A method for treating pig farm biogas slurry using a slanted plate photobioreactor with co-culture of algae and bacteria.
By using immobilized algae and bacteria culture in a sloping flat-plate photobioreactor, the problems of easy loss of algae and bacteria and difficulty in solid-liquid separation were solved, achieving efficient treatment of pig farm biogas slurry, increasing biomass and reducing harvesting costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YANTAI UNIV
- Filing Date
- 2024-01-05
- Publication Date
- 2026-07-31
AI Technical Summary
When using algae and bacteria to treat pig farm biogas slurry on a large scale, the problems of easy loss of algae and bacteria and difficulty in solid-liquid separation lead to low treatment efficiency.
An inclined plate photobioreactor was used for the immobilization and culture of algae and bacteria. Algae and bacteria cells were immobilized using carriers such as pine sawdust or waste cotton cloth. Combined with the flow design of the photobioreactor, effective separation and efficient treatment of algae and bacteria were achieved.
It increased biomass, reduced harvesting costs, and achieved efficient removal of COD, TP, and NH4+-N from pig farm biogas slurry, thus achieving the effect of large-scale treatment.
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Abstract
Description
Technical Field
[0001] This invention relates to the treatment of biomass wastewater, and more particularly to a method for treating pig farm biogas slurry using a slanted plate photobioreactor with algae and bacteria co-cultivation. Background Technology
[0002] Pig farm biogas slurry is usually rich in nitrogen, phosphorus and organic carbon. Improper treatment of pig farm biogas slurry and discharge into the environment can lead to water pollution, eutrophication, algal blooms, reduced dissolved oxygen (DO), altered aquatic ecosystems, and severe odor problems.
[0003] Existing mature methods for treating pig farm biogas slurry include composting, wastewater stabilization ponds, constructed wetlands for dilution and separation, aquatic plant absorption, and microalgae treatment. Among these, microalgae treatment has attracted significant attention due to its environmental friendliness, high efficiency, and low cost. Furthermore, microalgae have high protein, antioxidant, vitamin, and mineral content, making them suitable as feed additives for livestock and aquaculture. However, pig farm biogas slurry contains a large amount of alkaline substances, especially NH4+. 4+ The main component is NH4+, and the pH of the biogas slurry can approach 10. Different microalgae and different environmental conditions affect the NH4+ content. 4+ Different algae have different tolerances. For most algae, when the pH is 9 to 10, the growth of algae will be severely inhibited. Algae cannot continue to grow in the biogas slurry of pig farms and cannot continuously convert and utilize the elements in the biogas slurry. Therefore, the co-cultivation of microalgae and bacteria is usually adopted to carry out sustainable and large-scale harmless treatment of biogas slurry of pig farms.
[0004] Algae-bacteria co-culture systems can produce biomass energy while treating biogas slurry. However, in co-culture systems, microalgae and bacterial cells grow in suspension, which can lead to problems such as easy loss of algae and bacteria and difficulties in solid-liquid separation if scaled up in a reactor. Summary of the Invention
[0005] To address the problems of easy loss of algae and bacteria and difficulty in solid-liquid separation when using algae-bacteria co-culture for large-scale treatment of pig farm biogas slurry, this invention provides a method for treating pig farm biogas slurry using an slanted plate photobioreactor with algae-bacteria co-culture. This method employs immobilized algae-bacteria culture to achieve effective separation of algae-bacteria cells and culture medium, thereby increasing biomass and reducing biomass harvesting costs. The specific operation steps of this invention are as follows:
[0006] 1) Culturing single bacterial strains
[0007] Add agar to LB liquid culture medium, heat to sterilize and prepare LB solid medium. Spread the diluted solution containing Bacillus megaterium strain onto LB solid medium and incubate at 37°C for 1-2 days. Select single colonies of different morphologies into new LB solid medium and isolate and purify them by streak plating to screen out single strains of Bacillus megaterium.
