A forward osmosis reduced concentration coupled microalgae carbon fixation complementary hybrid system and method

Abstract

The application discloses a forward osmosis reduction concentration coupled microalgae carbon fixation complementary fusion system and method, and relates to the field of water treatment and carbon fixation. The system comprises a forward osmosis device and a microalgae carbon fixation device. The forward osmosis device comprises a forward osmosis membrane assembly and a feed liquid side and a driving liquid side separated by the forward osmosis membrane assembly. The microalgae carbon fixation device comprises a microalgae photobioreactor. Salt-resistant microalgae are used in the microalgae photobioreactor, and a magnesium chloride solution or a sodium chloride solution is used as microalgae growth liquid. Saline industrial wastewater enters the feed liquid side and, under the action of osmotic pressure, enters the driving liquid side through the forward osmosis membrane assembly to obtain water production. The growth liquid with increased concentration after the growth of microalgae in the microalgae photobioreactor enters the driving liquid side as driving liquid, and the water production dilutes the driving liquid and then returns to be used as microalgae growth liquid again. The application realizes energy saving, water saving and carbon fixation of microalgae while completing raw water treatment process, improves the utilization rate of wastewater resources, and further improves the CO2 absorption rate during microalgae carbon fixation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of water treatment and microalgae carbon fixation, and particularly relates to a forward osmosis concentration reduction coupled microalgae carbon fixation complementary fusion system and method. BACKGROUND

[0002] In the microalgae carbon fixation technology, a large amount of microalgae needs to be cultured rapidly. In the process of culturing microalgae, a large amount of water is consumed, and the cost is high. If industrial wastewater is used, the cost can be reduced to a certain extent, but microalgae cultivation has certain requirements for the growth environment and nutrients, and industrial wastewater often contains a large amount of toxic and harmful substances, so it is difficult for microalgae to grow in large quantities. How to use suitable process wastewater through suitable treatment to provide water for microalgae cultivation is a technical problem to be solved.

[0003] Moreover, the existing microalgae carbon fixation technology directly uses CO2 by microalgae, and the absorption rate of CO2 is low. SUMMARY

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present application is to provide a forward osmosis concentration reduction coupled microalgae carbon fixation complementary fusion system and method, which uses salt-containing industrial wastewater as raw water, completes the raw water treatment process, realizes energy-saving and water-saving microalgae carbon fixation, improves the utilization rate of wastewater resources, and further improves the absorption rate of CO2 during microalgae carbon fixation, solving the problem of difficult high-efficiency energy-saving and water-saving microalgae carbon fixation in the prior art.

[0005] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0006] A forward osmosis concentration reduction coupled microalgae carbon fixation complementary fusion system, comprising a forward osmosis device and a microalgae carbon fixation device; the forward osmosis device comprises a forward osmosis membrane assembly and a feed liquid side and a driving liquid side separated therefrom; the microalgae carbon fixation device comprises a microalgae photobioreactor, and salt-tolerant microalgae are used in the microalgae photobioreactor, and a magnesium chloride solution or a sodium chloride solution with a concentration of 1-2 mol / L is used as microalgae growth liquid;

[0007] The feed liquid side and a raw water pool loaded with salt-containing industrial wastewater form a circulating loop, the salt-containing industrial wastewater enters the feed liquid side, and under the action of osmotic pressure, the salt-containing industrial wastewater enters the driving liquid side through the forward osmosis membrane assembly to obtain water production, and the concentrated liquid returns to the raw water pool;

[0008] The driving liquid side and the microalgae photobioreactor form a circulating loop, the growth liquid with increased concentration after the growth of microalgae in the microalgae photobioreactor enters the driving liquid side as driving liquid, and the water production dilutes the driving liquid and returns to the microalgae photobioreactor to be used as microalgae growth liquid again.

[0009] In one embodiment, the salinity of the salt-containing industrial wastewater is between 1.0% and 3.0% by weight; after the microalgae grow, the concentration of the growth liquid increases, and the growth liquid can generate an osmotic pressure of 1.5-5 MPa in the forward osmosis device as the driving liquid; the permeate flux of the forward osmosis device is between 5-20 L / m -2 h -1 and the recovery rate is 50-60%.

[0010] In one embodiment, the forward osmosis membrane assembly is provided with symmetrical cavities on both sides as the feed liquid side and the driving liquid side, and the salt-containing industrial wastewater and the driving liquid are operated in cross flow, with a flow rate ranging from 9-20 cm / s.

[0011] In one embodiment, the top of the feed liquid side is the raw liquid inlet, and the bottom is the concentrated liquid outlet; the top of the driving liquid side is the dilute liquid outlet, and the bottom is the driving liquid inlet.

