Chlorella-based all-weather processing technology for biogas slurry of pig breeding

Abstract

The application discloses a kind of based on chlorella pig breeding biogas liquid all-weather processing technology, specifically: pig breeding manure is separated after dry and wet, and manure water enters anaerobic tank or black film methane tank and carries out anaerobic fermentation, and produces biogas liquid;When ambient temperature <15 ℃, biogas liquid is directly used as liquid organic fertilizer and is returned to field for crop planting;When ambient temperature >15 ℃, biogas liquid enters black film aeration tank and carries out aerobic biological treatment, effluent enters sedimentation tank and carries out sedimentation separation, and obtain supernatant and sludge, supernatant is treated by chlorella, effluent enters biological contact oxidation tank and carries out advanced treatment, finally into coagulation sedimentation tank;Or effluent directly into coagulation sedimentation tank, add coagulant and coagulation aid, after sedimentation, supernatant is discharged up to standard.The application is based on chlorella combined process to pig breeding biogas liquid all-weather processing, realize the unity of wastewater discharge up to standard and resource utilization, greatly reduce pig breeding wastewater treatment difficulty, reduce processing cost.

Description

Technical Field

[0001] This invention belongs to the field of aquaculture wastewater treatment and resource utilization technology, specifically involving an all-weather treatment process for swine aquaculture biogas slurry based on Chlorella, which is suitable for low-cost compliant discharge and resource utilization of anaerobic fermentation biogas slurry from large-scale swine farms. Background Technology

[0002] Pig farming wastewater is characterized by high concentrations of organic matter, high levels of ammonia nitrogen, high levels of suspended solids, and large fluctuations in water quality and quantity. If not properly treated, it can cause serious environmental pollution. Currently, there are two main models for treating wastewater from large-scale pig farms: Model 1: Resource utilization of biogas slurry after anaerobic fermentation of wastewater, applied to the field. This model involves applying biogas slurry directly or after dilution to the field. While it can absorb some nutrients, it presents challenges in supervision. Improper application can easily lead to soil salinization, nitrogen and phosphorus overload, and other environmental pollution. Furthermore, applying the biogas slurry requires a large amount of land and cannot be continuously utilized during winter or the off-season for crops.

[0003] Mode 2: Industrialized Wastewater Treatment. The typical process is "pretreatment + anaerobic digestion + A / O / A / O + end-of-pipe deep treatment". The treatment cost to meet the "Farmland Irrigation Water Quality Standard" (GB5084-2021) (dryland farming) is 8-14 yuan / ton (excluding labor costs), but the effluent has high salinity, which can easily lead to soil salinization after 2-3 years of discharge. The treatment cost to meet the "Integrated Wastewater Discharge Standard" (GB8978-1996) (Level 1) is 15-24 yuan / ton (excluding labor costs). This mode has high operating costs and complex operation, requiring operators with high comprehensive skills. Furthermore, the treatment system generates residual sludge containing polyaluminum chloride and polyacrylamide, causing secondary pollution and indirectly increasing wastewater treatment costs and difficulty.

[0004] In recent years, wastewater treatment technology based on microalgae has attracted attention due to its advantages such as simultaneous nitrogen and phosphorus removal, carbon fixation and oxygen production, and low energy consumption. However, traditional Chlorella treatment systems have the following drawbacks: (1) microalgae growth stagnates or even dies under low temperature (<15℃) conditions, making it impossible to operate stably throughout the year; (2) photoreactors mostly use high borosilicate glass tubes, resulting in high investment costs (approximately RMB 14,000 per ton of water); (3) algae-water separation is difficult, often requiring centrifugation or large-scale flocculation, increasing operating costs. Therefore, there is an urgent need to develop a new process for treating biogas slurry from pig farming that can achieve all-weather, low-cost, and stable compliance. Summary of the Invention

[0005] To address the aforementioned problems, this invention aims to provide a 24 / 7 treatment process and system for pig farming biogas slurry based on Chlorella. This invention utilizes a combined Chlorella process to treat pig farming biogas slurry around the clock, achieving a balance between wastewater discharge meeting standards and resource utilization, thereby significantly reducing the difficulty and cost of treating pig farming wastewater.

