A method for efficient treatment of biogas slurry from pig farms

Abstract

This invention belongs to the field of livestock wastewater treatment technology, and relates to a highly efficient method for treating biogas slurry from pig farms. The invention modifies bio-fiber materials, mineral materials, microbial carriers, and iron powder, then mixes and matures them with bio-activators and compound bacterial agents in a specific ratio to obtain a high-performance bio-matrix. Finally, a treatment system consisting of a stone support layer, a bio-matrix main reaction layer, and a modified bio-fiber material plant growth layer is constructed in the bio-matrix tank, and specific wetland plants are planted. This invention significantly improves the system's removal efficiency of pollutants from biogas slurry through multi-stage material modification and functional synergy, while effectively solving problems such as easy clogging, inhibited microbial activity, and unstable operation in traditional systems. This invention has low energy consumption, is easy to maintain, and can convert waste substrate into organic fertilizer base material, achieving an organic combination of pollution control and resource recycling, and possesses comprehensive advantages of high efficiency, stability, and economy.

Description

Technical Field

[0001] This invention belongs to the field of livestock wastewater treatment technology, and relates to a method for efficient treatment of biogas slurry from pig farms. Background Technology

[0002] Pig farm biogas slurry is a byproduct of pig farm wastewater fermentation, containing high concentrations of pollutants such as organic matter, ammonia nitrogen, phosphorus, suspended solids, and pathogenic microorganisms. Its treatment has always been a challenge in livestock wastewater management. Currently, common methods for treating pig farm biogas slurry mainly include physical methods (such as sedimentation and filtration), chemical methods (such as flocculation and oxidation), and biological methods (such as aerobic treatment and constructed wetlands). However, these methods have many shortcomings in practical applications:

[0003] 1. Low nitrogen and phosphorus removal efficiency: Traditional biological treatment methods, such as activated sludge processes or conventional constructed wetlands, have limited effectiveness in removing high concentrations of ammonia nitrogen and total phosphorus from biogas slurry. Due to a severe imbalance in the carbon-to-nitrogen ratio of biogas slurry (typically BOD / TN < 3), the carbon source for denitrification is insufficient, leading to low nitrogen removal efficiency. Meanwhile, phosphorus removal mainly relies on chemical precipitation or adsorption, but traditional adsorption materials are easily saturated and difficult to regenerate, resulting in a decline in treatment efficiency after long-term operation.

[0004] 2. The system is prone to clogging and requires frequent maintenance. High concentrations of suspended solids and colloidal substances in the biogas slurry can easily cause rapid clogging of the treatment system (such as biological filters or constructed wetlands), requiring frequent backwashing or replacement of packing materials, increasing operation and maintenance costs. Existing mineral adsorbent materials such as zeolite and bentonite, although having a certain adsorption capacity, lack surface modification and easily combine with negatively charged colloids in the biogas slurry, forming caking and shortening their service life.

[0005] 3. Microbial activity is inhibited. The biogas slurry contains high concentrations of ammonia nitrogen, salt, and heavy metals, which inhibit functional microorganisms (such as nitrifying and denitrifying bacteria). In traditional methods, the microbial carriers (such as straw and rice husks) are not enzymatically treated, resulting in slow and insufficient release of carbon sources, which cannot continuously stimulate the activity of denitrifying bacteria, leading to an unstable denitrification process.

[0006] 4. Secondary pollution and resource waste: In existing treatment processes, sludge and waste packing materials are often disposed of as solid waste, failing to achieve resource utilization. Furthermore, the use of chemical flocculants may introduce new pollutants, such as aluminum or iron salt residues, affecting the safety of the effluent.

[0007] 5. High energy consumption and complex operation: Aerobic treatment requires continuous aeration, resulting in huge energy consumption; while anaerobic treatment can produce biogas, the effluent still needs further treatment. The overall process is long and the management is complex, making it unsuitable for small and medium-sized pig farms.

