Method for efficiently removing nitrogen and phosphorus by using microalgae membrane reactor with alternate temperature

Abstract

The invention discloses a temperature-alternating microalgae membrane reactor high-efficiency nitrogen and phosphorus removal method, which comprises a reactor main body, a ceramic membrane assembly is arranged in the reactor, and microalgae are inoculated in the reactor; the reactor main body is internally provided with a stirring device for uniformly suspending microalgae in the reactor; the reactor main body is made of a transparent material, and a light source is arranged outside the reactor main body; the top of the reactor main body is communicated with a water inlet pipeline for water feeding, and the liquid level is controlled by a liquid level controller; the top of the ceramic membrane component is communicated with a water outlet pipeline; a water outlet pump is arranged on the water outlet pipeline; a temperature control device is arranged on the outer side of the reactor and can monitor, regulate and control the temperature of liquid in the reactor. According to the method, the microalgae are subjected to suspension culture in the microalgae membrane reactor in a temperature alternating manner, the sensitivity of the microalgae to the environment temperature is fully utilized, the method has the advantages of low energy consumption, few byproducts and the like, and the synchronous nitrogen and phosphorus removal efficiency of the microalgae can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a method for efficiently removing nitrogen and phosphorus in a temperature-alternating microalgae membrane reactor. Background Art

[0002] In the process of extensive and long-term application, my country's traditional sewage treatment process has certain limitations, such as the contradiction between the sludge age of activated sludge microorganisms, the competition of denitrifying bacteria for organic carbon sources affecting the phosphorus removal effect of polyphosphate bacteria, and the energy consumption in the aeration stage. In addition, my country's urban domestic sewage and black and smelly water bodies have the characteristics of low COD, and the lack of carbon sources affects the denitrification and phosphorus removal effect of sewage. Therefore, it is still a general trend to seek a new denitrification and phosphorus removal process with low carbon source demand and effective control of water eutrophication.

[0003] Microalgae are widely distributed, diverse, and numerous in nature. They have a relatively short growth cycle and are highly adaptable to extreme environments. In addition, microalgae can remove nitrogen and phosphorus from sewage through autotrophic growth and metabolism under oligotrophic conditions, and are suitable for sewage with low carbon sources and high nitrogen and phosphorus. Using microalgae to treat sewage, on the one hand, microalgae can use the excessive nutrient-rich substances in sewage as a nutrient source, effectively reduce the nutrient content in sewage, and play a role in purifying sewage; on the other hand, the algae can be used as biomass energy and chemical industry raw materials to produce high value-added products.

[0004] Microalgae remove pollutants such as nitrogen and phosphorus mainly through their own assimilation, converting various pollutants into their intracellular substances. If the microalgae cells cannot be separated from the water body, when the microalgae die for various reasons, the nitrogen, phosphorus and other substances in the cells will be released back into the water body as the algae cells lyse. Therefore, it is very necessary to separate the microalgae from the water body. The membrane bioreactor (MBR) can well combine the bioreactor and membrane separation technology, separating the microalgae while using microalgae to remove nitrogen and phosphorus and ensuring the continuous operation of the process.

[0005] However, microalgae are organisms that are sensitive to temperature, and different microalgae have different performances in nitrogen removal and phosphorus removal at different temperatures. After a large number of experiments, it was found that the nitrogen removal efficiency of Chlorella at 30°C was significantly higher than that at other temperatures, and the phosphorus removal efficiency at 25°C was significantly higher than that at other temperatures. Therefore, the nitrogen and phosphorus removal efficiency of the constant temperature microalgae membrane reactor for nitrogen removal and phosphorus removal is not ideal due to the influence of ambient temperature. When it is used to treat sewage, it is difficult to obtain stable effluent water quality that meets the standards. Summary of the invention

[0006] In view of this, the present invention aims to propose a method for efficient denitrification and phosphorus removal in a microalgae membrane reactor with alternating temperatures. A temperature control device is used on the outside of the microalgae membrane reactor to monitor and regulate the temperature of the microalgae membrane reactor, and the temperature sensitivity of microalgae and their different performances in denitrification and phosphorus removal at different temperatures are utilized to effectively promote the synchronous and efficient denitrification and phosphorus removal in the microalgae membrane reactor.

