Carbon and nitrogen dual-recovery method and device by collecting grease and phycocyanin

Abstract

The invention relates to a carbon and nitrogen dual-recovery method and device for collecting grease and phycocyanin in an algae-bacterium symbiotic sewage treatment system, and the method comprises the following steps: 1, carrying out mud-water separation on phycomycete suspension taken out from the sewage treatment system to obtain phycomycete biomass precipitate; 2, extracting grease in the precipitate in the first step by adopting a chloroform-methanol solution, and collecting the grease to recover carbon; and step 3, adding a hydrochloric acid solution into the biomass extracted in the step 2, heating and stirring, and collecting phycocyanin in supernate to recover nitrogen. According to the method disclosed by the invention, the mode of firstly collecting the grease to extract the carbon and then collecting the phycocyanin to extract the nitrogen is adopted, so that grease loss caused in the process of collecting the phycocyanin is avoided, the collection rate of the grease is improved, and dual recovery of the carbon and the nitrogen can be realized.

Description

Technical Field

[0001] The present invention relates to a method and device for recovering carbon and nitrogen in an algae-bacteria symbiotic sewage treatment system, and in particular to a method and device for recovering carbon and nitrogen by collecting oil and phycocyanin, belonging to the field of resource utilization of microalgae and sludge. Background Art

[0002] Traditional sewage treatment focuses on removing organic matter and pollutants such as nitrogen and phosphorus from sewage. However, with the increasing environmental protection requirements and the deepening of the concept of resource recycling, recycling carbon and nitrogen resources in sewage has become increasingly important. Sewage treatment plants are facing the huge challenge of transitioning from energy-intensive to carbon-neutral, nitrogen recovery and energy-saving systems. In wastewater treatment systems, algae-bacteria symbiotic systems have been widely studied and applied as an environmentally sustainable and cost-effective sewage treatment process. In the algae-bacteria symbiotic system, algae and bacteria benefit each other and promote each other's rapid growth. While removing carbon, nitrogen and phosphorus from wastewater to reduce eutrophication, algae use CO2 and some nitrogen-containing nutrients in water through photosynthesis to convert solar energy into chemical energy and biomass, among which biomass contains a large amount of high-value-added polymers.

[0003] Cyanocyanin, also known as phycocyanin granule polypeptide or poly-L-arginine-poly-L-aspartate, is a non-ribosomally synthesized amino acid polymer found in cyanobacteria and some heterotrophic bacteria. It mainly acts as a temporary storage compound for nitrogen and consists of aspartic acid in the main chain and arginine residues as side chains. As an intracellular polymer that is abundant in microalgae and activated sludge, phycocyanin has broad applications in food, medicine, cosmetics, agriculture and other fields due to its inherent biocompatibility, degradability, multiple amphoterics and rich nitrogen content, so it has great recycling potential. On the other hand, due to environmental and energy issues, it has become necessary to develop renewable biofuels such as bioethanol, biodiesel, biohydrogen and biogas. Microalgae and algae-bacteria are considered to be the most promising raw materials for biodiesel production and an important source of high value-added products for carbon recovery due to their fast growth rate and efficient oil accumulation ability.

[0004] At present, the extraction methods of phycocyanin from cyanobacteria and activated sludge have been widely reported. However, they all have the disadvantages of cumbersome acquisition process, strict conditions, high cost, low yield, etc., and are not suitable for the complex biological community of algae-bacteria symbiotic system. Moreover, for the extraction of oil, it is generally necessary to freeze-dry the microalgae or algae-bacteria biomass and then grind and extract it based on the Folch method, which greatly increases the economic cost and time cost of recycling. In addition, when the two products are extracted and recycled, there is no report that they can be recycled and reused at the same time, which has also caused a huge waste of algae-bacteria biomass to a certain extent. Based on this, in order to maximize the resource utilization of the unique biomass of microalgae (pure algae) and algae-bacteria symbiotic particles, it is urgent to develop an economical and efficient optimal extraction condition for phycocyanin and oil, as well as the joint extraction of phycocyanin and oil, to achieve the dual recovery of carbon and nitrogen, and to provide a concept of a combined recovery device for industrial resource utilization. Summary of the invention

[0005] In view of the problem that dual recovery of carbon and nitrogen cannot be achieved in the current algae-bacteria symbiotic sewage treatment system, the present invention proposes a method and device for dual recovery of carbon and nitrogen by collecting oil and phycocyanin, and realizes dual recovery of carbon and nitrogen by extracting phycocyanin to recover nitrogen and extracting oil to recover carbon.