[0008] 6. Poor system stability: Traditional constructed wetlands are greatly affected by seasons and temperature, with a significant decrease in treatment efficiency in winter; at the same time, the packing layer is prone to compaction, and the plant roots are hypoxic, causing the system's treatment capacity to decrease as the operating time increases. Summary of the Invention

[0009] To address the above problems, this invention provides a method for efficient treatment of biogas slurry from pig farms, specifically comprising the following steps:

[0010] Step 1: Crush the bio-cellulose material to 40-50 mesh, then mix it with alkaline solution at a mass ratio of 1:(3-4). Stir at 70-80℃ and 120-150rpm for 1-2 hours. This step effectively dissolves and removes impurities such as lignin and hemicellulose from the surface of the bio-cellulose, exposing abundant cellulose hydroxyl groups and large internal pores. After stirring, filter and remove the filtrate. Wash the filter residue with clean water until the washing liquid is neutral. Then, mix the filter residue with magnesium-iron catalytic solution at a mass ratio of 1:(3-4) and soak at 60-70℃ for 5.5-6.5 hours. This step loads iron and magnesium ions onto the fiber surface, which will become catalytic centers in subsequent processing. After soaking, filter and remove the filtrate. Irradiate the filter residue with microwave at 750-850W for 4-6 minutes to generate high temperature and pressure inside the material instantaneously, further expanding the pores. After holding the pressure at 1-2 MPa for 1.5-2.5 minutes, the pressure is released instantly. This synergistic treatment can greatly expand the pore structure of the material, increasing its specific surface area several times and obtaining abundant oxygen-containing functional groups, thus obtaining modified bio-fiber materials.

[0011] Preferably, the bio-fiber material is one or more selected from plant straw, rice husk, sawdust, and coconut shell. Most preferably, the bio-fiber material is corn straw, reed straw, rice husk, and coconut shell in a mass ratio of (20-30):(15-25):(8-12):(10-20).

[0012] Preferably, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution with a mass fraction of 4-6%.

[0013] Preferably, the magnesium-iron catalyst solution comprises 0.4-0.6 mol / L ferric sulfate and 0.2-0.4 mol / L magnesium chloride, with water as the reference.

[0014] Step two: Mix the mineral material with an ammonium-calcium solution at a mass ratio of 1:(8-10), and soak at 75-85℃ for 2-3 hours to achieve pre-loading of ammonium ions and opening of pores by calcium ions. After soaking, filter and remove the filtrate. Calcine the filter residue at 250-350℃ for 1-2 hours to fix the ammonium ions and partially dehydroxylate the layered structure, thereby stabilizing the expanded pores and preventing them from shrinking back in subsequent processing. The low-temperature calcination, being much lower than the sintering temperature, will not damage the crystal structure. After cooling to room temperature, mix with a 4-6% (w / w) polyepoxysuccinic acid (PESA) solution at a mass ratio of 1:(10-12), and shake at 200-300 rpm for 40-60 minutes to obtain the modified mineral material. The carboxyl groups on the PESA molecular chain are highly negatively charged and can adsorb onto the material surface, forming a strongly negatively charged polymer layer. Through electrostatic repulsion, the material effectively prevents negatively charged suspended matter such as colloids and humic substances in the biogas slurry from combining too quickly during subsequent treatment, thus delaying the clogging of the adsorption channels and extending the service life of the material. PESA itself is an excellent scale inhibitor; it can chelate calcium and magnesium ions in the biogas slurry, inhibiting the crystallization and precipitation of slightly soluble salts such as calcium carbonate in the pores of the material, thus preventing the formation of hard scale. This complements the material's own function of removing ammonium through ion exchange.

[0015] Preferably, the mineral material includes one or more of weathered coal, attapulgite, diatomite, bentonite, zeolite, vermiculite, sepiolite, and quartz sand. Most preferably, the mineral material includes attapulgite, diatomite, zeolite, and vermiculite in a mass ratio of (2-4):(4-6):(3-5):(2-3).

[0016] Preferably, the ammonium calcium solution comprises 1-3 mol / L ammonium chloride and 1-3 mol / L calcium chloride based on water.

