Method for constructing microalgae culture gas circuit under waste incineration flue gas condition

Abstract

The present application relates to the technical field of microalgae culture, and specifically discloses a method for constructing a microalgae culture gas circuit under waste incineration flue gas conditions, collecting component data of waste incineration flue gas; introducing a multivariate coupling algorithm based on the component data to calculate a dynamic mixing ratio of air and flue gas, obtaining mixed gas; performing fractional condensation dehumidification and isothermal saturation regulation on the mixed gas, reconstructing the thermodynamic state to obtain pretreated mixed gas; dividing the pretreated mixed gas into pulse air masses, and feeding them into the culture system after adaptively modulating the injection volume and frequency according to the real-time decay curve of dissolved carbon dioxide in the culture system; detecting the composition of the exhaust gas, and feeding back and correcting the dynamic mixing ratio and pulse modulation parameters; the present application can dynamically adjust the mixing ratio according to the flue gas composition, effectively control the temperature and humidity of the mixed gas, and maintain the carbon dioxide concentration in the culture system stable through pulse adaptive supply, thereby improving the carbon fixation efficiency of microalgae.

Description

Technical Field

[0001] This invention relates to the field of microalgae cultivation technology, specifically to a method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions. Background Technology

[0002] Microalgae carbon fixation technology is a carbon reduction method that utilizes the photosynthesis of microalgae to absorb carbon dioxide and convert it into biomass. The flue gas produced by waste incineration plants contains a high concentration of carbon dioxide (approximately 10% to 13% by volume), as well as acidic gases such as nitrogen oxides and sulfur dioxide, and a large amount of water vapor (up to 30% by volume). Directly introducing the waste incineration flue gas into a microalgae cultivation system can provide a carbon source for the microalgae, achieving the biological fixation of carbon dioxide from the flue gas.

[0003] Currently, technical solutions for cultivating microalgae using industrial flue gas mainly focus on algae selection, photobioreactor design, and flue gas pretreatment. Regarding algae selection, studies have shown that green algae such as *Chlorella* and *Scenedesmus* have a certain tolerance to high concentrations of carbon dioxide. However, residual nitrogen oxides and sulfur dioxide in waste incineration flue gas may have a synergistic inhibitory effect on microalgae growth. The adaptability of different algae species varies significantly, and there is a lack of methods for constructing and dynamically regulating gas pathways specifically for the components of waste incineration flue gas. In terms of flue gas pretreatment, existing technologies typically employ processes such as cooling, dust removal, and desulfurization and denitrification. However, they do not fully consider the impact of high water content in the flue gas on subsequent transportation and cultivation processes. In particular, the condensation of water vapor in the flue gas in flow meters and pipelines can lead to inaccurate flow control and equipment malfunctions. In terms of gas path control, the conventional approach is to mix air and flue gas in a fixed ratio and then continuously introduce it into the reactor. This method is difficult to adapt to the changes in carbon dioxide demand during microalgae growth and has not effectively solved the oxidative stress problem caused by dissolved oxygen supersaturation in the culture system. In particular, in column photoreactors, dissolved oxygen accumulation can easily lead to microalgae cell damage and a sharp drop in biomass.

[0004] Therefore, how to dynamically adjust the air-to-flue gas mixing ratio based on the real-time composition of waste incineration flue gas, and effectively dehumidify, regulate temperature and humidity, and supply the mixed gas in a pulsed manner to maintain the stability of carbon dioxide concentration in the culture system and reduce the stress of inhibitory components in the flue gas on microalgae, is a technical problem that urgently needs to be solved in the field of microalgae carbon fixation technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions, so as to solve the problems mentioned above.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for constructing gas pathways for microalgae cultivation under waste incineration flue gas conditions includes the following steps: S1, Collect composition data of waste incineration flue gas, including: carbon dioxide concentration, oxygen concentration, nitrogen oxide concentration and sulfur dioxide concentration; S2, Based on the composition data, a multivariate coupling algorithm is introduced to calculate the dynamic mixing ratio of air and waste incineration flue gas. The multivariate coupling algorithm includes the synergistic inhibition coefficient of carbon dioxide and nitrogen oxides and the oxygen compensation factor. The air and flue gas are mixed according to the dynamic mixing ratio to obtain a mixed gas with the target carbon dioxide concentration and carbon-nitrogen ratio. S3 involves performing staged condensation dehumidification and isothermal saturation regulation on the mixed gas. Based on the dew point temperature of the mixed gas and the temperature requirements of the microalgae cultivation system, the thermodynamic state of the mixed gas is reconstructed to obtain a pretreated mixed gas with controllable temperature and humidity. S4, the pretreated mixed gas is divided into multiple pulse gas clusters according to the time sequence. The injection volume and injection frequency of each pulse gas cluster are adaptively modulated according to the real-time decay curve of dissolved carbon dioxide in the culture system. The modulated pulse gas cluster is introduced into the culture system containing microalgae, wherein the microalgae are selected from Chlorella or Scenedesmus. S5 detects the composition of the gas emitted from the culture system, and adjusts the dynamic mixing ratio and pulse modulation parameters based on the detection results to maintain the carbon dioxide concentration in the culture system within the tolerance range for microalgae growth.

[0008] As a further aspect of the present invention: the multivariate coupling algorithm for calculating the dynamic mixing ratio of air and waste incineration flue gas specifically includes: The toxic synergistic equivalent is obtained by multiplying the collected nitrogen oxide concentration and sulfur dioxide concentration by the square root. Using toxicity synergistic equivalent as a variable, the corresponding oxygen compensation range is obtained by looking up a table, and the compensation range is superimposed on the baseline air flow rate to obtain the corrected air flow rate. Based on the corrected ratio of airflow to flue gas flow, the mixing ratio is adjusted sequentially until the carbon-nitrogen ratio of the mixture stabilizes within the preset threshold range.

[0009] As a further aspect of the present invention: the step of obtaining the corresponding oxygen compensation range by looking up a table specifically includes: A coefficient table is pre-constructed containing multiple toxicity synergistic equivalent ranges and their corresponding oxygen compensation ranges, wherein the lower the toxicity synergistic equivalent, the smaller the corresponding oxygen compensation range; Use the calculated toxicity synergistic equivalent as the search key to locate the interval to which it belongs in the coefficient table; Read the oxygen compensation range associated with the corresponding interval. If the toxicity co-equivalent falls exactly on the interval boundary, take the arithmetic mean of the two adjacent compensation ranges.

[0010] As a further aspect of the present invention: the staged condensation dehumidification and isothermal saturation conditioning of the mixed gas specifically includes: The mixed gas is passed sequentially through three condensing chambers with progressively decreasing temperatures. The set temperature of each condensing chamber is 5 to 8 degrees Celsius lower than the previous one, so that water vapor in the mixed gas is gradually released. The condensed and dehumidified mixed gas is introduced into a constant temperature saturation chamber, and the temperature inside the chamber is kept consistent with the temperature of the microalgae culture system. Using the real-time dew point temperature of the mixed gas as feedback, the water bath temperature in the constant temperature saturation chamber is adjusted to keep the relative humidity of the outlet mixed gas stable between 80% and 95%.