[0008] 2) Cultivating pure algae and single algal colonies
[0009] Add culture medium agar and penicillin to BG11 liquid medium, heat to 45°C and stir, let stand to solidify into BG11 solid medium. Dilute the culture medium containing Desmodesmus sp. microalgae with sterile water, spread the diluted solution on the solid medium, and incubate for 6 days. Pick single algal colonies of microalgae for streak plate separation. After 4 generations of separation, obtain pure Desmodesmus sp. single algal colonies. Store the solid medium with single algal colonies in a 4°C refrigerator for later use.
[0010] 3) Adjust the composition ratio of biogas slurry in pig farms
[0011] Filter the biogas slurry from the pig farm, take samples to test the C, N and P elements in the filtered biogas slurry, add soluble nitrates and / or soluble phosphates to adjust the C / N and N / P ratios, and transfer it to a storage tank for later use.
[0012] 4) Construct a sloping flat-plate photobioreactor
[0013] The reactor is a cuboid made of plexiglass, including a reaction tank and a top cover. The top cover can be opened, and a light source is installed inside the top cover. Several horizontal liquid inlets and outlets are respectively provided on the short vertical surfaces corresponding to the reaction tank. A filter plate parallel to the short vertical surfaces is provided in the reaction tank. The distance from the filter plate to the liquid outlet surface is 1 / 5 to 1 / 8 of the distance from the filter plate to the liquid inlet surface. The area between the filter plate and the liquid inlet surface is divided into several culture tanks along the direction of liquid flow. The culture tanks are filled with algae and bacteria carriers. The bottom surface of the reaction tank is raised by 3° to 7° from the filter plate to the liquid inlet surface, and the bottom surface of the reaction tank is raised by 12° to 18° from the liquid outlet surface to the filter plate. The liquid inlet is connected to a peristaltic pump, the peristaltic pump is connected to the outlet of the storage tank, and the liquid outlet is connected to the inlet of the storage tank.
[0014] 5) Algae and Bacteria Co-culture Treatment of Pig Farm Biogas Slurry
[0015] Desmodesmus sp. microalgae and Bacillus megaterium bacteria, cultured to the logarithmic growth phase, were added to the algae-bacterial carrier in a specific ratio. The carrier was then filled into the culture tank, the light source cover was closed, the peristaltic pump was turned on, and the light source was activated. The mixture was circulated at room temperature for 4–6 days, during which time samples were taken regularly to test the biogas slurry indicators. Once the indicators stabilized, circulation was stopped, and the microalgae were recovered.
[0016] Specifically, in step 3), the C / N ratio is adjusted to 100:(15-80), and the N / P ratio is (15-40):1; in step 4), the algae and bacteria carrier is pine sawdust or cotton cloth; in step 5), the ratio of Desmodesmus sp microalgae to Bacillus megaterium bacteria is (3-15):1.
[0017] This invention improves the symbiotic relationship between algae and bacteria by selecting single strains of Bacillus megaterium and pure algae of Desmodesmus sp., and adjusting the composition ratio of pig farm biogas slurry. This enhances the treatment capacity of pig farm biogas slurry while improving biomass conversion efficiency. The inclined plate photobioreactor of this invention allows for full contact between the flowing pig farm biogas slurry and the accompanying algae and bacteria on the carrier, enabling continuous, efficient, and harmless treatment of the pig farm biogas slurry. It is suitable for large-scale applications and harvesting algae and bacteria biomass. The algae and bacteria carrier of this invention is inexpensive, readily available, non-toxic, and has a high adhesion rate. The algae and bacteria are not easily lost in the circulating liquid, facilitating solid-liquid separation. Detailed Implementation
[0018] The present invention will be described below with reference to examples. These examples are only used to explain the present invention and are not intended to limit the scope of the present invention.
[0019] The algal species and sources used in this invention are as follows: *Chlorella vulgaris* (FACHB-1072), *Chlorella pyrenoidosa* (FACHB-10), and *Desmodesmus* sp. (FACHB-2919) were purchased from the freshwater algae strain bank of the Wuhan Institute of Hydrobiology, Chinese Academy of Sciences, and subsequently isolated and purified by the Marine Microalgae Biology Laboratory for later use; *Desmodesmus* sp. G41-M is a mutant algal strain with high biomass and high lipid production, isolated from inland river samples in Xinjiang by the Marine Microalgae Biotechnology Laboratory. The biogas slurry was obtained from a pig farm in Yantai City, Shandong Province.
