First, its discharge is dispersed and its volume fluctuates significantly, significantly affected by seasonal agricultural activities. Second, its pollutant composition is complex. Domestic sewage is rich in nutrients such as nitrogen and phosphorus, while livestock and poultry wastewater exhibits high levels of organic matter, ammonia nitrogen, and suspended solids. Agricultural non-point source pollution also introduces toxic substances such as pesticides and heavy metals. Third, its self-purification capacity is weak. Rural ponds are mostly enclosed water bodies with poor flow and insufficient reoxygenation capacity, leading to eutrophication, algae blooms, and even black and odorous water bodies. Furthermore, rural sewage treatment technology faces multiple challenges. On the one hand, the diverse sources of sewage, along with unstable water quality and quantity, make traditional centralized treatment models difficult to adapt. On the other hand, while advanced treatment technologies are highly efficient, they carry high investment and maintenance costs. This, combined with the weak rural economy and a shortage of professional operators, results in facilities being built but not used, or even failing to function. These factors collectively hinder the effective advancement of rural sewage treatment. Summary of the Invention

[0003] In view of this, the present invention proposes a rural sewage treatment process to solve the above problems.

[0004] The technical solution of the present invention is achieved as follows:

[0005] A rural sewage treatment process comprises the following steps:

[0006] S1. Pretreatment: During the dry and rainy season, clean up the garbage around the pond and set up a grid around the pond, then salvage the suspended matter and floating algae in the water;

[0007] S2. Coagulation and sedimentation: Add compound coagulant to the pond at a dosage of 1-3 kg / m 3 , treatment 12-24h;

[0008] S3. High-efficiency adsorption: After coagulation and sedimentation, add composite adsorbent into the pond at a dosage of 0.5-1.5 kg / m 3 , process for 24-48h;

[0009] S4. Temporary storage of pond water: After adsorption treatment, the water in the pond is pumped into a storage tank for temporary storage;

[0010] S4. Bottom mud cleaning: After pumping out the water, remove the bottom mud of the pond to a thickness of 8-15cm;

[0011] S5. Bottom mud improvement: Pump the water in the temporary storage tank back to the pond and add bottom mud improver at a dosage of 5-10kg / m 3 , treatment 72-120h;

[0012] S6. Ecological restoration: After improving the bottom sediment, plant emergent plants and submerged plants in the pond.

[0013] Furthermore, the composite coagulant in S2 is composed of PAC and PAM in a mass ratio of (8.5-9.5):(0.5-1.5).

[0014] Furthermore, the composite adsorbent in S3 is composed of cellulose-graphene aerogel, pectin-based heavy metal chelating agent, and biochar-based nitrogen and phosphorus capture agent in a mass ratio of (2.0-3.0):(0.5-1.0):(6.0-7.5).

[0015] Furthermore, the cellulose-graphene aerogel is prepared by the following method: weighing cellulose powder at a material-liquid ratio of g / mL of 1:(8-10) and adding it to a 10-15wt% NaOH solution precooled to 8-15°C, stirring until completely dissolved to form a cellulose solution; weighing graphene oxide at a material-liquid ratio of g / mL of 1:(10-12) and adding it to pre-deionized water, ultrasonically treating it at an ultrasonic power of 200-400W for 20-30min to form a graphene oxide dispersion. The mass ratio of cellulose powder to graphene oxide is (5-7):(3-5); the graphene oxide dispersion is slowly added to the cellulose solution, stirred at 400-600 rpm for 1.5-2.5 hours, then poured into a mold and heated to 40-60°C, then allowed to stand for 12-24 hours, and then transferred to a freeze dryer, frozen at -45 to -55°C for 30-60 minutes, and then freeze-dried at -60 to -80°C for 45-55 hours to obtain a cellulose-graphene aerogel.

[0016] Furthermore, the pectin-based heavy metal chelating agent is prepared by the following method: collecting discarded pineapple peels, washing, drying and crushing them to a particle size of 2-5 mm, then adding purified water according to a solid-liquid ratio of 1:10-15 g / mL, adding hydrochloric acid to adjust the pH to 1.5-2.0, heating to 85-90°C, stirring and extracting in a constant temperature water bath at 150-250 rpm for 3.5-4.5 hours, then filtering the filtrate with a 100-200 mesh sieve, centrifuging the filtrate at 3000-5000 rpm for 10-20 minutes, taking the supernatant to obtain a pectin solution; adding an equal volume of anhydrous ethanol to the pectin solution, stirring at 200-400 rpm for 20-30 minutes, and then centrifuging at 3000-5000 rpm. The method comprises the steps of: centrifuging for 10-15 minutes, collecting a precipitate, and washing the precipitate with anhydrous ethanol for 2-4 times; placing the precipitate in a drying oven and drying it at 50-60° C. for 8-12 hours to obtain pineapple pectin; mixing the pineapple pectin with EDTA-2Na at a mass ratio of 1:(0.2-0.3), adding deionized water to prepare a solution with a pectin concentration of 5-10wt%, adjusting the pH to 8.0-9.0 with sodium hydroxide, heating to 60-70° C. and maintaining a constant temperature, and stirring at 200-400 rpm for 3-5 hours. After the reaction is completed, adjusting the pH to neutral with hydrochloric acid, pouring the solution into a mold, freezing the solution at -35 to -45° C. for 10-15 hours, and then drying the solution at -60 to -80° C. for 24-36 hours to obtain a pectin-based chelating agent.

