Cascade microalgal concentration system and method based on hollow fiber membranes

Abstract

The application discloses a kind of cascade microalgae concentration systems and methods based on hollow fiber membrane, system includes: primary membrane processor, secondary membrane processor, raw water container, clean water container, controller.The cascade microalgae concentration system of the application is based on the realization microalgae concentration of outer pressure type hollow fiber membrane component, with good long-term flux and pollution resistance, by peristaltic pump to provide pressure to realize dead-end filtration, reduce the damage of shear force to microalgae cell, and realize two-stage concentration by cascade small and micro membrane processor, improve concentration efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microalgae analysis, and in particular to a cascaded microalgae concentration system and method based on hollow fiber membranes. BACKGROUND

[0002] Currently, microalgae concentration mainly includes flocculation, flotation, sedimentation, centrifugation, filtration, and combinations of various technologies. The efficiency of flocculation depends on the flocculant used, which changes the biochemical composition of microalgae and causes microalgae to form flocs. Flotation is based on the characteristics of some microalgae that produce biological hydrogen to make themselves float and thus achieve concentration. In addition, there are electroflocculation and electroflotation technologies, which are suitable for all microalgae species and do not require chemicals, but metal electrodes may cause metal pollution. These methods require a long standing time and are difficult to implement in environments such as research vessels. Centrifugation is most commonly used in laboratories, but has high operating costs and energy consumption, and can easily damage microalgae cells, making it unsuitable for long-term monitoring and morphological-based microalgae analysis.

[0003] Filtration is a common method for concentrating microalgae in the field of microalgae monitoring and analysis. Microalgae concentration systems based on filtration have various designs depending on separation precision, component structure, and hydrodynamic conditions.

[0004] Patent document CN112844048A discloses a gas pressure membrane concentration system and method for microalgae. The system includes a microporous filter membrane that divides the membrane processor into a shell side and a tube side. The shell side pressure is adjusted by a gas tank and valve to achieve concentration, and the tube side pressure is adjusted to reduce cell adhesion and discharge concentrated algae liquid. The structure of the membrane processor divided into shell and tube sides determines that the unit membrane area is small, and the hydrodynamic conditions are determined by the gas tank, making it difficult to calculate the volume concentration factor.

[0005] Patent document CN220265683U discloses an intelligent microalgae concentration and harvesting device. The device includes two sets of concentration systems integrated into an internal pressure type and an external pressure type. Both sets of concentration systems use a roll-type ultrafiltration membrane, share a raw material tank and a flushing tank, and achieve concentration through a booster pump and valve. The embedded system switches the concentration system as needed. The grid of the roll-type ultrafiltration membrane has dead points, resulting in poor backwashing effect and high energy consumption. SUMMARY

[0006] To solve the above problems, the present application provides a cascaded microalgae concentration system based on hollow fiber membranes. The system uses an external pressure hollow fiber membrane assembly to achieve microalgae concentration, has good long-term flux and pollution resistance, uses a peristaltic pump to provide pressure for dead-end filtration, reduces shear force damage to microalgae cells, and uses a cascaded small and micro membrane processor to achieve two-stage concentration, improving concentration efficiency.

[0007] A kind of hollow fiber membrane-based cascade microalgae concentration system, comprising:

[0008] Primary membrane processor, comprising first membrane pool and first outer pressure type hollow fiber membrane module installed in first membrane pool;

[0009] Secondary membrane processor, comprising second membrane pool and second outer pressure type hollow fiber membrane module installed in second membrane pool;

[0010] Raw water container, provides algae liquid to be concentrated for primary membrane processor, and is communicated with first membrane pool by pipeline;

[0011] Clean water container, for storing clean water obtained by primary membrane processor and secondary membrane processor, is communicated with water production cavity of first outer pressure type hollow fiber membrane module and second outer pressure type hollow fiber membrane module respectively by pipeline;

[0012] The bottom of first membrane pool and second membrane pool is equipped with water outlet;The water outlet of first membrane pool is communicated with second membrane pool by pipeline;

[0013] First pump, second pump, third pump, fourth pump and fifth pump are respectively arranged on the pipeline between raw water container and first membrane pool, the pipeline between clean water container and first outer pressure type hollow fiber membrane module, the pipeline between the water outlet of first membrane pool and second membrane pool, the pipeline between clean water container and second outer pressure type hollow fiber membrane module and the water outlet of second membrane pool;Second pump and fourth pump are bidirectional pumps;

[0014] Controller, according to program control first pump, second pump, third pump, fourth pump and fifth pump to execute two-stage concentration step.

