A method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater

Abstract

The present invention provides a method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater, which relates to sewage treatment technology, including: inoculating mature aerobic granular sludge into a photoreactor, so that the sludge concentration in the photoreactor reaches 5000 mg / L to 10000 mg / L; placing the photoreactor under illumination conditions, using low-concentration sewage as the photoreactor inlet water, and continuously culturing until filamentous algae are wrapped and covered on the surface of the granular sludge; replacing the inlet water of the photoreactor with ultra-low concentration wastewater to be treated, keeping the illumination conditions unchanged, and increasing the hydraulic retention time of the sewage in a gradient manner, so that the filamentous algae on the surface of the granular sludge gradually grow into the inside of the granules until the entire granules are covered, and the cultured bacteria-algae symbiotic granules are obtained. The bacteria-algae symbiotic granular sludge provided by the present invention has good ultra-low concentration wastewater nitrogen and phosphorus treatment effect, and has the advantages of high particle stability, no secondary pollution of nitrogen and phosphorus, low temperature resistance, simple preparation process, and low cost.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater. Background Art

[0002] Ultra-low concentration wastewater, such as secondary effluent from sewage treatment plants and wastewater from eutrophic water bodies, is widely produced or distributed in many sewage treatment plants and eutrophic natural water bodies in my country. When the organic matter content in the wastewater is too low, BOD5 < 50 mg / L, TN (total nitrogen) < 15 mg / L, TP (total phosphorus) < 1 mg / L, it will inhibit the growth of microorganisms in the water and make it difficult for microorganisms to remove nitrogen and phosphorus. Therefore, it is not suitable for treatment with mainstream activated sludge and biofilm methods. Bacteria-algae symbiotic granular sludge technology is a new type of sewage biological treatment technology derived from aerobic granular sludge technology in recent years. It has the characteristics of toxicity and high salt resistance, good sedimentation performance, small footprint, high degree of automation, and low operating energy consumption. It can be used to treat various types of domestic sewage and industrial wastewater. In addition, since the bacteria-algae symbiotic granular sludge contains a large amount of autotrophically grown microalgae, the bacteria-algae symbiotic sludge can adapt to wastewater with a lower concentration of carbon source organic matter than ordinary aerobic granules, greatly improving the ability to remove nitrogen and phosphorus under low organic matter conditions. In the process of realizing the present invention, the inventors found that the current bacteria-algae symbiotic granular sludge technology has the following problems: (1) Since the proportion of algae content is still small compared to bacteria, the ability to deeply remove nitrogen and phosphorus is still insufficient; (2) Ultra-low concentration wastewater will cause bacteria in the bacteria-algae symbiotic granules to die and decompose, aggravating the risk of granule disintegration and affecting the smooth operation and treatment effect of the system; (2) Bacteria are prone to release their own nitrogen and phosphorus elements during death and decomposition, causing reverse release of nitrogen and phosphorus and secondary pollution problems.

[0003] Therefore, how to effectively improve the treatment effect of bacteria-algae symbiotic granular sludge on ultra-low concentration wastewater and avoid the disintegration of particles and secondary pollution during the treatment process has become a technical problem that needs to be solved urgently. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art or related technology, and discloses a method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater. The method has good ultra-low concentration wastewater nitrogen and phosphorus treatment effects, and has the advantages of high particle stability, no secondary pollution of nitrogen and phosphorus, low temperature resistance, simple operation, low cost, etc. It is an efficient, economical and environmentally friendly sewage treatment strategy with great application prospects and significance.

[0005] The first aspect of the present invention discloses a method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater, comprising: S1, inoculating mature aerobic granular sludge into a photoreactor to make the sludge concentration in the photoreactor reach 5000 mg / L to 10000 mg / L; S2, placing the photoreactor under light conditions, using low-concentration sewage as the photoreactor inlet water, and continuously culturing until the filamentous algae are wrapped and covered on the surface of the granular sludge; S3, replacing the inlet water of the photoreactor with ultra-low concentration wastewater to be treated, keeping the light conditions unchanged, increasing the hydraulic retention time of the sewage in a gradient manner, and continuously culturing for 40 to 60 days, so that the filamentous algae on the surface of the granular sludge gradually grow into the inside of the granules until the entire granules are covered, thereby obtaining cultured bacteria-algae symbiotic granules.

