CN112899125B - Microalgae efficient carbon sequestration device and nutrient supplement control method - Google Patents
Microalgae efficient carbon sequestration device and nutrient supplement control method Download PDFInfo
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Abstract
The invention discloses a microalgae efficient carbon sequestration device and a nutrient supplement control method, which are applied to microalgae biomass production and carbon dioxide fixation. The invention mainly comprises a photo-biological reaction device determined according to a microalgae nutrient supplement method. The microalgae is firstly cultured by adopting a lower nutrient concentration, meanwhile, the nutrient concentration in the microalgae solution is monitored, and nutrient supplement is carried out in the reactor in a mode of constructing a correlation of the nutrient concentration and the growth rate, so that the microalgae is always maintained in a high-speed growth stage. The microalgae nutrient supplement method provides a universal microalgae nutrient supplement scheme. The invention has the advantages that based on the BG11 culture medium, compared with the traditional supplement scheme of single nutrient, the operation is simpler, the method has the characteristics of cost saving, convenient use and the like, and meanwhile, the obtained nutrient supplement scheme can effectively improve the carbon fixation efficiency of microalgae aiming at different algae species and different reactors, and meets the requirements of high-efficiency and low-cost microalgae culture and carbon fixation.
Description
Technical Field
The invention belongs to the technical field of microbial culture, relates to a microalgae biological culture reactor, and particularly relates to a microalgae efficient carbon fixation device and a nutrient supplement control method.
Background
In order to reduce the consumption rate of fossil energy, development of new energy sources including solar energy, biomass energy and the like is rapidly progressed, and microalgae is developed as a third-generation biological energy sourcePlatform, application potential is huge. Meanwhile, microalgae, which is one of microorganisms with a high photosynthesis rate, has the advantages of high growth rate, small floor area and the like, and is recently regarded as one of important ways for efficiently fixing carbon. The method has the advantages of high-efficiency carbon fixation and biological energy production, and wide research prospect. However, there are still some challenges in microalgae cultivation due to the difficulty in controlling optimal growth conditions for microalgae. During growth of microalgae, CO 2 The introduction amount, the illumination condition, the nutrient concentration and the like are main factors influencing the growth rate of the microalgae.
CO in the reactor 2 A plurality of factors such as concentration, nutrient concentration and light intensity have obvious influence on the growth of the microalgae, and the current research reveals the influence of the factors on the growth rate of the microalgae to a certain extent. In addition, the literature also shows that the growth rate of the microalgae is gradually reduced along with the reduction of the concentration of the nutrient, and multiple times of propagation and nutrient supplement are often required in the growth process of the microalgae. However, most of the existing models adopt microalgae growth models with single initial conditions and gradually reduced nutrient concentration, and no literature exists for researching nutrient supplement strategies and corresponding growth models in the microalgae growth process.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a microalgae high-efficiency carbon sequestration device and a nutrient supplement control method, establish a set of growth dynamics model suitable for a microalgae nutrient supplement strategy and a corresponding nutrient supplement strategy, optimize the growth condition of chlorella in a nutrient solution in a mode of designing the supplement strategy, regularly and quantitatively add nutrients in a microalgae solution in different times, and have the characteristics of saving the nutrients, effectively improving the growth rate of microalgae, being convenient to use and the like.
In order to achieve the purpose, the invention adopts the technical scheme that:
a microalgae high-efficiency carbon fixation device comprises a photobioreactor main body, a nutrient ion monitoring system and a nutrient ion supplementing system, wherein:
the photobioreactor main body provides an environment required by microalgae growth;
the nutrient ion monitoring system is connected with the photobioreactor main body, monitors the filtered microalgae supernatant, and obtains the nutrient ion concentration in real time;
the nutrient ion supplementing system is connected with the nutrient ion monitoring system to obtain a monitoring result, and nutrients are supplemented to the photobioreactor main body according to the monitoring result so as to prolong the rapid growth period of the microalgae, delay the microalgae to enter the death period and keep the microalgae to be stably grown at a high speed as long as possible.