[0011] As a further aspect of the present invention: the reconstructed thermodynamic state of the mixed gas specifically includes: The outlet dew point temperature and outlet dry bulb temperature of the mixed gas after passing through the constant temperature saturation chamber are collected simultaneously, and the difference between the two is calculated as the saturation deviation. The saturation deviation is compared with the preset allowable fluctuation range. If the deviation exceeds the range, the cooling power of the previous condenser is adjusted in reverse. Repeat the sampling and adjustment steps until the relative humidity and temperature of the outlet mixed gas simultaneously meet the inlet requirements of the culture system.

[0012] As a further aspect of the present invention: the process for obtaining the real-time decay curve of dissolved carbon dioxide is as follows: The rate of change of dissolved oxygen concentration was continuously monitored within the culture system, and the rate of increase of dissolved oxygen was used as an indirect characterization of the intensity of photosynthesis. When the rate of increase of dissolved oxygen is less than 30% of that in the previous period, the dissolved carbon dioxide in the culture system is determined to have entered the decay phase. Starting from the determination time, the dissolved oxygen concentration value is recorded at fixed time intervals, and the recorded value is converted into carbon dioxide consumption rate. The consumption rates at each time point are connected in series to form a real-time decay curve.

[0013] As a further aspect of the present invention: the injection volume and injection frequency of each pulsed gas cloud are adaptively modulated based on the real-time decay curve of dissolved carbon dioxide in the culture system, specifically including: The slope of the real-time decay curve is used as the modulation reference. The larger the absolute value of the slope, the faster the carbon dioxide is consumed. The injection volume of the next pulse gas mass is dynamically adjusted based on the slope value, so that the injection volume is proportional to the absolute value of the slope. The interval between two adjacent pulses was inversely correlated with the injection volume; the larger the injection volume, the shorter the interval, thus maintaining a stable fluctuation in the dissolved carbon dioxide concentration within the culture system.

[0014] As a further aspect of the present invention: the feedback correction process for the dynamic mixing ratio pair specifically includes: The carbon dioxide concentration at the inlet and outlet of the culture system were measured separately, and the difference between the two concentrations was calculated as a characterization value of carbon absorption efficiency. The carbon absorption efficiency characterization value is compared with the preset benchmark efficiency range. If the characterization value is lower than the lower limit of the benchmark range, it is determined that the carbon dioxide supply in the mixture is excessive. The dynamic mixing ratio is adjusted by reducing the flue gas flow rate by 5% for every unit deviation of the characterization value from the lower limit, until the carbon absorption efficiency characterization value returns to the benchmark range.

[0015] As a further aspect of the present invention: detect the residual concentration of nitrogen oxides in the exhaust gas at the outlet of the culture system, compare it with the initial concentration of nitrogen oxides at the inlet, and calculate the relative removal rate of nitrogen oxides. When the relative removal rate is lower than the preset tolerance threshold, it is determined that the current pulse air mass injection frequency is too high, resulting in the inhibition of microalgal metabolism. The pulse modulation parameters are adjusted sequentially by reducing the pulse injection frequency by 2% for every percentage point the relative removal rate falls below the threshold, until the relative removal rate recovers to above the threshold.

[0016] The beneficial effects of this invention are: (1) By collecting flue gas composition data and introducing a multivariate coupling algorithm that includes toxicity synergistic equivalent, the mixing ratio of air and flue gas is dynamically adjusted, which effectively reduces the synergistic inhibition efficiency of nitrogen oxides and sulfur dioxide in flue gas on microalgae, improves the adaptability of Chlorella and Scenedesmus to waste incineration flue gas, and achieves efficient carbon sequestration.

[0017] (2) This invention adopts a combination of staged condensation dehumidification and isothermal saturation regulation, which effectively solves the potential malfunctions of flow meters and cooling equipment caused by the high moisture content of waste incineration flue gas (up to 30%). The adaptive modulation of the pulsed gas mass and the feedback correction based on the nitrogen oxide removal rate avoid oxidative stress and a sharp drop in biomass caused by dissolved oxygen supersaturation (consistently above 5.5 mg / L) in the column reactor. Attached Figure Description

[0018] The invention will now be further described with reference to the accompanying drawings.

[0019] Figure 1 This is a flowchart of the method for constructing a gas path for microalgae cultivation under the flue gas conditions of waste incineration according to the present invention; Figure 2 This is the gas path design diagram for flue gas concentration in this invention; Figure 3 This is a graph showing the trend of light density value of Chlorella vulgaris changing over time during cultivation under flue gas and air in this invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figure 1 As shown, this invention provides a method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions, comprising the following steps: S1, Collect composition data of waste incineration flue gas, including: carbon dioxide concentration, oxygen concentration, nitrogen oxide concentration and sulfur dioxide concentration; S2, Based on the composition data, a multivariate coupling algorithm is introduced to calculate the dynamic mixing ratio of air and waste incineration flue gas. The multivariate coupling algorithm includes the synergistic inhibition coefficient of carbon dioxide and nitrogen oxides and the oxygen compensation factor. The air and flue gas are mixed according to the dynamic mixing ratio to obtain a mixed gas with the target carbon dioxide concentration and carbon-nitrogen ratio. S3 involves performing staged condensation dehumidification and isothermal saturation regulation on the mixed gas. Based on the dew point temperature of the mixed gas and the temperature requirements of the microalgae cultivation system, the thermodynamic state of the mixed gas is reconstructed to obtain a pretreated mixed gas with controllable temperature and humidity. S4, the pretreated mixed gas is divided into multiple pulse gas clusters according to the time sequence. The injection volume and injection frequency of each pulse gas cluster are adaptively modulated according to the real-time decay curve of dissolved carbon dioxide in the culture system. The modulated pulse gas cluster is introduced into the culture system containing microalgae, wherein the microalgae are selected from Chlorella or Scenedesmus. S5 detects the composition of the gas emitted from the culture system, and adjusts the dynamic mixing ratio and pulse modulation parameters based on the detection results to maintain the carbon dioxide concentration in the culture system within the tolerance range for microalgae growth.

[0022] Please see Figure 2 As shown, in Example 1, step S1 involves collecting composition data of waste incineration flue gas: First, compliant flue gas, treated by desulfurization, denitrification, dust removal, and cooling, is drawn from the exhaust duct of the municipal solid waste incineration power plant. A portable flue gas analyzer is used for real-time monitoring at the sampling port of the flue gas outlet. During monitoring, the sampling probe of the flue gas analyzer is inserted into the sampling port, maintaining a sampling flow rate of 0.5 liters per minute, and continuous monitoring for 3 minutes. A reading is recorded every minute, and the arithmetic mean of the three readings is taken as the composition data of this batch of flue gas. The collected composition data includes: carbon dioxide concentration, oxygen concentration, nitrogen oxide concentration, and sulfur dioxide concentration. In this embodiment, the measured carbon dioxide concentration was 12.5% ​​(volume fraction), the oxygen concentration was 15.2%, the nitrogen oxide concentration was 115 mg / m³, and the sulfur dioxide concentration was 8 mg / m³. These data will serve as the basis for calculating the dynamic mixing ratio in subsequent steps.