[0006] The inventors discovered that Chlorella's intracellular enzyme activity decreases and growth almost stops when temperatures are typically below 15°C. Therefore, the application of Chlorella in areas with frost periods is significantly limited when pig farms need to treat biogas slurry year-round. Based on this, this invention proposes a new time-series-based biogas slurry treatment model for pig farming: in the optimal temperature range (>15°C), Chlorella is used to purify the biogas slurry before discharge; in the unsuitable temperature range (<15°C), it is directly used as liquid organic fertilizer for crop cultivation. The two modes are dynamically switched according to the ambient temperature, achieving all-weather treatment.

[0007] The specific technical solution is as follows: A microalgae-based all-weather treatment process for biogas slurry from pig farming includes the following steps: (1) Pretreatment and anaerobic fermentation of manure: After solid-liquid separation, the manure from pig farming enters an anaerobic pond or a black film biogas digester for anaerobic fermentation to produce biogas slurry; In the unsuitable temperature range (ambient temperature <15℃), biogas slurry can be directly used as liquid organic fertilizer for crop planting. When the temperature is within the suitable range (ambient temperature > 15℃), the biogas slurry enters step (2) and performs the following procedures: (2) Aerobic nitrification treatment: The biogas slurry produced in step (1) enters the black film aeration tank for aerobic biological treatment, converting ammonia nitrogen into nitrate nitrogen and nitrite nitrogen. The effluent enters the sedimentation tank for sedimentation and separation, and obtains supernatant and sludge. The supernatant enters step (3). (3) Microalgae photobiological treatment: (3a) Algal culture: The biogas slurry from step (1) and the supernatant from step (3d) are diluted at a volume ratio of 1:5~10 and used to cultivate microalgae to obtain microalgae solution; (3b) Treatment in a black film microalgae corridor: The supernatant obtained in step (2) is mixed with the microalgae solution in step (3a) and introduced into a black film microalgae corridor. Under natural light, the microalgae and aerobic bacteria work together to absorb nitrogen and phosphorus and produce oxygen. (3c) Light-shielding sedimentation coarse separation: The effluent from step (3b) enters the black film algae-water separation tank. The entire process is light-shielded, which induces the natural sedimentation of microalgae, forming a high-concentration algae aggregation area at the bottom of the tank and a low-concentration algae-water mixing area at the top of the tank, thus achieving coarse separation of algae and water. (3d) Centrifugation: The high-concentration algae at the bottom of step (3c) is centrifuged to obtain microalgae mud and supernatant; when the effluent only needs to meet the irrigation water standard (GB5084-2021) for paddy or dryland farming, the mixture of the low-concentration algae water in the upper part of step (3c) and the supernatant of step (3d) directly enters step (5); when the effluent needs to meet the secondary standard of the integrated wastewater discharge standard (GB8978-1996), the mixture of the low-concentration algae water in the upper part of step (3c) and the supernatant of step (3d) enters step (4). (4) Biological contact oxidation treatment: The mixed liquid obtained in step (3d) enters the biological contact oxidation tank for deep treatment to remove residual organic matter and ammonia nitrogen; (5) Coagulation and sedimentation treatment: The mixed liquid from step (3d) or the effluent from step (4) enters the coagulation and sedimentation tank, and coagulants and coagulant aids are added to remove residual microalgae, suspended solids and total phosphorus. After sedimentation, the supernatant is discharged or reused if it meets the standards.

[0008] Furthermore, the black membrane aeration tank in step (2), the black membrane microalgae corridor tank in step (3b), and the black membrane algae-water separation tank in step (3c) are all constructed using HDPE geomembrane to replace reinforced concrete structures, significantly reducing infrastructure investment.

[0009] Furthermore, in step (2), the black film aeration tank uses a water pump connected in series with a Venturi jet to supplement carbon dioxide and propel the flow, without using a separate blower or propeller.