The photobioreactor main part is including the photobioreactor 1 that is used for holding little algae solution 2, nutrient ion monitoring system includes ion monitoring device 9, and ion monitoring device 9 is connected with the top of photobioreactor 1 through monitoring sampling tube 8, nutrient ion complementary system includes computer 7 and nutrient solution holding vessel 5 that has nutrient solution 6 stored, nutrient solution holding vessel 5 connects photobioreactor 1 through the nutrient supplement pipe 3 that has flow control valve 4, ion monitoring device 9's output and flow control valve 4's control end are connected to computer 7, and computer 7 controls flow control valve 4 at fixed time break-make according to the monitoring result.
The photobioreactor 1 is made of transparent materials and is a flat plate type photobioreactor, a column type photobioreactor, a tubular photobioreactor or a conical flask photobioreactor, and an LED lamp or a plant culture fluorescent lamp is arranged outside the photobioreactor 1 to provide a proper light source for microalgae growth.
The nutrient comprises inorganic salt ions such as carbonate, nitrate, phosphate and sulfate and metal ions required by microalgae growth.
The invention also provides a nutrient supplement control method based on the microalgae high-efficiency carbon fixation device, the growth period of the microalgae is divided into four stages, namely an environment adaptation period, a rapid growth period, a slow growth period and a death period according to nutrient consumption and specific growth rate change, the stage of the growth of the microalgae is judged by monitoring the concentration of nutrient ions in the microalgae solution in the photobioreactor main body, new nutrient solution is added when the rapid growth period is finished, and nutrient supplement is carried out on the microalgae, so that the rapid growth period of the microalgae is prolonged, the death period is delayed, and the microalgae is kept in the rapid growth state as far as possible.
In the microalgae growth cycle, the inoculated microalgae is in an environment adaptation period within 24 hours, and the microalgae nutrients are hardly consumed in the period; then entering a rapid growth phase, the specific growth rate of the microalgae and the consumption rate of the nutrients are obviously improved, and the nutrients are greatly consumed in the phase, and finally reach about 50 percent (± 5 percent) of the original nutrient concentration (with 0.3g/L NaNO) 3 For example, about 0.15 g/L); when the specific growth rate curve and the nutrient consumption curve show obvious gentle trends, the microalgae ends the rapid growth phase and enters the slow death phase, the nutrient consumption speed is slow at the phase, and finally the nutrient consumption speed reaches about 35 percent (plus or minus 5 percent) of the original nutrient concentration (with 0.3g/L NaNO) 3 For example, about 0.10 g/L); finally, when the growth rate of the microalgae is reduced, the microalgae enters a death phase, and the concentration of the nutrients is not reduced any more.
In the present invention, the nutrient solution 6 is a commercial BG11 medium, and when supplemented, the concentration of BG11 medium is regarded as the base concentration, and the concentration is 1BC, and the concentration is 1/xbc corresponding to the BG11 medium diluted by X times.
The method selects a growth kinetic Model which is optimized based on a Haldane-Like Model, selects main components in the nutrient solution, namely nitrate ions (nitrogen salt) and phosphate ions (phosphorus salt), as influence parameters of the Model, calculates a change curve of the specific growth rate of the microalgae along with time through the growth kinetic Model, and then determines a corresponding supplement strategy. According to the difference of the growth laws of the microalgae in the four stages, fitting the growth cycle of the microalgae by adopting a numerical simulation method to obtain a microalgae growth kinetic model from a rapid growth period to a microalgae death period, constructing a microalgae specific growth rate curve by combining the inhibition and limitation effects of nutrient concentration on the growth of the microalgae, recording the time from initial growth to reaching the highest specific growth rate as A hours, and recording the time from initial growth to death as B hours, wherein the nutrient supplement method comprises the following steps: BG11 medium with concentration of 0.2BC is added at the beginning for microalgae cultivation, the first supplement time is 24+ A hours, and then cyclic supplement of nutrients is carried out every A hours, wherein the supplement amount of the nutrients is BG11 medium of (A/B) BC at each time.