[0012] In one embodiment, the microalgae carbon fixation device further comprises an electronic scale, an aeration device, and a parallel light source; the electronic scale records the weight change of the microalgae photobioreactor in real time to measure the change of water flux; the aeration device is placed in the microalgae photobioreactor, and the parallel light source provides light energy for the microalgae photobioreactor, additionally supplies carbon source and light source for the growth of microalgae, and realizes energy-saving and water-saving microalgae carbon fixation.

[0013] In one embodiment, the microalgae photobioreactor is connected with a CO2 capture and absorbent regeneration device, the CO2 capture and absorbent regeneration device comprises an absorption tower loaded with a solution of alkaline absorbent, the alkaline absorbent is Na2CO3, the absorption tower is connected with a gas cylinder loaded with CO2 or CO2 mixed gas, the alkaline absorbent is converted into NaHCO3 after CO2 is introduced, and the NaHCO3 is provided to the microalgae photobioreactor as a carbon source required for the growth of microalgae; during the growth of microalgae, as the pH of the microalgae growth liquid increases, NaHCO3 is converted into Na2CO3 to realize the reduction and regeneration of the alkaline absorbent. Part of the microalgae growth liquid containing Na2CO3 is filtered through a filter and returned to the absorption tower; or the microalgae growth liquid containing Na2CO3 is first sent to the driving liquid side as the driving liquid, and then discharged to the absorption tower again after flowing back to the microalgae photobioreactor.

[0014] The application also provides a method for simultaneously treating salt-containing industrial wastewater and cultivating microalgae, which is realized by using the forward osmosis concentration coupling microalgae carbon fixation complementary fusion system, and comprises the following steps:

[0015] Step one, after the salt-tolerant microalgae are cultivated, the microalgae are inoculated into the microalgae photobioreactor, and the system is started after the microalgae grow into the stable phase;

[0016] Step two, the salt-containing industrial wastewater in the raw water pool is introduced into the feed liquid side to intercept pollutants and achieve concentration reduction;

[0017] Step three, the microalgae growth liquid in the microalgae photobioreactor is introduced into the driving liquid side as driving liquid to drive water molecules to pass through the forward osmosis membrane assembly into the driving liquid side by osmotic pressure;

[0018] Step four, the introduction of the first salt-containing industrial wastewater and the introduction of the first driving liquid are one cycle, after each cycle, deionized water is introduced into the feed liquid side to clean the forward osmosis membrane assembly, then the sodium chloride solution is backwashed in the feed liquid side and the deionized water is backwashed in the driving liquid side at the same flow rate, and finally the deionized water is introduced into the feed liquid side and the driving liquid side again to prepare for the next cycle.

[0019] In one embodiment, the weight change of the microalgae photobioreactor is recorded in real time by an electronic scale to measure the change of water flux; a conductivity meter is introduced into the raw water pool and the microalgae photobioreactor to measure the change of conductivity and solute concentration to calculate the osmotic pressure difference in the forward osmosis device.

[0020] In one embodiment, a CO2 capture and absorbent regeneration device is used to provide carbon source for the microalgae photobioreactor, the CO2 capture and absorbent regeneration device includes an absorption tower loaded with a solution of alkaline absorbent, the alkaline absorbent is Na2CO3, the absorption tower is connected to a gas cylinder loaded with CO2 or CO2 mixed gas, the alkaline absorbent is converted into NaHCO3 after being introduced into CO2, and is provided to the microalgae photobioreactor as a carbon source required for microalgae growth, during the growth of microalgae, with the increase of pH of the microalgae growth liquid, NaHCO3 is converted into Na2CO3 to realize the reduction and regeneration of the alkaline absorbent, a part of the microalgae growth liquid containing Na2CO3 is filtered through a filter and is returned to the absorption tower; or the microalgae growth liquid containing Na2CO3 is first sent to the driving liquid side as driving liquid, and then discharged to the absorption tower after returning to the microalgae photobioreactor; the gas cylinder is connected to a gas flow meter to control the CO2 content entering the absorption tower to maintain the stability of the NaHCO3 concentration in the absorption tower (10), and to control the NaHCO3 concentration sent into the microalgae photobioreactor (5) to be 0.1M±0.01M.

[0021] In one embodiment, the salt-tolerant microalgae selected by the present application can be Dunaliella salina, Spirulina, Chlorella, Haematococcus pluvialis, Dunaliella salina, Crypthecodinium cohnii, Nannochloropsis, etc.