[0017] Furthermore, the biochar-based nitrogen and phosphorus capture agent is prepared by the following method: placing dry rice husks in a pyrolysis furnace, heating the temperature to 500-600°C at a heating rate of 10°C / min under a nitrogen atmosphere, keeping the temperature for 1-2 hours, taking them out and naturally cooling them to room temperature, washing them with deionized water until they are neutral, and drying them at 100-110°C to constant weight to obtain biochar; weighing lanthanum nitrate and aluminum nitrate in a mass ratio of (7-9): (1-3), dissolving them in deionized water, and preparing a 0.5-1.5M mixed gold solution. The biochar was prepared by mixing the biochar with the mixed metal solution at a material-liquid ratio of g / mL of 1:(10-15), and ultrasonically treated at an ultrasonic power of 200-300 W for 30-60 min. The mixture was then allowed to stand for 12-24 h, and the biochar was filtered out. The mixture was dried at 50-60 ° C to constant weight. The dried biochar was placed in a muffle furnace, heated to 300-400 ° C at a heating rate of 2 ° C / min, and kept warm for 2-3 h. The mixture was taken out and naturally cooled to room temperature to obtain a biochar-based nitrogen and phosphorus capture agent.

[0018] Furthermore, the sediment improver in S5 is composed of a composite microbial agent and calcium oxide-bentonite-bone glue composite particles in a mass ratio of (0.5-1.5):(15-20).

[0019] Furthermore, the composite microbial agent is composed of Bacillus subtilis, nitrifying bacteria, denitrifying bacteria, and Pseudomonas in a mass ratio of (1.0-1.5):(1.5-2.0):(2.0-2.5):(1.5-2.0).

[0020] Furthermore, calcium oxide-bentonite-bone glue composite particles are prepared by the following method: calcium oxide, bentonite, and bone glue are weighed respectively in a mass ratio of (3-4):(4-5):(1-2), the bentonite and calcium oxide are evenly mixed, water is added to form a slurry, the bone glue is crushed to a particle size of 2-4 mm, added to the slurry, stirred at 800-1200 rpm for 8-12 minutes, placed in a granulator to prepare spherical particles of 1-3 mm, and then dried at 60-80° C. for 20-24 hours to obtain calcium oxide-bentonite-bone glue composite particles.

[0021] Furthermore, in S6, the submerged plants are one or a combination of Vallisneria, Dermatophyte, Foxtail Algae, Hydrilla, and Sea Lettuce, and the emergent plants are one or a combination of Cattail, Acorus, Onion, and Iris.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The composite adsorbent of the present invention, through a multi-component design, achieves the synergistic removal of multiple types of pollutants such as COD, NH3-N, TP, and heavy metals, breaking through the limitation of a single function. Among them, cellulose-graphene aerogel removes COD on a broad spectrum through physical-chemical synergistic adsorption; the pectin-based chelating agent, with the carboxyl group of the pectin skeleton and the chelation effect of EDTA as its core, efficiently adsorbs NH3-N, while the strong chelation ability of EDTA can simultaneously remove heavy metals; the biochar-based capture agent, with the precipitation effect of metal oxides as its core, efficiently fixes TP, while the porous structure of biochar can adsorb organic matter. Targeting organic matter, ammonia nitrogen, total phosphorus, and heavy metals, it covers the main types of pollution in sewage, achieving "one-stop" treatment, reducing the need for multi-stage treatment processes, and lowering treatment costs.

[0024] 2. The calcium oxide-bentonite-bone glue composite particles in this sediment improver achieve multi-target treatment of COD, NH3-N, and TP through the synergistic effects of calcium oxide's alkalinity and calcium source, bentonite's adsorption and ion exchange, and bone glue's chemical chelation. Granulation forms a stable covering layer, which not only reduces the release of pollutants into the overlying water but also immobilizes pollutants in situ through chemical and physical interactions, achieving sediment remediation. DETAILED DESCRIPTION

[0025] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0026] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0027] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0028] Example 1

[0029] A rural sewage treatment process comprises the following steps:

[0030] S1. Pretreatment: In the dry and rainy season, clean up the garbage around the pond and set up grilles around the pond, and then salvage the suspended matter and floating algae in the water.

[0031] S2. Coagulation and sedimentation: Add compound coagulant to the pond at a dosage of 1kg / m 3 The composite coagulant is composed of PAC and PAM with a mass ratio of 8.5:0.5.

[0032] S3. High-efficiency adsorption: After coagulation and sedimentation, add composite adsorbent into the pond at a dosage of 0.5kg / m 3 The composite adsorbent consists of cellulose-graphene aerogel, pectin-based heavy metal chelating agent, and biochar-based nitrogen and phosphorus capture agent in a mass ratio of 2.0:0.5:6.0.