Specifically, according to the difference of the growth laws of the microalgae in the four stages, a numerical simulation method is adopted to fit the growth cycle of the microalgae to obtain a microalgae growth kinetic model from a rapid growth period to a microalgae death period, the model combines the inhibition and restriction effects of nutrient concentration on the growth of the microalgae to construct a microalgae specific growth rate curve, the time from the initial growth of the microalgae to the achievement of the highest specific growth rate is recorded as A hours, the time from the initial growth of the microalgae to the death of the microalgae is recorded as B hours, and the nutrient supplement method comprises the following steps: BG11 medium with concentration of 0.2BC is added at the beginning for microalgae cultivation, the first supplement time is 24+ A hours, and then cyclic supplement of nutrients is carried out every A hours, wherein the supplement amount of the nutrients is BG11 medium of (A/B) BC at each time.
Compared with the prior art, the invention has the beneficial effects that:
(1) The original microalgae culture mode with single nutrient addition is changed, the mode of multiple nutrient addition is used for keeping the microalgae to always maintain a high-speed growth state, the nutrient supplement is carried out on the microalgae after the high-speed growth period, the concentration of nutrient ions in the solution is kept, and the method has important significance for improving the carbon fixation efficiency of the microalgae.
(2) Compared with the scheme of simply supplementing single or multiple kinds of nutrients, the nutrient supplement scheme based on the mature culture medium adopts BG11 or similar commercial culture medium which is widely applied at present, can simplify steps and save cost in the processes of early preparation and nutrient solution preparation, and can also select to directly purchase the commercial culture medium for microalgae culture.
(3) Compared with a reactor and a culture method which use an ion permeable membrane or slowly add nutrient solution, the invention adopts a mode of multiple, timed and quantitative supplement, can effectively reduce the culture cost, and has guiding significance for the problems of overhigh cost, slow growth rate and the like of the ion permeable membrane in the large-scale culture process.
(4) A universal microalgae nutrient supplement strategy is provided, guidance is provided for nutrient addition in a large-scale microalgae culture process, the culture cost of a slow-release culture reactor is effectively reduced, the using amount of a nutrient solution is saved, and the carbon sequestration efficiency of microalgae can be effectively improved.
Drawings
FIG. 1 is a schematic diagram of a high-efficiency carbon-fixing photobioreactor for microalgae.
FIG. 2 is a schematic diagram of a culture method.
FIG. 3 is a graph of microalgae concentration versus time obtained in the present example.
FIG. 4 is a graph of microalgae biomass concentration versus nutrient consumption in an embodiment of the invention.
FIG. 5 is a graph showing the average daily biomass of microalgae obtained in the present example for 8 parallel control groups.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the drawings and examples.
As shown in fig. 1, the high-efficiency carbon fixation device for microalgae of the present invention can be applied to microalgae biomass production and carbon dioxide fixation under large-scale laboratory and outdoor cultivation, and comprises three major parts, namely a photobioreactor main body, a nutrient ion monitoring system and a nutrient ion supplementing system, wherein:
the photobioreactor body provides the environment required for microalgae growth, e.g. suitable lighting conditions, CO 2 Supply conditions, etc., in which the microalgae are first cultured with a lower initial concentration. The photobioreactor main body mainly comprises a photobioreactor 1 for containing microalgae solution 2, the photobioreactor 1 is generally made of organic glass materials or transparent materials such as plastic films and the like, the structure of the photobioreactor can be flat plate type photobioreactors, column type photobioreactors, tubular photobioreactors, conical flask photobioreactors and other types of photobioreactors with different sizes, and the specific size can be adjusted as required in the actual use process; an LED lamp or a plant culture fluorescent lamp providing a suitable light source for the growth of microalgae is arranged outside the photobioreactor 1, and a lamp holder is selectedThe light source is formed by welding aluminum alloy or metal materials and the like, the stability of the light source is kept, the four sides or two sides of the photobioreactor 1 can be surrounded according to actual needs, an interface is reserved at the top of the photobioreactor 1 and is connected with a nutrient ion supplementing system and a nutrient ion monitoring system, and nutrient supplementation and solution sampling are conveniently carried out.
