Algal-bacterial symbiotic wastewater treatment method for recovering nitrogen by extracting phycocyanin

Abstract

An algal bacterial symbiosis wastewater treatment method for recovering nitrogen by extracting phycocyanin, comprising the following steps: first, domesticating seed sludge; second, treating wastewater in algal bacterial symbiosis under light / dark cycle, and when treating wastewater, the operation cycle is 2-12h, the hydraulic retention time is 4-24h, the dissolved oxygen control range is 0-5mg / L, the temperature control range is 15-26 DEG C, the pH control range is 6-8.5, and part of the sludge-water mixture is taken out to extract phycocyanin in the process of treating wastewater, and the volume ratio of the extraction amount of the sludge-water mixture to the total amount of wastewater is less than or equal to 0.16.The present application promotes the synthesis of phycocyanin and the recovery of nitrogen source by regulating the algal bacterial symbiosis system through light and dark alternation, promotes nitrogen assimilation, reduces greenhouse gas emissions, extracts materials to realize sludge resource, and provides a new method for high-yield phycocyanin and nitrogen recovery in algal bacterial symbiosis system.The reaction has low energy consumption and has good application prospect in the field of low carbon emission reduction.

Description

Technical Field

[0001] The present invention relates to a method for treating algae-bacteria symbiotic wastewater, and in particular to a method for treating algae-bacteria symbiotic wastewater by extracting phycocyanin and recovering nitrogen. Background Art

[0002] Wastewater contains abundant recoverable nitrogen (N) resources. Traditional wastewater treatment processes will inevitably produce harmful nitrogen oxides (N X O), and N2O accounts for 26% of greenhouse gases in sewage treatment. If assimilated nitrogen is recovered from wastewater, it can not only alleviate ecological and environmental problems such as eutrophication and N2O emissions, but also provide a supplementary nitrogen source for agricultural and industrial applications. At present, nitrogen recovery strategies are divided into physical and chemical methods and biological methods. Nitrogen recovery products include ammonium salts, struvite, liquid fertilizers, biomass, protein and soil conditioners. Its recovery process is costly and inefficient, and is not suitable for the low concentration of ammonium in most urban wastewater. Microbial nitrogen recovery is mainly through the assimilation of carbon and nitrogen, and further upgrading them into high-value chemicals. The algae-bacteria symbiotic system has an efficiency of up to 22-78% in nutrient removal and nitrogen recovery.

[0003] For example, the invention patent application with application number CN202110623891.6, entitled “Method for nitrogen and phosphorus resource recovery and carbon neutralization of high-concentration ammonia nitrogen wastewater after moderate nitrification coupled with filamentous algae”, uses filamentous algae to recover nitrogen in wastewater, but only mentions the treatment of ammonia nitrogen in wastewater by filamentous algae, and does not mention the complete process of how to continuously convert nitrogen pollutants in wastewater into recyclable raw materials. It remains in the experimental stage and cannot be directly industrialized.

[0004] Another example is the invention patent application with application number CN202211648315.8, entitled "A bacterial agent for treating and recovering carbon, nitrogen and phosphorus in high-salinity wastewater and its application". In this case, seawater microalgae and fungal mycelium are used as bacterial agents for recovering carbon, nitrogen and phosphorus in wastewater, but they are only in the experimental stage and cannot be used for industrial production of continuous production.

[0005] In addition, most heterotrophic bacteria and cyanobacteria can synthesize phycocyanin, and the nitrogen content in phycocyanin is as high as 24%, which is much higher than that of proteins (~13%-19%) and nucleic acids (~16%). Under light, cyanobacteria decompose phycocyanin as a nitrogen source to produce amino acids and synthesize them into proteins; under dark conditions, cyanobacteria absorb extracellular nitrogen and use the ATP produced during the light period to synthesize and accumulate phycocyanin. As an intracellular nitrogen reservoir, phycocyanin is soluble in strong acids and strong bases, insoluble in neutral water and organic solvents, and easy to separate and recycle. Compared with other industrial synthetic materials, it has good biodegradability and has broad commercial application prospects. Summary of the Invention

[0006] The present application aims at the problem of inconvenient direct recovery of nitrogen in current algae-bacteria symbiosis wastewater treatment, and provides an algae-bacteria symbiosis wastewater treatment method for recovering nitrogen by extracting phycocyanin, which can ensure continuous and stable wastewater treatment and regular recovery of blue algae to extract phycocyanin, so as to achieve the effect of stable nitrogen recovery.