[0023] Step S2: Calculate the dynamic mixing ratio based on the component data and prepare the mixed gas: After obtaining the flue gas composition data from step S1, a multivariate coupling algorithm is introduced to calculate the dynamic mixing ratio of air and waste incineration flue gas. The core of this algorithm is to establish a calculation model that includes a synergistic inhibition coefficient for carbon dioxide and nitrogen oxides, as well as an oxygen compensation factor. The specific calculation process is as follows: First, the nitrogen oxide concentration measured in step S1 is multiplied by the sulfur dioxide concentration. Then, the square root of the product is taken, and the resulting value is defined as the "toxic synergistic equivalent". In this embodiment, the nitrogen oxide concentration is 115 mg / m³, and the sulfur dioxide concentration is 8 mg / m³. Multiplying them gives 920, and taking the square root gives approximately 30.33. This value is the toxic synergistic equivalent, and its unit is milligrams per cubic meter.

[0024] Secondly, using the calculated toxicity synergistic equivalent as the independent variable, the corresponding oxygen compensation range was obtained by referring to a pre-constructed "toxicity synergistic equivalent - oxygen compensation range" table, i.e., Table 1. This table was constructed as follows: Under laboratory conditions, simulated flue gas with different toxicity synergistic equivalents (ranging from 0 to 100 mg / m³, with a gradient set every 10 mg / m³) was prepared. Chlorella was used as the test algae, and flue gas cultivation experiments were conducted in 500 ml Erlenmeyer flasks. The air flow rate was gradually increased until the optical density of the microalgae reached its maximum stable value. The increase relative to the pure air baseline flow rate was recorded; this increase is the oxygen compensation range corresponding to the toxicity synergistic equivalent. The compensation ranges corresponding to each gradient were tabulated to form a coefficient table. In this embodiment, the toxicity synergistic equivalent was 30.33, falling within the range of 30 to 40 mg / m³. Referring to the table, the oxygen compensation range corresponding to this range was found to be 0.25 L / min.

[0025] Then, the oxygen compensation margin obtained from the table is superimposed on the baseline air flow rate to obtain the corrected air flow rate. The baseline air flow rate is determined based on the total volume of the culture system and the preset gas-liquid ratio. In this embodiment, the total volume of the culture system is 50 liters, and the preset gas-liquid ratio is 0.5, so the baseline air flow rate is 25 liters per minute. After superimposing the compensation margin of 0.25 liters per minute, the corrected air flow rate is 25.25 liters per minute.

[0026] Finally, the mixing ratio is adjusted sequentially based on the corrected airflow rate to the current flue gas flow rate. The current flue gas flow rate is initially set to be the same as the baseline airflow rate, i.e., 25 liters per minute. The calculated corrected airflow rate to flue gas flow rate ratio is 25.25:25, or 1.01:1. This ratio is used as the mixing ratio, and the air and flue gas are introduced into the mixing tank for thorough mixing to obtain a mixed gas. Subsequently, the carbon-to-nitrogen ratio in the mixed gas (i.e., the ratio of carbon dioxide concentration to nitrogen oxide concentration, where carbon dioxide concentration is expressed as a volume fraction, and nitrogen oxide concentration is converted to a volume fraction before comparison; the conversion relationship is that under standard conditions, one milligram of nitrogen oxide per cubic meter is approximately equal to 0.0005 percentiles)) in the mixed gas is 12.5:0.0575 (115 milligrams of nitrogen oxide per cubic meter is converted to 0.0575% volume fraction), approximately 217:1. The preset carbon-to-nitrogen ratio threshold range is 200:1 to 250:1. Since this ratio falls within this range, no further adjustment is needed. If it exceeds the range, adjust the ratio gradually by increasing or decreasing the flue gas flow rate by 1% each time until the carbon-to-nitrogen ratio stabilizes within the threshold.

[0027] Step S3: Perform staged condensation dehumidification and isothermal saturation conditioning on the mixed gas. The mixed gas obtained in step S2 is introduced into a staged condensation dehumidification device through a pipeline. This device consists of three condensation chambers connected in series, each equipped with a refrigeration coil and a temperature sensor. The mixed gas first enters the first condensation chamber, with a temperature set at 10 degrees Celsius; then it enters the second condensation chamber, with a temperature set at 5 degrees Celsius; and finally, it enters the third condensation chamber, with a temperature set at 0 degrees Celsius. The set temperature of each condensation chamber is 5 degrees Celsius lower than the previous one. As the mixed gas passes through these three condensation chambers sequentially, the water vapor gradually condenses into liquid water due to the progressively decreasing temperature, and is discharged from the drain outlet at the bottom of the chamber. After this treatment, the relative humidity of the mixed gas decreases from nearly saturated (approximately 95% or higher) to approximately 40%.

[0028] Then, the condensed and dehumidified mixed gas is introduced into a constant-temperature saturation chamber. This constant-temperature saturation chamber is a closed water bath jacketed container, equipped with a temperature control device and a humidity sensor. The water bath temperature inside the constant-temperature saturation chamber is set to the same as the culture temperature of the microalgae culture system; in this embodiment, the culture temperature is 25 degrees Celsius, so the water bath temperature is also maintained at 25 degrees Celsius. The mixed gas is humidified to near saturation by passing through a certain depth of deionized water in the constant-temperature saturation chamber in a bubbling manner.

[0029] Simultaneously, the real-time dew point temperature of the mixed gas is used as feedback to adjust the water bath temperature within the constant-temperature saturation chamber. The dew point temperature is monitored in real-time by a dew point meter installed at the outlet of the constant-temperature saturation chamber. When the dew point temperature is below 23 degrees Celsius, it indicates that the humidity of the mixed gas is too low, so the water bath temperature is increased by 0.5 degrees Celsius; when the dew point temperature is above 27 degrees Celsius, it indicates that the humidity is too high, so the water bath temperature is decreased by 0.5 degrees Celsius. Through the above adjustments, the relative humidity of the outlet mixed gas is stabilized between 80% and 95%. In this embodiment, a pretreated mixed gas with a relative humidity of 88% and a temperature of 25 degrees Celsius is finally obtained, thus completing the reconstruction of the thermodynamic state of the mixed gas.