Nutrient ion monitoring system is connected with the photobioreactor main part, monitors the nutrient (nitrate, carbonate, phosphate, sulfate etc.) in the little algae supernatant after the suction filtration, acquires the nutrient ion concentration wherein in real time, nutrient ion monitoring system includes ion monitoring devices 9, ion monitoring devices 9 is connected with the top of photobioreactor 1 through monitoring sampling tube 8, little algae solution 2 detects the different ion concentration in solution in ion monitoring devices 9 after detecting sampling tube 3 and preliminary treatment.
The nutrient ion supplementing system is connected with the nutrient ion monitoring system to obtain a monitoring result, and according to the monitoring result, after the corresponding time and ion concentration are reached, nutrients are supplemented to the photobioreactor main body, and the sufficient nutrient concentration in the microalgae solution is supplied, so that the rapid growth period of the microalgae is prolonged, the death period is delayed, and the microalgae is kept to be stably grown at a high speed as long as possible. Specifically, the nutrient ion supplementing system comprises a computer 7 and a nutrient solution storage tank 5 which stores nutrient solution 6, wherein the nutrient solution storage tank 5 is connected with the photobioreactor 1 through a nutrient supplementing pipe 3 with a flow control valve 4, the computer 7 is connected with the output end of an ion monitoring device 9 and the control end of the flow control valve 4, the computer 7 controls the flow control valve 4 to be switched on and off at fixed time according to the monitoring result, and the nutrient solution 6 is added into the solution from the nutrient solution storage tank 5 at fixed time.
Referring to fig. 2, the present invention also provides a nutrient supplement control method based on a microalgae high-efficiency carbon fixation device, which divides microalgae growth from initial inoculation into a culture medium to final death into four stages: the method comprises the following steps of supplementing nutrient solution in a microalgae solution in batches in an environment adaptation period, a rapid growth period, a slow growth period and a death period, judging the growth stage of the microalgae by monitoring the concentration of nutrient ions in the microalgae solution in a photobioreactor main body, initially adding lower nutrient concentration, adding new nutrient solution after the rapid growth period is finished after the environment adaptation period and the rapid growth period, and supplementing the nutrients to the microalgae, so that the rapid growth period of the microalgae is prolonged, the death period is delayed, and the microalgae is kept in a rapid growth state as much as possible.
As can be seen from fig. 2, the microalgae in the microalgae-supplemented group remained in a high-growth state, and the microalgae in the unsupplemented group entered a slow-growth state until finally died. The reactor shape, the amount of nutrient supplement and the time of nutrient supplement in the figure are plotted according to an application example, and the amount of supplement and the time of supplement during a specific culture are determined by the nutrient supplement method provided by the invention.
In the invention, in order to conveniently feed supplement and microalgae culture, the nutrient solution 6 is a commercial BG11 culture medium, the BG11 is relatively mature, the instruction significance on the large-scale microalgae culture is obvious by reasonably allocating the use proportion and setting a reasonable supplement strategy, and compared with the traditional supplement scheme of one or more ions, the method has the characteristics of simpler operation, cultivation cost saving, effective improvement on the carbon sequestration efficiency of microalgae, convenient use and the like.
The invention adopts a mode of specific feeding times for nutrient supplement, for example, the initial nutrient concentration of microalgae culture is 0.2BC, the microalgae firstly passes through a nutrient adaptation period of 24 hours and then enters a circulating nutrient supplement stage, the microalgae is subjected to nutrient supplement every 72 hours, and nutrient solution of 0.3BC is supplemented every time, so that the high-speed growth of the microalgae is maintained.
According to the difference of the growth laws of the microalgae in the four stages, the invention adopts a numerical simulation method to fit the growth cycle of the microalgae so as to obtain a microalgae growth dynamic model from a rapid growth stage to a microalgae death stage, the model combines the inhibition and restriction effects of nutrient concentration on the growth of the microalgae to construct a microalgae specific growth rate curve, the time from the initial growth of the microalgae to the reaching of the highest specific growth rate is recorded as A hours, the time from the initial growth of the microalgae to the death of the microalgae is recorded as B hours, and the nutrient supplement method comprises the following steps: BG11 medium with concentration of 0.2BC is added at the beginning for microalgae cultivation, the first supplement time is 24+ A hours, and then cyclic supplement of nutrients is carried out every A hours, wherein the supplement amount of the nutrients is BG11 medium of (A/B) BC at each time. Can realize the quick growth of the microalgae, improve the carbon fixation efficiency of the microalgae and save nutrients.