[0015] Preferably, first outer pressure type hollow fiber membrane module and second outer pressure type hollow fiber membrane module are vertically installed in first membrane pool and second membrane pool respectively.

[0016] Preferably, first outer pressure type hollow fiber membrane module and second outer pressure type hollow fiber membrane module are made of hydrophilic outer pressure type hollow fiber membrane wire, and the pore size of the hollow fiber membrane wire is smaller than the diameter of microalgae.

[0017] Preferably, the clean water container is provided with overflow near the top position.

[0018] The first pump is installed on the pipeline connecting the raw water container and the first membrane pool, for pumping algae liquid to be concentrated from the raw water container into the first membrane pool.

[0019] The second pump is installed on the pipeline connecting the first outer pressure type hollow fiber membrane module and the clean water container, for pumping clean water filtered by the first outer pressure type hollow fiber membrane module into the clean water container, or backwashing the first outer pressure type hollow fiber membrane module with clean water in the clean water container.

[0020] The third pump is installed on the pipeline connecting the first-stage concentrated water outlet and the second membrane tank, and is used for pumping the first-stage concentrated algae solution from the first membrane tank into the second membrane tank.

[0021] The fourth pump is installed on the pipeline connecting the second outer-pressure type hollow fiber membrane assembly and the clean water container, and is used for pumping the clean water filtered by the second outer-pressure type hollow fiber membrane assembly into the clean water container, or back-flushing the second outer-pressure type hollow fiber membrane assembly with the clean water in the clean water container.

[0022] The fifth pump is connected with the second-stage concentrated water outlet through a pipeline.

[0023] The first pump, the second pump, the third pump, the fourth pump, the fifth pump and the controller are connected through signal lines.

[0024] Further, the second pump and the fourth pump can change the running direction according to the signal transmitted by the signal line.

[0025] Preferably, the first pump, the second pump, the third pump, the fourth pump and the fifth pump are peristaltic pumps.

[0026] The application also provides a hollow fiber membrane-based cascade microalgae concentration method, which comprises the step of concentrating the algae solution to be concentrated by using the above-mentioned hollow fiber membrane-based cascade microalgae concentration system, and comprises the following steps:

[0027] (1) setting concentration parameter independent variables, calculating concentration parameter dependent variables, and injecting the algae solution to be concentrated with a volume of at least the minimum consumption volume of raw water into the raw water container;

[0028] (2) according to the control program, the controller controls the first pump, the second pump, the third pump, the fourth pump and the fifth pump to perform the two-stage microalgae solution concentration step according to the concentration parameter independent variables and the concentration parameter dependent variables.

[0029] Specifically, the concentration parameter independent variables include: the running time flow rate v of the first pump during the sample injection step of the first-stage concentration phase 1_in , the algae solution volume V in the first membrane tank at the beginning of the concentration step of the first-stage concentration phase 1_start , the running time flow rates v of the first pump and the second pump during the concentration step and the back-flushing step of the first-stage concentration phase s_conc , the total back-flushing amount V during the first-stage concentration phase 1_back , the concentration base volume concentration factor A of the first-stage concentration phase 1_min , the first-stage concentration sub-cycle base number N 1_min , the first-stage concentration volume concentration factor A1, and the running time flow rate v of the third pump during the sample injection step of the second-stage concentration phase 2_in, the volume of algae liquid in the second membrane pool at the beginning of the concentration step of the secondary concentration stage V 2_start , the total amount of backwash during the secondary concentration stage V 2_back , the number of secondary concentration cycles N2, the running flow rate of the third pump and the fourth pump during the concentration step and the backwash step of the secondary concentration stage v m_conc , the running flow rate of the fifth pump when the secondary concentrated algae liquid is pumped out v output .