[0033] S4. Temporary storage of pond water: After adsorption treatment, the water in the pond is pumped into a storage tank for temporary storage.

[0034] S4. Bottom mud cleaning: After pumping out the water, remove the bottom mud of the pond to a thickness of 8cm.

[0035] S5. Bottom mud improvement: Pump the water in the temporary storage tank back to the pond and add bottom mud improver at a dosage of 5kg / m 3 The sediment conditioner is composed of a composite microbial agent and calcium oxide-bentonite-bone glue composite particles in a mass ratio of 0.5:15. The composite microbial agent is composed of Bacillus subtilis, nitrifying bacteria, denitrifying bacteria, and Pseudomonas in a mass ratio of 1.0:1.5:2.0:1.5.

[0036] S6. Ecological Restoration: After sediment improvement, emergent and submerged plants are planted in the pond. The submerged plants are a combination of Vallisneria and Ceratophyllum, and the emergent plant is Acorus.

[0037] The cellulose-graphene aerogel is prepared by the following method: weighing cellulose powder at a solid-liquid ratio of 1:8 g / mL and adding it to a 10wt% NaOH solution precooled to 8°C, stirring until completely dissolved to form a cellulose solution; weighing graphene oxide at a solid-liquid ratio of 1:10 g / mL and adding it to pre-deionized water, ultrasonically treating it at an ultrasonic power of 200W for 30 minutes to form a graphene oxide dispersion; the mass ratio of the cellulose powder to the graphene oxide is 5:3; slowly adding the graphene oxide dispersion to the cellulose solution, stirring at 400rpm for 2.5 hours, then pouring it into a mold and heating it to 40°C, then letting it stand for 24 hours, and then transferring it to a freeze dryer, freezing it at -45°C for 60 minutes and then freeze-drying it at -60°C for 55 hours to obtain a cellulose-graphene aerogel.

[0038] The pectin-based heavy metal chelating agent is prepared by the following method: collecting discarded pineapple peels, washing, drying and crushing them to a particle size of 2 mm, then adding purified water according to a solid-liquid ratio of 1:10 g / mL, adding hydrochloric acid to adjust the pH to 1.5, heating to 85°C, stirring and extracting at 150 rpm in a constant temperature water bath for 4.5 hours, then filtering the filtrate with a 100-mesh sieve, centrifuging the filtrate at 3000 rpm for 20 minutes, and taking the supernatant to obtain a pectin solution; adding an equal volume of anhydrous ethanol to the pectin solution, stirring at 200 rpm for 30 minutes, and then centrifuging at 3000 rpm to separate the supernatant. The mixture was centrifuged for 15 minutes, the precipitate was collected, and the precipitate was washed twice with anhydrous ethanol; the precipitate was placed in a drying oven and dried at 50°C for 12 hours to obtain pineapple pectin; the pineapple pectin and EDTA-2Na were mixed in a mass ratio of 1:0.2, deionized water was added to prepare a solution with a pectin concentration of 5wt%, the pH was adjusted to 8.0 with sodium hydroxide, the solution was heated to 60°C and kept at a constant temperature and stirred at 200rpm for 5 hours, and after the reaction was completed, the pH was adjusted to neutral with hydrochloric acid, and then poured into a mold, frozen at -35°C for 15 hours, and then dried at -60°C for 36 hours to obtain a pectin-based chelating agent.

[0039] The biochar-based nitrogen and phosphorus capture agent is prepared by the following method: placing dry rice husks in a pyrolysis furnace, heating them to 500°C at a heating rate of 10°C / min under a nitrogen atmosphere, keeping them warm for 2 hours, taking them out and naturally cooling them to room temperature, washing them with deionized water until they are neutral, and drying them at 100°C to constant weight to obtain biochar; weighing lanthanum nitrate and aluminum nitrate in a mass ratio of 7:1, dissolving them in deionized water to prepare a 0.5M mixed metal solution, mixing the biochar and the mixed metal solution in a material-liquid ratio of 1:10 g / mL, ultrasonically treating them at an ultrasonic power of 200W for 60 minutes, then letting them stand for 24 hours, filtering out the biochar, drying them to constant weight at 50°C, placing the dried biochar in a muffle furnace, heating them to 300°C at a heating rate of 2°C / min, keeping them warm for 3 hours, taking them out and naturally cooling them to room temperature to obtain a biochar-based nitrogen and phosphorus capture agent.

[0040] The calcium oxide-bentonite-bone glue composite particles are prepared by the following method: calcium oxide, bentonite, and bone glue are weighed respectively in a mass ratio of 3:4:1, the bentonite and calcium oxide are evenly mixed, and water is added to form a slurry, the bone glue is crushed to a particle size of 2 mm, added to the slurry, stirred at 800 rpm for 12 minutes, placed in a granulator to prepare 1 mm spherical particles, and then dried at 60°C for 24 hours to obtain calcium oxide-bentonite-bone glue composite particles.