[0030] Step S4: The pretreated mixed gas is divided into pulsed gas clouds and adaptively modulated before being introduced into the culture system. The temperature and humidity-controlled pretreated gas mixture obtained in step S3 is connected to a pulse generator, which consists of a solenoid valve and a programmable time controller. The pulse generator divides the continuously flowing gas mixture into multiple discrete pulse clusters according to a time sequence. The injection volume of each pulse cluster and the interval between two adjacent pulses (i.e., the injection frequency) are not fixed, but are adaptively modulated based on the real-time decay curve of dissolved carbon dioxide in the culture system.

[0031] First, it is necessary to obtain the real-time decay curve of dissolved carbon dioxide. In this embodiment, the dissolved carbon dioxide concentration is not directly measured, but an indirect method is used: the rate of change of dissolved oxygen concentration is continuously detected within the culture system (in this embodiment, a 50-liter tubular photobioreactor containing Chlorella culture medium). Specifically, a dissolved oxygen electrode is installed in the reactor, and the dissolved oxygen concentration value is recorded every 10 minutes. The difference between two adjacent records is divided by the time interval to obtain the dissolved oxygen rise rate. Since the photosynthetic rate of Chlorella is positively correlated with the carbon dioxide consumption rate, and the photosynthetic rate is directly reflected in the dissolved oxygen release rate, the dissolved oxygen rise rate can be used as an indirect characterization of photosynthetic intensity. When the dissolved oxygen rise rate is less than 30% of the value recorded in the previous 10-minute period, the dissolved carbon dioxide in the culture system is determined to have entered the decay phase. Starting from this determination point, the dissolved oxygen concentration value is recorded every 30 minutes, and this value is converted into the carbon dioxide consumption rate through a pre-calibrated conversion relationship (calibration method: under the same culture conditions, the dissolved oxygen concentration corresponding to different known dissolved carbon dioxide concentrations is measured, and a standard curve is plotted). Connecting the consumption rates at each moment in chronological order creates a real-time decay curve.

[0032] Then, adaptive modulation is performed. The slope of the real-time decay curve is used as the modulation reference. The slope is calculated as follows: take the carbon dioxide consumption rate values ​​at the two most recent time points, subtract the former from the latter, and divide by the time interval to obtain the slope value. The larger the absolute value of the slope, the faster the carbon dioxide consumption. In this embodiment, a reference slope value is set (e.g., 0.05 mg / L / min). When the measured absolute value of the slope is greater than the reference slope, the injection volume of the next pulse gas cluster is increased proportionally. The proportional relationship is: the injection volume increment equals the reference injection volume multiplied by (the measured absolute value of the slope divided by the reference slope and then subtracted by 1). The reference injection volume is set to 0.5% of the total volume of the culture system, i.e., 0.25 liters. For example, if the measured absolute value of the slope is 0.10, then the injection volume increment is 0.25 multiplied by (0.10 / 0.05-1) = 0.25 liters, so the actual injection volume is 0.5 liters. Conversely, if the absolute value of the slope is less than the reference slope, the injection volume is reduced. Simultaneously, the interval between two adjacent pulses is inversely correlated with the injection volume: the larger the injection volume, the shorter the interval. Specifically, the interval equals the baseline interval multiplied by (the baseline injection volume divided by the actual injection volume). The baseline interval is set to 30 minutes. For example, when the actual injection volume is 0.5 liters, the interval = 30 × (0.25 / 0.5) = 15 minutes. This modulation maintains a stable fluctuation in the dissolved carbon dioxide concentration within the culture system. The modulated pulsed gas mass is introduced into the culture system containing Chlorella from the bottom of the reactor through a distribution tube.

[0033] Step S5: Detect the composition of the discharged gas and provide feedback to correct the mixing ratio and pulse parameters. A gas sampling device was installed at the outlet of the culture system to periodically detect the composition of the exhaust gas. Specifically, samples were taken twice daily, at 10:00 AM and 4:00 PM, each lasting 2 minutes. The carbon dioxide, nitrogen oxide, and oxygen concentrations at the outlet were measured using the same flue gas analyzer as in step S1. Based on the detection results, feedback corrections were made to the dynamic mixing ratio in step S2 and the pulse modulation parameters in step S4.

[0034] (a) Correcting the dynamic mixing ratio: (II) First, read the carbon dioxide concentration at the inlet (i.e., the outlet of the mixing tank in step S2) and the outlet (i.e., the reactor exhaust port) of the culture system, respectively, and calculate the difference between the two. This difference is defined as the carbon absorption efficiency characterization value. For example, if the carbon dioxide concentration at the inlet is 12.5% ​​and the carbon dioxide concentration at the outlet is 3.2%, then the difference is 9.3%. The preset baseline efficiency range is 8% to 10%. If the carbon absorption efficiency characterization value is lower than 8%, for example, if the measured value is 7%, then it is determined that the carbon dioxide supply in the mixed gas is excessive, that is, the carbon dioxide introduced exceeds the absorption capacity of the microalgae, resulting in waste. At this time, the dynamic mixing ratio in step S2 is adjusted step by step according to the correction range of reducing the flue gas flow rate by 0.5% for every 0.1 percentage point below the lower limit. The specific operation is as follows: multiply the current flue gas flow rate by (1-0.5%×(8-7) / 0.1) to obtain 0.95 times the current flue gas flow rate, that is, reduce the flue gas flow rate by 5%. Then remix and test until the carbon absorption efficiency characterization value rises back to above 8%. If the carbon absorption efficiency rating is higher than 10%, it indicates that the carbon dioxide supply is insufficient, and the flue gas flow rate should be increased by the same amount.

[0035] (ii) Correcting pulse modulation parameters: First, the residual concentration of nitrogen oxides (NOx) in the exhaust gas from the culture system's outlet is detected and compared with the initial NOx concentration at the inlet measured in step S1. The relative removal rate is calculated using the formula: relative removal rate equals (initial NOx concentration minus outlet NOx concentration) divided by the initial NOx concentration, then multiplied by 100%. For example, if the initial NOx concentration is 115 mg / m³ and the residual concentration at the outlet is 23 mg / m³, the relative removal rate is 80%. The preset tolerance threshold is 75%. When the relative removal rate is below 75%, for example, if the measured value is 70%, it is determined that the current pulse gas injection frequency is too high, leading to inhibition of microalgal metabolism. This is because an excessively high frequency means that too much flue gas is introduced in a short period of time, and the residual NOx exceeds the microalgae's detoxification capacity. In this case, the pulse modulation parameters in step S4 are successively adjusted by reducing the pulse injection frequency by 2% for every percentage point the relative removal rate falls below the threshold. The specific operation is as follows: Multiply the current injection frequency (i.e., the number of pulses per unit time) by (1-2%×(75-70)) to obtain a frequency that is reduced by 10%. After the frequency is reduced, the interval between adjacent pulses is correspondingly extended. Rerun and detect until the relative removal rate recovers to above 75%.