[0022] In one embodiment, the reactor operation is stopped when the forward osmosis membrane water flux decreases to 20% of the maximum water flux, the concentrated solution is discharged from the system for subsequent treatment, the raw water tank is filled with the same amount of salt-containing industrial wastewater as in the previous cycle for treatment, and is used in the next cycle; when the microalgae biomass concentration in the microalgae photobioreactor reaches 1000-2000 mgCOD / L, 70-90% of the microalgae is removed, and fresh microalgae growth liquid is added to the microalgae photobioreactor to the initial volume; after one cycle, the forward osmosis membrane module is cleaned, and the next cycle is started after the initial maximum water flux is restored.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] (1) Culturing microalgae on the side of the forward osmosis driving liquid can increase the residence time of microalgae, increase the biomass concentration of microalgae, facilitate efficient separation of algal biomass and solids, reduce problems such as membrane fouling and clogging, increase the service life and efficiency of the membrane, and reduce the cost of membrane cleaning and replacement. The growth of microalgae on the driving liquid side does not affect the osmotic pressure gradient, ensuring a certain water flux of the forward osmosis membrane.

[0025] (2) The present application selects salt-tolerant microalgae to adapt to the high-salt environment of the driving liquid, and the relatively high salinity range of 50-150‰ is beneficial to the growth of salt-tolerant microalgae cells. Under high salt, the proportion of carotenes and the content of glycerol increase, the content of soluble proteins and starch in the cells is high, and the cells grow faster, with an average of 1.8 kg of CO2 fixed per production of 1 kg of microalgae biomass. The growth and metabolism process of microalgae requires a large amount of water, and the water consumption per ton of dry algae is 100-350 tons. The present system provides water for microalgae growth through a forward osmosis device, reducing water consumption by 30%, achieving a water consumption of less than 140 kg per kilogram of CO2 fixed, and realizing energy-saving, water-saving and carbon-fixing of microalgae.

[0026] (3) When bicarbonate is used as a carbon source in microalgae cultivation, CO2 is absorbed by an alkaline agent to convert it into an aqueous carbonate solution, which not only increases the absorption rate of CO2 and reduces the emission loss of CO2 into the atmosphere, but also reduces the costs of gaseous CO2 compression, transportation, storage, aeration, and other problems such as aeration shear force and light scattering. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The present application is a forward osmosis reduction and concentration coupled microalgae carbon fixation complementary fusion system.

[0028] Figure 2 The present application is a CO2 capture and absorbent regeneration device.

[0029] In the figure: 1-raw water pool; 2-feed liquid side; 3-driving liquid side; 4-positively osmosis membrane assembly; 5-microalgae photobioreactor; 6-electronic scale; 7-aeration device; 8-parallel light source; 9-peristaltic pump. 10-absorption tower; 11-gas cylinder; 12-basic absorbent; 5-microalgae photobioreactor; 13-filter. DETAILED DESCRIPTION

[0030] In order to make the person skilled in the art better understand the purpose, technical scheme and beneficial effects of the present application, the present application will be further described in detail below in combination with specific examples. The specific examples described are only for further explanation and illustration of the present application, and are not used to limit the present application. Based on the examples in the present application, all other examples obtained by the person skilled in the art without making creative labor are within the scope of protection of the present application.

[0031] As described before, it is difficult for microalgae in the prior art to efficiently save energy, save water and fix carbon, therefore, the present application provides a positively osmosis reduction concentration coupled microalgae carbon fixation complementary fusion system, which adopts salt-tolerant microalgae, and provides water source for microalgae growth by positively osmosis technology with salt-containing industrial wastewater. Moreover, the present application can increase the residence time of microalgae and increase the biomass concentration of microalgae by culturing microalgae on the driving liquid side of positively osmosis. In the further scheme of the present application, a better CO2 capture method is also provided.

[0032] Firstly referring to Figure 1 As shown in the figure, the positively osmosis reduction concentration coupled microalgae carbon fixation complementary fusion system of the present application comprises a positively osmosis device and a microalgae carbon fixation device. The positively osmosis device comprises a cavity with a built-in positively osmosis membrane assembly 4, which is divided into left and right two cavities by the positively osmosis membrane assembly 4, which are respectively the feed liquid side 2 and the driving liquid side 3. The microalgae carbon fixation device mainly comprises a microalgae photobioreactor 5, in the present application, salt-tolerant microalgae is adopted as the cultivation growth object, the microalgae is placed into the microalgae photobioreactor 5 after cultivation, and the microalgae photobioreactor 5 uses magnesium chloride solution or sodium chloride solution with a concentration of 1-2 mol / L as microalgae growth liquid.