[0041] Example 2

[0042] A rural sewage treatment process comprises the following steps:

[0043] S1. Pretreatment: In the dry and rainy season, clean up the garbage around the pond and set up grilles around the pond, and then salvage the suspended matter and floating algae in the water.

[0044] S2. Coagulation and sedimentation: Add compound coagulant to the pond at a dosage of 2kg / m 3 The composite coagulant is composed of PAC and PAM in a mass ratio of 9.0:1.0.

[0045] S3. High-efficiency adsorption: After coagulation and sedimentation, add composite adsorbent into the pond at a dosage of 1.0 kg / m 3 The composite adsorbent consists of cellulose-graphene aerogel, pectin-based heavy metal chelating agent, and biochar-based nitrogen and phosphorus capture agent in a mass ratio of 2.5:0.8:6.7.

[0046] S4. Temporary storage of pond water: After adsorption treatment, the water in the pond is pumped into a storage tank for temporary storage.

[0047] S4. Bottom mud cleaning: After pumping out the water, remove the bottom mud of the pond to a thickness of 12cm.

[0048] S5. Bottom mud improvement: Pump the water in the temporary storage tank back to the pond and add bottom mud improver at a dosage of 7.5kg / m 3 The sediment conditioner is composed of a composite microbial agent and calcium oxide-bentonite-bone glue composite particles in a mass ratio of 1.0:17.5. The composite microbial agent is composed of Bacillus subtilis, nitrifying bacteria, denitrifying bacteria, and Pseudomonas in a mass ratio of 1.2:1.8:2.2:1.8.

[0049] S6. Ecological Restoration: After sediment improvement, emergent and submerged plants are planted in the pond. The submerged plants are a combination of Vallisneria and Seaweed, while the emergent plants are a combination of Acorus calamus and Scutellaria scabra.

[0050] The cellulose-graphene aerogel is prepared by the following method: weighing cellulose powder at a solid-liquid ratio of 1:9 g / mL and adding it to a 12wt% NaOH solution precooled to 12°C, stirring until completely dissolved to form a cellulose solution; weighing graphene oxide at a solid-liquid ratio of 1:11 g / mL and adding it to pre-deionized water, ultrasonically treating it at an ultrasonic power of 300W for 25 minutes to form a graphene oxide dispersion; the mass ratio of the cellulose powder to the graphene oxide is 5:4; slowly adding the graphene oxide dispersion to the cellulose solution, stirring at 500rpm for 2.0h, then pouring it into a mold, heating it to 50°C, then letting it stand for 18h, and then transferring it to a freeze dryer, freezing it at -50°C for 45min and then freeze-drying it at -70°C for 50h to obtain a cellulose-graphene aerogel.

[0051] The pectin-based heavy metal chelating agent is prepared by the following method: collecting discarded pineapple peels, washing, drying and crushing them to a particle size of 3 mm, then adding purified water according to a solid-liquid ratio of 1:12.5 g / mL, adding hydrochloric acid to adjust the pH to 1.8, heating to 88°C, stirring in a constant temperature water bath at 200 rpm for 4.0 hours, then filtering the filtrate with a 150-mesh sieve, centrifuging the filtrate at 4000 rpm for 15 minutes, and taking the supernatant to obtain a pectin solution; adding an equal volume of anhydrous ethanol to the pectin solution, stirring at 300 rpm for 25 minutes, and then centrifuging at 4000 rpm. The method comprises the following steps: heating the mixture for 12.5 min, collecting the precipitate, and washing the precipitate 3 times with anhydrous ethanol; placing the precipitate in a drying oven and drying it at 55° C. for 10 h to obtain pineapple pectin; mixing the pineapple pectin and EDTA-2Na at a mass ratio of 1:0.25, adding deionized water to prepare a solution with a pectin concentration of 8 wt%, adjusting the pH to 8.5 with sodium hydroxide, heating to 65° C. and maintaining a constant temperature, and stirring at 300 rpm for 4 h. After the reaction is completed, adjusting the pH to neutral with hydrochloric acid, pouring the solution into a mold, freezing the solution at -40° C. for 12.5 h, and then drying the solution at -70° C. for 30 h to obtain a pectin-based chelating agent.

[0052] The biochar-based nitrogen and phosphorus capture agent is prepared by the following method: placing dry rice husks in a pyrolysis furnace, heating them to 500-600°C at a heating rate of 10°C / min under a nitrogen atmosphere, keeping them warm for 1-2 hours, taking them out and naturally cooling them to room temperature, washing them with deionized water until they are neutral, and drying them at 105°C to constant weight to obtain biochar; weighing lanthanum nitrate and aluminum nitrate in a mass ratio of 8:2, dissolving them in deionized water to prepare a 1.0M mixed metal solution, mixing the biochar and the mixed metal solution at a material-liquid ratio of 1:12.5 g / mL, ultrasonically treating them at an ultrasonic power of 250W for 45 minutes, then letting them stand for 18 hours, filtering out the biochar, drying them to constant weight at 55°C, placing the dried biochar in a muffle furnace, heating them to 350°C at a heating rate of 2°C / min, keeping them warm for 2.5 hours, taking them out and naturally cooling them to room temperature to obtain a biochar-based nitrogen and phosphorus capture agent.