[0036] Through the closed-loop control of steps S1 to S5 above, this embodiment successfully realizes the dynamic construction and adaptive adjustment of the microalgae cultivation gas path under the flue gas conditions of waste incineration, so that the carbon dioxide concentration in the cultivation system is always maintained within the tolerance range of microalgae growth (i.e., carbon dioxide volume fraction between 3% and 8%, which may be slightly adjusted according to the microalgae species and growth stage), ensuring the efficient carbon fixation and stable growth of microalgae.

[0037] Example 2, regarding the specific implementation of obtaining the oxygen compensation range by looking up a table in step S2: First, a coefficient table, Table 1, was pre-constructed as follows: In the laboratory, a gradient experiment was conducted using simulated flue gas. The simulated flue gas was prepared by mixing carbon dioxide, nitrogen, sulfur dioxide, and nitrogen oxides in different proportions, with toxicity synergistic equivalents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / m³. For each toxicity synergistic equivalent value, *Chlorella vulgaris* was used as the test algae in the same photobioreactor (50-liter tubular type), and the simulated flue gas was introduced for cultivation. The initial baseline air flow rate was set at 25 liters per minute, with a gas-liquid ratio of 0.5. The air flow rate was then gradually increased by 0.5 liters per minute each time, and the change in the optical density value of *Chlorella vulgaris* was observed. When the optical density value reached its maximum and further increases in air flow rate no longer significantly improved the optical density value, the total increase in air flow rate at this point was recorded. This increase represents the oxygen compensation amplitude corresponding to that toxicity synergistic equivalent. Each toxicity synergistic equivalent value and its corresponding compensation amplitude were entered into the table to form the coefficient table. To handle non-integer values, the toxicity synergistic equivalent is divided into several continuous intervals, each corresponding to a compensation range. The interval division rules are as follows: 0 ≤ toxicity synergistic equivalent value ≤ 5, 5 < toxicity synergistic equivalent value ≤ 15, 15 < toxicity synergistic equivalent value ≤ 25, 25 < toxicity synergistic equivalent value ≤ 35, 35 < toxicity synergistic equivalent value ≤ 45, 45 < toxicity synergistic equivalent value ≤ 55, 55 < toxicity synergistic equivalent value ≤ 65, 65 < toxicity synergistic equivalent value ≤ 75, 75 < toxicity synergistic equivalent value ≤ 85, 85 < toxicity synergistic equivalent value ≤ 95, 95 < toxicity synergistic equivalent value ≤ 105 (all units are milligrams per cubic meter). The compensation range corresponding to the midpoint of each interval is taken as the representative value of that interval. For example, a toxicity synergistic equivalent of 30 falls into the interval 25 to 35, the midpoint of which is 30, and the corresponding compensation range is 0.25 liters per minute.

[0038] Table 1. Correspondence between toxicity synergistic equivalent range and oxygen compensation range:

[0039] In practice, the toxicity synergistic equivalent calculated in step S2 (e.g., 30.33 mg / m³) is used as the search key to locate its corresponding interval in the coefficient table. Since 30.33 is greater than 25 and less than 35, it belongs to the interval between 25 and 35.

[0040] Finally, read the oxygen compensation margin associated with this interval, which is 0.25 liters per minute. If the toxicity synergistic equivalent falls exactly on the interval boundary, for example, exactly equal to 25, then take the arithmetic mean of the compensation margins of the two adjacent intervals (15 to 25 and 25 to 35). For example, if the compensation margin for the 15 to 25 interval is 0.20 and for the 25 to 35 interval is 0.25, then the average is 0.225 liters per minute.

[0041] Example 3, regarding the specific implementation of staged condensation dehumidification and isothermal saturation regulation in step S3: The mixed gas obtained in step S2 is sequentially fed into three condensing chambers through pipelines. The cooling temperature of the first condensing chamber is set to 10 degrees Celsius, the second condensing chamber to 5 degrees Celsius, and the third condensing chamber to 0 degrees Celsius. Each condensing chamber is equipped with a spiral metal coil, within which the refrigerant circulates. The mixed gas enters from the bottom of the chamber, flows upward, and contacts the surface of the coil. Water vapor condenses into water droplets, which flow along the inner wall of the chamber to the bottom water collection tank and are discharged through an automatic drain valve. The condensing chambers are designed with an inner diameter of 200 mm and a height of 500 mm to ensure that the residence time of the mixed gas in the chamber is no less than 2 seconds. After the three condensing chambers are connected in series, the relative humidity of the mixed gas can be reduced from an initial level of over 95% to approximately 40%.

[0042] Then, the condensed and dehumidified mixed gas is introduced into a constant-temperature saturation chamber. This saturation chamber is a cylindrical, sealed container with a diameter of 300 mm and a height of 600 mm, filled with deionized water to a depth of 200 mm. The outer wall of the chamber has a water bath jacket, through which constant-temperature water is circulated. The water temperature is maintained at 25 degrees Celsius (consistent with the incubation temperature) by a heater and temperature controller. The mixed gas is dispersed into small bubbles through a microporous distribution plate (0.5 mm pore size) at the bottom, rising in the deionized water for isothermal humidification. A temperature and humidity sensor and a dew point meter are installed at the outlet of the saturation chamber.

[0043] Finally, closed-loop regulation is performed using the real-time dew point temperature of the air-fuel mixture as feedback. The dew point meter reads data every 30 seconds. If the dew point temperature is below 23 degrees Celsius, the controller issues a command to increase the water bath temperature by 0.5 degrees Celsius; if the dew point temperature is above 27 degrees Celsius, the water bath temperature is decreased by 0.5 degrees Celsius. After 3 to 5 adjustments, the dew point temperature can be stabilized within the range of 25 ± 0.5 degrees Celsius, at which point the corresponding relative humidity is approximately 88% to 92%. If the relative humidity still exceeds the range of 80% to 95%, the water bath temperature is fine-tuned, adjusted by 0.2 degrees Celsius each time, until the requirement is met.

[0044] Example 4, regarding the acquisition of the real-time decay curve of dissolved carbon dioxide in step S4: A dissolved oxygen electrode (model: Leici DO-957) was installed in the photobioreactor and connected to a data acquisition unit, sampling once per minute. The data acquisition unit continuously recorded the dissolved oxygen concentration value in milligrams per liter (mg / L). Simultaneously, under the same culture conditions, a calibration experiment was performed beforehand: a series of culture media with known dissolved carbon dioxide concentrations (concentration range 0 to 50 mg / L, with a gradient of 5 mg / L) were prepared, and their steady-state dissolved oxygen concentrations were measured under the same temperature and light conditions, generating a dissolved carbon dioxide concentration-dissolved oxygen concentration standard curve. In this embodiment, the calibration results showed a linear relationship: dissolved carbon dioxide concentration equals 0.32 multiplied by dissolved oxygen concentration minus 0.58, with a correlation coefficient of 0.99.