[0017] Step 3: Mix the microbial carrier with the compound enzyme solution at a mass ratio of 1:(4-6), soak at 45-55℃ for 4-5 hours, filter, remove the filtrate, and the filter residue is the enzymatically hydrolyzed microbial carrier. This process can partially degrade the microbial carrier, releasing some short-chain polysaccharides and oligosaccharides. These sugars can act as a slow-release carbon source in the matrix, continuously stimulating the activity of heterotrophic denitrifying bacteria and solving the problem of carbon-nitrogen imbalance in biogas slurry.

[0018] Preferably, the microbial carrier includes one or more of sugarcane bagasse, corn cob, mushroom residue, and distiller's grains. Most preferably, the microbial carrier includes sugarcane bagasse and corn cob in a mass ratio of (1-3):(1-3).

[0019] Preferably, the composite enzyme solution comprises, based on water, 4000-5000 U / g cellulase, 2000-3000 U / g pectinase, and 2500-3500 U / g xylanase.

[0020] Step four: Mix iron powder and silane coupling solution at a mass ratio of 1:(2-3), and sonicate at 40-50 kHz for 25-35 min to form a dense hydrophobic protective film on the iron powder surface, isolating it from air and slowing down oxidation. Filter, remove the filtrate, and mix the filter residue with an organic acid solution at a mass ratio of 1:(3-4). Stir at 40-50℃ and 150-200 rpm for 1-1.5 h to obtain modified iron powder. The organic acid can react with the residual oxides on the iron surface to form a stable iron citrate complex layer. Simultaneously, the numerous carboxyl groups on the surface change the zero-valent iron surface from hydrophobic to hydrophilic and negatively charged. This treatment greatly improves the dispersibility of zero-valent iron in hydrophilic biological matrices, preventing its aggregation and sedimentation. More importantly, its negative surface charge allows it to tightly adsorb around positively charged pollutants through electrostatic interactions, achieving targeted reduction. This also avoids direct contact with functional microorganisms, eliminating their bioinhibitory properties.

[0021] Preferably, the silane coupling solution comprises 1.5-2.5 g / L of 3-aminopropyltriethoxysilane and 0.4-0.6 g / L of γ-(2,3-epoxypropoxy)propyltrimethoxysilane, based on anhydrous ethanol.

[0022] Preferably, the organic acid solution is a citric acid solution with a mass fraction of 4-6% or an acetic acid solution with a mass fraction of 5-7%.

[0023] Step 5: Mix the modified bio-fiber material, modified mineral material, enzymatically hydrolyzed microbial carrier, modified iron powder, bioactivator, and compound bacterial agent in a twin-shaft mixer at a mass ratio of (45-55):(20-30):(10-15):(8-12):(2-4):(0.4-0.6). During the mixing process, spray deionized water to bring the moisture content to 30-35%. After mixing, age and mature at room temperature for 22-26 hours to allow the components to fully interact and balance the moisture, thus obtaining the bio-matrix.

[0024] Preferably, the bioactivator is one or more selected from sodium alginate powder, polyvinyl alcohol, guar gum, xanthan gum, polyglutamic acid, and carboxymethyl cellulose. Most preferably, the bioactivator is sodium alginate powder.

[0025] Preferably, the compound microbial agent includes nitrifying bacteria, denitrifying bacteria, photosynthetic bacteria, Bacillus subtilis, and Bacillus mucilaginosus, in a mass ratio of (35-45):(25-35):(10-20):(8-12):(4-6).

[0026] Step six, in the biological substrate tank (volume 0.15-0.2 m³) 3In a pig farm (with a stock of pigs), a 10-12cm layer of stones is laid from bottom to top as a support layer, an 80-100cm layer of biological substrate as the main reaction layer, and a 10-15cm layer of modified biological fiber material as a plant growth layer. Wetland plants with oxygen-secreting properties, such as calamus and water celery, can be planted at a density of 5-7 plants / m². 2 .