[0030] Specifically, the expression of the concentration parameter dependent variable is as follows:

[0031]

[0032] Where V raw is the minimum consumption volume of raw water, N1 is the total number of primary concentration cycles, T 1_conc is the concentration cycle of the first-stage concentration stage, T 1_back is the recoil period of the first stage of concentration, T 2_conc is the concentration cycle of the secondary concentration stage, T 2_back This is the backwash cycle of the secondary concentration stage.

[0033] The further two-stage concentration step of the microalgae solution includes:

[0034] (2-1) In the first concentration stage, the sample injection step is to cause the first pump to inject the algae solution to be concentrated from the raw water container into the first membrane pool;

[0035] (2-2) In the primary concentration stage, the first pump injects the algae solution to be concentrated from the raw water container into the first membrane tank, while the second pump injects the filtered clean water from the first external pressure hollow fiber membrane module into the clean water container;

[0036] (2-3) a backwash step in the primary concentration stage, wherein the second pump injects clean water from the clean water container into the first external pressure type hollow fiber membrane module to achieve backwashing;

[0037] (2-4) Repeat steps (2-2) to (2-3) until the number of executions i1 of steps (2-2) to (2-3) reaches N1;

[0038] (2-5) In the secondary concentration stage, the third pump injects the primary concentrated algae solution from the first membrane pool into the second membrane pool;

[0039] (2-6) In the secondary concentration stage, the third pump injects the primary concentrated algae solution from the first membrane tank into the second membrane tank, while the fourth pump injects the filtered clean water from the second external pressure hollow fiber membrane module into the clean water container;

[0040] (2-7) Secondary concentration stage backflush step, let the fourth pump inject clean water from the clean water container to the second outer pressure type hollow fiber membrane assembly to realize backflushing;

[0041] (2-8) Repeat steps (2-6) to (2-7) until the number of times i2 of steps (2-6) to (2-7) reaches N2.

[0042] (2-9) Secondary concentration algal liquid pumping step, let the fifth pump pump the secondary concentration algal liquid from the second membrane pool to the system outlet.

[0043] Specifically, the two-stage concentration algal liquid is concentrated by a volume concentration factor relative to the to-be-concentrated algal liquid, and the expression is as follows:

[0044]

[0045] In the formula, A2 is the secondary concentration volume concentration factor, and A is the total concentration volume concentration factor, that is, the volume concentration factor of the secondary concentration algal liquid relative to the to-be-concentrated algal liquid.

[0046] Compared with the prior art, the beneficial effects of the present application are:

[0047] (1) The present application realizes microalgae concentration based on an outer pressure type hollow fiber membrane assembly, has good long-term flux and pollution resistance, occupies small space, and is convenient for obtaining concentrated samples required for microalgae analysis in a water quality monitoring site.

[0048] (2) The present application realizes dead-end filtration by providing pressure by a pump, reduces the damage of shear force to microalgae cells, and obtains concentrated algal liquid suitable for microscopic examination method, microscopic imaging, computer vision and other morphological-based microalgae analysis methods.

[0049] (3) The present application realizes two-stage concentration by cascading the first and second membrane processors, improves the concentration efficiency, and reduces the energy consumption. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 It is a structure schematic diagram of a cascaded microalgae concentration system based on a hollow fiber membrane;

[0051] In the figure, 1 is a raw water container; 2 is a first membrane processor; 3 is a second membrane processor; 4 is a clean water container; 5 is a first pump; 6 is a second pump; 7 is a third pump; 8 is a fourth pump; 9 is a fifth pump; 21 is a small membrane pool; 22 is a small membrane assembly; 31 is a micro membrane pool; 32 is a micro membrane assembly; 41 is an overflow port; 211 is a first concentration effluent port; 311 is a second concentration effluent port;

[0052] Figure 2 It is a flow schematic diagram of a cascaded microalgae concentration method based on a hollow fiber membrane;