[0045] In the actual cultivation process, the data acquisition system calculates the dissolved oxygen rise rate every 10 minutes, which is calculated by subtracting the dissolved oxygen concentration from 10 minutes ago from the current dissolved oxygen concentration and then dividing by 10 minutes. When this rise rate is less than 30% of the value recorded in the previous 10-minute period, a decay judgment is triggered. For example, if the rise rate in the previous period was 0.05 mg / L / min and the current period is 0.014 mg / L / min, which is below the 30% threshold, then the decay phase is determined. At this point, starting from this judgment time, the dissolved oxygen concentration value is recorded every 30 minutes. The recorded dissolved oxygen concentration value is substituted into the calibration formula (expressed as: dissolved carbon dioxide concentration equals 0.32 multiplied by dissolved oxygen concentration minus 0.58) to calculate the corresponding carbon dioxide consumption rate (note: changes in dissolved oxygen concentration indirectly reflect carbon dioxide consumption, but the dissolved carbon dioxide concentration is calculated directly, and its rate of change over time is the consumption rate). Specific calculation: Let the dissolved oxygen concentration at time t1 be D1, and convert it to the dissolved carbon dioxide concentration C1; let the dissolved oxygen concentration at time t2 (t2 = t1 + 30 minutes) be D2, and convert it to C2. Then the carbon dioxide consumption rate is equal to (C1 minus C2) divided by 0.5 hours. Plot the consumption rate at each time point in chronological order to form a curve, which is the real-time decay curve.

[0046] Example 5: Specific implementation of the feedback correction pulse modulation parameters in step S5: Nitrogen oxide (NOx) sensors (using electrochemical principles, measuring range 0 to 200 mg / m³, accuracy ±1 mg / m³) were installed at the inlet and outlet of the culture system. The inlet sensor continuously monitored the initial NOx concentration in the incoming flue gas, which was recorded as the initial NOx concentration. The outlet sensor monitored the residual NOx concentration in the exhaust gas. The data logger recorded the readings of both sensors hourly.

[0047] The relative removal rate is calculated as follows: the relative removal rate equals (initial nitrogen oxide concentration minus outlet nitrogen oxide concentration) divided by the initial nitrogen oxide concentration, then multiplied by 100%. For example, if the initial nitrogen oxide concentration is 115 mg / m³ and the outlet concentration is 23 mg / m³, then the relative removal rate is (115-23) / 115×100%=80%.

[0048] The preset tolerance threshold was determined based on previous experiments: in a small-scale test in a 500 ml conical flask, when Chlorella grew in a pure flue gas environment, the optical density value began to decrease when the nitrogen oxide removal rate was below 75%, indicating that the microalgal metabolism was inhibited. Therefore, in this embodiment, the tolerance threshold was set at 75%.

[0049] When the measured relative removal rate is below 75%, for example, 70%, the current pulse injection frequency is determined to be too high. The correction method is as follows: for every percentage point below the threshold (i.e., 75% - 70% = 5 percentage points), the pulse injection frequency is reduced by 2%, and this is repeated sequentially. That is, the new injection frequency equals the current frequency multiplied by (1 - 2% × 5) = the current frequency multiplied by 0.9. If the current frequency is twice per hour (i.e., once every 30 minutes), then after correction it will be 1.8 times per hour, corresponding to an interval time extended from 30 minutes to 33.3 minutes. After correction, the relative removal rate is retested. If it is still below 75%, the frequency is reduced by the same amount until the relative removal rate recovers to above 75%. Conversely, if the relative removal rate is above 85%, the frequency is appropriately increased (increasing by 1% for every percentage point above 85%) to improve carbon dioxide supply efficiency.

[0050] Through the above feedback correction, this embodiment achieves dynamic optimization of pulsed air mass parameters, which ensures that microalgae fully absorb carbon dioxide while avoiding excessive accumulation of inhibitory components such as nitrogen oxides.

[0051] Example 6, Adaptability verification for different photoreactor types: Following steps S1 to S5, the pretreated mixed gas was introduced into a 50-liter column photoreactor and a 50-liter tubular photoreactor, respectively. The initial inoculation optical density (680 nm wavelength) was 0.3, the incubation temperature was 25 degrees Celsius, the light intensity was 5000 lux, and the light-dark ratio was 12 hours to 12 hours. Continuous monitoring was conducted for 9 days.

[0052] In the column reactor, the optical density value increased from 0.31 to 0.613 over the first 6 days, but after reaching 0.665 on the 7th day, it rapidly decreased, dropping to 0.340 on the 8th day and 0.330 on the 9th day. Analysis suggests that the dissolved oxygen concentration within the column reactor remained consistently high, between 5.54 and 5.88 mg / L. This excessively high dissolved oxygen, combined with residual nitrogen oxides in the flue gas, created synergistic oxidative stress, leading to cell damage. Simultaneously, the large-scale adsorption of algal cells onto the reactor's inner wall restricted light penetration, further inhibiting growth.

[0053] In the tubular reactor, the optical density value steadily increased from 0.313 on day 1 to 1.025 on day 9 without a sudden drop. The forced degassing device in the tubular reactor (releasing supersaturated oxygen as the circulating liquid passes through the degassing tank) effectively reduced the dissolved oxygen concentration from 5.56 mg / L on day 1 to 4.77 mg / L on day 9, thus avoiding oxidative stress. Furthermore, the turbulence within the pipe inhibited algal cell settling and adhesion. Therefore, this method performs better in tubular photoreactors and is recommended as the preferred reactor type for industrial implementation.

[0054] Example 7, Regarding the handling of the moisture content problem in flue gas: This embodiment adds a pretreatment measure to step S3: before the mixed gas enters the first condensing chamber, it passes through a cyclone gas-water separator. This separator uses centrifugal force to throw large-diameter water droplets against the wall and collect them for discharge, reducing the moisture content from 30% to about 15%. Then, three-stage condensation dehumidification is performed. With this improvement, the flow meter reading is stable, the condensing chamber drainage is reduced by about 50%, and the equipment's operational reliability is improved.

[0055] Please see Figure 3 As shown in Example 8, the specific parameters of the culture system are as follows: This embodiment provides a complete application example: A 50-liter tubular photobioreactor is filled with 40 liters of BG-11 culture medium and inoculated with Chlorella to achieve an initial optical density (680 nm) of 0.5. The culture temperature is controlled at 25 ± 0.5 degrees Celsius, the light intensity is 5000 lux, and the light-dark cycle is 12 hours of light and 12 hours of darkness. The flue gas is taken from a waste incineration plant and, after testing in step S1, contains: carbon dioxide 12.8%, oxygen 14.9%, nitrogen oxides 108 mg / m³, and sulfur dioxide 6 mg / m³. Step S2 calculates the toxicity co-equivalent to 25.5, and from a table, the oxygen compensation margin is 0.20 L / min. After correction, the air flow rate is 25.20 L / min, the flue gas flow rate is 25 L / min, and the carbon-to-nitrogen ratio of the mixed gas is approximately 210:1. Step S3 obtains a pretreated mixed gas with a relative humidity of 90% and a temperature of 25 degrees Celsius. In step S4, the initial pulse volume was 0.2 liters, with an interval of 30 minutes, adaptively modulated according to the dissolved oxygen decay curve. In step S5, the exhaust port was monitored daily. The carbon dioxide concentration decreased from 12.8% at the inlet to 2.5% at the outlet, and the carbon absorption efficiency was 10.3%, within the baseline range; the nitrogen oxide removal rate was 82%, higher than 75%. After 14 days of continuous culture, the optical density of Chlorella reached 1.8, the cumulative dry weight biomass was 1.2 grams per liter, and the carbon fixation efficiency was approximately 0.5 kg of carbon dioxide fixed per cubic meter of culture medium per day.