[0006] In this technical solution, the bacteria-algae symbiotic particles are irregular brown particles, and filamentous algae grow in large quantities in the particles, which improves the stability of the particles and the treatment effect on ultra-low concentration wastewater. The cultured bacteria-algae symbiotic granular sludge has a high content of filamentous algae and has high stability. The particles are not easy to disintegrate and break under ultra-low concentration wastewater conditions (BOD5 < 50 mg / L, TN < 15 mg / L, TP < 1 mg / L), and have a good effect on the removal of nitrogen and phosphorus in wastewater.

[0007] According to the method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, it also includes: using the cultivated bacteria-algae symbiotic granules for treating ultra-low concentration wastewater. According to the method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, in step S1, the sewage used for aerobic granular sludge cultivation is artificially prepared sewage or actual wastewater, wherein the artificially prepared sewage contains COD 400 mg / L to 800 mg / L, NH4 + -N 40 mg / L~60 mg / L, PO4 3- -P 5 mg / L~15 mg / L.

[0008] According to the method for acclimating and culturing bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, in step S1, aerobic granular sludge is cultured in an SBR reactor, and the culture conditions include: cyclic operation in the manner of water inlet-standing-aeration-sedimentation-drainage, with a hydraulic retention time of 8 hours, 6 cycles per day, and an operation cycle of 4 hours. In each cycle, water inlet is 3 minutes, standing is 30 minutes, aeration is 199 minutes, sedimentation is 5 minutes, and drainage is 3 minutes. The inlet and outlet water are both controlled by a peristaltic pump, the volume replacement rate is 50%, and aeration is provided by an aeration pump connected to the bottom of the reactor and is controlled to 3L / min by a gas flowmeter.

[0009] In this technical solution, the hydraulic retention time (HRT) is an important parameter in water treatment engineering. Each cycle (4 hours) treats half of the reactor volume of water, so it takes 2 cycles to treat 1 volume of water, that is, 8 hours.

[0010] According to the method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, the operation mode of the photoreactor in step S2 is consistent with the cultivation conditions during the aerobic granular sludge cultivation period, and the continuous cultivation time is 30 days.

[0011] According to the method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, in step S2, the influent COD, NH4 + -N, PO4 3- -P concentration gradient is divided into 3 stages, and the concentration range of each stage is: the first stage COD 250 mg / L~350 mg / L, NH4 + -N 20 mg / L~30 mg / L, PO4 3- -P 4 mg / L~6mg / L; second stage COD 80 mg / L~120 mg / L, NH4 + -N 10 mg / L~20 mg / L, PO4 3- -P 1 mg / L~3mg / L; the third stage is prepared according to the COD, TN, and TP concentrations measured in the actual low-concentration wastewater, and each of the above stages is cultured for 10 days.

[0012] According to the method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, in step S3, the hydraulic retention time ranges from 8 hours to 24 hours, and within this range it can be increased in a gradient of 8 hours, 12 hours, 16 hours, and 24 hours, and each gradient is cultivated for 10 days to 15 days.

[0013] According to the method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, the process of treating ultra-low concentration wastewater adopts an SBR photoreactor, and the treatment conditions include: light intensity of 270 µmol·m -2 s -1 , hydraulic retention time 24 hours.

[0014] According to the method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, in step S2, the light source includes: sunlight, LED lamp or fluorescent lamp.

[0015] According to the method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater disclosed in the present invention, preferably, in step S2, the photosynthetically active irradiance is 90 to 270 µmol·m -2 s -1 The optimal light intensity is 270 µmol·m -2 s -1 .