The Model is based on a Model optimized by a Haldane-Like Model, main components of nitrate ion nitrogen salt and phosphate ion phosphorus salt in the nutrient solution are selected as influence parameters of the Model, a change curve of the specific growth rate of microalgae along with time is calculated through a growth dynamics Model, and then a corresponding supplement strategy is determined:
wherein μ represents the specific growth rate of microalgae, μ max Denotes the maximum specific growth rate, S N 、S P Expressing the concentration of nitrogen and phosphorus elements in the microalgae solution, K S,N 、K I,N 、K S,P 、K I,P Parameters obtained by experimental fitting;
the method can construct a microalgae nutrient supplement method aiming at different algae species and different photobioreactors by constructing a microalgae growth kinetic model.
In a specific embodiment of the present invention, the following specific procedures and specific choices are specifically adopted:
1) A500 mL conical flask photobioreactor in a laboratory is selected for testing, the size and specification of the reactor are shown in table 1, the reactor is placed in an illumination incubator (GXZ intelligent instrument factory in Ningbo Jiangnan), 6 14W LED lamps are used for illumination, the light-dark period is 12h/12h, the culture temperature is set to 25 ℃, an air pump is connected with a vent pipe and inserted into the bottom of the conical flask, air is introduced at a uniform rate (the volume fraction of CO2 is 0.04%), and the air inlet rate of each control group is controlled to be consistent. Before the experiment, a high-speed centrifuge (TDL 80-2B of Shanghai' an Tingning scientific instruments factory) is used for centrifuging the microalgae cultured in advance to remove nutrient ions in the microalgae, and nutrient solution with corresponding concentration is added according to the requirement.
Table 1 microalgae reactor dimensions
| Item | Numerical value |
| Total heat transfer power/MW | 22.58 |
| Inlet temperature/deg.C of lead | 560 |
| Lead exit temperature/. Degree.C | 440 |
| Mass flow of lead/kg.s -1 | 959.66 |
| S-CO 2 Inlet temperature/. Degree.C | 364.12 |
| S-CO 2 Outlet temperature/. Degree.C | 550 |
2) The experiment adopts Chlorella pyrenoidosa (GY-D12) purchased from Shanghai plain Biotechnology Limited, and the microalgae nutrient solution (providing nutrient substances required for growth of microalgae) selected in the experiment is a commonly used BG11 formula, and the specific formula is 1.5g/L of Nano 3 ,0.04g/L K 2 HPO 4 ,0.075g/L MgSO 4 ·7H 2 O,0.036g/L CaCl 2 ·2H 2 O,0.006g/L citric acid, 0.006g/L ferric ammonium citrate, 0.001g/L EDTANA 2 ,0.02g/L Na 2 CO 3 Macroelements and 1ml A5 microelement (0.222 g/L ZnSO) 4 ·7H 2 O,0.079g/L CuSO 4 ·5H 2 O,0.015g/L MoO 3 ,0.036g/L CaCl 2 ·2H 2 O,2.86g/L H 3 BO 3 ,0.006g/L MnCl 2 ·4H 2 O)。
3) By setting up 3 sets of control experiments (as shown in table 2) the optimal growth conditions for chlorella were explored. The first group of experiments are experiments for determining the initial concentration of the optimal nutrient, the biomass concentration of the chlorella is determined every 2 hours by setting different initial nutrient concentrations, and the optimal initial nutrient concentration of the chlorella is obtained by continuously measuring for 120 hours; the second group of experiments are experiments for determining the optimal daily supplement amount, different supplement amounts are set, concentration change in the growth process of the chlorella is monitored, and the optimal average daily supplement amount of the chlorella is obtained.