[0033] The feed liquid side 2 is connected to the salt-containing industrial wastewater, specifically, the salt-containing industrial wastewater is loaded in the raw water pool 1, and the feed liquid side 2 and the raw water pool 1 form a circulating loop. That is, the salt-containing industrial wastewater enters the feed liquid side 2 from the raw liquid inlet, and under the action of osmotic pressure, it enters the driving liquid side 3 through the positively osmosis membrane assembly 4 to obtain water, the positively osmosis membrane assembly 4 can intercept most of the pollutants in the wastewater, reduce the concentration of the wastewater, and reduce the burden of the subsequent treatment facilities. At the same time, water molecules are transferred to the driving liquid side 3 under the osmotic pressure, providing a large amount of water source for the growth of microalgae, realizing the utilization of wastewater resources, and the concentrated liquid obtained is returned to the raw water pool 1 from the bottom concentrated liquid outlet.

[0034] The driving liquid side 3 forms a circulation loop with the microalgae photobioreactor 5, specifically, after the microalgae grow in the microalgae photobioreactor 5, the concentration of the growth liquid increases, and the growth liquid is directly introduced into the driving liquid side 3 as the driving liquid, and cooperates with the salt-containing industrial wastewater to provide the osmotic pressure. On the driving liquid side 3, the obtained product water dilutes the driving liquid, and then flows back to the microalgae photobioreactor 5, and again serves as the microalgae growth liquid, and provides a large amount of water source for the growth of the microalgae.

[0035] According to the above system, the application concentrates the wastewater by using the forward osmosis technology, generates a large amount of water resources that can be used by the microalgae, improves the utilization rate of the wastewater resources, and realizes the energy-saving and water-saving goals. Meanwhile, high-quality salt-tolerant microalgae that can adapt to high salinity and high CO2 concentration are selected, and typical examples are Dunaliella salina, Spirulina, Chlorella, Haematococcus pluvialis, Dunaliella salina, Crypthecodinium cohnii, and Nannochloropsis, which can realize the microalgae proliferation in a large amount and rapidly under suitable conditions, rapidly and massively cultivate the microalgae, greatly improve the carbon fixation efficiency of the microalgae, realize high-efficiency carbon fixation, and reduce the greenhouse effect caused by CO2. Therefore, the application can generate greater economic benefits, and has a wide application prospect.

[0036] The forward osmosis technology is a technology that uses the osmotic pressure difference between the two sides of the forward osmosis membrane as the driving force, so that water molecules spontaneously enter the draw solution from the raw material liquid, and the pollutants are intercepted on one side of the membrane, so as to separate the pollutants and water. The application uses the forward osmosis technology to treat the salt-containing industrial wastewater, and can concentrate by reduction, and reduce the pressure of the subsequent treatment facilities.

[0037] In the embodiment of the application, the salt-containing industrial wastewater mainly refers to wastewater containing a small amount of salt generated in some industrial production processes, such as food processing, textile printing and dyeing, papermaking and the like, and the salt content is between 1.0% and 3.0%. The driving liquid is a magnesium chloride solution or a sodium chloride solution containing microalgae suspensions, the concentration of the magnesium chloride or the sodium chloride is 1-2 mol / L, and the generated osmotic pressure is between 1.5-5 MPa. The residence time of the microalgae in the microalgae photobioreactor 5 is generally 15-30 h, and after the microalgae grow, the growth liquid generally contains algal suspensions with a biomass concentration of 400-700 mg COD / L, and these suspensions will not affect the function of the driving liquid.

[0038] In the embodiment of the application, the forward osmosis membrane assembly 4 needs to operate under suitable conditions, for example, pH 2-12, temperature 20-25℃. The permeate water flux of the forward osmosis device is 5-20 L / m -2 h -1Between these parameters, the recovery rate can reach 50-60%. The forward osmosis membrane module can operate in two modes: with the active layer facing the draw solution or with the active layer facing the feed solution. In practical applications, due to scaling and clogging, the forward osmosis membrane needs to be cleaned when the water flux decreases significantly to restore the initial water flux. In this invention, the entire experimental cycle is controlled by the membrane flux; the reaction process is stopped when the membrane flux decreases significantly.

[0039] In this embodiment of the invention, the feed liquid side 2 and the driving liquid side 3 are symmetrical cavities disposed on both sides of the forward osmosis membrane assembly 4, made of plexiglass, with each cavity having a volume of 10-20 cm³. 2 Between these two systems, saline industrial wastewater and the driving fluid flow in a cross-flow configuration with a velocity range of 9-20 cm / s. In practical applications, to prevent concentration polarization, the cross-flow velocity can be increased to reduce eddies.