[0016] The beneficial effects of the present invention include at least: 1. The present invention promotes the growth of filamentous algae in aerobic granular sludge by gradually reducing the influent concentration and gradually increasing the hydraulic retention time under suitable light conditions, forming a bacterial-algae symbiotic granular sludge with good stability and sedimentation, which can significantly improve the removal capacity of nitrogen and phosphorus in ultra-low concentration wastewater. 2. The bacterial-algae symbiotic particles of the present invention can avoid breaking and disintegrating in ultra-low concentration wastewater during the cultivation process, wherein the filamentous algae are not only the main body of nitrogen and phosphorus removal, but also play an important role in maintaining the stability and sedimentation of the particles in ultra-low concentration wastewater. 3. The nitrogen and phosphorus nutrients contained in the bacterial-algae symbiotic particles cultivated by the present invention have been fully absorbed and utilized by the filamentous algae, and the reverse release of nitrogen and phosphorus and secondary pollution will not occur. 4. The bacterial-algae symbiotic particles cultivated by the present invention have a certain ability to operate at low temperatures in winter (influent <10°C). 5. The acclimation and cultivation method of the present invention is simple to operate, stable and reliable, low cost, and does not require the addition of chemicals. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the surface morphology of bacteria-algae symbiotic granular sludge at different stages according to an embodiment of the present invention is shown.

[0018] Figure 2 A schematic diagram showing the appearance of bacteria-algae symbiotic granular sludge according to an embodiment of the present invention is shown.

[0019] Figure 3 A schematic diagram showing the change in TN removal rate in wastewater by bacteria-algae symbiotic granular sludge according to an embodiment of the present invention is shown.

[0020] Figure 4 A schematic diagram showing the change in TP removal rate in wastewater by bacteria-algae symbiotic granular sludge according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0021] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the limitations of the specific embodiments disclosed below.

[0022] According to an embodiment of the present invention, a method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater is disclosed, comprising: (1) inoculating mature aerobic granular sludge cultivated under ordinary domestic sewage conditions into a transparent photoreactor (reactor) to make the sludge concentration in the reactor 5000-10000 mg / L; (2) placing the reactor under light conditions, the operation mode of the reactor remains unchanged during the cultivation period, using artificially prepared low-concentration sewage as reactor influent, and cultivating continuously for 30 days, during which the sewage concentration is gradually reduced, during which the filamentous algae will grow rapidly and in large quantities, covering the surface of the granular sludge; (3) after 30 days, the reactor influent is replaced with ultra-low concentration wastewater to be treated, the light conditions remain unchanged, the hydraulic retention time of the sewage is gradually increased, and the cultivation is continued for 40-60 days, during which the filamentous algae that originally grew mainly on the surface gradually grow into the inside of the granules until they cover the entire granules. (4) The cultivated bacteria-algae symbiotic granules are used for treating ultra-low concentration wastewater.

[0023] According to the above embodiment, preferably, in step (1), the sewage used for aerobic granular sludge cultivation can be artificially prepared sewage or actual wastewater. Artificially prepared sewage preferably has a COD of 400-800 mg / L and NH4 + -N 40~60 mg / L, PO4 3- -P 5~15 mg / L.

[0024] According to the above embodiment, preferably, in step (1), the aerobic granular sludge culture method can be carried out in an SBR reactor, and the reactor is operated in a cycle of water inlet-standing-aeration-sedimentation-drainage. The hydraulic retention time is preferably 8 hours, that is, the operation cycle is 4 hours, and each cycle includes water inlet for 3 minutes, standing for 30 minutes, aeration for 199 minutes, sedimentation for 5 minutes, and drainage for 3 minutes. The inlet and outlet water are both controlled by a peristaltic pump, and the volume replacement rate is 50%. Aeration is provided by an aeration pump connected to the bottom of the reactor and is controlled to 3 L / min by a gas flow meter.

[0025] According to the above embodiment, preferably, in step (2), the light source can be sunlight, LED light, or fluorescent light, and the photosynthetically active irradiance is 90 to 270 µmol·m -2 s -1 The optimal light intensity is 270 µmol·m -2 s -1 .

[0026] According to the above embodiment, preferably, in step (2), the influent COD and NH4 are artificially prepared. + -N, PO4 3--P concentration gradient should be divided into three stages, and the concentration range of each stage is approximately: the first stage COD 250 ~ 350 mg / L, NH4 + -N 20~30 mg / L, PO4 3- -P 4~6 mg / L; second stage COD 80~120 mg / L, NH4 + -N 10~20 mg / L, PO4 3- -P 1~3 mg / L; the third stage is prepared according to the COD, TN, and TP concentrations measured in the actual low-concentration wastewater. Each of the above stages is cultured for 10 days.