[0053] Figure 3For this embodiment, the three-dimensional fluorescence spectrum contour map of the gradient dilution algal liquid of the marine coccoid algae and the product of the cascading microalgae concentration system;

[0054] Figure 4 For this embodiment, the microscopic images of the original algal liquid of the marine coccoid algae and the product of the cascading microalgae concentration system under a 20-fold objective lens. DETAILED DESCRIPTION

[0055] For the convenience of those skilled in the art to understand, the technical solutions in the embodiments of the present application will be further described in detail below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0056] As Figure 1 shown, a cascading microalgae concentration system based on hollow fiber membranes includes an original water container 1, a first-stage membrane processor 2, a second-stage membrane processor 3, a clean water container 4, and a controller.

[0057] The original water container 1 is connected to the first-stage membrane processor 2 through a pipeline to provide the algal liquid to be concentrated for the first-stage membrane processor 2. The first-stage membrane processor 2 is connected to the second-stage membrane processor 3 through a pipeline to provide the algal liquid concentrated at the first stage for the second-stage membrane processor 3. The clean water container 4 is connected to the first-stage membrane processor 2 and the second-stage membrane processor 3 through a pipeline to temporarily store the clean water obtained by the first-stage concentration and the second-stage concentration.

[0058] The first-stage membrane processor 2 is composed of a small membrane assembly 22 vertically installed in a small membrane pool 21. The second-stage membrane processor 3 is composed of a micro membrane assembly 32 vertically installed in a micro membrane pool 31. The original water container 1 is connected to the small membrane pool 21 through a pipeline.

[0059] In this embodiment, the small membrane assembly 22 and the micro membrane assembly 32 are made of hydrophilic outer pressure type hollow fiber membrane filaments. The small membrane assembly 22 is connected to the clean water container 4 through a pipeline. The micro membrane assembly 32 is connected to the clean water container 4 through a pipeline. The technical parameters of the membrane filaments selected in this embodiment are shown in Table 1.

[0060] Table 1 Technical parameters of selected membrane filaments

[0061]

[0062]

[0063] In this embodiment, the design parameters of the small membrane assembly 22 and the micro membrane assembly 32 are shown in Table 2.

[0064] Table 2 Design parameters of membrane assemblies

[0065]

[0066] The clean water container 4 in the embodiment also has an overflow port 41 at a certain height from the bottom, so that the liquid in the clean water container 4 exceeding 1L is discharged from the overflow port 41.

[0067] The bottom of the small membrane pool 21 is provided with a first concentrated water outlet 211, and the bottom of the micro membrane pool 31 is provided with a second concentrated water outlet 311. The first concentrated water outlet 211 and the micro membrane pool 31 are connected by a pipeline.

[0068] The pipeline between the raw water container 1 and the small membrane pool 21 is provided with a first pump 5, which is used to pump the raw algal liquid from the raw water container 1 into the small membrane pool 21.

[0069] The pipeline between the small membrane assembly 22 and the clean water container 4 is provided with a second pump 6, which is used to pump the clean water filtered by the small membrane assembly 22 into the clean water container 4, or to backwash the small membrane assembly 22 with the clean water in the clean water container 4.

[0070] The pipeline between the first concentrated water outlet 211 and the micro membrane pool 31 is provided with a third pump 7, which is used to pump the first concentrated algal liquid from the small membrane pool 21 into the micro membrane pool 31.

[0071] The pipeline between the micro membrane assembly 32 and the clean water container 4 is provided with a fourth pump 8, which is used to pump the clean water filtered by the micro membrane assembly 32 into the clean water container 4, or to backwash the micro membrane assembly 32 with the clean water in the clean water container 4.

[0072] The fifth pump 9 is connected to the second concentrated water outlet 311 by a pipeline.

[0073] In the embodiment, the pipeline is a silicone hose with an inner diameter of 2mm and an outer diameter of 4mm.

[0074] The first pump 5, the second pump 6, the third pump 7, the fourth pump 8, the fifth pump 9 and the controller are connected by signal lines.