TABLE 2 microalgae control test control group design protocol
4) Measuring microalgae biomass by spectrophotometry: the measurement is carried out by using a UV-1800240V ultraviolet visible light spectrophotometer produced by SHIMADZU company, and according to the previous experiment, the linear relation between the microalgae concentration and the absorbance value at 681nm is calibrated, as shown in the formula (1):
c＝0.394OD 681 +0.055 (1)
wherein c is microalgae concentration, OD 681 The absorbance of the microalgae solution was 681 nm. By the relational expression, the microalgae biomass concentration can be quickly calculated by measuring the absorbance.
5) On the basis of a Monod Model, a Haldane-Like Model with modified nutrient inhibition effect under high concentration is used, and a microalgae growth multi-factor influence Model is established by considering two nutrient influence factors of nitrogen and phosphorus; and through subsequent experiments, a model of nutrient supplement strategy is established.
6) The specific growth rate of microalgae is represented by formula (2):
wherein μ represents the specific growth rate of microalgae, X represents the microalgae biomass concentration, and t represents time.
7) In a single-factor-influenced microalgae growth Model, pico-Marco E and the Like are improved on the basis of a Monod Model, the nutrient inhibition effect under high concentration is considered, the growth rule of microalgae under a single influence factor is better simulated, and a Haldane-Like Model is provided, as expressed by formula (3):
wherein μ represents the specific growth rate of microalgae, μ max Represents the maximum specific growth rate of the microalgae, S is the nutrient concentration, K S ，K I Parameters in the growth kinetics model fit.
8) According to the invention, based on a Haldane-Like Model, the influence rule of nutrient concentration N and P on the growth of microalgae is simulated, and the specific growth rate of the microalgae is expressed as shown in formula (4) under the condition of considering N, P coupled multi-factor:
wherein μ represents a specific growth rate of microalgae, μ max Denotes the maximum specific growth rate, S N 、S P Expressing the concentration of nitrogen and phosphorus elements in the microalgae solution, K S,N 、K I,N 、K S,P 、K I,P Are parameters obtained by experimental fitting.
9) For the consumption rate of nutrients, literature studies show that the ion concentration consumed by microalgae for each growth of a certain biomass concentration is fixed, i.e. the growth amount of microalgae is proportional to the nutrient consumption, and is marked as Y, and is represented by formula (5):
wherein X 1 、X 2 Indicating the microalgae biomass concentration, S, at different times 1 、S 2 Indicating the concentration of nutrients in the microalgal solution at different times.
10 ) the optimization is carried out by adopting a least square method, and the optimization parameter is the variance of an experimental value and a simulation value:
wherein D represents the variance, X sim And X exp Respectively representing the biomass concentration of microalgae obtained by simulation and experiment at the same time, N represents the total number of points, and when the variance is minimum, recording optimized parameters. The final optimized parameters obtained are shown in Table 3, Y N 、Y P Respectively, the consumption rates of nitrogen and phosphorus.
TABLE 3 optimized parameters
| Numbering | Parameter(s) | |
| 1 | μ max | 0.04h -1 |
| 2 | K S,N | 0.03g L -1 |
| 3 | K I,N | 0.75g L -1 |
| 4 | K S,P | 0.0105g L -1 |
| 5 | K I,P | 0.53g L -1 |
| 6 | Y N | 0.0810mg·mg -1 |
| 7 | Y P | 0.0238mg·mg -1 |
11 By changing the initial nutrient concentration, taking a microalgae culture medium BG11 commonly used in microalgae culture at present as an example, the initial nutrient concentration is changed, an experiment is performed according to the setting of the first group of control groups in table 2, 8 groups of control groups are totally set, the microalgae concentration is measured every 2 hours in the first 48 hours, the change condition of the microalgae biomass concentration in 120 hours is recorded, the curve of the microalgae concentration and the time shown in fig. 3 is obtained, and the initial nutrient concentration most suitable for the growth of the microalgae in the first 48 hours is 0.2BC.
