Method for synthesizing PHA (polyhydroxyalkanoate) through anaerobic digestion of carbon material reinforced excess activated sludge

Abstract

The invention provides a method for synthesizing PHA through anaerobic digestion of carbon material reinforced excess activated sludge, and relates to the technical field of excess activated sludge treatment.The method comprises the steps that S1, sewage from an aerobic tank of a sewage plant is subjected to standing and layering; s2, removing part of a liquid layer from the water solution after standing and layering to obtain a residual sludge suspension with a certain solid-liquid volume ratio, and adjusting the pH value; s3, adding a predetermined amount of carbon material into the excess sludge turbid liquid, and uniformly mixing; s4, carrying out anaerobic digestion on the uniformly mixed residual sludge suspension at a certain temperature; and S5, sampling and analyzing at regular time in the anaerobic digestion process, stopping anaerobic digestion when the content of PHA in the thalli meets the requirement, and separating the PHA. According to the method provided by the invention, the sludge does not need to be domesticated and cultured, an additional carbon source does not need to be added, the PHA can be directly synthesized through anaerobic digestion under the action of a carbon material, the technological process is simple, the production cost of the PHA can be greatly reduced, and the method has a very good application prospect in the field of residual activated sludge treatment.

Description

Technical Field

[0001] The invention relates to the synthesis of PHA, in particular to a method for synthesizing PHA by anaerobic digestion of excess activated sludge, and relates to the technical field of excess activated sludge treatment. Background Art

[0002] Polyhydroxyalkanoates (PHAs), abbreviated as PHAs, are a class of polyester polymers synthesized intracellularly by microorganisms. Their physical and chemical properties are similar to those of traditional petroleum-based polymers such as polyethylene and polypropylene, but PHAs can be completely degraded into harmless monomers in the natural environment. Therefore, the application of PHAs holds promise for addressing the "white pollution" caused by traditional plastics and the harmful effects of "microplastics" on the human body. However, the high production cost of traditional fermentation methods significantly limits their widespread application. The production of PHA using excess activated sludge is an important supplement to fermentation methods.

[0003] Currently, wastewater treatment plants generally use the A / O (anaerobic-aerobic) process to treat wastewater, with the anaerobic tank positioned in front and the aerobic tank in the back. The microorganisms in the anaerobic tank are primarily anaerobic and facultative bacteria, which reproduce slowly. These bacteria contain some PHA-producing bacteria, which can convert carbon sources such as acetate into PHA for storage within their cells. The microorganisms in the aerobic tank are primarily aerobic and facultative bacteria, which reproduce rapidly. These bacteria also contain some PHA-producing bacteria, which can convert carbon sources such as acetate into PHA for storage within their cells. Due to the rapid reproduction of aerobic bacteria in the aerobic tank, a portion of these bacteria must be removed from the aerobic tank to maintain a balanced microbial balance. Some of these bacteria are returned to the anaerobic tank for microbial replenishment, while the remaining portion is discharged from the sewage treatment system. This removed portion of the aerobic and facultative bacteria is referred to as excess activated sludge. Therefore, excess activated sludge contains PHA-producing bacteria, laying the theoretical foundation for the excess activated sludge process for PHA production. However, the content of PHA-synthesizing bacteria in residual activated sludge is low, with the PHA content per gram of dry sludge being less than 200 mg, which lacks commercial competitiveness.

[0004] In order to improve the commercial competitiveness of PHA production by the excess activated sludge method, this can be achieved by increasing the proportion of PHA-synthesizing bacteria in the excess activated sludge. The anaerobic-aerobic and starvation-feast methods can be used to enrich PHA-synthesizing bacteria in the excess activated sludge, thereby increasing the proportion of PHA-synthesizing bacteria. Veolia Group and Paques Biomaterials of the Netherlands used this method to establish a PHA pilot production plant, with the PHA content in each gram of dry sludge reaching 470 mg; CN100445362C and others separated PHA-synthesizing bacteria from excess activated sludge, and added them to the excess activated sludge after cultivation to increase the proportion of PHA-synthesizing bacteria. However, these process steps are complex and require the addition of additional carbon sources, which increases production costs.