[0075] In the embodiment, the signal line is an RS485 signal bus, the controller includes an STM32F103RCT6, a power supply, a clock circuit, a UART and an RS485 level conversion circuit, a key circuit, the first pump 5, the second pump 6, the third pump 7, the fourth pump 8 are step motors with a flow range of 15-40mL / min, and the fifth pump 9 is a step motor with a flow range of 0.13-45mL / min.

[0076] Before use, first set the concentration parameter independent variable, and then the program automatically calculates the concentration parameter dependent variable according to the concentration parameter independent variable, and injects the algal liquid to be concentrated into the raw water container 1, the volume of which is at least the minimum consumption volume of the raw water.

[0077] The independent variables of the concentration parameters include: the flow rate v of the first pump 5 during the injection step of the first concentration stage 1_in At the beginning of the concentration step in the first concentration stage, the volume of algae liquid in the small membrane pool 21 is V 1_start , the flow rate v when the first pump 5 and the second pump 6 are running during the concentration step of the first concentration stage and the backwash step of the first concentration stage s_conc , the total amount of backwash during the first stage of concentration V 1_back , the basic volume concentration factor A in the primary concentration stage 1_min , the basic number of first-stage concentration cycles N 1_min , the volume concentration factor A1 of the first stage concentration, the flow rate v of the third pump 7 during the injection step of the second stage concentration 2_in At the beginning of the concentration step in the secondary concentration stage, the volume of algae solution in the micro membrane pool 31 is V 2_start , the total amount of backwash during the secondary concentration stage V 2_back , the number of secondary concentration cycles N2, the flow rate v when the third pump 7 and the fourth pump 8 are running during the secondary concentration stage concentration step and the secondary concentration stage backwash step m_conc , the flow rate v when the fifth pump 9 is running when the secondary concentrated algae liquid is pumped out output ;

[0078] In this embodiment, the concentration parameter independent variable setting is realized by modifying the burning program of STM32F103RCT6, wherein the first-level concentration volume concentration factor A1 can also be set by the key circuit with the first-level concentration stage basic volume concentration factor A 1_min Increase or decrease the step length.

[0079] In this embodiment, pure water was injected into the primary membrane processor 2 and the secondary membrane processor 3 for testing. When 150 mL of pure water was injected into the primary membrane processor 2, the membrane filaments of the small membrane assembly 22 were completely immersed. When 47 mL of pure water was injected into the secondary membrane processor 3, the membrane filaments of the micro membrane assembly 32 were completely immersed. The maximum liquid volume of the primary membrane processor 2 was 290 mL, and the maximum liquid volume of the secondary membrane processor 3 was 62 mL.

[0080] The conditions and set values ​​of the concentration parameter independent variables in this embodiment are shown in Table 3.

[0081] Table 3 Conditions and set values ​​of concentration parameter independent variables

[0082]

[0083] The expression of the enrichment parameter dependent variable is as follows:

[0084]

[0085] Where V rawis the minimum consumption volume of raw water, N1 is the total number of primary concentration cycles, T 1_conc is the concentration cycle of the first-stage concentration stage, T 1_back is the recoil period of the first stage of concentration, T 2_conc is the concentration cycle of the secondary concentration stage, T 2_back This is the backwash cycle of the secondary concentration stage.

[0086] The calculation results of the concentration parameter dependent variables in this embodiment are shown in Table 4.

[0087] Table 4 Calculation results of concentration parameter dependent variables

[0088]

[0089] like Figure 2 As shown, the controller controls the first pump 5, the second pump 6, the third pump 7, the fourth pump 8, and the fifth pump 9 according to the concentration parameter independent variable and the concentration parameter dependent variable to perform the secondary concentration step of the microalgae solution. The secondary concentration step of the microalgae solution is as follows:

[0090] Step 1: In the first concentration stage, the first pump 5 is used to inject the algae solution to be concentrated from the raw water container 1 into the small membrane pool 21;

[0091] Step 2: Primary concentration stage. In the concentration step, the first pump 5 injects the algae solution to be concentrated from the raw water container 1 into the small membrane pool 21, while the second pump 6 injects the filtered clean water from the small membrane module 22 into the clean water container 4.