[0040] In this embodiment of the invention, the raw liquid inlet of the feed liquid side 2 is located at the top of the chamber, and the concentrated liquid outlet is located at the bottom of the chamber. The diluent outlet of the driving liquid side 3 is located at the top of its chamber, and the driving liquid inlet is located at the bottom of the chamber. To achieve the above two-loop circulation, a peristaltic pump 9 is installed in each loop. The raw water tank 1 is connected to the raw liquid inlet of the feed liquid side 2 via a pipe, and a peristaltic pump 9 is installed on this pipe. The saline industrial wastewater in the raw water tank 1 enters the feed liquid side 2 as the wastewater raw liquid, and the concentrated wastewater from the feed liquid side 2 then enters the raw water tank 1. The raw water tank 1 can be made of plexiglass and can be cylindrical or any other shape. The microalgae photobioreactor 5 is connected to the driving liquid inlet of the driving liquid side 3 via a pipe, and a peristaltic pump 9 is installed on this pipe to transfer the increased concentration of the growth liquid in the microalgae photobioreactor 5 to the driving liquid side 3. A flow meter can be installed to monitor the liquid flow rate.

[0041] In this embodiment of the invention, the main body of the microalgae photobioreactor 5 is a cylindrical organic glass structure. The microalgae carbon fixation device also includes an electronic scale 6, an aeration device 7, and a parallel light source 8. The microalgae photobioreactor 5 is placed on the electronic scale 6, which records the weight change of the microalgae photobioreactor 5 in real time to measure the water flux change. The aeration device 7 is placed inside the microalgae photobioreactor 5. The parallel light source 8 provides light energy to the microalgae photobioreactor 5, additionally supplementing the carbon source and light source for microalgae growth, achieving energy-saving and water-saving microalgae carbon fixation. After one or several experimental cycles, the content of suspended algae in the growth solution is monitored. If it is too high, it indicates that the growth has achieved the desired effect, and excess microalgae can be removed. The remaining growth solution can be recycled, used for seawater aquaculture, or directly discharged into marine conservation and coastal areas.

[0042] In the embodiment of the present application, in order to further improve the CO2 capture capacity, improve the growth rate and carbon fixation efficiency of microalgae, regulate and optimize the culture conditions of microalgae, introduce an alkaline absorbent, and at the same time design the regeneration of the absorbent, thereby providing a CO2 capture and absorbent regeneration device, connecting the device with the microalgae photobioreactor 5 and providing the absorbent to it. Specifically, as shown in Figure 2 The device includes an absorption tower 10, a gas cylinder 11 and a filter 13. The absorption tower 10 is loaded with a solution of alkaline absorbent 12, the alkaline absorbent 12 of the present application is Na2CO3, the gas cylinder 11 is loaded with CO2 or CO2-rich mixed gas, the gas cylinder 11 is connected with the absorption tower 10, CO2 or CO2-rich mixed gas is introduced into the absorption tower 10, according to the principle of microalgae carbon fixation, Na2CO3 is converted into NaHCO3 which is relatively stable in solution after CO2 is introduced, after a proper time, the main component in the solution is NaHCO3, and the obtained NaHCO3 is provided to the microalgae photobioreactor 5 as a carbon source required for the growth of microalgae, which is finally converted into organic matter in cells through photosynthesis. At the same time, during the growth of microalgae, the metabolism of algal cells causes the pH of the microalgae growth liquid to rise continuously, and NaHCO3 is converted into Na2CO3, after a proper time, the main component in the solution in the microalgae photobioreactor 5 is changed to Na2CO3 again, thereby realizing the reduction and regeneration of the alkaline absorbent 12, a part of the microalgae growth liquid containing Na2CO3 is filtered through the filter and returned to the absorption tower; or the microalgae growth liquid containing Na2CO3 is first sent to the driving liquid side as the driving liquid, and then discharged to the absorption tower after returning to the microalgae photobioreactor, thereby realizing the cyclic regeneration of the absorbent. The gas flow meter can be connected to the gas cylinder 11 to control the CO2 content entering the absorption tower 10, so as to maintain the stability of the NaHCO3 concentration in the absorption tower 10. Preferably, the concentration of 0.1M NaHCO3 is the most beneficial to the carbon fixation growth of microalgae, and the efficient reduction and regeneration of the carbonate absorbent can be realized. Moreover, the quality of the absorbent needs to be measured regularly, and new absorbent needs to be replaced when necessary.