[0027] Preferably, the stone material includes one or more of marble, granite, dolomite, limestone, sandstone, shale, slate, pebbles, vermiculite, and zeolite.

[0028] Preferably, the plant growth layer is planted with one or more of the following: calamus, water celery, water lily, cattail, reed, taro, water star anise, water sedge, reed, dawn redwood, water pine, and water spinach.

[0029] Step six: After the biogas slurry from the pig farm is passed through a screen to remove large suspended solids, the pH is adjusted to 6.5-7.5 with dilute sulfuric acid at a concentration of 0.5-0.8 mg / L. 3 The effluent enters the bio-matrix tank at a rate of [ / h], flowing slowly towards the end via surface runoff and internal infiltration. A recirculation system at the end of the tank returns 25-35% of the effluent to the beginning, mixing it with fresh biogas slurry. This recirculation ratio design serves two purposes: firstly, it carries back nitrite and nitrate generated in the main reaction layer to the front, where denitrification is completed under the action of zero-valent iron and anaerobic microorganisms; secondly, the acclimation microorganisms in the recirculated water accelerate the degradation of newly introduced pollutants. The entire hydraulic retention time is 6-8 days. The system operates continuously. Every quarter, the top 8-12cm of bio-matrix is ​​inspected. If compaction is found, it is removed and replaced with an equal amount of newly prepared bio-matrix. The replaced old substrate, rich in nutrients, can serve as a high-quality organic fertilizer substrate, achieving a complete resource cycle.

[0030] Preferably, multiple biological substrate tanks can be connected in series. Hydraulic impact aerators (Φ215mm) are installed at the bottom of the substrate tanks, 250-270mm from the bottom. The air duct design should use a ring network layout, with a branch pipe flow velocity of 5m / s and a main pipe flow velocity of 10-15m / s. Aeration should be performed for 1 hour each at 7:00 AM and 7:00 PM daily, and aeration should be stopped at other times.

[0031] The present invention has the following advantages:

[0032] (1) High-efficiency nitrogen and phosphorus removal and pollutant removal: Through the synergistic effect of modified bio-fiber materials and mineral materials, the system forms a multi-level adsorption-catalysis-biodegradation chain. The modified bio-fiber materials have an ultra-large specific surface area and abundant functional groups, which can efficiently adsorb organic matter and ammonia nitrogen; the modified mineral materials are treated with PESA, and the surface carries a strong negative charge, which delays clogging through electrostatic repulsion, while stabilizing ammonia removal through ion exchange; the compound bacterial agents (nitrifying, denitrifying, photosynthetic bacteria, etc.) form a dominant bacterial community in the biological matrix, which significantly improves the nitrogen and phosphorus removal efficiency. In particular, through the reflux system, nitrates in the effluent are brought back to the front end, and denitrification is completed under the action of modified iron powder and anaerobic microorganisms, which completely solves the problem of carbon-nitrogen imbalance, greatly improves the removal rate of ammonia nitrogen and total phosphorus, and the effluent quality is stable and meets the standards.

[0033] 2) Long-lasting anti-clogging and stable system operation: This invention fundamentally alleviates clogging problems through material modification and structural design. Mineral materials, after calcination with calcium ammonium solution and modification with PESA, form stable, expandable pores and a negatively charged protective layer, effectively resisting the adsorption of colloids and humic substances. The loose structure of the biological matrix layer, combined with the stone support layer, ensures smooth water flow. The system only requires inspection and replacement of the top layer of compacted material quarterly, resulting in low maintenance frequency and operational stability far exceeding that of traditional constructed wetlands or biological filters.

[0034] 3) Continuous activation of microbial activity: Enzymatically hydrolyzed microbial carriers (such as sugarcane bagasse and corn cobs) are treated with compound enzymes to release short-chain polysaccharides and oligosaccharides as slow-release carbon sources, continuously stimulating the activity of denitrifying bacteria and solving the problem of insufficient carbon source in biogas slurry. At the same time, modified iron powder is treated with organic acids, making its surface hydrophilic and negatively charged. This allows it to target and reduce pollutants while avoiding inhibition of functional microorganisms, ensuring the health and sustainability of the microbial system.