[0053] The calcium oxide-bentonite-bone glue composite particles are prepared by the following method: calcium oxide, bentonite, and bone glue are weighed respectively in a mass ratio of 3.5:4.5:1.5, the bentonite and calcium oxide are evenly mixed, and water is added to form a slurry. The bone glue is crushed to a particle size of 3 mm, added to the slurry, stirred at 1000 rpm for 10 minutes, placed in a granulator to prepare 2 mm spherical particles, and then dried at 70°C for 22 hours to obtain calcium oxide-bentonite-bone glue composite particles.

[0054] Example 3

[0055] A rural sewage treatment process comprises the following steps:

[0056] S1. Pretreatment: In the dry and rainy season, clean up the garbage around the pond and set up grilles around the pond, and then salvage the suspended matter and floating algae in the water.

[0057] S2. Coagulation and sedimentation: Add compound coagulant to the pond at a dosage of 1-3 kg / m 3 The composite coagulant is composed of PAC and PAM in a mass ratio of 9.5:1.5.

[0058] S3. High-efficiency adsorption: After coagulation and sedimentation, add composite adsorbent into the pond at a dosage of 1.5 kg / m 3 The composite adsorbent is composed of cellulose-graphene aerogel, pectin-based heavy metal chelating agent, and biochar-based nitrogen and phosphorus capture agent in a mass ratio of 3.0:1.0:7.5.

[0059] S4. Temporary storage of pond water: After adsorption treatment, the water in the pond is pumped into a storage tank for temporary storage.

[0060] S4. Bottom mud cleaning: After pumping out the water, remove the bottom mud of the pond to a thickness of 8-15cm.

[0061] S5. Bottom mud improvement: Pump the water in the temporary storage tank back to the pond and add bottom mud improver at a dosage of 10kg / m 3 The sediment conditioner is composed of a composite microbial agent and calcium oxide-bentonite-bone glue composite particles in a mass ratio of 1.5:20. The composite microbial agent is composed of Bacillus subtilis, nitrifying bacteria, denitrifying bacteria, and Pseudomonas in a mass ratio of 1.5:2.0:2.5:2.0.

[0062] S6. Ecological Restoration: After sediment improvement, emergent and submerged plants are planted in the pond. The submerged plants are a combination of foxtail and black algae, while the emergent plants are a combination of cattail, water plantain, and iris.

[0063] The cellulose-graphene aerogel is prepared by the following method: weighing cellulose powder at a solid-liquid ratio of 1:10 g / mL and adding it to a 15wt% NaOH solution precooled to 15°C, stirring until completely dissolved to form a cellulose solution; weighing graphene oxide at a solid-liquid ratio of 1:12 g / mL and adding it to pre-deionized water, ultrasonically treating it at an ultrasonic power of 400W for 20 minutes to form a graphene oxide dispersion; the mass ratio of the cellulose powder to the graphene oxide is 7:5; slowly adding the graphene oxide dispersion to the cellulose solution, stirring at 600rpm for 1.5 hours, then pouring it into a mold and heating it to 60°C, then letting it stand for 12 hours, and then transferring it to a freeze dryer, freezing it at -55°C for 30 minutes and then freeze-drying it at -60°C for 45 hours to obtain a cellulose-graphene aerogel.

[0064] The pectin-based heavy metal chelating agent is prepared by the following method: collecting discarded pineapple peels, washing, drying and crushing them to a particle size of 5 mm, then adding purified water according to a solid-liquid ratio of 1:15 g / mL, adding hydrochloric acid to adjust the pH to 2.0, heating to 90°C, stirring and extracting at 250 rpm in a constant temperature water bath for 3.5 hours, then filtering the filtrate with a 200-mesh sieve, centrifuging the filtrate at 5000 rpm for 10 minutes, and taking the supernatant to obtain a pectin solution; adding an equal volume of anhydrous ethanol to the pectin solution, stirring at 400 rpm for 20 minutes, and then centrifuging at 5000 rpm to separate the supernatant. The mixture was centrifuged for 10 minutes, the precipitate was collected, and the precipitate was washed with anhydrous ethanol 4 times; the precipitate was placed in a drying oven and dried at 60°C for 8 hours to obtain pineapple pectin; the pineapple pectin and EDTA-2Na were mixed in a mass ratio of 1:0.3, deionized water was added to prepare a solution with a pectin concentration of 10wt%, the pH was adjusted to 9.0 with sodium hydroxide, the solution was heated to 70°C and kept at a constant temperature and stirred at 400rpm for 3 hours, and after the reaction was completed, the pH was adjusted to neutral with hydrochloric acid, and then poured into a mold, frozen at -45°C for 10 hours, and then dried at -80°C for 24 hours to obtain a pectin-based chelating agent.