[0006] A method for recovering both carbon and nitrogen by collecting oil and phycocyanin, wherein the first step is to separate the algae-bacteria suspension taken out of the sewage treatment system from mud and water to obtain an algae-bacteria biomass precipitate; the second step is to extract the oil in the precipitate in the first step using a chloroform-methanol solution, and collect the oil to recover carbon; the third step is to add a hydrochloric acid solution to the biomass extracted in the second step, and collect the phycocyanin in the supernatant after heating and stirring to recover nitrogen. The order of collecting oil first to recover carbon and then collecting phycocyanin to recover nitrogen can maximize the recovery amount.

[0007] Furthermore, the algae-fungus biomass precipitate in the first step is obtained by the following method: centrifuging the algae-fungus suspension and discarding the supernatant, or filtering and retaining the algae-fungus suspension, or allowing the algae-fungus suspension to settle and discarding the supernatant.

[0008] Furthermore, the volume ratio of the extractant chloroform to the methanol solution in the second step is 2:1.

[0009] Furthermore, in the second step, the ratio of the volume of the extractant to the dry weight of the precipitated material is 1:200±20 (g / mL).

[0010] Furthermore, in the second step, the chloroform phase is baked until constant weight is reached, and the chloroform and oil are collected separately. The collected chloroform can be reused.

[0011] Furthermore, the baking temperature in the second step is 50-70°C.

[0012] Furthermore, in the second step, the extractant is added and stirred, followed by centrifugation or standing for stratification.

[0013] Furthermore, the stirring time in the second step is 1-1.5h.

[0014] Furthermore, in the third step, the ratio of the biomass dry weight to the hydrochloric acid volume is 1:100±20 (g / mL), wherein the hydrochloric acid concentration is 1 mol / L.

[0015] Furthermore, the heating temperature in the third step is 60-100°C.

[0016] Preferably, the heating temperature is 80°C.

[0017] Furthermore, the stirring time in the third step is 1-1.5 h.

[0018] Preferably, the stirring time is 1 h.

[0019] Furthermore, in the third step, the mixture is heated and stirred, then centrifuged, and then the supernatant is extracted; or the mixture is heated and stirred, then filtered to separate the solid from the liquid.

[0020] Furthermore, during the filtration in the third step, a filter membrane with a pore size of 0.22-0.45 μm is used to filter out impurities and cell debris.

[0021] Furthermore, the centrifugation or filtration in the third step is performed under low temperature conditions (4-10°C).

[0022] Furthermore, the solution separated in the third step is filtered and retained by an ultrafiltration membrane to separate phycocyanin and hydrochloric acid.

[0023] Furthermore, when filtering with an ultrafiltration membrane in the third step, a 30-20 kda filter membrane is first used to retain most of the phycocyanin, and then a 10-1 kda filter membrane is used to retain the remaining phycocyanin.

[0024] A carbon and nitrogen dual recovery device for collecting oil and phycocyanin comprises an oil extraction tank, an evaporation tank and a phycocyanin extraction tank respectively connected to the lower layer liquid outlet of the oil extraction tank and the biomass outlet of the middle layer, a filtering device connected to the liquid outlet of the phycocyanin extraction tank, and a membrane device connected to the liquid outlet of the filtering device, wherein the oil extraction tank and the phycocyanin extraction tank are both provided with a feed port and a stirring device.

[0025] Furthermore, both the evaporation tank and the phycocyanin extraction tank are provided with a heating device.