12 To determine the optimal replenishment time point while simultaneously studying the full life cycle law for microalgae, microalgae were continuously cultured starting from low concentration inoculation until a drop in microalgae concentration was observed. Experiments show that the whole process lasts about 280 hours, the microalgae concentration tends to be flat after 220 hours, and the microalgae concentration decreases about 270 hours. From fig. 4, it can be seen that the growth of microalgae can be divided into 4 stages, the first stage is a culture environment adaptation period, and the growth rate of the stage is slow; the second stage is a rapid growth stage of the microalgae, which is the rapid growth stage of the microalgae and has the fastest growth rate; the third stage is a slow growth stage, at which the nutrients are nearly or completely consumed and grow depending on the nutrients in the cells, and the growth of the microalgae tends to be slow; the fourth stage is the death phase, when the microalgae can not keep growing, the concentration is unchanged or even reduced.
13 According to the conclusion of the experiment, the experiment is carried out through the experiment of the third group of control groups in the table 2, the optimal single supplement amount is explored, 8 groups of control groups are arranged, the biomass concentration of the microalgae is measured every 12 hours, supplement is started from 100 hours, different supplement strategies are respectively arranged, and the supplement amount is varied from 0.05BC to 0.4BC in a daily supplement mode. The average daily biomass change of microalgae was calculated to obtain the average daily biomass change curve of microalgae of 8 parallel control groups as shown in fig. 5, and it can be seen that when the average daily supplement of 0.1BC-0.15BC is selected to be most beneficial to the growth of microalgae, the average daily supplement of 0.1BC can be selected as the daily supplement for saving nutrients. In addition, experiments are designed to study the supplement intervals of the microalgae, the growth conditions of the microalgae under the conditions of daily supplement, every two days supplement, every three days supplement and every four days supplement are respectively studied, and finally the conclusion is obtained that the supplement effect is optimal every 72 hours, and the supplement amount is 0.3BC every time.
14 Through two aspects of researches of experiments and numerical simulation, the optimized culture condition of microalgae is preliminarily determined, and the traditional strategy of adopting 1BC to not supplement is changed into the strategy of adopting 0.2BC initial concentration, starting supplement at 100 hours, supplementing the nutrient once every 72 hours and supplementing the nutrient once every 0.3BC. Experiments are designed to verify the supplement scheme, and the supplement scheme is proved to be capable of effectively improving the growth rate of microalgae, and compared with a control group which is not supplemented, the biomass concentration is improved by 34.2% in 200 hours.
The nutrient supplement scheme of the invention can be changed aiming at different algae species and different reactors, has the characteristic of diversity, designs the culture strategy according to different microalgae concentrations and nutrient conditions, and meets the requirements of high-efficiency and low-cost microalgae culture and carbon sequestration.
Claims (5)
1. The nutrient supplement control method based on the microalgae high-efficiency carbon fixation device comprises the steps that the microalgae high-efficiency carbon fixation device consists of a photobioreactor main body, a nutrient ion monitoring system and a nutrient ion supplement system;
the photobioreactor main body provides an environment required by microalgae growth;
the nutrient ion monitoring system is connected with the photobioreactor main body, monitors the filtered microalgae supernatant, and obtains the nutrient ion concentration in real time;
the nutrient ion supplementing system is connected with the nutrient ion monitoring system to obtain a monitoring result, and nutrients are supplemented to the photobioreactor main body according to the monitoring result so as to prolong the rapid growth period of the microalgae and delay the microalgae to enter the death period;
the method is characterized in that the growth period of the microalgae is divided into four stages, namely an environment adaptation period, a rapid growth period, a slow growth period and a death period according to nutrient consumption and specific growth rate change, the stage of the growth of the microalgae is judged by monitoring the concentration of nutrient ions in a microalgae solution in a photobioreactor main body, new nutrient solution is added when the rapid growth period is finished, and the nutrient supplement is carried out on the microalgae, so that the rapid growth period of the microalgae is prolonged, the death period is delayed, and the microalgae is kept in a rapid growth state as much as possible;