[0035] 4) Resource recycling and no secondary pollution: This invention achieves full recycling of waste. The replaced old biological substrate, rich in organic matter and nutrients, can be directly used as a high-quality organic fertilizer base for farmland or horticulture, avoiding the generation of solid waste. The entire treatment process is mainly based on biological and natural methods, without the need to add chemical flocculants, and the effluent is non-toxic and harmless, in line with the concept of green agriculture.

[0036] 5) Low energy consumption and economical operating costs: This invention combines surface runoff and internal infiltration, resulting in a long hydraulic retention time and extremely low energy consumption. Only one hour of aeration is required each morning and evening, far lower than the continuous aeration requirements of traditional aerobic processes. The raw materials for preparing the biological substrate are widely available (such as straw, rice husks, and weathered coal), making it inexpensive and suitable for large-scale promotion.

[0037] 6) Strong adaptability and long-term high efficiency: This invention considers the variable factors in actual operation. By connecting multiple biological substrate tanks in series and controlling the reflux ratio, it adapts to different concentrations and volumes of biogas slurry; the oxygen secretion of wetland plants (such as calamus and water celery) enhances the aerobic-anaerobic alternation environment of the substrate layer, improving the treatment stability throughout the four seasons. Long-term operation shows that the system can operate sustainably and efficiently for many years without large-scale modifications, with no significant decline in treatment effect. Attached Figure Description

[0038] 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.

[0039] Figure 1 This is a diagram showing the series connection of the biological substrate pool in Example 1. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0041] Example 1

[0042] Raw material preparation:

[0043] Bio-fiber materials: corn stalks, reed stalks, rice husks and coconut shells, in a mass ratio of 25:25:10:15.

[0044] Magnesium-iron catalyst solution: based on water, it includes 0.5 mol / L ferric sulfate and 0.3 mol / L magnesium chloride.

[0045] Mineral materials: attapulgite, diatomite, zeolite and vermiculite, in a mass ratio of 3:5:4:1.5.

[0046] Ammonium-calcium solution: Based on water, it consists of 2 mol / L ammonium chloride and 2 mol / L calcium chloride.

[0047] Microbial carriers: sugarcane bagasse and corn cobs in a 1:1 mass ratio.

[0048] Complex enzyme solution: Based on water, it contains 4500 U / g cellulase, 2500 U / g pectinase and 3000 U / g xylanase.

[0049] Silane coupling solution: Based on anhydrous ethanol, it includes 2 g / L of 3-aminopropyltriethoxysilane and 0.5 g / L of γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0050] Compound microbial agents: nitrifying bacteria (purchased from Guangzhou Qingwo Biotechnology Co., Ltd.), denitrifying bacteria (purchased from Hubei Zhongyan Biotechnology Co., Ltd.), photosynthetic bacteria (purchased from Jinan Shengshi Biotechnology Co., Ltd.), Bacillus subtilis (purchased from Shandong Borui Chemical Co., Ltd.), and Bacillus mucilaginosus (purchased from Hubei Xingdongcheng Chemical Co., Ltd.), with a mass ratio of 40:30:15:10:5.

[0051] Stone materials: marble, granite and pebbles, in a mass ratio of 2:1:5.

[0052] Wetland plants: sweet flag, cattail, and reed, with a plant ratio of 1:3:2.

[0053] Step 1: Crush the bio-cellulose material to 45 mesh, then mix it with a 5% sodium hydroxide solution at a mass ratio of 1:3, stir at 75℃ and 135 rpm for 1.5 h, filter, remove the filtrate, wash the filter residue with water until the washing liquid is neutral, then mix the filter residue with magnesium iron catalytic solution at a mass ratio of 1:4, soak at 65℃ for 6 h, filter, remove the filtrate, irradiate the filter residue with 800W microwave for 5 min, hold at 1.5 MPa for 2 min and then release the pressure instantly to obtain the modified bio-cellulose material.