[0005] To enhance the commercial competitiveness of PHA production using excess activated sludge, another approach is to increase the PHA synthesis rate of PHA-synthesizing bacteria in excess activated sludge. Numerous literature reports (e.g., CN114934078A) have documented various methods for increasing the yield of carbon sources such as acetic acid during anaerobic digestion of excess activated sludge. However, the rate at which PHA-synthesizing bacteria utilize carbon sources such as acetic acid for PHA synthesis is low, resulting in some conversion of acetic acid and other carbon sources to methane and hydrogen. Therefore, increasing the rate at which PHA-synthesizing bacteria utilize carbon sources such as acetic acid for PHA synthesis can effectively inhibit the conversion of acetic acid and other carbon sources to methane and hydrogen, fully utilizing acetic acid and other carbon sources for PHA synthesis, thereby increasing the PHA yield during anaerobic digestion of excess activated sludge and enhancing the competitiveness of PHA production using excess activated sludge. However, no research in this area has been reported domestically or internationally. Summary of the Invention

[0006] To address the above problems, the present invention provides a method for synthesizing PHA by anaerobic digestion of excess activated sludge using carbon materials, thereby increasing the rate at which PHA-synthesizing bacteria in excess activated sludge synthesize PHA using carbon sources such as acetic acid generated in situ during anaerobic digestion, and at the same time increasing the proportion of PHA-synthesizing bacteria in excess activated sludge.

[0007] To achieve the above object, the technical solution of the present invention is: a method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials, comprising the following steps: S1: The sewage from the aerobic tank of the sewage treatment plant is allowed to stand and separate into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer. S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a certain solid-liquid volume ratio, and adjusting the pH value to 6.1-6.9; S3: adding a predetermined amount of carbon material to the residual sludge suspension in step S2 and mixing uniformly; S4: performing anaerobic digestion on the residual sludge suspension mixed evenly in step S3 at a certain temperature; S5: During the anaerobic digestion process in step S4, samples are taken and analyzed regularly. When the PHA content in the bacteria reaches the required level (above 470 mg), the anaerobic digestion is stopped and the PHA is separated.

[0008] Furthermore, in step S1, the sewage is allowed to stand for 4 hours to 48 hours.

[0009] Furthermore, in step S1, the sewage is allowed to stand for 10 hours to 36 hours; in step S2, the solid-liquid volume ratio is 0.5-10, and the pH value is adjusted to 6.1-6.9.

[0010] Furthermore, in step S2, the solid-liquid volume ratio is 4-8.

[0011] Furthermore, in step S3, the carbon material is any one of graphite, wood activated carbon, coal-based activated carbon, or a mixture of several of them.

[0012] Furthermore, in step S3, the redox characteristics of the carbon material are determined by cyclic voltammetry. In the cyclic voltammetry curve, the oxidation peak is 1.3 V and the reduction peak is 1.4 V; the current when the oxidation peak is measured is 0.0015 mA to 0.0019 mA, and the current when the reduction peak is measured is -0.0021 mA to -0.0024 mA.

[0013] Furthermore, in step S3, the average particle size of the carbon material is 5-100 mesh, and the specific surface area of ​​the carbon material is 5-80m 2 / g, the amount of carbon material added is 0.05-20g / 1 liter of residual sludge suspension.

[0014] Furthermore, in step S3, the average particle size of the carbon material is 10-50 mesh, and the specific surface area of ​​the carbon material is 10-50m 2 / g, the amount of carbon material added is 0.1-10g / 1 liter of residual sludge suspension.

[0015] Furthermore, in step S4, the temperature of anaerobic digestion is 10-40° C., and the time of anaerobic digestion is 3-20 days.

[0016] Furthermore, in step S4, the temperature of anaerobic digestion is 15-35° C., and the time of anaerobic digestion is 6-15 days.

[0017] The beneficial effects of the method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by a carbon material of the present invention are: The present invention uses excess activated sludge discharged from sewage treatment plants as raw material to produce PHA. The excess activated sludge comes from aerobic pools of sewage treatment plants and is mainly composed of aerobic bacteria and facultative bacteria. It is solid waste discharged from sewage treatment plants and has an abundant source.