[0007] The technical means adopted by the present application to solve the above problems is an algae-bacteria symbiosis wastewater treatment method for recovering nitrogen by extracting phycocyanin, comprising the following steps: first, domesticating seed sludge; second, treating wastewater in algae-bacteria symbiosis under light / dark cycle, and when treating wastewater, the operation cycle is 2-12h, the hydraulic retention time is 4-24h, the dissolved oxygen control range is 0-5mg / L, the temperature control range is 15-26℃, the pH control range is 6-8.5, and part of the sludge-water mixture is taken out during the treatment of wastewater to extract phycocyanin, and the volume ratio of the extraction amount of the sludge-water mixture to the total amount of wastewater is less than or equal to 0.16.

[0008] Further, the seed sludge is taken from the aerobic tank of a sewage treatment plant.

[0009] Further, the light / dark cycle period is 4-24h, the light / dark cycle length ratio in one light / dark cycle period is 1:5-5:1, and the length of darkness in one light / dark cycle period cannot be greater than 12h. Therefore, when the total length of the whole light / dark cycle period is 24h, the minimum value of the light / dark cycle length ratio is 1:1, which ensures that the continuous darkness time will not exceed 12h. In other light / dark cycle periods with different total lengths, it is also necessary to consider selecting a suitable light / dark cycle length ratio to ensure that the continuous darkness time will not exceed 12h.

[0010] Further, the average illumination during the treatment process is 20-140μmol·m -2 ·s -1 .

[0011] Further, the flow of one operation cycle includes water inlet, standing, aeration, sedimentation and water outlet.

[0012] Further, the time ratio of standing, aeration and sedimentation in one operation cycle is 17:48-52:1-5.

[0013] Further, the water inlet amount in one operation cycle is half of the total amount of wastewater in the reaction system. The water outlet is arranged at the position of the middle height of the reaction tank to make the water outlet as little as possible to take away sludge.

[0014] Further, when no sludge-water mixture is taken out in one operation cycle, the water inlet amount is equal to the water outlet amount; when sludge-water mixture is taken out in one operation cycle, the water inlet amount is equal to the water outlet amount plus the total amount of sludge-water mixture.

[0015] Furthermore, the mud-water mixture is taken out when the mud and water are completely mixed during the aeration stage.

[0016] Furthermore, the frequency of taking out the mud-water mixture is once a week.

[0017] Furthermore, the COD value in the wastewater is 100-300 mg / L.

[0018] Furthermore, during domestication, the seed sludge and wastewater are poured into the reaction tank and mixed, and then aerated. After a period of standing, aeration and sedimentation, the process is carried out normally according to the steps of water intake, standing, aeration, sedimentation and water discharge.

[0019] Furthermore, the initial MLSS after mixing was 3000 mg / L.

[0020] Furthermore, during mixing, the COD value of the wastewater was 100 mg / L.

[0021] Furthermore, during the acclimation operation, the COD value of the wastewater in the influent gradually increased to the normal value.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention provides a new method for recovering nitrogen sources by high-yield phycocyanin in an algae-bacteria symbiotic system. By regulating the algae-bacteria symbiotic system through alternating light and dark, the synthesis of phycocyanin is promoted to recover nitrogen sources, thereby promoting nitrogen assimilation. While reducing greenhouse gas emissions, sludge resource utilization is achieved by extracting phycocyanin.

[0024] 2. The seed sludge of the present invention does not need to be specially prepared, nor does it need to be cultured under special conditions. Instead, it can be directly obtained from the existing environment and then directly cultured and domesticated in the wastewater treatment environment, thereby enabling industrial wastewater treatment to be achieved more simply and quickly.

[0025] 3. The present invention provides a complete nitrogen recovery solution, and recovers nitrogen by extracting phycocyanin. The operation is simple and convenient, providing a new perspective for nitrogen recovery in wastewater.

[0026] 4. The reaction energy consumption of the present invention is low, and it has good application prospects in the field of low-carbon emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the pollutant removal effect in the three reactors during the stable operation stage in Example 1;

[0028] Figure 2 These are optical microscope, fluorescence microscope, and scanning electron microscope images of the microstructure of the algae-bacteria symbiosis in the three reactors during the stable operation phase in Example 1, where ad represents the structure within R1, eh represents the structure within R2, and il represents the structure within R0;

[0029] Figure 3 Variation of phycobiliprotein content in each reactor from the 41st day to the 200th day of Example 1;

[0030] Figure 4 Variation of water quality in each of R1 and R2 in one cycle of light and dark environment, respectively, of Example 1;

[0031] Figure 5 Variation of water quality in each of the three reactors in four cycles of 24h of Example 1;

[0032] Figure 6 (a) phycobiliprotein content at the end of each of the four cycles of 24h in the three reactors of Example 1, wherein the light / dark duration is 12h / 12h, respectively; (b) phycobiliprotein content variation diagram in each of R1 and R2 in two cycles of 6h, wherein the light / dark duration is 4.5h / 1.5h, respectively; (c) phycobiliprotein content variation diagram in each of the three reactors in 12h, wherein the light / dark duration is 6h / 6h, respectively. DETAILED DESCRIPTION

[0033] The present application is further described below with reference to the accompanying drawings.