[0026] Furthermore, one discharge port of the evaporation tank is connected to the feed port of the oil extraction tank, so that the chloroform evaporates from the evaporation tank and enters the oil extraction tank for reuse; one discharge port of the membrane device is connected to the feed port of the phycocyanin extraction tank, so that the separated hydrochloric acid enters the phycocyanin extraction tank for reuse.

[0027] The beneficial effects of the present invention are: 1. The present invention adopts the method of first collecting oil to extract carbon, and then collecting phycocyanin to extract nitrogen, thereby avoiding oil loss in the process of collecting phycocyanin, improving the oil collection rate, and realizing the dual recovery of carbon and nitrogen.

[0028] 2. The chloroform and hydrochloric acid used in the extraction of oil and phycocyanin in the present invention can be recovered and reused, which is beneficial to saving costs and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the content of fat in the mixed solution under different amounts of extractant in Example 1; Figure 2 is the fat content in the mixed solution at different stirring times in Example 1; Figure 3 is the phycocyanin content obtained under different hydrochloric acid conditions in Example 2; Figure 4 is the phycocyanin content obtained when stirring at different temperatures in Example 2; Figure 5 is the phycocyanin content obtained under different stirring times in Example 2, wherein A is stirred at 80°C and B is stirred at 100°C; Figure 6 The phycocyanin content collected in different extraction orders in Example 3 (FL is to extract the oil first and then the phycocyanin; FC1, FC2, and FC3 extract the phycocyanin first and then use 40mL, 50mL, and 60mL of chloroform-methanol mixed solution to extract the oil, respectively); Figure 7 The oil content collected in different extraction orders of Example 3 (FL is to extract oil first and then extract phycocyanin; FC1, FC2, FC3 extract phycocyanin first and then extract oil with 40mL, 50mL, and 60mL of chloroform-methanol mixture respectively); Figure 8 Comparison of phycocyanin production in two algae-bacteria symbiotic systems in Example 4; Fig. 9 Comparison of oil yields of two algae-bacteria symbiotic systems in Example 4; Fig.10 This is a schematic diagram of a device of Embodiment 5; In the figure: 1. Constant temperature heating device; 2. Evaporation tank; 3. Feed valve; 4. Stirring motor; 5. Stirring paddle; 6. Oil extraction tank; 7. Feed port; 8. Phycocyanin extraction tank; 9. Filtration device; 10. Membrane device; 11. Water production valve; 12. Backwash valve; 13. Discharge valve; 14. Backwash pump; 15. Water tank; 16. Phycocyanin collector; 17. Discharge tank; 18. Discharge port. DETAILED DESCRIPTION Embodiment 1

[0030] This example optimizes the oil extraction conditions. The algae suspension taken out from the sewage treatment system is centrifuged, and the supernatant is discarded to obtain the algae biomass precipitate. A chloroform-methanol mixture (2:1, v / v) is added to the precipitate for extraction, and then centrifuged at 800rpm at room temperature to accelerate stratification. The solution formed by methanol and water is located at the top layer, the biomass containing phycocyanin is located in the middle layer, and the oil is dissolved in the chloroform at the bottom layer. The chloroform phase is dried at 70°C to constant weight, the chloroform is evaporated, and the oil is collected. The oil can also be collected simultaneously when the chloroform is evaporated for extraction again.

[0031] The optimization process of the amount of the extractant is as follows: 20mL, 30mL, 50mL, 60mL, and 80mL of chloroform-methanol solution were added to the five groups of precipitates for extraction, and then the oil was collected respectively. The results are as follows: Figure 1 As shown in the figure, the amount of extractant added has a great influence on the oil extraction content. When the content of the extractant is too little, its solubility in the oil limits the extraction of the oil; when the content of the extractant is too high, it will not only cause a huge waste of cost, but also cause a certain degree of loss in oil production, which will reduce the content of oil dissolved in the chloroform phase, reduce the density, and form a situation where the biomass is evenly mixed in the organic phase, increasing the difficulty of separation. When the ratio of precipitate dry weight (g): chloroform methanol mixture (mL) ≈ 1:200 is added, the oil collection amount is the largest and the effect is the best.