[0018] During the anaerobic digestion process of this invention, the carbon material can alter the bacterial structure of the aerobic activated sludge, increasing the proportion of PHA-producing bacteria. Therefore, using the carbon material to enhance the direct anaerobic digestion of aerobic activated sludge from the aerobic tank to synthesize PHA eliminates the need for pretreatment of the remaining activated sludge and simplifies the process.

[0019] During the anaerobic digestion process of the present invention, the carbon material can increase the rate at which PHA-synthesizing bacteria in aerobic activated sludge utilize carbon sources such as acetic acid to synthesize PHA, thereby inhibiting the conversion of carbon sources such as acetic acid into methane and hydrogen. Therefore, there is no need to add other carbon sources. The remaining activated sludge can be directly anaerobically digested under the catalysis of activated carbon to synthesize PHA with high yield, greatly reducing the production cost of PHA.

[0020] The pilot production device established using the technology of the present invention has a maximum PHA content of 600 mg per gram of dry sludge, which is much higher than the 470 mg of the pilot production device of the Veolia Group of the Netherlands, and has greater industrial promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] Figure 1 is the cyclic voltammogram of carbon materials; Figure 2 It is a three-dimensional fluorescence spectrum diagram of the anaerobic digestion process of excess activated sludge; among them, a) represents wood activated carbon, b) represents graphite, c) represents coal-based activated carbon, and d) represents blank; Figure 3 This is a graph showing the change in the concentration of carbon sources such as acetic acid during anaerobic digestion of excess activated sludge over digestion time; the blue line represents wood activated carbon, the yellow line represents graphite, the red line represents coal-based activated carbon, and the green line represents blank; Figure 4A This is a diagram of the changes in the bacterial community structure of the residual activated sludge, specifically a diagram of the changes in the bacterial community structure at the phylum level; among them, control is the blank experimental group, 1 is the wood activated carbon experimental group, 2 is the graphite experimental group, and 3 is the coal-based activated carbon experimental group; Figure 4B , is a diagram of the changes in the bacterial community structure of the residual activated sludge, specifically a diagram of the changes in the structure of the Proteobacteria genus; among them, control is the blank experimental group, 1 is the wood activated carbon experimental group, 2 is the graphite experimental group, and 3 is the coal-based activated carbon experimental group; Figure 5 is a gas chromatography-mass spectrometry (GC-MS) graph of PHA extracted according to an embodiment of the present invention; Figure 6 This is a hydrogen nuclear magnetic resonance spectrum of PHA extracted in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0024] The residual activated sludge from the aerobic tank of the sewage treatment plant is mainly composed of aerobic bacteria and facultative bacteria. The microbial cells contain a large amount of water-soluble extracellular secretions and water-insoluble proteins and other organic matter. During the anaerobic digestion process, these organic matter will be decomposed by acid-producing bacteria to produce short-chain volatile fatty acids such as acetic acid, propionic acid, butyric acid and valeric acid. These fatty acids are excellent carbon sources required for microbial synthesis of PHA. However, the proportion of PHA-synthesizing bacteria in the residual activated sludge is relatively low, and the rate at which PHA-synthesizing bacteria synthesize PHA using volatile fatty acids such as acetic acid during anaerobic digestion is low, resulting in a large amount of volatile fatty acids such as acetic acid being converted into methane, thereby resulting in the waste of volatile fatty acids such as acetic acid. The carbon material provided by the present invention has good electrochemical properties. The activated carbon was measured by cyclic voltammetry. In the cyclic voltammetry curve, the oxidation peak of the carbon material is 1.3V and the reduction peak is -1.4V ( Figure 1 In addition, the carbon material provided by the present invention has the above-mentioned electrochemical characteristics and has a small specific surface area (5-80m 2 / g) and a larger average particle size (5-100 mesh) can enhance the efficient synthesis of PHA in the anaerobic digestion process of residual activated sludge.