[0007] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0008] A microalgae membrane reactor comprises a reactor body, wherein a ceramic membrane assembly is arranged inside the reactor and microalgae are inoculated; a stirring device is arranged inside the reactor body to evenly suspend the microalgae in the reactor; the reactor body is made of a transparent material (such as transparent organic glass), and a light source is arranged outside the reactor body; the top of the reactor body is connected to a water inlet pipeline, water is introduced by gravity or a water inlet pump, and the liquid level is controlled by a liquid level controller; the top of the ceramic membrane assembly is connected to a water outlet pipeline, and a water outlet pump is arranged on the water outlet pipeline;

[0009] The present invention sets a temperature control device outside the reactor body to monitor and control the temperature of the microalgae membrane reactor in real time, and utilizes the sensitivity of microalgae to temperature and its different performances in denitrification and phosphorus removal at different temperatures to effectively promote the simultaneous and efficient denitrification and phosphorus removal of the microalgae membrane reactor. During the operation of the reactor, sewage enters the reactor body from the top. Under the illumination of the light source outside the reactor body, the microalgae will perform photosynthesis and respiration, using the nitrogen and phosphorus in the sewage for its own growth and reproduction, removing pollutants such as nitrogen and phosphorus in the sewage, and the treated sewage passes through the ceramic membrane assembly and flows out of the reactor through the outlet pipe. Due to the metabolism of microalgae, the concentration of microalgae cells in the reactor will continue to increase, and a certain amount of microalgae will be attached to the surface of the hollow flat ceramic membrane. The hollow flat ceramic membrane is regularly cleaned, and the algae can be recycled and utilized as biomass energy and chemical industry raw materials to produce high value-added products, while maintaining the stable operation of the microalgae membrane reactor.

[0010] Therefore, the microalgae membrane reactor in the present invention carries out suspension culture of microalgae, which significantly improves the removal efficiency of nitrogen and phosphorus in sewage; and the hollow flat ceramic membrane helps to recover and utilize the microalgae cells that proliferate during the sewage treatment process, avoiding excessive algae cell concentration in the microalgae membrane reactor or excessive contamination of the ceramic membrane, which leads to a serious decrease in membrane flux and affects the denitrification and phosphorus removal efficiency of the microalgae membrane reactor, so that the reactor shows excellent removal effects on total nitrogen, nitrate nitrogen, ammonia nitrogen and total phosphorus in sewage.

[0011] Preferably, the membrane assembly is an alumina hollow flat ceramic membrane assembly with a membrane pore size of 0.1 to 1 μm and a membrane flux of 10 to 15 L / (m 2 h).

[0012] Preferably, the microalgae is Chlorella vulgaris; the inoculation amount of the microalgae is 10% to 20% of the reactor body.

[0013] The present invention further provides a method for using the microalgae membrane reactor:

[0014] (1) Preparation of algae seeds: The culture medium is placed in a container and sterilized in an autoclave at 121°C for 30 min. After cooling to room temperature, the container is further sterilized by irradiation with an ultraviolet lamp for 30 min. The microalgae culture is inoculated into the container under a sterile environment at 25°C for 12 to 15 days. The culture is manually shaken 2 to 3 times a day, and the algae liquid in the rapid proliferation period is taken as the algae seeds.

[0015] (2) Domestication of microalgae: Algae in the rapid growth stage were inoculated into the reactor; the concentration of the algae solution after inoculation was about 2×10 6 cells / ml, and add culture medium, domesticate the microalgae for 4-5 days under the conditions of 12h light and 12h dark in the light cycle, 12h temperature alternation cycle of 25℃ and 12h temperature, and 6h lag behind the light and dark change time node in the temperature change time node to complete the domestication;

[0016] (3) Starting the reactor: After the acclimation is completed, the culture medium in the microalgae membrane reactor is replaced with the sewage to be treated within 1 to 2 days. After the replacement is completed, the culture is continued for 4 to 5 days and then the outlet pump is started.

[0017] Preferably, the culture medium used in step (1) and step (2) is BG-11 culture medium.

[0018] Preferably, the illumination culture intensity in step (1) is 2000 Lux, and the illumination intensity in step (2) and step (2) is 3000 Lux.

[0019] Preferably, the speed of the stirring device inside the microalgae membrane reactor in step (2) and step (3) is 200 to 300 rpm;

[0020] Therefore, the present invention has the following beneficial effects:

[0021] 1. The microalgae membrane reactor in the present invention controls the temperature by alternating temperatures, utilizing the sensitivity of microalgae to temperature and their different performances in nitrogen and phosphorus removal at different temperatures, thereby effectively promoting the simultaneous and efficient nitrogen and phosphorus removal in the microalgae membrane reactor.