[0043] By using the above-mentioned forward osmosis reduction concentration coupled microalgae carbon fixation complementary fusion system, the present application can realize simultaneous large-scale treatment and utilization of salt-containing industrial wastewater and rapid cultivation of microalgae, and realize energy-saving, water-saving and carbon fixation of microalgae, which mainly includes the following steps:

[0044] Step one, obtain salt-tolerant microalgae resistant to high salinity and high concentration of CO2, inoculate in the microalgae photobioreactor 5 after culture under suitable conditions, and start the system after the microalgae grow into the stable period.

[0045] Step two, introduce the salt-containing industrial wastewater in the raw water pool 1 into the feed liquid side 2, trap most of the pollutants in the wastewater, realize wastewater reduction concentration, and reduce the burden of the subsequent treatment process.

[0046] Step three, the microalgae growth liquid in the microalgae photobioreactor 5 is used as the driving liquid to be introduced into the driving liquid side 3, to drive water molecules to pass through the forward osmosis membrane assembly 4 into the driving liquid side 3 by osmotic pressure, and to additionally supplement carbon source and light source for the microalgae growth, so as to realize the energy-saving and water-saving microalgae carbon fixation.

[0047] Step four, the once-salt-containing industrial wastewater and the once-driving liquid are introduced for one cycle, after each cycle, deionized water is introduced into the feed liquid side 2 to clean the forward osmosis membrane assembly 4, then the sodium chloride solution is used to backwash the feed liquid side 2 and the deionized water is used to backwash the driving liquid side 3 at the same flow rate, finally the deionized water is introduced into the feed liquid side 2 and the driving liquid side 3 again, to prepare for the next cycle.

[0048] During the process, the weight change of the microalgae photobioreactor 5 can be recorded in real time by the electronic scale 6, to measure the water flux change; and the conductivity instrument can be introduced into the raw water pool 1 and the microalgae photobioreactor 5, to measure the conductivity and solute concentration change, to calculate the osmotic pressure difference in the forward osmosis device. A certain amount of diluted driving liquid can be taken to measure the biomass, absorbance and TOC of the algal liquid, to judge the microalgae growth and carbon fixation.

[0049] With the passage of time, when the forward osmosis membrane water flux decreases to 20% of the maximum water flux, the reactor operation is stopped, the concentrated liquid is discharged for subsequent treatment, the same amount of salt-containing industrial wastewater to be treated as in the previous cycle is loaded into the raw water pool 1 again, and is used in the next cycle; when the microalgae biomass concentration in the microalgae photobioreactor reaches 1000-2000 mgCOD / L, 70-90% of the microalgae is taken out, and fresh microalgae growth liquid is added into the microalgae photobioreactor 5 to the initial volume; after one cycle, the forward osmosis membrane assembly 4 is cleaned, and the next cycle is carried out after the initial maximum water flux is restored.

[0050] Through the above steps, the present application realizes the complementary fusion of the water reduction in the nutrient solution in the carbon fixation microalgae culture process and the water increase in the driving liquid in the forward osmosis process with the low-concentration salt-containing industrial wastewater. The efficient utilization of industrial wastewater resources is realized, and has a broad application prospect.

[0051] The following is a specific embodiment of the present application.

[0052] 2L of low-concentration salt-containing industrial wastewater with a COD concentration of 3500 mg / L, TN of 1000 mg / L and NaCl of 10 g / L is used as raw material liquid, and is placed in the raw water pool 1. The selected algal species is Dunaliella salina, and the algal culture is mixed with 1L of fresh f / 2 medium in a 2L conical flask, and after incubation for 10 days, sufficient algal biomass is obtained.

[0053] The cultured microalgae is added to the microalgae photobioreactor 5, a 2L NaCl solution with a concentration of 1.5M is used as the growth liquid, a peristaltic pump 9 is used to move the raw liquid from the raw liquid pool 1 to the feed liquid side 2, and another peristaltic pump 9 is used to move the driving liquid in the microalgae photobioreactor 5 to the driving liquid side 3. Due to the osmotic pressure generated by the concentration difference between the driving liquid and the feed liquid, the wastewater in the feed liquid is filtered by the forward osmosis membrane to become clean water, which enters the microalgae photobioreactor to provide the required water source for the growth of microalgae.

[0054] In this embodiment, NaHCO3 with a concentration of 0.1M is selected as the carbon source required for the growth of algae, which is beneficial to the carbon fixation growth of microalgae. Under this condition, the biomass concentration of microalgae is increased by 65.9% compared with the condition of 0.05M NaHCO3. At this time, the carbon utilization rate of microalgae is 42.0%, and high-efficiency reduction and regeneration of the carbonate absorbent can be realized.