[0056] Example 9, Validation of the method for calculating toxicity synergistic equivalents: To verify the rationality of the toxicity synergistic equivalent calculation formula, a comparative experiment was conducted in this embodiment. Three groups of identical simulated flue gas were used: the first group contained only sulfur dioxide (concentration 10 mg / m³), the second group contained only nitrogen oxides (concentration 120 mg / m³), and the third group contained both sulfur dioxide (10 mg / m³) and nitrogen oxides (120 mg / m³). The toxicity synergistic equivalent was calculated for each group: 0 for the first group (because the nitrogen oxide concentration was 0), 0 for the second group, and 34.64 for the third group. Chlorella was cultured under the same conditions, and its optical density growth rate was measured. The results showed that the growth rates of the first and second groups were not significantly different from the air control group, while the growth rate of the third group decreased by 15%. This indicates that the inhibitory effect produced when the two pollutants are present simultaneously is much greater than the simple sum of their individual forms, and the square root of the toxicity synergistic equivalent precisely reflects this synergistic effect. The oxygen compensation margin obtained from the table was 0.30 L / min in the third group, significantly greater than the 0.05 L / min in the first and second groups, proving that the compensation method is effective.

[0057] Example 10: Calibration of the ratio between slope and injection volume in pulse modulation: This embodiment provides a method for calibrating the relationship between slope and injection volume ratio. A small-scale test was conducted in a 500 mL Erlenmeyer flask with an initial inoculation optical density of 0.5. Simulated flue gas was introduced, and the carbon dioxide consumption rate was varied (achieved by changing the light intensity). The minimum pulse injection volume required to maintain a stable dissolved carbon dioxide concentration at different consumption rates was recorded. Using the injection volume (0.02 L) corresponding to a baseline consumption rate (0.05 mg / L / min) as a benchmark, a curve showing the relationship between the consumption rate ratio and the injection volume ratio was plotted. Experimental data show a linear proportional relationship with a proportionality coefficient of 1.0. That is, for every doubling of the consumption rate, the injection volume should also double. Therefore, this embodiment adopts a relationship where the injection volume is directly proportional to the absolute value of the slope.

[0058] Example 11: Screening Experiment and Results of Dominant Algal Species. This example was used to verify the tolerance and carbon fixation capacity of the microalgae Chlorella and Scenedesmus selected by the method of the present invention to waste incineration flue gas. The experiment was conducted in 500 mL Erlenmeyer flasks with a liquid volume of 400 mL. The initial inoculation optical density (680 nm wavelength) was 0.3 to 0.5, the culture temperature was 25 ± 1 °C, the light intensity was 5000 lux, and the light-dark ratio was 12 hours of light and 12 hours of darkness. The flue gas group was continuously introduced with waste incineration flue gas that had undergone desulfurization, denitrification, dust removal, and cooling treatment. The volume fraction of carbon dioxide in the flue gas was 10% to 13%, the concentration of nitrogen oxides was less than 120 mg / m³, and the concentration of sulfur dioxide was less than 10 mg / m³. The aeration rate was 0.5 L / min (i.e., 0.5 vvm). The air group was introduced with an equal volume of compressed air as a control group. Each group had 3 parallel samples, and the culture period was 9 days.

[0059] Daily samples were taken to measure the optical density (680 nm wavelength) of microalgae, pH of the culture medium, dissolved oxygen content, maximum photochemical efficiency of photosystem II, and the content of photosynthetic pigments (chlorophyll a, chlorophyll b, and carotenoids). The measurement methods are as follows: optical density was measured using a spectrophotometer at 680 nm wavelength; pH was directly measured using a portable pH meter; dissolved oxygen content was measured using a dissolved oxygen meter; maximum photochemical efficiency was measured using a chlorophyll fluorometer; and photosynthetic pigment content was determined using the acetone extraction method.

[0060] The experimental results showed that the optical density of *Chlorella* in the flue gas group increased from 0.50 on day 1 to 1.49 on day 7, and then decreased slightly, while the optical density in the air group increased from 0.50 to 1.34 on day 8. After day 3, the biomass in the flue gas group was consistently higher than that in the air group. The optical density of *Scenedesmus* in the flue gas group showed a similar trend to that of *Chlorella*, but with a slightly lower peak and a decrease in the later stages of cultivation. The optical density of *Spirulina* in the flue gas group continuously decreased from 0.31 on day 1 to 0.12 on day 5, a decrease of 61.3%, indicating that *Spirulina* could not adapt to the flue gas environment.

[0061] Regarding the pH of the culture medium, the pH of the flue gas group for *Chlorella* and *Scenedesmus* decreased from an initial 8.58 to 6.65 and stabilized at around 6.5, within the tolerance range of both microalgae (6.0 to 10.0). This slightly acidic environment was also conducive to the dissolution and absorption of carbon dioxide. The pH of the air group, however, increased to 10 to 11. The pH of the *Spirulina* flue gas group decreased to 7.34, deviating from its optimal growth range (8.5 to 11.0), resulting in metabolic inhibition.

[0062] Regarding dissolved oxygen content, the dissolved oxygen in the Chlorella flue gas group increased from 4.38 mg / L on day 1 to 6.18 mg / L on day 7, higher than that in the air group, indicating enhanced photosynthetic oxygen production capacity. The dissolved oxygen change trend in the Scenedesmus flue gas group was similar to that of Chlorella, but the peak value was slightly lower. The dissolved oxygen in the Spirulina flue gas group, however, continuously decreased from 3.94 mg / L to 2.95 mg / L, indicating severely impaired oxygen production capacity.

[0063] Regarding maximum photochemical efficiency, the values ​​for Chlorella and Scenedesmus in the flue gas group remained within a reasonable range of 0.5 to 0.7, with no significant difference from the air group, indicating that the flue gas did not damage their photosystem II. However, the value for Spirulina in the flue gas group continuously decreased from 0.68 to 0.41, indicating irreversible damage to photosystem II.