[0010] Furthermore, the microalgae species described in step (3a) are predominantly Chlorella, with an initial density of 3 × 10⁻⁶. 6 ~6.0×10 6 cells / mL; after 2-5 days of culture, the microalgae density reached 1.0 × 10⁻⁶ cells / mL. 7 ~3.0×10 7 The concentration of cells / mL is used to replenish the microalgae solution in the black film microalgae corridor. Based on the biogas slurry treatment volume, 30-60 L of microalgae solution is needed to replenish every ton of biogas slurry treated. The algae culture medium can be a commercially available nutrient solution meeting industry standards, or it can be prepared using agricultural fertilizers according to the BG11 culture medium formula. Because a sterile environment cannot be guaranteed in actual operation, other microalgae species will be cultured simultaneously during the Chlorella cultivation process; therefore, the Chlorella solution added to the black film microalgae corridor is collectively referred to as microalgae solution.

[0011] Furthermore, in step (3b), a high-transmittance acrylic tube is laid in the black film microalgae corridor pool as a photobioreactor.

[0012] Furthermore, the coagulant used in step (5) for coagulation and sedimentation is one or more of polyaluminum chloride, polyferric chloride, and ferrous sulfate, and the coagulant aid is polyacrylamide.

[0013] It should be noted that this invention selects the biogas slurry treatment method based on ambient temperature. This selection process can be achieved by combining an ambient temperature sensor with an automatic switching device. Both the ambient temperature sensor and the automatic switching device can be conventional equipment with this function, and there are no special requirements.

[0014] Compared with the prior art, the present invention has the following beneficial effects: (1) All-weather operation: Through temperature zone parallel mode, Chlorella can be used to efficiently purify and discharge in the suitable temperature period, and in the unsuitable temperature period, it can be directly used as liquid organic fertilizer for crop planting, which completely solves the problem of low temperature failure of traditional Chlorella system and realizes uninterrupted treatment throughout the year.

[0015] (2) Significantly reduce infrastructure investment: aeration time is shortened, system energy consumption is reduced, and equipment investment is reduced; black membrane tanks are used instead of reinforced concrete, acrylic tubes are used instead of high borosilicate glass tubes, and Venturi jets are used instead of blowers and propellers, resulting in a significant reduction in overall equipment investment and infrastructure investment.

[0016] (3) Reduce environmental risks: Only during the unsuitable temperature period (winter + spring) is biogas slurry returned to the field in a limited manner, which greatly reduces the accumulation of soil salinity and nitrogen and phosphorus load, and avoids soil salinization and pollution risks caused by uncontrolled return to the field throughout the year; at the same time, it reduces the amount of flocculants, coagulants, oxidants used and the secondary polluting sludge generated. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of an all-weather treatment process for biogas slurry from pig farming based on Chlorella, according to Embodiment 1 of the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0019] It should be noted that in Tables 1-4, serial number ① represents the black film aeration tank, serial number ② represents the black film microalgae corridor tank, serial number ③ represents the black film algae-water separation tank, serial number ④ represents the biological contact oxidation tank, and serial number ⑤ represents the coagulation sedimentation tank.

[0020] Example 1

[0021] A large-scale pig farm in Xiangxiang City produces ≤4,000 fattening pigs annually. Biogas slurry is the treatment target. The pig fattening farm produces an average of 40.0±1.0 tons of biogas slurry per day. The biogas slurry treatment target is to meet the Class II standard of the "Integrated Wastewater Discharge Standard" (GB8978-1996).