[0055] In this embodiment, the forward osmosis membrane material is cellulose acetate, the effective membrane surface area is 15cm 3 , and the membrane is oriented with the active layer facing the driving liquid side. Symmetrical cavities are arranged on both sides of the forward osmosis membrane in the forward osmosis device as the feed liquid side 2 and the driving liquid side 3, which are made of organic glass, and each cavity has a size of 6cm×2.5cm×1cm. The fixed flow rate of the two peristaltic pumps is 300mL / min (corresponding to a cross-flow speed of 9.0cm / s). At the end of each forward osmosis cycle, the water flux decreases by about 20%, and the average water flux is 12m - 2 hr -1 . However, the membrane fouling and clogging are reversible through membrane cleaning after each forward osmosis cycle, and after three continuous cycles, the initial water flux of the system is restored by more than 91%.

[0056] Under this condition, the forward osmosis membrane has a pollutant interception rate of 95% for the raw liquid, and the volume of the raw liquid is concentrated by 45%, and the water consumption of the system is reduced by about 30% compared with the normal requirement for the growth of microalgae.

[0057] The above only describes the preferred embodiments of the present application, and does not make any limitation on the technical scope of the present application, so any changes or modifications made in accordance with the claims and description of the present application shall be within the scope of the present application.

Claims

1. A complementary fusion system of forward osmosis reduction concentration coupled with microalgae carbon fixation, characterized in that, It includes a forward osmosis device and a microalgae carbon fixation device; the forward osmosis device includes a forward osmosis membrane module (4) and a feed liquid side (2) and a drive liquid side (3) separated therefrom; the microalgae carbon fixation device includes a microalgae photobioreactor (5), an electronic scale (6), an aeration device (7) and a parallel light source (8), wherein the microalgae photobioreactor (5) uses salt-tolerant microalgae, and a magnesium chloride solution or sodium chloride solution with a concentration of 1-2 mol / L is used as the microalgae growth solution; The feed liquid side (2) forms a circulation loop with the raw water tank (1) containing saline industrial wastewater. The saline industrial wastewater enters the feed liquid side (2) and enters the driving liquid side (3) through the forward osmosis membrane module (4) under the action of osmotic pressure to obtain product water. The concentrate is returned to the raw water tank (1). The driving liquid side (3) forms a circulation loop with the microalgae photobioreactor (5). The growth liquid with increased concentration after the growth of microalgae in the microalgae photobioreactor (5) is used as the driving liquid and enters the driving liquid side (3). The produced water dilutes the driving liquid and returns it to the microalgae photobioreactor (5) again as the microalgae growth liquid. The salinity of the saline industrial wastewater is between 1.0% and 3.0% by weight; after microalgae grow in the microalgae photobioreactor (5), the concentration of the growth liquid increases, which serves as the driving liquid to generate an osmotic pressure of 1.5-5 MPa in the forward osmosis device. The electronic scale (6) records the weight change of the microalgae photobioreactor (5) in real time to measure the water flux change; the aeration device (7) is placed in the microalgae photobioreactor (5); the parallel light source (8) provides light energy to the microalgae photobioreactor (5), and additionally supplements the carbon source and light source for microalgae growth, so as to realize energy-saving and water-saving microalgae carbon fixation.

2. The forward osmosis reduction concentration coupled with microalgae carbon fixation complementary fusion system according to claim 1, characterized in that, The permeate flux of the forward osmosis unit is 5-20 L / m³. -2 h -1 The recovery rate is between 50-60%.

3. The forward osmosis reduction concentration coupled with microalgae carbon fixation complementary fusion system according to claim 1, characterized in that, The forward osmosis membrane module (4) has symmetrical cavities on both sides as the feed liquid side (2) and the driving liquid side (3). The saline industrial wastewater and the driving liquid flow in a cross-flow manner with a flow rate range of 9-20 cm / s.

4. The forward osmosis reduction concentration coupled with microalgae carbon fixation complementary fusion system according to claim 1, characterized in that, The top of the feed liquid side (2) is its raw liquid inlet, and the bottom is its concentrated liquid outlet; the top of the drive liquid side (3) is its diluted liquid outlet, and the bottom is its drive liquid inlet.

5. The forward osmosis reduction concentration coupled with microalgae carbon fixation complementary fusion system according to claim 1, characterized in that, The microalgae photobioreactor (5) is connected to a CO2 capture and absorbent regeneration device. The CO2 capture and absorbent regeneration device includes an absorption tower (10) containing a solution of alkaline absorbent (12). The alkaline absorbent (12) is Na2CO3. The absorption tower (10) is connected to a gas cylinder (11) containing CO2 or a CO2 mixture. After CO2 is introduced, the alkaline absorbent (12) is converted into NaHCO3 and provided to the microalgae photobioreactor (5) as a carbon source required for microalgae growth. During the microalgae growth process, as the pH of the microalgae growth solution increases, NaHCO3 is converted into Na2CO3 to achieve the reduction and regeneration of the alkaline absorbent (12). A portion of the microalgae growth solution containing Na2CO3 is filtered through a filter (13) and returned to the absorption tower (10). Alternatively, the microalgae growth solution containing Na2CO3 is first sent to the driving liquid side (3) as the driving liquid and then discharged back to the absorption tower (10) after being returned to the microalgae photobioreactor (5).