[0027] According to the above embodiment, preferably, in step (3), the hydraulic retention time ranges from 8 to 24 hours, and within this range, the hydraulic retention time can be increased in a gradient of 8, 12, 16, and 24 hours, and each gradient is cultured for 10 to 15 days.

[0028] According to the above embodiment, preferably, in step (4), the ultra-low concentration wastewater treatment is preferably carried out using an SBR photoreactor, and the treatment conditions are as follows: -2 s -1 , the best treatment effect is achieved when the hydraulic retention time is 24 hours.

[0029] According to another embodiment of the present invention, an experimental process of sewage treatment effect of bacteria-algae symbiotic granular sludge is also disclosed. The specific experimental process is as follows:

[0030] Four groups of reactors (R1, R2, R3, and R4) were set up. The first group R1 cultured ordinary aerobic granular sludge (control group), and the second group R2, the third group R3, and the fourth group R4 all cultured bacteria-algae symbiotic granular sludge (experimental group). The reactor was a cylindrical transparent reactor with an inner diameter of 10 cm and a height of 100 cm. The four groups of reactors were placed in a culture cabinet. R1 was shielded from light, and R2, R3, and R4 were equipped with LED white light sources of different intensities. The four groups of reactors were connected to aeration pumps to provide aeration, and the aeration intensity was set to 3 L / min. The initial inoculum sludge of the reactor was the activated sludge collected from the secondary sedimentation tank of the sewage treatment plant. The particles were cultured for a total of 260 days, which was divided into 11 stages. The COD and NH4 + -N, PO4 3- -P, light intensity and hydraulic retention time (HRT) are shown in Table 1.

[0031]

[0032] In Table 1, light was applied starting from stage 2, and the influent water of each group of reactors was gradually reduced from stage 3 to stage 5. In stage 5, the influent COD and NH4 + -N, PO4 3--P was reduced to 20 mg / L, 10 mg / L, and 0.5 mg / L, respectively, to promote the rapid growth of filamentous algae. In stage 5, the algae-symbiotic granular sludge has been initially formed. From stage 6 to stage 9, the hydraulic retention time was gradually increased, and in stage 9, the hydraulic retention time of each group of reactors was increased to 24 hours, so that the algae-symbiotic granules were finally formed. In stage 10, the hydraulic retention time was changed to 16 hours, and an experimental comparison of the ultra-low concentration sewage treatment effect was carried out. Then in stage 11, the inlet temperature of each group of reactors was controlled to be below 10°C to explore the effect of low temperature on the algae-symbiotic granular sludge and test the low temperature resistance of the particles.

[0033] The reactors (R1, R2, R3, and R4) were operated in a sequential batch cycle, with each cycle consisting of water inlet, static, aeration, sedimentation, drainage, and idleness. The aeration rate during the aeration period was 3 L / min. After the reactors started operating, the granular sludge characteristics and N and P treatment effects were tested.

[0034] Figure 1 The surface morphology of the granules of the bacterial-algae symbiotic granular sludge in reactors R1-R4 under a microscope at different stages. Figures a-d (microscope images) show the morphology of aerobic granular sludge in R1-R4 on the 40th day, and Figures e-h (microscope images) show the morphology of sludge in R1-R4 on the 105th day. When the culture was carried out for 40 days, aerobic granular sludge was gradually formed in R1-R4. At 80 days, R2-R4 was subjected to light with increasing intensity. In stage 3 (89-99 days), with the decrease of influent nutrient concentration (COD 300 mg / L, N 25 mg / L, P 5 mg / L), the ordinary aerobic granules in R1 disintegrated, while the granules in R2-R4 did not disintegrate, but a large number of filamentous algae attached and grew, indicating that the large growth of filamentous algae enhanced the stability of the granules and prevented the granules from disintegrating and breaking when the influent concentration decreased. Among them, the ordinary aerobic granular sludge in R1 disintegrated and collapsed on the 90th day of system operation, and almost all the sludge in the system was lost. The granular morphology of R2~R4 remained intact. On the 260th day, the appearance of reactors R2~R4 was brown, indicating that the sludge maintained a certain concentration and the system was able to operate normally and stably.