[0025] The carbon material having the above characteristics has the following properties: Ⅰ can increase the rate at which acid-producing bacteria in excess activated sludge utilize extracellular secretions, proteins, etc. to synthesize carbon sources such as acetic acid during anaerobic digestion. Three-dimensional fluorescence spectroscopy (3D-EEM) analysis showed that ( Figure 2 ), the fluorescence intensity of carbon sources such as acetic acid gradually increased in the early stage of anaerobic digestion of residual activated sludge, indicating that activated carbon promoted the metabolism of acid-producing bacteria, and the concentration of carbon sources such as acetic acid gradually increased, providing sufficient carbon sources for the high-yield synthesis of PHA. Figure 2 Each set of images, from left to right, shows the fluorescence intensity of carbon sources such as acetic acid in the digestate at different stages from the start to the end of anaerobic digestion. The stronger the fluorescence intensity, the higher the concentration of carbon sources such as acetic acid in the digestate. It can be seen that: ① In the experimental groups with different carbon materials added, the fluorescence intensity of the digestate gradually increased with the extension of anaerobic digestion time, and the fluorescence intensity was higher than that of the blank experimental group, indicating that the addition of carbon materials increased the rate at which acid-producing bacteria synthesized carbon sources such as acetic acid during the anaerobic digestion of excess activated sludge. ② In the blank experimental group d) without the addition of carbon materials, the fluorescence intensity at different anaerobic digestion stages was the weakest (the red dots with very strong fluorescence intensity in the second image are substances other than carbon sources such as acetic acid), indicating that in the absence of carbon materials, the rate at which acid-producing bacteria synthesized carbon sources such as acetic acid during the anaerobic digestion of excess activated sludge was lower.

[0026] The changes of carbon sources such as acetic acid with anaerobic digestion time show that ( Figure 3), in the early stage of anaerobic digestion of excess activated sludge, the concentrations of carbon sources such as acetic acid in the digestate were higher than those in the blank test group, indicating that the addition of carbon materials increased the rate at which acid-producing bacteria synthesized carbon sources such as acetic acid during anaerobic digestion of excess activated sludge. In the later stage of anaerobic digestion, the concentrations of proteins and extracellular secretions in the digestate gradually decreased, and the rate at which acid-producing bacteria synthesized carbon sources such as acetic acid began to decrease. At the same time, PHA-synthesizing bacteria used carbon sources such as acetic acid to synthesize PHA, resulting in a gradual decrease in the concentration of carbon sources such as acetic acid in the digestate. Specifically, by Figure 3 The results show that: ① After six days of anaerobic digestion of excess activated sludge in the experimental groups with different carbon materials added, the concentrations of carbon sources such as acetic acid in the anaerobic digestion liquid were higher than those in the blank control group, indicating that the addition of carbon materials increased the rate at which acid-producing bacteria synthesized carbon sources such as acetic acid during the anaerobic digestion of excess activated sludge. ② During the first six days of anaerobic digestion, the concentrations of protein and extracellular secretions in the digestion liquid were high, and acid-producing bacteria rapidly utilized these substances to produce carbon sources such as acetic acid. After six days of anaerobic digestion, the concentrations of protein and extracellular secretions in the digestion liquid gradually decreased, and the rate at which acid-producing bacteria synthesized carbon sources such as acetic acid began to decrease. At the same time, PHA-synthesizing bacteria used carbon sources such as acetic acid to synthesize PHA, resulting in a gradual decrease in the concentrations of carbon sources such as acetic acid in the digestion liquid. This is completely consistent with the laws governing anaerobic digestion of excess activated sludge.

[0027] Ⅱ can increase the proportion of PHA-synthesizing bacteria in excess activated sludge ( Figure 4A 、 Figure 4B After adding wood activated carbon, coal activated carbon and graphite, the Proteobacteria (Proteobacteria, Figure 4A The red part in the figure) accounted for 13.94%, 21.42%, and 18.37% of the total phylum, respectively. The Bacteroidetes Figure 4A The blue part in the figure) accounted for 30.40%, 27.96%, and 26.64% respectively, and the unclassified Comamonasaceae (unclassified_Comamonadaceae, Figure 4B The yellow part in the figure) increased by 1.85%, 7.83%, and 23.09% respectively, (Candidatus_Competibacter, Figure 4B The sky blue part in the figure) is a glycogen-accumulating bacterium that can synthesize PHA, with the proportions increasing by 12.58%, 6.06%, and 25.62% respectively), Ottowia ( Figure 4BThe proportion of the green part in the figure) increased by 22.23%, 26.22%, and 31.95%, respectively. These bacteria are all PHA-synthesizing bacteria, and Proteobacteria and Bacteroidetes are both PHA-synthesizing bacteria and acid-producing bacteria that synthesize carbon sources such as acetic acid. The increase in the proportion of these bacteria indicates that the addition of the carbon material provided by the present invention is beneficial to the enrichment of PHA-synthesizing bacteria in the residual activated sludge, and is beneficial to the conversion of organic matter such as extracellular secretions and proteins into volatile fatty acids such as acetic acid, providing an excellent carbon source for PHA-synthesizing bacteria, thereby increasing the synthesis rate of PHA.