[0034] Example 1

[0035] An algal-bacterial symbiotic wastewater treatment method for recovering nitrogen by extracting phycobiliprotein, the present example uses an SBR reactor with an effective volume of 2.3L, and a cold white light LED lamp is arranged on one side of the reactor, the LED lamp has a constant light (12h, 8:00-20:00 every day) / dark (12h, 20:00-8:00 the next day) cycle. The seed sludge is taken from the aerobic tank of a municipal wastewater treatment plant, and the amount is such that when the seed sludge is mixed with the wastewater to fill the reactor, the initial MLSS is 3000mg / L. The entire experimental period is two hundred days, and three reactors R0, R1 and R2 are set up for comparative experiments, wherein R0 is operated under no light conditions throughout the experimental period, R1 is operated under no light for forty days and then under light / dark cycle for one hundred and sixty days, and R2 is directly under light / dark cycle for two hundred days. The wastewater under stable operation is artificially configured using a mixed carbon source of sodium acetate and glucose (1:1, calculated based on COD), and the specific components are shown in Table 1 below:

[0036] Table 1. Pollutant content in wastewater during stable operation

[0037]

[0038] Among them, sodium bicarbonate is used to adjust the pH of the wastewater, and the specific concentration is selected according to the actual situation during the treatment process.

[0039] During the stable operation of the entire experiment, the operation cycle was 6 hours, including 5 minutes of water intake, 85 minutes of standing, 240 minutes of aeration, 25 minutes of sedimentation and 5 minutes of water discharge (of course, the specific duration of each stage may vary due to different operations, but it is still adjusted around the above duration to keep an operation cycle of 6 hours). The hydraulic retention time is 12 hours, and the outlet of the reactor is set at a height of half the reactor volume to minimize the amount of sludge taken away each time the water is discharged. The dissolved oxygen in the aeration stage was maintained at 2 mg / L, and the temperature and pH were 25°C and 8, respectively. Under light conditions, the average illumination inside R1 and R2 was set to 70 μmol·m -2 ·s -1 .

[0040] In this example, the acclimation phase, which primarily aims to enrich microalgae, optimize reactor operation, and promote algae-bacteria symbiosis, lasts from 0 to 139 days. The stable operation phase lasts from 140 to 200 days. Before operation, each reactor was filled with seed sludge and wastewater with a COD of approximately 100, resulting in an initial MLSS of 3000 mg / L. Over 30 days, the wastewater COD was gradually increased to 300. The improvement process is shown in Table 2 below:

[0041] Table 2 Increase of wastewater COD from 100 to 300 within the first 30 days of the acclimation phase

[0042] Stage (days) COD (mg / L) Ammonia nitrogen (mg / L) TP (mg / L) 1-15 100 10 4 16-29 200 20 4 After 30 days 300 30 4

[0043] The operating cycle for the first 30 days is shown in Table 3 below:

[0044] Table 3 Operation cycle within the first 30 days of the acclimation stage

[0045] Stage (days) Water inlet (min) Anaerobic (min) Aeration (min) Sedimentation (min) Drainage (min) 0-7 0 85 250 25 0 8-14 5 85 245 20 5 15-21 5 85 250 10 5 22-29 5 85 255 5 5 30 5 85 240 25 5

[0046] Starting from the 31st day, the operating cycle of the acclimatization phase is the same as that of the stable operation phase.

[0047] During the stable operation phase, the removal of pollutants in the water was tested every three days. The results were as follows: Figure 1 As shown in the data, more than 90% of COD and more than 99% of ammonia nitrogen were effectively removed in the three reactors. The removal capacities of R1 and R2 for TN and TP were similar, with the removal rates of TN and TP in R1 being 53.2±4.3% and 90.5±1.7%, respectively, and the removal rates of TN and TP in R2 being 53.7±3.4% and 90.7±2.2%, respectively, while the removal rates of TN and TP in R0 were 42.4±2.8% and 76.6±1.8%, respectively. It can be seen that due to the continuous proliferation of microalgae, the algae-bacteria symbiotic system showed better nitrogen and phosphorus removal effect (P<0.05).