[0065] The biochar-based nitrogen and phosphorus capture agent is prepared by the following method: placing dry rice husks in a pyrolysis furnace, heating them to 600°C at a heating rate of 10°C / min under a nitrogen atmosphere, keeping them warm for 1 hour, taking them out and naturally cooling them to room temperature, washing them with deionized water until they are neutral, and drying them at 110°C to constant weight to obtain biochar; weighing lanthanum nitrate and aluminum nitrate in a mass ratio of 9:3, dissolving them in deionized water to prepare a 1.5M mixed metal solution, mixing the biochar and the mixed metal solution in a material-liquid ratio of 1:15 g / mL, ultrasonically treating them at an ultrasonic power of 300W for 30 minutes, then letting them stand for 12 hours, filtering out the biochar, drying them to constant weight at 60°C, placing the dried biochar in a muffle furnace, heating them to 400°C at a heating rate of 2°C / min, keeping them warm for 2 hours, taking them out and naturally cooling them to room temperature to obtain a biochar-based nitrogen and phosphorus capture agent.

[0066] The calcium oxide-bentonite-bone glue composite particles are prepared by the following method: calcium oxide, bentonite, and bone glue are weighed respectively in a mass ratio of 4:5:2, the bentonite and calcium oxide are evenly mixed, and water is added to form a slurry, the bone glue is crushed to a particle size of 4 mm, added to the slurry, stirred at 1200 rpm for 8 minutes, placed in a granulator to prepare 3 mm spherical particles, and then dried at 80°C for 20 hours to obtain calcium oxide-bentonite-bone glue composite particles.

[0067] Comparative Example 1

[0068] Compared with Example 2, this comparative example differs in that the composite adsorbent does not contain cellulose-graphene aerogel, and is composed of a pectin-based heavy metal chelating agent and a biochar-based nitrogen and phosphorus capture agent in a mass ratio of (0.5-1.0): (6.0-7.5).

[0069] Comparative Example 2

[0070] Compared with Example 2, this comparative example differs in that EDTA-2Na is used in the composite adsorbent instead of the pectin-based heavy metal chelating agent.

[0071] Comparative Example 3

[0072] Compared with Example 2, this comparative example differs in that the biochar-based nitrogen and phosphorus capture agent is replaced by biochar in the composite adsorbent.

[0073] Comparative Example 4

[0074] Compared with Example 2, this comparative example differs in that calcium oxide in the sediment improver is replaced by calcium oxide-bentonite-bone glue composite particles.

[0075] Experimental verification

[0076] In a town in Qiongshan District, Haikou City, Hainan Province, 7 ponds with similar pollution levels and areas were selected for sewage treatment. The treatment processes of Examples 1-3 and Comparative Examples 1-4 were respectively carried out. The chemical oxygen demand (COD) concentration, ammonia nitrogen (NH3-N) concentration, and total phosphorus (TP) concentration were measured before and after treatment. The concentrations were measured 5 times and the average value was taken. The COD, NH3-N, and TP removal rates after treatment were then calculated. The results are shown in Table 1.

[0077] Table 1.

[0078]

[0079] As can be seen from Table 1, Examples 1-3 have good removal effects on COD, NH3-N, and TP, among which Example 2 has the best effect.

[0080] Comparing Example 2 with Comparative Example 1, the lack of cellulose-graphene aerogel in the composite adsorbent significantly weakens the treatment effect, especially the COD removal effect. This is because the cellulose-graphene aerogel forms a three-dimensional porous structure through processes such as freeze-drying, with a porosity of over 90%, providing a large number of adsorption sites for organic pollutants. Furthermore, the hydroxyl groups of the cellulose adsorb oxygen- and hydroxyl-containing organic compounds, such as sugars and alcohols, through hydrogen bonding. The π-π conjugated structure of the graphene produces a π-π stacking effect on aromatic organic compounds, such as benzene and polycyclic aromatic hydrocarbons, targeting the adsorption of aromatic organic compounds. Cellulose forms hydrogen bonds with organic pollutants through its abundant hydrophilic groups, such as hydroxyl groups, while the hydrophobic surface of the graphene adsorbs aromatic organic compounds through π-π conjugation. The synergistic effect of the two achieves broad-spectrum adsorption of complex organic compounds. Furthermore, under sunlight, the cellulose-graphene aerogel accelerates water evaporation through the photothermal effect, while promoting the oxidative degradation of organic compounds, further reducing COD.

[0081] By comparing Example 2 with Comparative Example 2, the treatment effect of replacing the pectin-based heavy metal chelating agent with EDTA-2Na in the composite adsorbent is weakened, especially the removal effect of NH3-N is more significantly reduced. In addition to efficiently adsorbing heavy metals in wastewater, the pectin-based heavy metal chelating agent of the present invention can also effectively remove NH3-N. This is because the carboxyl group of the pectin of the present invention is dissociated into -COO after alkalization during the preparation process. - , while NH3-N is mainly NH4 + In this case, -COO - With NH4 + It is combined through electrostatic attraction, thereby effectively adsorbing NH3-N.