[0022] 2. The hollow flat ceramic membrane in the present invention helps to recycle and utilize the microalgae cells that proliferate during the sewage treatment process, avoiding excessive algae cell concentration in the microalgae membrane reactor or excessive pollution of the ceramic membrane, which leads to a serious decrease in membrane flux and affects the denitrification and phosphorus removal efficiency of the microalgae membrane reactor, thereby stabilizing the effluent water quality.

[0023] 3. In the present invention, the microalgae produce oxygen through photosynthesis, and no aeration is required. The entire microalgae membrane reactor has low energy consumption for nitrogen and phosphorus removal and can treat sewage with low carbon source and high nitrogen and phosphorus. The proliferated microalgae can also be used as biomass energy and chemical industry raw materials to produce high value-added products, which is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of a microalgae membrane reactor of the present invention;

[0025] Explanation of the reference numerals: 1. water inlet pool; 2. water inlet pipe; 3. liquid level controller; 4. reactor body; 5. hollow flat ceramic membrane assembly; 6. water outlet pipe; 7. peristaltic pump; 8. light source; 9. stirring device; 10. temperature control device. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Many modifications and changes to the embodiments of the present invention are obvious to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and design various embodiments with various modifications suitable for specific purposes.

[0027] Example 1

[0028] The structure of the microalgae membrane reactor used in the embodiment of the present invention is as follows: Figure 1 As shown, it includes a reactor body 4 made of organic glass with a thickness of 4 mm. The dimensions of the reactor body are: length × width × height = 0.24m × 0.24m × 0.5m, and the effective volume is 21.6L. A ceramic membrane component 5 is arranged in the reactor body and inoculated with microalgae, which is Chlorella vulgaris, and the inoculation amount of the microalgae is 10-20% of the effective volume in the reactor body; the membrane component adopts an alumina hollow flat ceramic membrane with a membrane pore size of 0.5μm and a total membrane area of ​​0.09m 2 , membrane flux 10L / (m 2·h). A stirring device 9 is provided inside the reactor body to make the microalgae in the reactor evenly suspended, with a rotation speed of 300rpm. A light source 8 is provided outside the reactor body, and the light source is provided by a surrounding LED light strip. There is a circle around the reactor body and a circle 0.3m above the reactor body. The light intensity is about 3000Lux, and the light cycle is 12h light and 12h dark; the temperature alternation cycle is 25℃12h, 30℃12h, and the temperature change time node lags behind the light and dark change time node by 6h. The sewage in the inlet pool 1 flows through the inlet pipe 2 and the liquid level controller 3 into the reactor body 4. Under the irradiation of the light source 8, the microalgae are denitrified and dephosphorized. After purification, they are separated from the microalgae through the alumina hollow flat ceramic membrane 5 and enter the outlet pipe 6 and the peristaltic pump 7 to obtain effluent with stable water quality.

[0029] The method of using the microalgae membrane reactor is as follows:

[0030] (1) Preparation of algae: BG-11 culture medium was placed in a triangular flask and sterilized in an autoclave at 121°C for 30 min. After cooling to room temperature, it was further sterilized by irradiation with ultraviolet light for 30 min. Chlorella (obtained from the Freshwater Algae Seed Bank of the Chinese Academy of Sciences) was inoculated into the triangular flask under a sterile environment. The culture temperature was 25°C and the light intensity was 2000 Lux. The culture was carried out for 12 days and manually shaken 2 to 3 times a day. The Chlorella algae liquid in the rapid proliferation period was taken as the algae seed;

[0031] (2) Domestication of microalgae: Chlorella species in the rapid proliferation period were inoculated into the reactor; the concentration of Chlorella after inoculation was about 2×10 6 cells / ml, and added BG-11 culture medium, domesticated Chlorella for 4-5 days under the conditions of light intensity of 3000 Lux, light cycle of 12h light, 12h dark, temperature alternation cycle of 25℃12h, 30℃12h, and temperature change time node lagging 6h behind light and dark change time node, to complete domestication;

[0032] (3) Starting the reactor: After the acclimation is completed, the culture medium in the microalgae membrane reactor is replaced with the sewage to be treated within 1 to 2 days. After the replacement is completed, the culture is continued for 4 to 5 days and then the outlet pump is started.

[0033] In this embodiment, the total nitrogen in the wastewater to be treated mainly exists in the form of nitrate nitrogen, and the concentration of nitrate nitrogen is about 75 mg / L, and the total phosphorus mainly exists in the form of phosphate, and the concentration is about 20 mg / L.

[0034] Example 2

[0035] The difference between Example 2 and Example 1 is that the total nitrogen in the sewage to be treated is mainly in the form of ammonia nitrogen, and the ammonia nitrogen concentration is about 75 mg / L. The rest is the same as in Example 1.