[0048] like Figure 2 As shown, the sludge in reactor R0 without light was loose flocculent sludge, and the filamentous microalgae in reactors R1 and R2 with light / dark cycle proliferated and aggregated with activated sludge during the cultivation process, and finally formed fine particles. The scanning electron microscope images showed that a large number of filamentous microalgae aggregated on the surface of algal-bacterial community, and it could be seen that the surface of microalgae adhered to many caked particles and bacteria. Moreover, the amount of microalgae in R1 and R2 did not differ much, and both reached a stable value, only the internal community of each was different.

[0049] During the entire operation period, the content of mycosporine-like amino acids in the sludge and water in each reactor was detected every ten days at the time when the sludge and water were completely mixed before the end of aeration, starting from the forty-first day, as shown in Figure 3 As shown, the content of mycosporine-like amino acids in each reactor gradually increased and then remained constant, and the average content of crude mycosporine-like amino acids in R1 and R2 was 115 mg / g MLSS, while the average content of crude mycosporine-like amino acids in R0 was 103 mg / g MLSS. It can be seen that the symbiosis between microalgae and bacteria significantly increased the production of mycosporine-like amino acids by 11.7%-20.4% (P<0.001), which was more conducive to nitrogen recovery.

[0050] In order to compare the operation of each reactor in light and dark environments, the water quality in R1 and R2 was monitored in a cycle in light and dark environments, respectively, as shown in Figure 4 As shown, in the two reactors R1 and R2, the pollution ability of pollutants in the light environment (8:00-20:00) was better than that in the dark environment (20:00-8:00 the next day), which may be due to the assimilation of algae in the light period can remove part of the pollutants.

[0051] In addition, the effluent of the three reactors in four operation cycles within 24h was monitored. As shown in Figure 5 As shown in the four operation cycles of the three reactors, the content of mycosporine-like amino acids in R1 and R2 was higher than that in R0, and the removal effect of pollutants in R1 and R2 was better than that in R0, which further proved that the algal-bacterial symbiotic system could better synthesize mycosporine-like amino acids, and also better remove pollutants.

[0052] In order to compare the content change of mycosporine-like amino acids in the three reactors under different light / dark cycle conditions, the production of mycosporine-like amino acids in each reactor in four cycles within 24h was monitored. As shown in Figure 6 As shown in (a) of Figure 6As shown in (b), when the light / dark durations were set to 4.5 h / 1.5 h (dark period was 8:00-9:30 and 14:00-15:30, light period was 9:30-14:00 and 15:30-20:00), in R1 and R2, phycocyanin accumulated in the dark period and began to degrade under light. Figure 6 As shown in (c), when the light / dark cycle is set to 6h / 6h (light period 8:00-14:00, dark period 14:00-20:00), in R1 and R2, phycocyanin also accumulates in the dark period and begins to degrade under light. Therefore, phycocyanin accumulation is highest during the dark period, making it suitable for phycocyanin extraction and nitrogen recovery.

[0053] In order to detect the nitrogen conversion efficiency under each reaction condition, the phycocyanin in each reactor was starved for 24 h in a dark environment, and then a cycle was run. The content of phycocyanin in each reactor was detected by elemental analyzer. (CGP) (mg / gMLSS), the nitrogen content α in 1g of phycocyanin, and the mass of suspended solids per liter of mixed solution MLSS (mg / L), and then calculate the efficiency of nitrogen conversion to phycocyanin η(N) (%) according to the following formula:

[0054] (S1)η(N)=(Δm (CGP) *α*MLSS / C0(N))*100%

[0055] Wherein CO(N) (mg / L) is the nitrogen concentration of the influent in the reactor, which is 30 in this embodiment. The data are shown in Table 4 below:

[0056] Table 4 Nitrogen conversion rate of phycocyanin in one operation cycle

[0057]

[0058] Note: This calculation ignores biomass growth during the period.

[0059] It can be seen that the algae-bacteria symbiotic system can greatly increase the amount of phycocyanin in the sludge, thereby greatly improving the efficiency of nitrogen conversion into organic matter, that is, reducing the emission of N2O and CO2 through denitrification.