[0035] Figure 2 This is the morphology of the bacteria-algae symbiotic granular sludge on day 260. The sludge was taken out as irregular green particles.

[0036] Figure 3The change of TN removal rate of particles in reactors R1 to R4 in wastewater. The data show that the TN removal rate in reactors R1 to R4 was maintained at about 50% from 55 to 80 days. At this time, no light was added to the reactors. The particles in the four groups of reactors were all aerobic granular sludge, and the removal rate of N and P was low. In the sludge acclimation stage and the comparative experiment stage, the removal rate of TN by the bacterial and algal symbiotic granular sludge in R2, R3, and R4 was higher than that of the aerobic granular sludge in R1. The reason is that on the one hand, the low concentration of nutrients inhibits the activity of heterotrophic microorganisms, resulting in the fragmentation and disintegration of granular sludge in R1, a significant decrease in sludge concentration, and a reduction in treatment effect. On the other hand, R2, R3, and R4 contain a large amount of filamentous algae that can absorb and utilize N and P in the water. In addition, the experiment found that when the HRT was 12 hours, the TN removal rate of reactors 3 and 4 exceeded 95%. When the HRT reached 24 hours, the TN removal rate of reactor 2 also gradually increased, eventually exceeding 90%. During the experimental stage, the HRT was reduced to 16 hours again, and the removal rate dropped again. The experiment also found that the inlet water temperature below 10°C would significantly reduce the TN removal rate of reactors 2 and 3. In summary, an HRT of 24 hours can make the light intensity at 90 µmol m -2 s -1 The above algae-bacteria symbiotic particles have a TN removal rate of more than 90%, which is the optimal HRT and the strongest light intensity (270 µmol m -2 s -1 )'s R4 reactor can effectively resist the low temperature limit below 10°C.

[0037] Figure 4The removal rate of TP in wastewater by particles in reactors R1 to R4 changes. It can be seen from the data that the TP removal rate is basically maintained at about 30% from 29 to 81 days. As the nutrient concentration of the influent decreases, the TP removal rate of R1 to R4 decreases rapidly on the 90th day. This is because the reduction of nutrients is not enough to maintain the metabolic activity of heterotrophic microorganisms. At this time, the aerobic granular sludge structure in R1 is destroyed, and it is unable to provide anaerobic conditions for polyphosphate bacteria. After that, due to the addition of light to the outside of R2, R3, and R4, filamentous algae began to gradually grow on the surface of the particles, wrapping the granular sludge, maintaining the compact structure of the particles on the one hand, and strengthening the autotrophic absorption of P on the other hand. The experiment found that when the HRT is 12 hours, the TP removal rate of R3 and R4 can exceed 80%, because the filamentous algae in the particles of the two groups of reactors need to absorb P for large-scale growth and reproduction. When the HRT reaches 24 hours, the TP removal rate of R2, R3, and R4 can exceed 80%. In the comparative experiment stage, the HRT was reduced to 16 h again, and the removal rates of R2, R3, and R4 decreased again. However, after a long period of cultivation, the TP removal rates of R3 and R4 were increased to more than 95% under the HRT of 16 h. In addition, the inlet water temperature below 10 °C significantly reduced the TP removal rates of R2, R3, and R4, but R3 and R4 could still achieve a removal rate level of more than 80%. In summary, HRT of 24 h can make the TP removal rate of 90 µmol m -2 s -1 The above bacteria-algae symbiotic particles have a TP removal rate of more than 80%, which is the optimal HRT. The light intensity is strong (180 µmol m -2 s -1 , 270 µmol m -2 s -1 )'s R3 and R4 can effectively resist the low temperature limit below 10℃.