[0028] After adding the wood activated carbon, coal activated carbon and graphite provided by the present invention, other bacterial genera also changed during the anaerobic digestion of the residual activated sludge, and the Planctomycetes ( Figure 4A The light green part in the figure) decreased by 43.48%, 61.52%, and 50.07% respectively, and the Acidobacteriota Figure 4A The purple part in the figure) increased by 22.16%, 23.67%, and 28.05% respectively, and the Actinobacteria (Actinobacteriota, Figure 4A The gray part in the figure) increased by 35.72%, 41.61% and 55.23% respectively, and the Desulfobacterota ( Figure 4A The dark green portion of the sludge decreased by 3.67%, 25.52%, and 22.79%, respectively. Although microorganisms from these genera and phyla cannot directly synthesize PHA, they promote PHA synthesis in other ways, further demonstrating that the carbon materials provided by this invention can alter the bacterial community structure of residual activated sludge.

[0029] Therefore, the present technology does not require pretreatment such as acclimation of excess activated sludge from aerobic tanks, nor does it require the addition of other carbon sources. After adding the carbon material provided by the present invention, excess activated sludge from aerobic tanks can be directly anaerobic digested to produce PHA in high yields, making the excess activated sludge process simpler and more commercially viable. Research and production of PHA from excess activated sludge enhanced by direct anaerobic digestion using carbon materials has not been reported domestically or internationally.

[0030] Based on the above research results of the present invention, the present invention provides a method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials, comprising the following steps: S1: Let the sewage from the aerobic tank of the sewage treatment plant stand for 4-48 hours (preferably 10-36 hours) and separate the layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer. S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a certain solid-liquid volume ratio, and adjusting the pH value to 6.1-6.9; the solid-liquid volume ratio is 0.5-10, preferably 4-8; S3: Add a predetermined amount of carbon material to the residual sludge suspension of step S2 and mix them evenly; the carbon material is any one of graphite, wood activated carbon, coal-based activated carbon, or a mixture of several thereof; the redox characteristics of the carbon material are determined by cyclic voltammetry, and in the cyclic voltammetry curve, the oxidation peak is 1.3V and the reduction peak is -1.4V; the current when the oxidation peak is measured is 0.0015mA to 0.0019mA, and the current when the reduction peak is measured is -0.0021mA to -0.0024mA; the average particle size of the carbon material is 5-100 mesh, and the specific surface area of ​​the carbon material is 5-80m 2 / g, the amount of carbon material added is 0.05-20 g / 1 liter of excess sludge suspension; further preferably, the average particle size of the carbon material is 10-50 mesh, the specific surface area of ​​the carbon material is 10-50 m2 / g, and the amount of carbon material added is 0.1-10 g / 1 liter of excess sludge suspension; S4: performing anaerobically digestion on the residual sludge suspension mixed uniformly in step S3 at a certain temperature; the temperature of anaerobic digestion is 10-40°C, and the time of anaerobic digestion is 3-20 days; preferably, the temperature of anaerobic digestion is 15-35°C, and the time of anaerobic digestion is 6-15 days; S5: During the anaerobic digestion process in step S4, samples are taken and analyzed regularly. When the PHA content in the bacteria reaches the required level (above 470 mg), the anaerobic digestion is stopped and the PHA is separated. Example 1

[0031] S1: Let the sewage from the aerobic tank of the sewage treatment plant stand for 4 hours and separate into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer.