[0020] Add 1.6% agar (by weight of the culture medium) and 25 U / mL penicillin to BG11 liquid medium. Heat to 45°C, stir to coagulate, and allow to stand to solidify into BG11 solid medium. Dilute the microalgae culture medium of *Desmodesmus* sp. with sterile water, spread the diluted solution on the solid medium, and incubate for 6 days. Then, pick single algal colonies for streak plating to separate them. After 4 generations, pure algal colonies are obtained. Store the solid medium containing single algal colonies at 4°C for later use. The formulation of BG11 liquid medium is shown in Table 1.
[0021] Table 1. Formulation of BG11 liquid culture medium
[0022]
[0023] The biogas slurry from the pig farm was gradually diluted with sterile water at a ratio of 1:10 to obtain 10. -4 ~10 -6 Diluted biogas slurry was added to LB liquid culture medium with 1.5% agar by weight. After heat sterilization, LB solid culture medium was prepared. The diluted biogas slurry was spread onto the LB solid culture medium and incubated at 37°C for 2 days. Single colonies of different morphologies were selected and transferred to new LB solid culture medium for isolation and purification using the streak plating method until a single strain of Bacillus megaterium was screened out. The formulation of LB liquid culture medium is shown in Table 2.
[0024] Table 2. Formulation of LB liquid culture medium
[0025]
[0026]
[0027] The biogas slurry from the pig farm is filtered, and samples are taken to test the C, N, and P elements in the filtered biogas slurry. Soluble nitrates and / or soluble phosphates are added to adjust the C / N ratio to between 100:(15-80) and the N / P ratio to between (15-40):1. The slurry is then transferred to a storage tank for later use.
[0028] A sloping flat-plate photobioreactor was constructed. The reactor is a cuboid made of plexiglass and includes a reaction tank and a top cover. The top cover can be opened, and a light source is located inside the top cover. Several horizontal liquid inlets and outlets are respectively provided on the short vertical surfaces corresponding to the reaction tank. A filter plate parallel to the short vertical surfaces is installed in the reaction tank. The distance from the filter plate to the outlet surface is between 1 / 5 and 1 / 8 of the distance from the filter plate to the inlet surface. The area between the filter plate and the inlet surface is divided into several culture tanks along the direction of liquid flow. The culture tanks are filled with algae and bacteria carriers. The bottom surface of the reaction tank is raised by 3° to 7° from the filter plate to the inlet surface, and raised by 12° to 18° from the outlet surface to the filter plate. The inlet is connected to a peristaltic pump, the peristaltic pump is connected to the outlet of the storage tank, and the outlet is connected to the inlet of the storage tank.
[0029] Desmodesmus sp. microalgae and Bacillus megaterium bacteria, cultured to the logarithmic growth phase, were added to the algae-bacterial carrier in a specific ratio. The carrier was then filled into the culture tank, the light source cover was closed, the peristaltic pump was turned on, and the light source was activated. The mixture was circulated at room temperature for 4–6 days, during which time samples were taken regularly to test the biogas slurry indicators. Once the indicators stabilized, circulation was stopped, and the microalgae were recovered.
[0030] 1. When the immobilized algae and bacteria system using pine sawdust as a carrier was applied in a vertical flat-plate photobioreactor, its cell dry weight reached 2.05 g / L, which significantly reduced COD, TP, and NH3 in the biogas slurry. 4+ The removal rates of TP and NH4+-N reached 91%, 89%, and 74%, respectively, which were 61% and 73% higher than when applied in conical flasks.
[0031] 2. When the immobilized algae and bacteria system using waste cotton cloth as a carrier was applied in a slanted plate photobioreactor, its cell dry weight reached 3.45 g / L, which significantly reduced COD, TP, and NH3 in the biogas slurry. 4+ The removal rates of -N reached 100%, 98% and 93%, respectively. Compared with its application in conical flasks, the removal rates of COD, TP and NH4+-N were increased by 32%, 52% and 42%, respectively.