[0038] In summary, the above embodiment of the present invention discloses a method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater: inoculating mature aerobic granular sludge into a transparent photoreactor, placing the reactor under illumination conditions, using artificially prepared wastewater as influent, and culturing continuously for 30 days, during which the influent nutrient concentration is gradually reduced, and after 30 days, bacteria-algae symbiotic granular sludge with filamentous algae attached and grown is initially formed. Then the influent is replaced with the ultra-low concentration wastewater to be treated, the hydraulic retention time is gradually increased, and the culture is continuously cultivated for 40 to 60 days to cultivate bacteria-algae symbiotic granular sludge with filamentous algae growing through it. The bacteria-algae symbiotic granular sludge cultivated by the present invention has a good ultra-low concentration wastewater nitrogen and phosphorus treatment effect, and has the advantages of high particle stability, no secondary pollution of nitrogen and phosphorus, low temperature resistance, simple operation, low cost, etc. It is an efficient, economical and environmentally friendly sewage treatment strategy with great application prospects and significance.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater, characterized in that: include: S1, inoculating the cultured mature aerobic granular sludge into a photoreactor, so that the sludge concentration in the photoreactor reaches 5000 mg / L to 10000 mg / L; S2, placing the photoreactor under light conditions, using low-concentration sewage as the photoreactor inlet, and continuously culturing until the filamentous algae wrap and cover the surface of the granular sludge; S3, replacing the influent of the photoreactor with ultra-low concentration wastewater to be treated, wherein the ultra-low concentration wastewater is wastewater with BOD5 < 50 mg / L, TN < 15 mg / L, and TP < 1 mg / L, maintaining the same illumination conditions, increasing the hydraulic retention time of the wastewater in a gradient manner, and continuously cultivating for 40 to 60 days, so that the filamentous algae on the surface of the granular sludge gradually grow into the inside of the granules until the entire granules are covered, thereby obtaining cultivated bacteria-algae symbiotic granules; In step S2, prepare the influent COD and NH4 + -N, PO4 3- -P concentration gradient is divided into 3 stages, and the concentration range of each stage is: the first stage COD 250 mg / L~350 mg / L, NH4 + -N 20 mg / L~30 mg / L, PO4 3- -P 4 mg / L~6mg / L; second stage COD 80 mg / L~120 mg / L, NH4 + -N 10 mg / L~20 mg / L, PO4 3- -P 1 mg / L~3mg / L; the third stage is prepared according to the COD, TN, and TP concentrations measured in the actual low-concentration wastewater, and each of the above stages is cultured for 10 days; In step S3, the hydraulic retention time ranges from 8 hours to 24 hours, and the time range is increased in a gradient of 8 hours, 12 hours, 16 hours, and 24 hours, and each gradient is cultured for 10 days to 15 days; In step S1, the sewage used for aerobic granular sludge cultivation is artificially prepared sewage or actual wastewater, wherein the artificially prepared sewage contains COD 400 mg / L to 800 mg / L, NH4 + -N 40 mg / L~60 mg / L, PO4 3- -P 5 mg / L~15 mg / L; In step S1, the aerobic granular sludge is cultured in an SBR reactor, and the culture conditions include: cyclic operation in the manner of water inlet-standing-aeration-sedimentation-drainage, with a hydraulic retention time of 8 hours, 6 cycles per day, and an operation cycle of 4 hours. In each cycle, water inlet is 3 minutes, standing is 30 minutes, aeration is 199 minutes, sedimentation is 5 minutes, and drainage is 3 minutes. The inlet and outlet water are controlled by a peristaltic pump, the volume replacement rate is 50%, and aeration is provided by an aeration pump connected to the bottom of the reactor and is controlled to 3L / min by a gas flow meter; The operation mode of the photoreactor in step S2 is consistent with the culture conditions during the aerobic granular sludge culture period, and the continuous culture time is 30 days.

2. The method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater according to claim 1, characterized in that: Also includes: The cultured bacteria-algae symbiotic particles are used for treating ultra-low concentration wastewater.

3. The method for acclimating and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater according to claim 2, characterized in that: The ultra-low concentration wastewater treatment process uses an SBR photoreactor, and the treatment conditions include: light intensity 270 µmol·m -2 s -1 , hydraulic retention time 24 hours.

4. The method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater according to any one of claims 1 to 3, characterized in that: In step S2, the light source includes: sunlight, LED lamp or fluorescent lamp.

5. The method for acclimatizing and cultivating bacteria-algae symbiotic granular sludge for treating ultra-low concentration wastewater according to any one of claims 1 to 3, characterized in that: In step S2, the photosynthetically active irradiance is 90 to 270 µmol·m -2 s -1 The optimal light intensity is 270 µmol·m -2 s -1 .

Images