[0082] By comparing Example 2 with Comparative Example 3, the removal efficiency of NH3-N and TP is greatly reduced when biochar is used instead of biochar-based nitrogen and phosphorus capture agent in the composite adsorbent. This is because the biochar-based nitrogen and phosphorus capture agent of the present invention is introduced by aluminum nitrate, which generates an aluminum oxide coating during pyrolysis. The hydroxyl groups on the surface of the aluminum oxide can dissociate into -O in the solution. - , adsorbing NH4 by electrostatic attraction + At the same time, Al 3+ The empty orbital can be combined with NH4 + The nitrogen atoms in the carbon form coordination bonds, enhancing the adsorption stability, thereby effectively removing NH3-N. The biochar-based nitrogen and phosphorus capture agent of the present invention generates aluminum oxide and lanthanum oxide during pyrolysis by introducing aluminum nitrate and lanthanum nitrate. The surface hydroxyl groups of aluminum oxide dissociate into -O in the solution. - , with PO4 3- The O atoms in the Al 3+ With PO4 3- Combined to form AlPO4 precipitation, La in lanthanum oxide 3+ With PO4 3- It has a stronger affinity and can quickly generate LaPO4 precipitation to effectively remove TP.

[0083] By comparing Example 2 with Comparative Example 4, the calcium oxide-bentonite-bone glue composite particles of the present application have a better treatment effect. This is because the calcium oxide in it generates calcium hydroxide when it meets water, which significantly increases the pH value of the water body. Under alkaline conditions, organic matter is prone to hydrolysis and decomposes into small molecular substances, thereby reducing COD. At the same time, Ca 2+ Combined with the negatively charged groups in organic matter, neutralizes its charge and accelerates the sedimentation of organic matter. Bentonite has a layered silicate structure and a high specific surface area, which can adsorb large molecular organic matter. And the interlayer cations of bentonite, such as Na + , Ca 2+ It can exchange with charged groups in organic matter, thereby fixing organic pollutants. The proteins and collagen in bone glue adsorb organic matter through hydrogen bonds and van der Waals forces. In addition, the amino acids and peptides slowly released by bone glue can provide carbon and nitrogen sources for microorganisms in the composite microbial agent, promote their metabolic activity, and accelerate the biodegradation of organic matter. Bentonite adsorbs large molecular organic matter, calcium oxide precipitates small molecular organic matter, and bone glue ultimately removes COD through biodegradation, effectively removing COD through multi-stage adsorption and precipitation. In addition, the high cation exchange capacity of bentonite can adsorb NH4 in the pore water of the sediment. + NH4 + It is fixed between the layers, reducing its release to the overlying water; at the same time, the layered structure can physically intercept NH3 molecules. Calcium oxide increases the pH of the system, making NH4 + Converted into NH3 and escaped; at the same time, high pH promoted the reaction of NH3 and Ca2+ Forming calcium ammonium complex, further fix NH3. In addition, CaO hydrolysis generates Ca 2+ With PO4 3- Reaction to generate calcium phosphate precipitation, which can effectively fix PO4 3- At the same time, high pH promotes the hydrolysis of organic phosphorus to PO4 3- , and is further removed by precipitation.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A rural sewage treatment process, characterized in that: The following steps are involved: S1. Pretreatment: During the dry and rainy season, clean up the garbage around the pond and set up a grid around the pond, then salvage the suspended matter and floating algae in the water; S2. Coagulation and sedimentation: Add compound coagulant to the pond at a dosage of 1-3 kg / m 3 , treatment 12-24h; S3. High-efficiency adsorption: After coagulation and sedimentation, add composite adsorbent into the pond at a dosage of 0.5-1.5 kg / m 3 , process for 24-48h; S4. Temporary storage of pond water: After adsorption treatment, the water in the pond is pumped into a storage tank for temporary storage; S4. Bottom mud cleaning: After pumping out the water, remove the bottom mud of the pond to a thickness of 8-15cm; S5. Bottom mud improvement: Pump the water in the temporary storage tank back to the pond and add bottom mud improver at a dosage of 5-10kg / m 3 , treatment 72-120h; S6. Ecological restoration: After improving the bottom sediment, plant emergent plants and submerged plants in the pond.

2. A rural sewage treatment process according to claim 1, characterized in that: The composite coagulant in S2 is composed of PAC and PAM in a mass ratio of (8.5-9.5): (0.5-1.5).

3. A rural sewage treatment process according to claim 1, characterized in that: The composite adsorbent in S3 is composed of cellulose-graphene aerogel, pectin-based heavy metal chelating agent, and biochar-based nitrogen and phosphorus capture agent in a mass ratio of (2.0-3.0):(0.5-1.0):(6.0-7.5).