[0032] The optimization process of mixing time is as follows: After adding the extractant to the five groups of precipitates, they were stirred for 0.5h, 1h, 1.5h, 2h, and 2.5h respectively, and then centrifuged. The chloroform layer was dried to constant weight, and the oil was collected separately. The results are as follows: Figure 2 As shown in the figure, when the stirring time is too short, some of the oil in the algae biomass will not be fully in contact with the organic phase, and the extraction content will decrease. However, the oil content does not increase with the increase of stirring time. There is a peak value between the oil amount and stirring time. For example, when the stirring time exceeds 1h, the oil content does not increase or decrease significantly. It can be seen that the best stirring time is 1h.

[0033] When performing extraction in this embodiment, the mixture may be allowed to stand for stratification after stirring. Embodiment 2

[0034] This example optimizes the extraction conditions of phycocyanin. The algae suspension taken out from the sewage treatment system was centrifuged, and the supernatant was discarded to obtain the algae biomass precipitate. 1M HCl solution was added to the precipitate, heated and stirred in a water bath, and then the mixture was centrifuged at a high speed of 1000rpm or more, 14000rpm, and 4°C for 15min, and the supernatant was taken, and most of the phycocyanin was retained by ultrafiltration with a 30kda filter membrane, and the remaining phycocyanin was retained by ultrafiltration with a 10kda filter membrane.

[0035] The optimization process of the amount of hydrochloric acid solution added is as follows: The amount of 1M HCl added to the five groups of precipitates was 10 mL, 20 mL, 30 mL, 40 mL, and 50 mL, respectively. Figure 3 As shown. It can be seen that although the effect of the amount of hydrochloric acid added on the yield of phycocyanin is relatively small, there is also an optimal ratio, and its yield will decrease with the increase of hydrochloric acid. This shows that when extracting phycocyanin with a large volume of hydrochloric acid, it will not only cause a waste of cost but also cause a small amount of hydrolysis of phycocyanin and reduce the yield. It was calculated that adding hydrochloric acid at a ratio of biomass dry weight (g): 1M HCl (mL) ≈ 1:100 can achieve better results.

[0036] The optimization process of temperature during stirring is as follows: After adding hydrochloric acid to the five groups of precipitates, stirring was carried out at 25°C, 40°C, 60°C, 80°C, and 100°C for 1 h. Figure 4 As shown, it can be seen that temperature has a great influence on the extraction of phycocyanin, and its yield increases with the increase of temperature. In this embodiment, the stirring effect is best under the condition of 100°C.

[0037] The optimization process of stirring time is as follows: In order to save costs, this embodiment only optimizes the stirring time during the heating time at 80° C. and 100° C.

[0038] Four groups were added to the precipitate after hydrochloric acid was stirred at 80°C for 0.5h, 1h, 1.5h, and 2h, respectively, and the other four groups were stirred at 100°C for 0.5h, 1h, 1.5h, and 2h, respectively. Figure 5 As shown, no matter at which temperature, if the heating time is too short, the phycocyanin production will be greatly reduced. When the heating time exceeds 1 hour, the content of arginine in the side chain of phycocyanin will decrease with the heating time. This is because the side chain arginine of phycocyanin will fall off to a certain extent under acidic conditions for a long time, especially under high temperature environment (100°C). Therefore, in order to maximize the benefits during the extraction of phycocyanin, it is most reasonable to heat and stir at 80°C for 1 hour.

[0039] In this embodiment, the mixture after heating and stirring can also be filtered instead of centrifuged for solid-liquid separation, such as using a filter membrane with a pore size of 0.22 μm to filter out impurities and cell debris.