[0092] Step 3, backwashing step of the primary concentration stage, causing the second pump 6 to inject clean water from the clean water container 4 into the small membrane module 22 to achieve backwashing;

[0093] Step 4: Repeat steps 2 to 3 until the number of times i1 of step 2 and step 3 is executed reaches N1;

[0094] Step 5, the sampling step of the secondary concentration stage, causes the third pump 7 to inject the primary concentrated algae solution from the small membrane pool 21 into the micro membrane pool 31;

[0095] Step 6: Secondary concentration stage. In the concentration step, the third pump 7 injects the primary concentrated algae solution from the small membrane pool 21 into the micro membrane pool 31 , while the fourth pump 8 injects the filtered clean water from the micro membrane module 32 into the clean water container 4 .

[0096] Step 7, backwashing step in the secondary concentration stage, causing the fourth pump 8 to inject clean water from the clean water container 4 into the micro membrane module 32 to achieve backwashing;

[0097] Step 8: Repeat steps 6 and 7 until the number of times i2 of steps 6 and 7 is executed reaches N2.

[0098] Step 9, the step of pumping out the secondary concentrated algae liquid, in which the fifth pump 9 pumps out the secondary concentrated algae liquid from the micro-membrane pool 31 to the system outlet.

[0099] In this embodiment, the total concentrated volume concentration factor is calculated as 20 times according to the expression. The total concentrated volume concentration factor expression is as follows:

[0100]

[0101] Where A2 is the volume concentration factor of the secondary concentration, and A is the volume concentration factor of the total concentration, that is, the volume concentration factor of the secondary concentrated algae solution compared to the algae solution to be concentrated.

[0102] In this embodiment, 2.344×10 7 The 1L algae solution obtained by diluting the marine cardun algae solution by 20 times was used as the algae solution to be concentrated for testing.

[0103] like Figure 3 Shown are three-dimensional fluorescence spectrum contour maps of the gradient diluted algae solution of marine algae and the products of the cascade microalgae concentration system.

[0104] like Figure 4 Shown are microscopic images of the original algae liquid of marine cardun algae and the product of the cascade microalgae concentration system under a 20x objective lens;

[0105] In this example, the density of marine algae was calculated using a plankton counting frame for the product of the cascade microalgae concentration system, and the calculated result was 1.627×10 7 cells / L, which is about 2 / 3 of the original algae liquid density of marine cardun algae.