[0022] The following steps are used for processing: (1) Pretreatment and anaerobic fermentation of manure: The manure from the pigsty is separated into solid and liquid phases by a solid-liquid separator. The manure residue is transported to an organic fertilizer plant for fermentation and processing. The manure sludge enters an anaerobic tank (300 m³). 3 Anaerobic fermentation, with a hydraulic retention time of 7.5 days, produces biogas slurry; (2) Aerobic nitrification treatment: The biogas slurry enters the black film aeration tank (80 m³). 3 (HRT=2 days), Venturi jets are installed at the bottom of the pool, and the water pump flow rate is 25 m³ / h. 3 / h, dissolved oxygen is controlled at 2~3 mg / L; the effluent enters the sedimentation tank for sedimentation and separation to obtain supernatant and sludge. The sludge is used for composting, and the supernatant enters step (3). (3) Temperature range treatment (summer + autumn, average water temperature 25~29℃): (3a) Algal culture: Dilute biogas slurry with treated wastewater at a ratio of 1:8, inoculate with Chlorella vulgaris, and culture in high-permeability acrylic tubes (tube diameter 60mm~110mm); initial density 5.0×10⁻⁶ 6 cells / mL; after 3 days of culture, the density of Chlorella reached 2.0 × 10⁻⁶ cells / mL. 7 When the number of cells / mL is around 1, Chlorella solution can be added to the black film microalgae corridor. Based on the amount of biogas slurry treated, 50L of cultured microalgae solution needs to be added for every ton of biogas slurry treated. (3b) Black film microalgae corridor: Mix the supernatant from step (2) with the cultured algae and enter the black film microalgae corridor (volume ≥ 320 m³). 3 HRT ≥ 8 days), natural light, daytime light intensity 20,000~60,000 lux; microalgae concentration maintained at 3.0 × 10⁻⁶. 7 cells / mL up to 7.0 × 10⁻⁶ 7 cells / mL range; (3c) Light-shielded sedimentation coarse separation: The effluent enters the black film algae separation tank (80 m 3 (HRT=2 days), black film covering to block light, inducing natural sedimentation of microalgae; after 1 day, a high-concentration algae aggregation zone is formed at the bottom of the pool and a low-concentration algae-water mixing zone is formed at the top of the pool, achieving coarse separation of algae and water; (3d) Centrifugal separation: The high-concentration algae at the bottom is separated by a disc centrifuge (4000 rpm) to obtain microalgae mud with a water content of 85% (used as a high-nitrogen and high-phosphorus additive for solid organic fertilizer). The supernatant is combined with the low-concentration algae water. (4) Biological contact oxidation: The combined liquid enters the biological contact oxidation tank (effective volume ≥ 32 m³). 3 (HRT≥0.8 days), the packing material is an elastic three-dimensional packing material with microporous aeration; (5) Coagulation and sedimentation: The effluent from biological contact oxidation enters the coagulation and sedimentation tank, and polyaluminum chloride (PAC mass concentration 10%, dosage 8~12 ml / L) and polyacrylamide (PAM mass concentration 1‰, dosage 1~2 ml / L) are added. See Table 1 and Table 2 for the effluent after sedimentation.

[0023] (6) Treatment in non-suitable temperature range (winter + spring): In step (1), the biogas slurry does not enter the microalgae system, but is directly transported to the surrounding supporting farmland by a vacuum truck (the disposal area is 2.3 pig equivalents / mu·season). In accordance with the principle that the amount of biogas slurry applied per mu per year shall not exceed 30 tons, 2.3 pig equivalents / mu·season shall be applied, and the remainder shall be stored in the black film biogas slurry pond (volume 7200 m³). 3 ).

[0024] Table 1. Pollution Removal Status of Each Process in the Treatment of Pig Farm Biogas Slurry in Example 1 (COD) Cr (and ammonia nitrogen)

[0025] Table 2. Pollution removal status of each process in the treatment of pig farm biogas slurry in Example 1 (total nitrogen and total phosphorus).

[0026] Example 2

[0027] A large-scale pig farm in Ningxiang City produces 2,000 fattening pigs annually. Biogas slurry is the treatment target. The pig fattening farm produces an average of 25±0.5 tons of biogas slurry per day. The biogas slurry treatment target is to meet the dryland standard of the "Standard for Irrigation Water in Farmland" (GB5084-2021).