[0040] In the above embodiments, the algae-fungus suspension taken out from the sewage treatment system can also be filtered or allowed to settle to separate the solid from the liquid to obtain the algae-fungus biomass. Embodiment 3

[0041] This example is to optimize the extraction sequence of oil and phycocyanin The same batch of algae biomass was divided into two groups, and the optimal conditions of Example 1 and Example 2 were used. One group extracted phycocyanin first and then extracted oil, and the other group extracted oil first and then extracted phycocyanin. For the method of extracting phycocyanin first, in order to explore whether extracting oil later would affect the amount of chloroform-methanol mixture, three groups were divided and different amounts of extractants were added for analysis. The results are shown in Figure 6 and Figure 7 As shown in the figure, extracting phycocyanin first or extracting oil first from the same batch of algae biomass has no significant effect on the content of phycocyanin, but has a significant effect on the content of oil. This may be because when extracting phycocyanin at high temperature, it will cause the decomposition of oil, thus reducing the oil yield. It can be seen that extracting oil first and then phycocyanin is a practical solution to maximize the recycling of carbon and nitrogen resources.

[0042] The above-mentioned embodiments 1 to 3 are all from the low abundance of microalgae (the following SBR reactor R A ) experimental data on algae-bacteria mixtures in sewage treatment systems. Embodiment 4

[0043] This example is to test the effect of using the optimal extraction scheme in sewage treatment systems with different algae and fungi contents From two SBR reactors R B (high abundance of microalgae) and R A (microalgae abundance is low) Take out 100ml of algae-fungus mixture, add chloroform-methanol mixture to the biomass precipitate after centrifugation at a ratio of biomass dry weight (g): chloroform-methanol mixture (mL) ≈ 1:200, and stir at room temperature for 1h. Then let the mixture stand, take out the lower chloroform layer, and bake it in a 60℃ oven to constant weight to obtain the oil content. Take the biomass precipitate in the middle layer, add hydrochloric acid at a ratio of biomass dry weight (g): 1M HCl (mL) ≈ 1:100, and stir at 80℃ for 1h. Then adjust the centrifuged hydrochloric acid supernatant to pH=7.5 with NaOH, and use colorimetry to quantify the products obtained in the two reactors. Figure 8 and Fig. 9The results show that the above method is also applicable in the reactor R1 with a higher algae content, and the recovery rates of oil and phycocyanin reach 327.7 mg / g and 79.7 mg / g, respectively. This indicates that in biomass with a higher microalgae content, this method is not only equally applicable, but also has a greater recovery value. Embodiment 5

[0044] This embodiment is a carbon and nitrogen dual recovery device by collecting oil and phycocyanin, such as Fig.10 As shown, it includes a fat extraction tank 6, an evaporation tank 2, a phycocyanin extraction tank 8, a filtering device 9, a membrane device 10, a water tank 15 and a discharge pool 17. The fat extraction tank 6 and the phycocyanin extraction tank 8 are both provided with a feed port 7 and a stirring paddle 5 driven by a stirring motor 4. The evaporation tank 22, the phycocyanin extraction tank 8 and the discharge pool 17 are all connected to the discharge port 18 of the fat extraction tank 6. When the algae and fungi biomass is added to the fat extraction tank 6 for extraction, considering the cost problem, the fat extraction tank 6 is allowed to stand for stratification, the methanol and water solution is located at the top layer, the biomass including phycocyanin is located in the middle, and the chloroform solution dissolved in the fat is located at the bottom layer. The chloroform solution dissolved in the fat is discharged into the evaporation tank 2 through different discharge orders, the biomass enters the phycocyanin extraction tank 8, and the methanol and water are finally discharged into the discharge pool 17.

[0045] The evaporation tank 2 and the phycocyanin extraction tank 8 are both provided with a constant temperature heating device 1, so that the chloroform in the evaporation tank 2 evaporates and the oil is separated, and the chloroform outlet of the evaporation tank 2 is connected to the oil extraction tank 6 for reuse, which is controlled by the feed valve 3. The constant temperature heating device 1 allows the phycocyanin extraction tank 8 to be heated during stirring. In order to reduce costs, the filter device 9 is connected to the discharge port 18 of the phycocyanin extraction tank 8, such as using a 0.22μm filter membrane to filter impurities and cell debris. The discharge port 18 of the filter device 9 is also connected to the membrane device 10, such as first passing through a 30kda ultrafiltration membrane to intercept most of the phycocyanin, and then passing through a 10kda ultrafiltration membrane to intercept the remaining phycocyanin. The hydrochloric acid outlet after passing through the membrane is connected to the phycocyanin extraction tank 8 for recycling, and the retained phycocyanin is collected into the phycocyanin collector 16 through the discharge valve. The membrane device 10 is also connected to the water tank 15, and the phycocyanin retained on the ultrafiltration membrane is flushed through the cooperation of the backwash valve 12 and the backwash pump 14.