[0036] Example 3

[0037] The difference between Example 3 and Example 1 is that the total nitrogen in the sewage to be treated exists in the form of nitrate nitrogen:ammonia nitrogen=1:1, the nitrate nitrogen concentration and the ammonia nitrogen concentration are both 37.5 mg / L, the total nitrogen concentration is 75 mg / L, and the rest is the same as in Example 1.

[0038] Example 4

[0039] The difference between Example 4 and Example 1 is that in step (3), after the acclimation is completed, the culture in the microalgae membrane reactor is replaced with the wastewater to be treated within 1 to 2 hours. After the replacement is completed, the outlet pump is shut down, and water samples are taken at the temperature alternation node to explore the nitrogen and phosphorus removal efficiency in a typical temperature alternation cycle, which are divided into two groups: first 25°C and then 30°C, and first 30°C and then 25°C.

[0040] Comparative Example 1

[0041] In order to highlight the simultaneous denitrification and phosphorus removal effect of the described embodiment, under the same conditions as in Example 1, a microalgae membrane reactor was used to remove nitrogen and phosphorus from sewage at a constant temperature of 25°C. The method of using the microalgae membrane reactor is as follows:

[0042] (1) Preparation of algae: BG-11 culture medium was placed in a triangular flask and sterilized in an autoclave at 121°C for 30 min. After cooling to room temperature, it was further sterilized by irradiation with ultraviolet light for 30 min. Chlorella (obtained from the Freshwater Algae Seed Bank of the Chinese Academy of Sciences) was inoculated into the triangular flask under a sterile environment. The culture temperature was 25°C and the light intensity was 2000 Lux. The culture was carried out for 12 days and manually shaken 2 to 3 times a day. The Chlorella algae liquid in the rapid proliferation period was taken as the algae seed;

[0043] (2) Domestication of microalgae: Chlorella species in the rapid proliferation period were inoculated into the reactor; the concentration of Chlorella after inoculation was about 2×10 6 cells / ml, and added BG-11 medium, and domesticated Chlorella for 4-5 days under the conditions of light intensity of 3000 Lux, light cycle of 12 h light, 12 h dark, and constant temperature of 25°C to complete the domestication;

[0044] (3) Starting the reactor: After the acclimation is completed, the culture medium in the microalgae membrane reactor is replaced with the sewage to be treated within 1 to 2 days. After the replacement is completed, the culture is continued for 4 to 5 days and then the outlet pump is started.

[0045] Comparative Example 2

[0046] The difference between Comparative Example 2 and Comparative Example 1 is that the constant temperature of the microalgae membrane reactor in step (2) and step (3) is 30° C., and the rest is the same as in Comparative Example 1.

[0047] Comparative Example 3

[0048] The difference between Comparative Example 3 and Example 4 is that constant temperature is used for acclimation. After the acclimation is completed, the culture in the microalgae membrane reactor is replaced by the sewage to be treated within 1 to 2 hours. After the replacement is completed, the outlet pump is shut down, and water samples are taken at 12 hours and 24 hours to explore the efficiency of nitrogen and phosphorus removal in a typical cycle, which are divided into two groups at 25°C and 30°C.

[0049] Table 1 Example TN removal rate test results

[0050]

[0051] Table 2 Example TP removal rate test results

[0052]

[0053] Table 3 Comparative Example TN removal rate test results

[0054]

[0055] Table 4 Comparative Example TP removal rate test results

[0056]

[0057] Table 5 Nitrogen removal and phosphorus removal efficiency in a typical temperature alternation cycle

[0058] Example 4 0h-12h 12h-24h 24h 0h-12h 12h-24h 24h temperature 25℃ 30℃ 30℃ 25℃ TN removal rate (%) 27.3 36.4 63.7 37.1 26.9 64.0 TP removal rate (%) 43.3 33.8 77.1 32.9 42.3 75.2

[0059] Table 6 Nitrogen removal and phosphorus removal efficiency in a typical cycle at constant temperature

[0060]

[0061] It can be seen from Table 1 and Table 2 that when the microalgae membrane reactor of the present invention is used to continuously and dynamically treat low-carbon source, high-nitrogen and high-phosphorus wastewater in Examples 1 to 3, the reactor can treat nitrate nitrogen (NO 3 ——N), ammonia nitrogen (NH 4 +—N), total nitrogen (TN) and total phosphorus (TP) all showed excellent removal efficiency.