[0028] The following steps are used for processing: (1) Pretreatment and anaerobic fermentation of manure: The manure from the pigsty is separated into solid and liquid phases by a solid-liquid separator. The manure residue is transported to an organic fertilizer plant for fermentation and processing. The manure sludge enters a black film biogas digester (volume 2250 m³). 3 Anaerobic fermentation, with a hydraulic retention time of 90 days, produces biogas slurry; (2) Aerobic nitrification treatment: The biogas slurry enters the black film aeration tank (effective volume 37.5 m³). 3HRT=1.5 days), Venturi jets are installed at the bottom of the pool, the water pump flow rate is 25 m³ / h, and the dissolved oxygen is controlled at 2~3 mg / L; the effluent enters the sedimentation tank for sedimentation and separation to obtain supernatant and sludge. The sludge is used for composting, and the supernatant enters step (3). (3) Temperature range treatment (summer + autumn, average water temperature 25~29℃): (3a) Algal culture: Dilute biogas slurry with treated wastewater at a ratio of 1:8, inoculate with Chlorella vulgaris, and culture in high-permeability acrylic tubes (tube diameter 60mm~110mm); initial density 5.0×10⁻⁶ 6 cells / mL; after 3 days of culture, the Chlorella density reached 2.0 × 10⁻⁶ cells / mL. 7 When the number of cells / mL is around 1, Chlorella solution can be added to the black film microalgae corridor. Based on the amount of biogas slurry treated, 50L of cultured microalgae solution needs to be added for every ton of biogas slurry treated. (3b) Black film microalgae corridor: Mix the supernatant from step (2) with the cultured algae and enter the black film microalgae corridor (effective volume 250 m³). 3 HRT=10 days), natural light, daytime light intensity 20,000~60,000 lux; microalgae concentration maintained at 3.0×10⁻⁶. 7 cells / mL up to 7.0 × 10⁻⁶ 7 cells / mL range; (3c) Light-shielded sedimentation coarse separation: The effluent enters the black film algae separation tank (effective volume 25 m³). 3 (HRT=1 day) The black film covers the area to block light, inducing the natural sedimentation of microalgae. After 1 day, a high-concentration algae aggregation zone forms at the bottom of the pool, and a low-concentration algae-water mixing zone forms at the top of the pool, achieving coarse separation of algae and water; (3d) Centrifugal separation: The high-concentration algae at the bottom is separated by a disc centrifuge (4000 rpm) to obtain microalgae mud with a water content of 85% (used as a high-nitrogen and high-phosphorus additive for solid organic fertilizer). The supernatant is combined with the low-concentration algae water. (4) Coagulation and sedimentation: The combined liquid enters the coagulation and sedimentation tank, and polyaluminum chloride (PAC mass concentration 10%, dosage 8~12 ml / L) and polyacrylamide (PAM mass concentration 1‰, dosage 1~2 ml / L) are added. See Table 3 and Table 4 for the effluent after sedimentation.

[0029] (5) Treatment in non-suitable temperature range (winter + spring): In step (1), the biogas slurry does not enter the microalgae system, but is directly transported to the surrounding supporting farmland by a vacuum truck (the disposal area is 2.3 pig equivalents / mu·season). According to the principle that the amount of biogas slurry applied per mu per year should not exceed 30 tons, 2.3 pig equivalents / mu is applied, and the rest is stored in the black film biogas slurry pond (effective volume 4500 m³). 3 ).

[0030] Table 3. Pollution Removal Status of Each Process in the Treatment of Pig Farming Biogas Slurry in Example 2 (COD) Cr (and ammonia nitrogen)

[0031] Table 4. Pollution removal status of each process in the treatment of biogas slurry from pig farming in Example 2 (total nitrogen and total phosphorus).