6. A method for simultaneously treating saline industrial wastewater and cultivating microalgae, implemented using the forward osmosis reduction concentration coupled with microalgae carbon fixation complementary fusion system as described in any one of claims 1 to 5, comprising the following steps: Step 1: After culturing salt-tolerant microalgae, inoculate them into the microalgae photobioreactor (5). Start the system after the microalgae have entered the stable growth period. Step 2: The saline industrial wastewater in the raw water tank (1) is introduced into the feed liquid side (2) to intercept pollutants and achieve volume reduction and concentration; Step 3: The microalgae growth liquid in the microalgae photobioreactor (5) is used as the driving liquid and introduced into the driving liquid side (3) to drive water molecules through the forward osmosis membrane assembly (4) into the driving liquid side (3) by osmotic pressure. Step 4: One cycle consists of introducing saline industrial wastewater and one cycle of driving fluid. After each cycle, deionized water is introduced into the feed liquid side (2) to clean the forward osmosis membrane module (4). Then, sodium chloride solution is used to backwash the feed liquid side (2) and deionized water is used to backwash the driving fluid side (3) at the same flow rate. Finally, deionized water is introduced into the feed liquid side (2) and the driving fluid side (3) again to prepare for the next cycle.

7. The method for simultaneously treating saline industrial wastewater and cultivating microalgae according to claim 6, characterized in that, The weight change of the microalgae photobioreactor (5) is recorded in real time by an electronic scale (6) to measure the change in water flux; a conductivity meter is introduced into the raw water tank (1) and the microalgae photobioreactor (5) to measure the changes in conductivity and solute concentration in order to calculate the osmotic pressure difference in the forward osmosis device.

8. The method for simultaneously treating saline industrial wastewater and cultivating microalgae according to claim 6, characterized in that, A CO2 capture and absorbent regeneration device is used to provide a carbon source for the microalgae photobioreactor (5). The CO2 capture and absorbent regeneration device includes an absorption tower (10) containing a solution of alkaline absorbent (12), which is Na2CO3. The absorption tower (10) is connected to a gas cylinder (11) containing CO2 or a CO2 mixture. After CO2 is introduced, the alkaline absorbent (12) is converted into NaHCO3, which is provided to the microalgae photobioreactor (5) as a carbon source required for microalgae growth. During microalgae growth, as the pH of the microalgae growth solution increases, NaHCO3 is converted into Na2. CO3 is used to regenerate the alkaline absorbent (12). A portion of the microalgae growth liquid containing Na2CO3 is filtered through filter (13) and returned to the absorption tower (10). Alternatively, the microalgae growth liquid containing Na2CO3 is first sent to the driving liquid side (3) as the driving liquid, and then discharged back to the absorption tower (10) after being returned to the microalgae photobioreactor (5). The gas cylinder (11) is connected to a gas flow meter to control the CO2 content entering the absorption tower (10) so as to maintain the NaHCO3 concentration in the absorption tower (10) stable and control the NaHCO3 concentration sent into the microalgae photobioreactor (5) to be 0.1M±0.01M.

9. The method for simultaneously treating saline industrial wastewater and cultivating microalgae according to claim 8, characterized in that, The salt-tolerant microalgae are Dunaliella salina, Spirulina, Chlorella, Haematococcus pluvialis, Dunaliella salina, Cryptodinium coccidioides, or Micrococcus pluvialis.

10. The method for simultaneously treating saline industrial wastewater and cultivating microalgae according to claim 6, characterized in that, When the forward osmosis membrane water flux drops to 20% of the maximum water flux, the reactor operation is stopped, and the concentrate is discharged from the system for subsequent treatment. The same amount of saline industrial wastewater to be treated is added to the raw water tank (1) as in the previous cycle, to be used in the next cycle. When the concentration of microalgae biomass in the microalgae photobioreactor reaches 1000-2000 mg COD / L, 70-90% of the microalgae are removed, and fresh microalgae growth solution is added to the microalgae photobioreactor (5) to the initial volume. After one cycle, the forward osmosis membrane module (4) is cleaned, and the initial maximum water flux is restored before the next cycle.

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