selecting main components in the nutrient solution, namely nitrate ions, namely nitrogen salt and phosphate ions, namely phosphorus salt, as influence parameters of the Model by adopting a microalgae growth dynamics Model optimized based on a Haldane-Like Model, calculating a change curve of the specific growth rate of microalgae along with time through the Model, and determining a corresponding supplement strategy;
according to the difference of the growth laws of the microalgae in the four stages, fitting the growth cycle of the microalgae by adopting a numerical simulation method to obtain a microalgae growth kinetic model from a rapid growth period to a microalgae death period, constructing a microalgae specific growth rate curve by combining the inhibition and limitation effects of nutrient concentration on the growth of the microalgae, recording the time from initial growth to reaching the highest specific growth rate as A hours, and recording the time from initial growth to death as B hours, wherein the nutrient supplement method comprises the following steps: adding BG11 culture medium with the concentration of 0.2BC at the beginning, culturing microalgae, wherein the first supplement time is 24+ A hours, and then circularly supplementing nutrients every A hours, wherein the nutrient supplement amount of BG11 culture medium for each time is (A/B) BC;
based on a microalgae growth kinetic Model optimized by a Haldane-Like Model, the specific growth rate of microalgae is expressed as shown in the following formula:
wherein μ represents the specific growth rate of microalgae, μ max Denotes the maximum specific growth rate, S N 、S P Expressing the concentration of nitrogen and phosphorus elements in the microalgae solution, K S,N 、K I,N 、K S,P 、K I,P Parameters obtained by experimental fitting;
the microalgae growth is proportional to nutrient consumption, denoted as Y, and is represented by the formula:
wherein X 1 、X 2 Indicating the microalgae biomass concentration, S, at different times 1 、S 2 Representing the concentration of nutrients in the microalgae solution at different moments;
and (3) optimizing by adopting a least square method, wherein the optimization parameter is the variance between an experimental value and a simulation value:
wherein D represents the variance, X sim And X exp Respectively representing the microalgae biomass concentration obtained by simulation and experiment at the same time, N represents the total number of points, and when the variance is minimum, recording optimized parameters.
2. The nutrient supplement control method of claim 1, wherein in the microalgae growth cycle, microalgae 24 hours after inoculation are in an environment adaptation period in which little microalgae nutrient is consumed; then entering a rapid growth phase, obviously improving the specific growth rate of microalgae and the consumption rate of nutrients, and finally reaching 50 +/-5% of the original nutrient concentration due to the large consumption of nutrients in the phase; when the specific growth rate curve and the nutrient consumption curve have obvious gentle trends, the microalgae ends the rapid growth phase and enters the slow death phase, the nutrient consumption speed is lower in the phase, and finally the nutrient concentration reaches 35 +/-5% of the original nutrient concentration; finally, when the growth rate of the microalgae is reduced, the microalgae enters a death phase, and the concentration of the nutrients is not reduced any more.
3. The nutrient supplement control method according to claim 1, wherein the nutrient solution (6) is a commercial BG11 medium, and the concentration of the BG11 medium is set as a base concentration at the time of supplement, and is set as 1BC, and the concentration of the BG11 medium diluted by X is set as 1/X BC.
4. The nutrient supplement control method according to claim 1, wherein the photobioreactor body comprises a photobioreactor (1) for containing a microalgae solution (2), the nutrient ion monitoring system comprises an ion monitoring device (9), the ion monitoring device (9) is connected with the top of the photobioreactor (1) through a monitoring sampling pipe (8), the nutrient ion supplementing system comprises a computer (7) and a nutrient solution storage tank (5) for storing nutrient solution (6), the nutrient solution storage tank (5) is connected with the photobioreactor (1) through a nutrient supplement pipe (3) with a flow control valve (4), the computer (7) is connected with the output end of the ion monitoring device (9) and the control end of the flow control valve (4), and the computer (7) controls the flow control valve (4) to be on and off at fixed time according to the monitoring result.
5. The nutrient supplement control method according to claim 4, wherein the nutrient comprises inorganic salt ions including carbonate, nitrate, phosphate and sulfate, and metal ions required for growth of microalgae.
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