[0032] 3. Using pine sawdust and waste cotton cloth as immobilization carriers for algae and bacteria, and applying them in a slanted-plate photobioreactor, allows for the large-scale treatment of biogas slurry while simultaneously harvesting algae and bacteria biomass. The biogas slurry treated by the reactor contains COD, TP, and NH3. 4+ -N concentrations all meet the requirements of the "Emission Standard of Pollutants for Livestock and Poultry Breeding Industry GB 18596-2001".
[0033] 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 within the protection scope of the present invention.
Claims
1. A method for treating pig farm biogas slurry using a slanted plate photobioreactor with co-cultivation of algae and bacteria, characterized in that, Includes the following steps: 1) Culturing single bacterial strains Add 1.5% agar by weight to LB liquid culture medium, sterilize by heating to prepare LB solid culture medium, and then add the contents of the solid medium. Bacillus megaterium The diluted bacterial strain was spread onto LB agar and incubated at 37°C for 1-2 days. Single colonies of different morphologies were selected and transferred to fresh LB agar for isolation and purification using the streak plating method. The strain was then screened for... Bacillus megaterium Single strain; 2) Cultivating pure algae and single algal colonies Add 1.6% (by weight) agar and 25 U / mL penicillin to BG11 liquid medium, heat to 45°C, stir, and allow to solidify into BG11 solid medium. Desmodesmus The culture medium of the microalgae was diluted with sterile water, and the diluted solution was spread on a solid culture medium. After 6 days of culture, single microalgal colonies were picked and streaked onto plates for isolation. After 4 generations, the microalgae were obtained. Desmodesmus sp. pure algae single algal colonies: solid culture medium with single algal colonies is stored in a 4°C refrigerator for later use; 3) Adjust the composition ratio of biogas slurry in pig farms Filter the biogas slurry from the pig farm, take samples to test the C, N and P elements in the filtered biogas slurry, add soluble nitrates and / or soluble phosphates to adjust the C / N and N / P ratios, and transfer it to a storage tank for later use. 4) Construct a sloping flat-plate photobioreactor The reactor is a cuboid made of plexiglass, including a reaction tank and a top cover. The top cover can be opened, and a light source is installed inside the top cover. Several horizontal liquid inlets and outlets are respectively provided on the short vertical surfaces corresponding to the reaction tank. A filter plate parallel to the short vertical surfaces is provided in the reaction tank. The distance from the filter plate to the liquid outlet surface is 1 / 5 to 1 / 8 of the distance from the filter plate to the liquid inlet surface. The area between the filter plate and the liquid inlet surface is divided into several culture tanks along the direction of liquid flow. The culture tanks are filled with algae and bacteria carriers. The bottom surface of the reaction tank is raised by 3° to 7° from the filter plate to the liquid inlet surface, and the bottom surface of the reaction tank is raised by 12° to 18° from the liquid outlet surface to the filter plate. The liquid inlet is connected to a peristaltic pump, the peristaltic pump is connected to the outlet of the storage tank, and the liquid outlet is connected to the inlet of the storage tank. 5) Algae and Bacteria Co-culture Treatment of Pig Farm Biogas Slurry To be cultivated to the logarithmic growth phase Desmodesmus sp. microalgae and Bacillus megaterium Bacteria are added to the algae-bacterial carrier in a specific ratio. The algae-bacterial carrier is then filled into the culture tank. The light source cover is closed, the peristaltic pump is turned on, and the light source is activated. The mixture is circulated at room temperature for 4-6 days. During this period, samples are taken regularly to test the biogas slurry indicators. Once the indicators stabilize, circulation is stopped, and the microalgae are recovered.
2. The method of claim 1, wherein, In step 3), adjust C / N to 100:(15~80) and N / P to (15~40):
1.
3. The method of claim 2, wherein, In step 4), the algae carrier is pine wood chips or cotton cloth.
4. The method of claim 3, wherein, In step 5), Desmodesmus sp. microalgae and Bacillus megaterium The number ratio of bacteria is (3~15):1.