[0054] Step 2: Mix the mineral material with calcium ammonium solution at a mass ratio of 1:9, soak at 80℃ for 2.5h, filter, remove the filtrate, calcine the filter residue at 300℃ for 1.5h, mix with 5% PESA solution at a mass ratio of 1:11, and shake at 250rpm for 50min to obtain the modified mineral material.

[0055] Step 3: Mix the microbial carrier and the compound enzyme solution at a mass ratio of 1:5, soak at 50℃ for 4.5 hours, filter, remove the filtrate, and the filter residue is the enzymatically hydrolyzed microbial carrier.

[0056] Step 4: Mix iron powder and silane coupling solution at a mass ratio of 1:2.5, sonicate at 45 kHz for 30 min, filter, remove filtrate, mix the filter residue with 5% citric acid solution at a mass ratio of 1:3, stir at 45 ℃ and 175 rpm for 1.25 h to obtain modified iron powder.

[0057] Step 5: The modified bio-fiber material, modified mineral material, enzymatically hydrolyzed microbial carrier, modified iron powder, sodium alginate powder and compound bacterial agent are thoroughly mixed in a twin-shaft mixer at a mass ratio of 50:25:13:10:3:0.5. During the mixing process, deionized water is sprayed to make the water content reach 32%. After mixing, the mixture is aged at room temperature for 24 hours to obtain the bio-matrix.

[0058] Step six, in a volume of 0.18m³ 3 In the bio-matrix pool for each head of pig (175cm deep), from bottom to top, an 11cm layer of stones is laid as a support layer, a 90cm layer of bio-matrix as the main reaction layer, and a 13cm layer of modified bio-fiber material as a plant growth layer. Wetland plants are then planted at a density of 6 plants / m². 2 .

[0059] Step seven, as Figure 1 As shown, three biological substrate tanks (primary, secondary, and tertiary tanks) are connected in series by PVC pipes. The walls and bottom of the biological substrate tanks are waterproof. The walls are made of brick-concrete structure with a thickness of 27cm, and the bottom is made of concrete structure with a thickness of 20cm. Hydraulic impact aerators with a diameter of Φ215mm are installed at the bottom of the substrate tanks, 260mm from the bottom. The air duct design adopts a ring network layout, with a branch pipe flow velocity of 5m / s and a main pipe flow velocity of 12m / s.

[0060] After large suspended solids are removed from the biogas slurry from the pig farm through a screen, the pH is adjusted to 7.0±0.5 with dilute sulfuric acid, and then... 3 The water enters the primary tank from the upper inlet at a rate of [amount missing] / h, then flows into the secondary tank through the lower pipe, and then into the tertiary tank through the upper pipe at the end of the secondary tank. Finally, it flows out from the bottom outlet at the end of the tertiary tank (30% of the effluent is returned to the primary tank inlet). Aeration is carried out for 1 hour each at 7:00 AM and 7:00 PM daily, and aeration is stopped at other times. The total hydraulic retention time is 7 days. The system operates continuously. Every quarter, the top 10cm of the biological substrate can be inspected. If compaction is found, it should be removed and replaced with an equal amount of newly prepared biological substrate. The replaced old substrate, due to its rich nutrients, can be used as a high-quality organic fertilizer substrate, achieving a complete resource cycle.

[0061] Experimental Example 1

[0062] The method described in Example 1 was used to treat the biogas slurry from a local pig farm. Sampling began after the system had been running stably for 30 days. Influent and effluent samples were collected weekly for four consecutive weeks, and the average value was taken as the final result. The results are shown in Table 1. Water quality analysis methods: COD was determined according to the "Determination of Chemical Oxygen Demand in Water - Dichromate Method" (HJ 828-2017); ammonia nitrogen was determined according to the "Determination of Ammonia Nitrogen in Water - Nessler's Reagent Spectrophotometric Method" (HJ 535-2009); total phosphorus was determined according to the "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB / T 11893-1989); suspended solids (SS) were determined according to the "Determination of Suspended Solids in Water - Gravimetric Method" (GB 11901-89). Removal rate = (Influent concentration - Effluent concentration) / Influent concentration × 100%.