[0062] It can be seen from Tables 5 and 6 that in Example 4, within a typical temperature alternation, the removal rate of TP by the microalgae membrane reactor at 25°C is significantly higher than that at 30°C; the removal rate of TN at 30°C is significantly higher than that at 25°C. After temperature alternation, within a typical cycle, the microalgae membrane reactor exhibits high efficiency in simultaneous nitrogen and phosphorus removal.

[0063] It can be seen from Tables 3 and 4 that the removal rate of nitrate nitrogen by the microalgae membrane reactor in Comparative Example 1 is significantly lower than that in Example 1; the removal rate of total phosphorus by the microalgae membrane reactor in Comparative Example 2 is significantly lower than that in Example 2. Chlorella has different performances on the removal rates of nitrogen and phosphorus in sewage at different ambient temperatures, and Example 1 improves the denitrification and phosphorus removal efficiency of the microalgae membrane reactor by temperature alternation to obtain stable effluent water quality.

[0064] In Examples 1 to 3 and Comparative Examples 1 to 2, Chlorella will perform photosynthesis and respiration under the illumination of a light source outside the reactor body, and utilize nitrogen and phosphorus in the sewage for its own growth and reproduction. At the same time, a certain amount of Chlorella will adhere to the surface of the hollow flat ceramic membrane. The hollow flat ceramic membrane is cleaned every 15 days, and the algae can be recycled and utilized as biomass energy and chemical industry raw materials to produce high value-added products, while maintaining stable operation of the microalgae membrane reactor.

[0065] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for efficient nitrogen and phosphorus removal in a temperature alternating microalgae membrane reactor, characterized in that: The microalgae membrane reactor comprises a reactor body, a ceramic membrane assembly is installed in the reactor body, and microalgae are inoculated, and a stirring device is provided inside the reactor to make the microalgae in the reactor evenly suspended, and the rotation speed is 200-300rpm; The reactor is made of transparent material, and an LED lighting device is installed outside the reactor body, with a light intensity of 2000-3000 Lux and a light cycle of 12 hours of light and 12 hours of darkness, simulating the natural living habits of microalgae; The top of the reactor is connected to the water inlet pipeline, and water is fed in by gravity or a water inlet pump, the liquid level is controlled by a liquid level controller, and the water outflow is controlled by a peristaltic pump; A temperature control device is provided on the outside of the reactor to monitor and regulate the liquid temperature in the reactor in real time. The temperature alternation cycle is 25°C for 12 hours and 30°C for 12 hours. The temperature change time node lags behind the light and dark change time node by 6 hours.

2. The method according to claim 1, characterized in that The microalgae is Chlorella vulgaris; the inoculation amount of the microalgae is 10% to 20% of the effective volume of the reactor body.

3. The method according to claim 1, characterized in that The ceramic membrane assembly is an alumina hollow flat ceramic membrane assembly with a membrane pore size of 0.1 to 1 μm and a membrane flux of 10 to 15 L / (m 2 h).

4. The method according to claim 1, characterized in that: The microalgae membrane reactor is used to simultaneously and efficiently remove nitrogen and phosphorus from sewage, which specifically includes the following steps: (1) Preparation of algae seeds: The culture medium is placed in a container and sterilized in an autoclave at 121°C for 30 min. After cooling to room temperature, it is further sterilized by irradiation with an ultraviolet lamp for 30 min. The microalgae culture is inoculated into the above container under a sterile environment at a temperature of 25°C and a light intensity of 2000 Lux. The culture is cultured for 12 to 15 days, and the culture is manually shaken 2 to 3 times a day. The algae liquid in the rapid proliferation period is taken as the algae seeds; (2) Domestication of microalgae: Algae in the rapid proliferation stage were inoculated into the reactor; the concentration of the algae solution after inoculation was 2×10 6 cells / ml, and add culture medium, domesticate the microalgae for 4-5 days under the conditions of light intensity of 3000 Lux, light cycle of 12h light, 12h dark, temperature alternation cycle of 25℃12h, 30℃12h, and temperature change time node lagging 6h behind light and dark change time node, to complete domestication; (3) Starting the reactor: After the acclimation is completed, the culture medium in the microalgae membrane reactor is replaced with the sewage to be treated within 1 to 2 days. After the replacement is completed, the culture is continued for 4 to 5 days and then the outlet pump is started.

5. The method according to claim 4, characterized in that The culture medium used in step (1) and step (2) is BG-11 culture medium.

6. The method according to claim 4, characterized in that The total nitrogen concentration of the wastewater to be treated is 70-80 mg / L, the total phosphorus concentration is 15-25 mg / L, and the trace elements are the same as those contained in BG-11.

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