[0060] Due to the proliferation of algae and fungi, the biomass in the reactor continues to increase. Therefore, the reactor needs to regularly discharge the remaining algae sludge to maintain the algae sludge concentration at around 3000 mg / L. According to experiments, the SRT (sludge retention time) is about 32 days. Every week, 500 mL of the mud-water mixture is taken out during the aeration stage when the phycocyanin concentration is the highest and the mud-water is completely mixed. Both R1 and R2 reactors can operate stably while maintaining a high decontamination capacity. At this time, if Figure 6As shown in Figure 2, the average crude phycocyanin content in R1 and R2 is 150 mg / g MLSS and 137 mg / g MLSS, respectively. Therefore, based on the experimental results of the two reactors R1 and R2, the average sustainable recovery of phycocyanin per cubic reactor per day in this algae-bacteria symbiotic wastewater treatment system is approximately: 0.5 L * 3 g / L * 150 mg / g * ​​1000 / (2.3 L * 7) = 14 g / m 3 ,0.5L*3g / L*137mg / g*1000 / (2.3*7)=12.8g / m 3 Alternatively, the amount of phycocyanin that can be recovered from each ton of dry algae-bacteria sludge discharged from the system is: 137-150 mg / g * ​​1000 kg = 137-150 kg. For large-scale wastewater treatment plants, due to their large volume and biomass, the amount of phycocyanin that can be extracted and recovered during the treatment process is very substantial. Therefore, this wastewater treatment method, which utilizes algae-bacteria symbionts to assimilate nitrogen into phycocyanin for nitrogen removal and recovery, has excellent application prospects.

[0061] The above embodiments are only for the purpose of illustrating the present invention, and are not intended to limit the present invention. Those skilled in the art 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 scope of protection of the present invention, and the scope of protection of the present invention should be defined by the claims.

Claims

1. A method for treating algae-bacteria symbiotic wastewater by extracting phycocyanin to recover nitrogen, characterized by: The following steps are involved: The first step is to acclimate the seed sludge; the second step is to treat the wastewater by algae-bacteria symbiosis under a light / dark cycle environment, and when treating the wastewater, the operation cycle is 2-12 hours, the hydraulic retention time is 4-24 hours, the dissolved oxygen control range is 0-5 mg / L, the temperature control range is 15-26°C, and the pH control range is 6-8.5; and in the process of treating the wastewater, part of the mud-water mixture is taken out to extract phycocyanin, and the volume ratio of the extracted amount of the mud-water mixture to the total amount of wastewater is less than or equal to 0.

16.

2. The algae-bacteria symbiotic wastewater treatment method for recovering nitrogen by extracting phycocyanin as claimed in claim 1, characterized in that: The seed sludge was taken from the aerobic tank of the sewage treatment plant.

3. The algae-bacteria symbiotic wastewater treatment method for recovering nitrogen by extracting phycocyanin as claimed in claim 1, characterized in that: The light / dark cycle period is 4-24 hours, the light / dark cycle ratio within one light / dark cycle is 1:5 to 5:1, and the darkness time within one light / dark cycle cannot exceed 12 hours.

4. The algae-bacteria symbiotic wastewater treatment method for recovering nitrogen by extracting phycocyanin as claimed in claim 1, characterized in that: The average illumination during the treatment process was 20-140 μmol·m -2 ·s -1 .

5. The method for treating algae-bacteria symbiotic wastewater by extracting phycocyanin and recovering nitrogen as claimed in claim 4, characterized in that: The process of one operation cycle includes: water intake, standing, aeration, sedimentation and water discharge; and within one operation cycle, the time ratio of standing, aeration and sedimentation is 17:48-52:1-5.

6. The method for treating algae-bacteria symbiotic wastewater by extracting phycocyanin and recovering nitrogen as claimed in claim 1, characterized in that: The time to remove the mud and water mixture is when the mud and water are completely mixed during the aeration stage.

7. The method for treating algae-bacteria symbiotic wastewater by extracting phycocyanin and recovering nitrogen as claimed in claim 1, characterized in that: The frequency of removing the mud-water mixture is once a week.

8. The method for treating algae-bacteria symbiotic wastewater by extracting phycocyanin to recover nitrogen as claimed in claim 1, characterized in that: The COD value in the wastewater is 100-300 mg / L.

9. The method for treating algae-bacteria symbiotic wastewater by extracting phycocyanin to recover nitrogen as claimed in claim 1, characterized in that: During domestication, the seed sludge and wastewater are poured into the reaction tank and mixed, and then aerated. After a period of standing, aeration and sedimentation, the normal operation is carried out according to the steps of water intake, standing, aeration, sedimentation and water discharge.

10. The algae-bacteria symbiotic wastewater treatment method for recovering nitrogen by extracting phycocyanin as claimed in claim 9, characterized in that: The initial MLSS after mixing was 3000 mg / L; during mixing, the COD value of the wastewater was 100 mg / L; during acclimatization operation, the COD value of the wastewater in the influent gradually increased to a normal value.

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