[0032] S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a solid-liquid volume ratio of 0.5, and adjusting the pH value to 6.1; S3: Add wood activated carbon with a particle size of 5 mesh (specific surface area 50 m 2 / g, oxidation peak 1.3V, current 0.0019mA; reduction peak -1.4V, current -0.0024mA), the addition amount is 20g / 1L of excess sludge suspension, and mixed evenly; S4: The excess sludge suspension from step S3 is subjected to anaerobically digestion at 10°C for 20 days; S5: Sampling was performed and analyzed by UV spectrophotometry. When the PHA content in 1 gram of dry cells reached 549 mg, anaerobic digestion was stopped and the cells were centrifuged to obtain the cells. PHA was extracted by sodium hypochlorite cell wall breaking-chloroform extraction. 25 g of PHA was produced per liter of digestion fluid. The extracted PHA was tested, such as Figure 5 and Figure 6 As shown, Figure 5 : Figure 5 This is the gas chromatography-mass spectrometry (GC-MS) graph of the extracted PHA. PHA is a large class of polyester-based biodegradable polymer materials synthesized intracellularly by microorganisms. The PHA synthesized by the present invention is one of them. It is a copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid (PHBV for short). Therefore, the chemical structure of PHBV is usually characterized by analyzing the molecular ion peaks of 3-hydroxybutyric acid and 3-hydroxyvaleric acid. Figure 6 This is the H NMR spectrum of the extracted PHA. Example 2

[0033] S1: Let the sewage from the aerobic tank of the sewage treatment plant stand for 48 hours and separate into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer.

[0034] S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a solid-liquid volume ratio of 10, and adjusting the pH value to 6.9; S3: Add coal-based activated carbon with a particle size of 100 mesh (specific surface area 5m 2 / g; oxidation peak 1.3V, current 0.0015mA; reduction peak -1.4V, current -0.0021mA), the addition amount is 10g / 1L of excess sludge suspension, and mixed evenly; S4: The excess sludge suspension from step S3 is subjected to anaerobically digestion at 35°C for 3 days; S5: Sampling was performed and analyzed by UV spectrophotometry. When the PHA content in 1 gram of dry bacterial cells reached 509 mg, anaerobic digestion was stopped and the bacterial cells were obtained by centrifugation. PHA was extracted by sodium hypochlorite cell wall disruption-chloroform extraction, and 20 g of PHA was produced per liter of digestion fluid. Example 3

[0035] S1: Let the sewage from the aerobic tank of the sewage treatment plant stand for 10 hours and separate into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer.

[0036] S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a solid-liquid volume ratio of 5, and adjusting the pH value to 6.5; S3: Add coal-based activated carbon with a particle size of 80 mesh (specific surface area 80m2) to the residual sludge suspension in step S2. 2 / g; oxidation peak 1.3V, current 0.0016mA; reduction peak -1.4V, current -0.0022mA), the addition amount is 0.05g / 1 liter of excess sludge suspension, and mixed evenly; S4: The excess sludge suspension from step S3 is subjected to anaerobically digestion at 25°C for 10 days; S5: Sampling was performed and analyzed by UV spectrophotometry. When the PHA content in 1 gram of dry bacterial cells reached 589 mg, anaerobic digestion was stopped and the bacterial cells were obtained by centrifugation. PHA was extracted by sodium hypochlorite cell wall disruption-chloroform extraction, and 32 g of PHA was produced per liter of digestion fluid. Example 4

[0037] S1: The sewage from the aerobic tank of the sewage treatment plant is allowed to stand for 36 hours and then separated into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer.

[0038] S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a solid-liquid volume ratio of 8, and adjusting the pH value to 6.3; S3: Add wood activated carbon with a particle size of 10 mesh (specific surface area 20m2) to the residual sludge suspension in step S2. 2 / g; oxidation peak 1.3V, current 0.0018mA; reduction peak -1.4V, current -0.0023mA), the addition amount is 5g / 1L of excess sludge suspension, and mixed evenly; S4: The excess sludge suspension from step S3 is subjected to anaerobically digestion at 40°C for 6 days; S5: Sampling was performed and analyzed by UV spectrophotometry. When the PHA content in 1 gram of dry bacterial cells reached 600 mg, anaerobic digestion was stopped, the bacterial cells were obtained by centrifugation, and PHA was extracted by sodium hypochlorite cell wall disruption-chloroform extraction. 41 g of PHA was produced per liter of digestion fluid. Example 5

[0039] S1: Let the sewage from the aerobic tank of the sewage treatment plant stand for 24 hours and separate into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer.