4. A rural sewage treatment process according to claim 3, characterized in that: The cellulose-graphene aerogel is prepared by the following method: weighing cellulose powder at a solid-liquid ratio of 1:(8-10) g / mL and adding it to a 10-15wt% NaOH solution precooled to 8-15°C, stirring until completely dissolved to form a cellulose solution; weighing graphene oxide at a solid-liquid ratio of 1:(10-12) g / mL and adding it to pre-deionized water, and ultrasonically treating it at an ultrasonic power of 200-400W for 20-30 minutes to form a graphene oxide dispersion; The mass ratio of the cellulose powder to the graphene oxide is (5-7):(3-5); the graphene oxide dispersion is slowly added to the cellulose solution, stirred at 400-600 rpm for 1.5-2.5 hours, then poured into a mold and heated to 40-60° C., then allowed to stand for 12-24 hours, and then transferred to a freeze dryer, frozen at -45 to -55° C. for 30-60 minutes, and then freeze-dried at -60 to -80° C. for 45-55 hours to obtain a cellulose-graphene aerogel.

5. A rural sewage treatment process according to claim 3, characterized in that: The pectin-based heavy metal chelating agent is prepared by the following method: collecting discarded pineapple peels, washing, drying and crushing them to a particle size of 2-5 mm, then adding purified water according to a solid-liquid ratio of 1:10-15 g / mL, adding hydrochloric acid to adjust the pH to 1.5-2.0, heating to 85-90° C., stirring and extracting at 150-250 rpm in a constant temperature water bath for 3.5-4.5 hours, then filtering through a 100-200 mesh sieve to obtain a filtrate, centrifuging the filtrate at 3000-5000 rpm for 10-20 minutes, and taking a supernatant to obtain a pectin solution; adding an equal volume of anhydrous ethanol to the pectin solution, stirring at 200-400 rpm for 20-30 minutes, and then centrifuging at 3000-5000 rpm to separate the pectin solution. The method comprises the following steps: heating the mixture for 10-15 minutes, collecting a precipitate, and washing the precipitate with anhydrous ethanol for 2-4 times; placing the precipitate in a drying oven and drying it at 50-60° C. for 8-12 hours to obtain pineapple pectin; mixing the pineapple pectin with EDTA-2Na at a mass ratio of 1:(0.2-0.3), adding deionized water to prepare a solution with a pectin concentration of 5-10wt%, adjusting the pH to 8.0-9.0 with sodium hydroxide, heating the solution to 60-70° C., maintaining a constant temperature, and stirring the solution at 200-400 rpm for 3-5 hours. After the reaction is completed, adjusting the pH to neutral with hydrochloric acid, pouring the solution into a mold, freezing the solution at -35--45° C. for 10-15 hours, and then drying the solution at -60--80° C. for 24-36 hours to obtain a pectin-based chelating agent.

6. A rural sewage treatment process according to claim 3, characterized in that: The biochar-based nitrogen and phosphorus capture agent is prepared by the following method: placing dry rice husks in a pyrolysis furnace, heating the temperature to 500-600° C. at a heating rate of 10° C. / min under a nitrogen atmosphere, keeping the temperature for 1-2 hours, taking out and naturally cooling to room temperature, washing with deionized water until neutral, and drying at 100-110° C. to constant weight to obtain biochar; weighing lanthanum nitrate and aluminum nitrate in a mass ratio of (7-9): (1-3), dissolving them in deionized water to prepare a 0.5-1.5M mixed metal solution; The biochar was mixed with the mixed metal solution at a material-liquid ratio of g / mL of 1:(10-15), and ultrasonically treated at an ultrasonic power of 200-300 W for 30-60 min. The mixture was then allowed to stand for 12-24 h, and the biochar was filtered out and dried at 50-60 ° C to constant weight. The dried biochar was placed in a muffle furnace, heated to 300-400 ° C at a heating rate of 2 ° C / min, and kept warm for 2-3 h. After being taken out, it was naturally cooled to room temperature to obtain a biochar-based nitrogen and phosphorus capture agent.

7. A rural sewage treatment process according to claim 1, characterized in that: The S5 bottom mud improver is composed of a composite microbial agent and calcium oxide-bentonite-bone glue composite particles in a mass ratio of (0.5-1.5):(15-20).

8. A rural sewage treatment process according to claim 7, characterized in that: The composite microbial agent consists of Bacillus subtilis, nitrifying bacteria, denitrifying bacteria and Pseudomonas in a mass ratio of (1.0-1.5):(1.5-2.0):(2.0-2.5):(1.5-2.0).

9. A rural sewage treatment process according to claim 7, characterized in that: The calcium oxide-bentonite-bone glue composite particles are prepared by the following method: calcium oxide, bentonite, and bone glue are weighed respectively in a mass ratio of (3-4):(4-5):(1-2), the bentonite and calcium oxide are evenly mixed, water is added to form a slurry, the bone glue is crushed to a particle size of 2-4 mm, the slurry is added to the slurry, and the mixture is stirred at 800-1200 rpm for 8-12 minutes. The mixture is placed in a granulator to prepare spherical particles of 1-3 mm, and then dried at 60-80° C. for 20-24 hours to obtain the calcium oxide-bentonite-bone glue composite particles.

10. A rural sewage treatment process according to claim 1, characterized in that: The submerged plants in S6 are one or a combination of Vallisneria, Dermatophyte, Foxtail Algae, Hydrilla, and Sea Lettuce, and the emergent plants are one or a combination of Cattail, Acorus, Onion, and Iris.

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