[0046] The collection method of oil and phycocyanin in the above-mentioned embodiment can be applied not only to the recovery of carbon and nitrogen in an algae-bacteria symbiotic environment, but also to the recovery of carbon and nitrogen in an activated sludge and microalgae environment.

[0047] The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. Technicians in the relevant technical field may make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions should also fall within the protection scope of the present invention, and the protection scope of the present invention should be defined by the claims.

Claims

1. A method for recovering carbon and nitrogen by collecting oil and phycocyanin, characterized in that: The first step is to separate the algae-fungus suspension taken out from the sewage treatment system into mud and water to obtain the algae-fungus biomass precipitate; the second step is to use chloroform-methanol solution to extract the oil in the precipitate of the first step, and collect the oil to recover the carbon; the third step is to add hydrochloric acid solution to the biomass extracted in the second step, heat and stir, and collect the phycocyanin in the supernatant to recover the nitrogen.

2. The method for recovering carbon and nitrogen by collecting oil and phycocyanin as claimed in claim 1, characterized in that: The volume ratio of chloroform to methanol solution in the second step's extractant was 2:1, and the ratio of the volume of the extractant to the dry weight of the precipitate was 1:200±20 (g / mL).

3. The method for recovering carbon and nitrogen by collecting oil and phycocyanin as claimed in claim 2, characterized in that: After adding the extractant, stir and then centrifuge or let stand to separate the layers.

4. The method for recovering carbon and nitrogen by collecting oil and phycocyanin as claimed in claim 1, characterized in that: In the third step, the ratio of the biomass dry weight to the volume of hydrochloric acid is 1:100±20 (g / mL), wherein the concentration of hydrochloric acid is 1 mol / L.

5. The method for recovering carbon and nitrogen by collecting oil and phycocyanin as claimed in claim 1, characterized in that: The heating temperature in the third step is 60-100°C.

6. The method for recovering carbon and nitrogen by collecting oil and phycocyanin as claimed in claim 1, characterized in that: In the third step, the mixture is heated and stirred, then centrifuged, and then the supernatant is extracted; or the mixture is heated and stirred, then filtered to separate the solid and liquid.

7. The method for recovering carbon and nitrogen by collecting oil and phycocyanin as claimed in claim 6, characterized in that: Centrifugation or filtration is performed at low temperature.

8. The method for recovering carbon and nitrogen by collecting oil and phycocyanin as claimed in claim 6, characterized in that: The separated solution is filtered through an ultrafiltration membrane to separate phycocyanin and hydrochloric acid.

9. A carbon and nitrogen dual recovery device by collecting oil and phycocyanin, characterized in that: The invention comprises a fat extraction tank, an evaporation tank and a phycocyanin extraction tank respectively connected to the liquid outlet of the lower layer of the fat extraction tank and the biomass outlet of the middle layer, a filtering device connected to the liquid outlet of the phycocyanin extraction tank, and a membrane device connected to the liquid outlet of the filtering device, wherein the fat extraction tank and the phycocyanin extraction tank are both provided with a feed port and a stirring device; and the evaporation tank and the phycocyanin extraction tank are both provided with a heating device.

10. The carbon and nitrogen dual recovery device by collecting oil and phycocyanin as claimed in claim 9, characterized in that: One discharge port of the evaporation tank is connected to the feed port of the oil extraction tank, so that the chloroform evaporates from the evaporation tank and enters the oil extraction tank for reuse; one discharge port of the membrane device is connected to the feed port of the phycocyanin extraction tank, so that the separated hydrochloric acid enters the phycocyanin extraction tank for reuse.

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