[0063] Table 1 Removal effect

[0064]

[0065] As shown in Table 1, the efficient treatment method for pig farm biogas slurry of this invention achieves extremely high removal rates (all exceeding 93%) for COD, ammonia nitrogen, total phosphorus, and SS, with consistently compliant effluent quality. The system operates stably, requiring minimal maintenance except for quarterly checks, demonstrating its advantages in long-term anti-clogging and resource recycling. The synergistic effect of modified materials (such as modified bio-fiber materials and modified mineral materials), along with the application of compound microbial agents and enzymatic microbial carriers, effectively solves the problems of carbon-nitrogen ratio imbalance and microbial inhibition, ensuring treatment efficiency. Experimental data verify that this invention achieves efficient treatment with low energy consumption (only 2 hours of aeration per day), making it suitable for large-scale application of pig farm biogas slurry.

[0066] Furthermore, existing wastewater treatment projects require the construction of anaerobic ponds, aeration tanks, and the installation of corresponding mechanical equipment such as blowers and aerators. The construction and equipment investment for a wastewater treatment project for a pig farm with 1000 pigs typically ranges from 1.5 million to 2 million yuan, which is unaffordable for most small businesses. The pig farm biogas slurry treatment method of this invention has a one-time total investment cost plus annual operating expenses of only about 210,160 yuan. Even with subsequent ecological treatment projects, the annual operating cost is 66,000 yuan, and the total expenditure is only 276,160 yuan, less than one-fifth of the cost of conventional industrial wastewater treatment projects. Therefore, the pig farm biogas slurry treatment method of this invention is generally acceptable to pig farmers.

[0067] Existing conventional wastewater treatment technologies all require electricity for aeration equipment. Taking the UASB-SBBR (coagulation-flotation) combined process for treating wastewater from a 1000-head pig farm as an example, the typical electricity cost is about 30 yuan / day, and the average daily cost of chemicals is about 100 yuan. Including labor and maintenance costs, the total annual operating cost is about 84,000 yuan. In contrast, the aeration equipment in this treatment method aerates for 2 hours per day with a power of 5.5kW, and the electricity cost is 100 yuan / month. The total operating cost of this system mainly includes the addition of substrate materials 2-3 times a year and the cost of back-end labor maintenance, totaling about 92,000 yuan. If we deduct the annual wetland plant revenue of 20,000-30,000 yuan, the net annual operating cost of the system of this invention is only about 60,000-70,000 yuan.

[0068] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for efficient treatment of pig farm biogas slurry, characterized by, The method comprises the following steps: Step one, after the biological fiber material is crushed, it is mixed with lye according to a mass ratio of 1:(3-4), stirred, filtered, the filtrate is removed, the residue is washed with clean water, then mixed with magnesium-iron catalytic liquid according to a mass ratio of 1:(3-4), soaked, filtered, the filtrate is removed, the residue is subjected to microwave irradiation and high-pressure treatment in sequence, and a modified biological fiber material is obtained; Step two, mineral material is mixed with ammonium-calcium solution according to a mass ratio of 1:(8-10), soaked, filtered, the filtrate is removed, the residue is calcined at 250-350℃ for 1-2h, mixed with PESA solution according to a mass ratio of 1:(10-12), and oscillated, and a modified mineral material is obtained; Step three, microbial carrier is mixed with composite enzyme solution according to a mass ratio of 1:(4-6) after being soaked, and an enzymatic microbial carrier is obtained; Step four, iron powder is mixed with silane coupling solution according to a mass ratio of 1:(2-3) under ultrasonic, filtered, the filtrate is removed, the residue is mixed with organic acid solution according to a mass ratio of 1:(3-4) and stirred, and a modified iron powder is obtained; Step five, the modified biological fiber material, the modified mineral material, the enzymatic microbial carrier, the modified iron powder, biological activator and composite microbial agent are mixed according to a mass ratio of (45-55):(20-30):(10-15):(8-12):(2-4):(0.4-0.6), during the mixing process, deionized water is sprayed to make the water content reach 30-35%, and then the mixture is matured at room temperature for 22-26h, and a biological substrate is obtained. Step six, in the biological matrix pool, 10-12 cm of stone, 80-100 cm of biological matrix and 10-15 cm of modified biological fiber material are laid in turn from bottom to top, and wetland plants are planted on the modified biological fiber material, with a planting density of 5-7 plants / m 2 ; Step seven, the pig farm biogas slurry is adjusted to pH 6.5-7.5 by dilute sulfuric acid after removing large suspended solids by a grid, and is fed into the first end of the biological matrix pool at a speed of 0.5-0.8 m 3 / h, and 25-35% of the effluent is backflowed to the first end to mix with fresh biogas slurry, with a hydraulic retention time of 6-8 d, and the system is continuously operated, and every time a quarter is run, the material in the upper 8-12 cm of the biological matrix is checked, and if it is found to be hardened, it is removed and replaced with an equal amount of biological matrix, and the old matrix that is replaced can be used as high-quality organic fertilizer base material.