[0106] The above embodiments provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements, and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cascade microalgae concentration method, characterized in that: Based on the cascade microalgae concentration system, it includes the following steps: (1) setting the independent variable of the concentration parameter, calculating the dependent variable of the concentration parameter, and injecting the algae liquid to be concentrated into the raw water container with a volume at least equal to the minimum consumption volume of the raw water; The independent variables of concentration parameters include: the running flow rate v of the first pump during the injection step of the first concentration stage 1_in , the volume of algae liquid in the first membrane pool at the beginning of the concentration step of the first concentration stage V 1_start , the running flow rate v of the first pump and the second pump during the concentration step of the first concentration stage and the backwash step of the first concentration stage s_conc , the total amount of backwash during the first stage of concentration V 1_back , the concentration factor A of the primary concentration stage base volume 1_min , the basic number of first-stage concentration cycles N 1_min , the first-stage concentration volume concentration factor A1, the runtime flow rate of the third pump during the injection step of the second-stage concentration stage v 2_in , the volume of algae liquid in the second membrane pool at the beginning of the concentration step of the secondary concentration stage V 2_start , the total amount of backwash during the secondary concentration stage V 2_back , the number of secondary concentration cycles N2, the running flow rate of the third pump and the fourth pump during the concentration step and the backwash step of the secondary concentration stage v m_conc , the running flow rate of the fifth pump when the secondary concentrated algae liquid is pumped out v output ; Concentration parameter dependent variables include: minimum raw water consumption volume V raw , the total number of first-stage concentration cycles N1, the first-stage concentration cycle T 1_conc , the recoil cycle T of the first stage concentration 1_back , concentration cycle T in the secondary concentration stage 2_conc , secondary concentration stage recoil cycle T 2_back ; The expression of the concentration parameter dependent variable is as follows: (2) According to the control program, the controller controls the first pump, the second pump, the third pump, the fourth pump, and the fifth pump according to the concentration parameter independent variable and the concentration parameter dependent variable to perform the two-stage concentration step of the microalgae solution; The cascade microalgae concentration system comprises: A primary membrane processor comprises a first membrane pool and a first external pressure hollow fiber membrane assembly installed in the first membrane pool; A secondary membrane processor, comprising a second membrane tank and a second external pressure hollow fiber membrane assembly installed in the second membrane tank; The raw water container provides the algae liquid to be concentrated for the first membrane processor and is connected to the first membrane tank through a pipeline; The clean water container is used to store the clean water obtained by the primary membrane processor and the secondary membrane processor, and is connected to the water production chamber of the first external pressure type hollow fiber membrane module and the second external pressure type hollow fiber membrane module through pipelines respectively; The bottom of the first membrane pool and the second membrane pool are both provided with a water outlet; the water outlet of the first membrane pool is connected to the second membrane pool through a pipeline; A first pump, a second pump, a third pump, a fourth pump, and a fifth pump are respectively provided on the pipeline between the raw water container and the first membrane pool, on the pipeline between the clean water container and the first external pressure type hollow fiber membrane module, on the pipeline between the water outlet of the first membrane pool and the second membrane pool, on the pipeline between the clean water container and the second external pressure type hollow fiber membrane module, and at the water outlet of the second membrane pool; the second pump and the fourth pump are bidirectional pumps; The controller controls the first pump, the second pump, the third pump, the fourth pump, and the fifth pump according to a program to perform a two-stage concentration step.

2. The cascade microalgae concentration method according to claim 1, characterized in that: Step (2) includes: (2-1) In the first concentration stage, the first pump injects the algae solution to be concentrated from the raw water container into the first membrane pool; (2-2) In the primary concentration stage, the first pump injects the algae solution to be concentrated from the raw water container into the first membrane tank, while the second pump injects the filtered clean water from the first external pressure hollow fiber membrane module into the clean water container; (2-3) a backwash step in the primary concentration stage, wherein the second pump injects clean water from the clean water container into the first external pressure type hollow fiber membrane module to achieve backwashing; (2-4) Repeat steps (2-2) to (2-3) until the number of executions i1 of steps (2-2) to (2-3) reaches N1; (2-5) In the secondary concentration stage, the third pump injects the primary concentrated algae solution from the first membrane pool into the second membrane pool; (2-6) In the secondary concentration stage, the third pump injects the primary concentrated algae solution from the first membrane tank into the second membrane tank, while the fourth pump injects the filtered clean water from the second external pressure hollow fiber membrane module into the clean water container; (2-7) a backwash step in the secondary concentration stage, wherein the fourth pump injects clean water from the clean water container into the second external pressure type hollow fiber membrane module to achieve backwashing; (2-8) Repeat steps (2-6) to (2-7) until the number of executions i2 of steps (2-6) to (2-7) reaches N2; (2-9) The step of pumping out the secondary concentrated algae liquid is to cause the fifth pump to pump out the secondary concentrated algae liquid from the second membrane pool to the system outlet.

3. The cascade microalgae concentration method according to claim 1, characterized in that: The first external pressure hollow fiber membrane assembly and the second external pressure hollow fiber membrane assembly are both made of hydrophilic external pressure hollow fiber membrane yarns, and the pore diameter of the hollow fiber membrane yarns is smaller than the diameter of the microalgae.

4. The cascade microalgae concentration method according to claim 1, characterized in that: The clean water container is provided with an overflow port near the top thereof.

5. The cascade microalgae concentration method according to claim 1, characterized in that: The first pump, the second pump, the third pump, the fourth pump and the fifth pump are peristaltic pumps.

Images