[0040] S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a solid-liquid volume ratio of 6, and adjusting the pH value to 6.7; S3: Add graphite with a particle size of 50 mesh (specific surface area of ​​10m 2 / g; oxidation peak 1.3V, current 0.0019mA; reduction peak -1.4V, current -0.0024mA), the addition amount is 2g / 1L of excess sludge suspension, and mixed evenly; S4: The excess sludge suspension from step S3 is subjected to anaerobically digestion at 35°C for 15 days; S5: Sampling was performed and analyzed by UV spectrophotometry. When the PHA content in 1 gram of dry bacterial cells reached 591 mg, anaerobic digestion was stopped and the bacterial cells were obtained by centrifugation. PHA was extracted by sodium hypochlorite cell wall disruption-chloroform extraction, and 32 g of PHA was produced per liter of digestion fluid.

[0041] Comparative Example 1 S1: The sewage from the aerobic tank of the sewage treatment plant is allowed to stand for 36 hours and then separated into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer.

[0042] S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a solid-liquid volume ratio of 8, and adjusting the pH value to 6.3; S3: The excess sludge suspension from step S2 is subjected to anaerobically digestion at 40°C for 6 days; S4: Sampling was performed and analyzed using a UV spectrophotometer. When the maximum PHA content in 1 gram of dry cells reached 385 mg, anaerobic digestion was stopped, the cells were obtained by centrifugation, and PHA was extracted using a sodium hypochlorite cell wall-breaking-chloroform extraction method. 8.7 g of PHA was produced per liter of digestion fluid.

[0043] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

Claims

1. A method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials, characterized in that: The steps include: S1: The sewage from the aerobic tank of the sewage treatment plant is allowed to stand and separate into layers. The upper clear liquid is called the liquid layer, and the lower dark microbial layer is called the solid layer. S2: removing part of the liquid layer from the aqueous solution after standing and stratifying in step S1 to obtain a residual sludge suspension with a certain solid-liquid volume ratio, and adjusting the pH value; S3: adding a predetermined amount of carbon material to the residual sludge suspension in step S2 and mixing uniformly; S4: performing anaerobic digestion on the residual sludge suspension mixed evenly in step S3 at a certain temperature; S5: The digestion liquid of step S4 is sampled and analyzed regularly. When the PHA content per gram of dry bacteria reaches 470 mg or more, anaerobic digestion is stopped and PHA is separated.

2. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 1, characterized in that: The sewage is left to stand for 4 to 48 hours in step S1.

3. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 1, characterized in that: In step S1, the sewage is allowed to stand for 10 to 36 hours; in step S2, the solid-liquid volume ratio is 0.5-10, and the pH value is adjusted to 6.1-6.

9.

4. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 3, characterized in that: In step S2, the solid-liquid volume ratio is 4-8.

5. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 1, characterized in that: In step S3, the carbon material is any one of graphite, wood activated carbon, coal-based activated carbon, or a mixture of several of them.

6. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 1, characterized in that: In step S3, the redox characteristics of the carbon material are determined by cyclic voltammetry. In the cyclic voltammetry curve, the oxidation peak is 1.3 V and the reduction peak is 1.4 V. The current when the oxidation peak is measured is 0.0015 mA to 0.0019 mA, and the current when the reduction peak is measured is -0.0021 mA to -0.0024 mA.

7. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 1, 5 or 6, characterized in that: In step S3, the average particle size of the carbon material is 5-100 mesh, and the specific surface area of ​​the carbon material is 5-80m 2 / g, the amount of carbon material added is 0.05-20g / 1 liter of residual sludge suspension.

8. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 7, characterized in that: In step S3, the average particle size of the carbon material is 10-50 mesh, and the specific surface area of ​​the carbon material is 10-50 m 2 / g, the amount of carbon material added is 0.1-10g / 1 liter of residual sludge suspension.

9. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 1, characterized in that: In step S4, the temperature of anaerobic digestion is 10-40° C., and the time of anaerobic digestion is 3-20 days.

10. The method for synthesizing PHA by anaerobic digestion of excess activated sludge enhanced by carbon materials according to claim 9, characterized in that: In step S4, the temperature of anaerobic digestion is 15-35° C., and the time of anaerobic digestion is 6-15 days.

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