2. The method for high efficiency treatment of pig farm biogas slurry according to claim 1, characterized in that, The biological fiber material in step one is one or more of plant straw, rice husk, wood chips and coconut shell.

3. The method according to claim 1, wherein, The lye in step one is sodium hydroxide solution with a mass fraction of 4-6% or potassium hydroxide solution with a mass fraction of 4-6%; and the magnesium-iron catalytic liquid comprises 0.4-0.6mol / L of iron sulfate and 0.2-0.4mol / L of magnesium chloride with water as a reference.

4. The method according to claim 1, wherein, The mineral material in step two comprises one or more of weathered coal, attapulgite, diatomite, bentonite, zeolite, vermiculite, sepiolite and quartz sand.

5. The method according to claim 1, wherein, The ammonium-calcium solution in step two comprises 1-3mol / L of ammonium chloride and 1-3mol / L of calcium chloride with water as a reference.

6. The method of claim 1, wherein the method further comprises: The microbial carrier in step three comprises one or more of sugarcane residue, corn cob, mushroom residue and vinasse, and the composite enzyme solution comprises 4000-5000U / g of cellulase, 2000-3000U / g of pectinase and 2500-3500U / g of xylanase with water as a reference.

7. The method according to claim 1, wherein the method is characterized by, The silane coupling solution in step four comprises 1.5-2.5g / L of 3-aminopropyltriethoxysilane and 0.4-0.6g / L of γ-(2,3-epoxypropoxy)propyltrimethoxysilane with anhydrous ethanol as a reference, and the organic acid solution is citric acid solution with a mass fraction of 4-6% or acetic acid solution with a mass fraction of 5-7%.

8. The method for high efficiency treatment of swine farm biogas slurry according to claim 1, characterized in that, The biological activator in step five is one or more of sodium alginate powder, polyvinyl alcohol, guar gum, xanthan gum, polyglutamic acid and carboxymethyl cellulose.

9. The method according to claim 1, wherein, The composite microbial agent in step five includes nitrifying bacteria agent, denitrifying bacteria agent, photosynthetic bacteria agent, bacillus subtilis agent and bacillus mucilaginosus agent, and the mass ratio is (35-45):(25-35):(10-20):(8-12):(4-6).

10. The method of claim 1, wherein the method is characterized by, The stone in step six includes one or more of marble, granite, dolomite, limestone, sandstone, shale, slate, pebble, vermiculite and zeolite, and the wetland plant includes one or more of acorus calamus, oenanthe javorica, nymphaea tetragona, typha angustifolia, phragmites communis, alocasia macrorrhiza, decaspermum gracilentum, acorus calamus, arundo donax, metasequoia glyptostrobo, and menyanthes trifoliata.

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