Claims

1. A 24 / 7 treatment process for biogas slurry from pig farming based on Chlorella, characterized in that, Includes the following steps: (1) Pretreatment and anaerobic fermentation of manure: After solid-liquid separation, the manure from pig farming enters an anaerobic pond or a black film biogas digester for anaerobic fermentation to produce biogas slurry; When the ambient temperature is below 15℃, the biogas slurry can be directly used as liquid organic fertilizer for crop cultivation. When the ambient temperature is >15℃, the biogas slurry enters step (2) and performs the following procedures: (2) Aerobic nitrification treatment: The biogas slurry produced in step (1) enters the black film aeration tank for aerobic biological treatment, converting ammonia nitrogen into nitrate nitrogen and nitrite nitrogen. The effluent enters the sedimentation tank for sedimentation and separation, and obtains supernatant and sludge. The supernatant enters step (3). (3) Microalgae photobiological treatment: (3a) Algal culture: The biogas slurry from step (1) and the supernatant from step (3d) are diluted at a volume ratio of 1:5~10 and used to cultivate microalgae to obtain microalgae solution; (3b) Treatment in a black film microalgae corridor: The supernatant obtained in step (2) is mixed with the microalgae solution in step (3a) and introduced into a black film microalgae corridor. Under natural light, the microalgae and aerobic bacteria work together to absorb nitrogen and phosphorus and produce oxygen. (3c) Light-shielding sedimentation coarse separation: The effluent from step (3b) enters the black film algae-water separation tank. The entire process is light-shielded, which induces the natural sedimentation of microalgae, forming a high-concentration algae aggregation area at the bottom of the tank and a low-concentration algae-water mixing area at the top of the tank, thus achieving coarse separation of algae and water. (3d) Centrifugation: The high-concentration algae at the bottom of step (3c) is centrifuged to obtain microalgae mud and supernatant; when the effluent only needs to meet the irrigation water standard of farmland irrigation or dryland farming, the mixture of the low-concentration algae water at the top of step (3c) and the supernatant of step (3d) directly enters step (5); when the effluent needs to meet the secondary standard of the integrated wastewater discharge standard, the mixture of the low-concentration algae water at the top of step (3c) and the supernatant of step (3d) enters step (4). (4) Biological contact oxidation treatment: The mixed liquid obtained in step (3d) enters the biological contact oxidation tank for deep treatment to remove residual organic matter and ammonia nitrogen; (5) Coagulation and sedimentation treatment: The mixed liquid from step (3d) or the effluent from step (4) enters the coagulation and sedimentation tank, and coagulants and coagulant aids are added to remove residual microalgae, suspended solids and total phosphorus. After sedimentation, the supernatant is discharged or reused if it meets the standards.

2. The all-weather treatment process for biogas slurry from pig farming based on Chlorella as described in claim 1, characterized in that, The black membrane aeration tank in step (2), the black membrane microalgae corridor tank in step (3b), and the black membrane algae-water separation tank in step (3c) are all constructed using HDPE geomembrane.

3. The all-weather treatment process for biogas slurry from pig farming based on Chlorella as described in claim 1, characterized in that, The black film aeration tank described in step (2) uses a water pump connected in series with a Venturi jet for aeration and flow propulsion.

4. The all-weather treatment process for biogas slurry from pig farming based on Chlorella as described in claim 1, characterized in that, The microalgae species mentioned in step (3a) are predominantly Chlorella, with an initial density of 3 × 10⁻⁶. 6 ~6.0×10 6 cells / mL; after 2-5 days of culture, the microalgae density reached 1.0 × 10⁻⁶ cells / mL. 7 ~3.0×10 7 The microalgae solution is added to the black film microalgae corridor pool at cells / mL. Based on the amount of biogas slurry treated, 30-60 L of microalgae solution needs to be added for every ton of biogas slurry treated.

5. The all-weather treatment process for biogas slurry from pig farming based on Chlorella as described in claim 1, characterized in that, In step (3b), a high-transmittance acrylic tube is laid in the black film microalgae corridor pool as a photobioreactor.

6. The all-weather treatment process for biogas slurry from pig farming based on Chlorella as described in claim 1, characterized in that, The coagulant used in step (5) for coagulation and sedimentation is one or more of polyaluminum chloride, polyferric chloride, and ferrous sulfate, and the coagulant aid is polyacrylamide.

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