[0064] Regarding photosynthetic pigment content, the chlorophyll a, chlorophyll b, and carotenoid contents in the Chlorella flue gas group peaked between days 5 and 7, all higher than those in the air group, with the sum of chlorophyll a and chlorophyll b reaching 14.9 mg / L. The photosynthetic pigment content in the Scenedesmus flue gas group was higher than that in the air group in the early stages of cultivation, but decreased in the later stages. In the Spirulina flue gas group, chlorophyll b was almost completely degraded, and carotenoid synthesis was inhibited.

[0065] Based on the above experimental results, both Chlorella and Scenedesmus exhibit good tolerance to the deeply treated flue gas from waste incineration. The high concentration of carbon dioxide in the flue gas effectively promotes their biomass accumulation and photosynthesis, while Spirulina is not suitable for this flue gas environment. Therefore, the selection of Chlorella or Scenedesmus as the microalgae in the method of this invention is well-founded by experimental evidence.

[0066] Example 12, Conclusion and Validation of Dominant Algal Species Screening: Based on the experimental data of Example 11, this embodiment further summarizes the differences in the adaptability of Chlorella, Scenedesmus, and Spirulina to waste incineration flue gas, providing a complete experimental basis for the selection of microalgae species in the method of this invention.

[0067] The physiological indicators of the three microalgae in Example 11 under flue gas culture conditions were summarized and compared. The specific results are as follows.

[0068] After 9 days of cultivation in flue gas, *Chlorella vulgaris* achieved a peak optical density of 1.49, a peak dissolved oxygen level of 6.18 mg / L, and a peak sum of chlorophyll a and chlorophyll b of 14.9 mg / L. The maximum photochemical efficiency remained consistently between 0.5 and 0.7, and the pH of the culture medium remained stable at around 6.5. All these indicators were superior to those of the air control group, indicating that *Chlorella vulgaris* can fully utilize carbon dioxide in the flue gas as a carbon source. Its photosystem II was not significantly inhibited by nitrogen oxides and sulfur dioxide in the flue gas, exhibiting good suspension growth characteristics without adhesion to the walls or settling to the bottom.

[0069] After 9 days of cultivation in flue gas, the peak optical density of *Scenedesmus* was lower than that of *Chlorella*, and the optical density decreased in the later stages of cultivation. The peak dissolved oxygen was also lower than that of *Chlorella*. The maximum photochemical efficiency dropped to around 0.55 in the later stages of cultivation, and the photosynthetic pigment content showed a decreasing trend in the later stages of cultivation. *Scenedesmus* exhibited significant adhesion and sedimentation during cultivation, with cells agglomerating, leading to uneven photosynthetic reactions. These results indicate that *Scenedesmus* is also tolerant to flue gas environments, but its overall carbon fixation performance is slightly lower than that of *Chlorella*.

[0070] After 5 days of cultivation in flue gas, the light density of Spirulina decreased from 0.31 to 0.12, a drop of over 60%. The pH of the culture medium decreased from 8.44 to 7.34, deviating from its optimal growth range. Dissolved oxygen decreased from 3.94 mg / L to 2.95 mg / L, and the maximum photochemical efficiency decreased from 0.68 to 0.41. Chlorophyll b was almost completely degraded. These results indicate that Spirulina is extremely sensitive to the acidic environment induced by flue gas and residual toxic components, making it impossible to effectively utilize the carbon source from flue gas.

[0071] Based on the above comparison results, Chlorella is the preferred core algae species for biological carbon sequestration of waste incineration flue gas. Scenedesmus can be used as an auxiliary mixed culture algae species in combination with Chlorella, while Spirulina is not suitable for carbon sequestration scenarios in waste incineration flue gas.

[0072] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions, characterized in that, Includes the following steps: S1, Collect composition data of waste incineration flue gas, including: carbon dioxide concentration, oxygen concentration, nitrogen oxide concentration and sulfur dioxide concentration; S2, Based on the composition data, a multivariate coupling algorithm is introduced to calculate the dynamic mixing ratio of air and waste incineration flue gas. The multivariate coupling algorithm includes the synergistic inhibition coefficient of carbon dioxide and nitrogen oxides and the oxygen compensation factor. The air and flue gas are mixed according to the dynamic mixing ratio to obtain a mixed gas with the target carbon dioxide concentration and carbon-nitrogen ratio. S3 involves performing staged condensation dehumidification and isothermal saturation regulation on the mixed gas. Based on the dew point temperature of the mixed gas and the temperature requirements of the microalgae cultivation system, the thermodynamic state of the mixed gas is reconstructed to obtain a pretreated mixed gas with controllable temperature and humidity. S4, the pretreated mixed gas is divided into multiple pulse gas clusters according to the time sequence. The injection volume and injection frequency of each pulse gas cluster are adaptively modulated according to the real-time decay curve of dissolved carbon dioxide in the culture system. The modulated pulse gas cluster is introduced into the culture system containing microalgae, wherein the microalgae are selected from Chlorella or Scenedesmus. S5 detects the composition of the gas emitted from the culture system, and adjusts the dynamic mixing ratio and pulse modulation parameters based on the detection results to maintain the carbon dioxide concentration in the culture system within the tolerance range for microalgae growth.

2. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 1, characterized in that, The multivariate coupling algorithm calculates the dynamic mixing ratio of air and waste incineration flue gas, specifically including: The toxic synergistic equivalent is obtained by multiplying the collected nitrogen oxide concentration and sulfur dioxide concentration by the square root. Using toxicity synergistic equivalent as a variable, the corresponding oxygen compensation range is obtained by looking up a table, and the compensation range is superimposed on the baseline air flow rate to obtain the corrected air flow rate. Based on the corrected ratio of airflow to flue gas flow, the mixing ratio is adjusted sequentially until the carbon-nitrogen ratio of the mixture stabilizes within the preset threshold range.

3. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 2, characterized in that, The process of obtaining the corresponding oxygen compensation range by looking up a table specifically includes: A coefficient table is pre-constructed containing multiple toxicity synergistic equivalent ranges and their corresponding oxygen compensation ranges, wherein the lower the toxicity synergistic equivalent, the smaller the corresponding oxygen compensation range; Use the calculated toxicity synergistic equivalent as the search key to locate the interval to which it belongs in the coefficient table; Read the oxygen compensation range associated with the corresponding interval. If the toxicity co-equivalent falls exactly on the interval boundary, take the arithmetic mean of the two adjacent compensation ranges.

4. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 1, characterized in that, The process of staged condensation dehumidification and isothermal saturation conditioning of the mixed gas specifically includes: The mixed gas is passed sequentially through three condensing chambers with progressively decreasing temperatures. The set temperature of each condensing chamber is 5 to 8 degrees Celsius lower than the previous one, so that water vapor in the mixed gas is gradually released. The condensed and dehumidified mixed gas is introduced into a constant temperature saturation chamber, and the temperature inside the chamber is kept consistent with the temperature of the microalgae culture system. Using the real-time dew point temperature of the mixed gas as feedback, the water bath temperature in the constant temperature saturation chamber is adjusted to keep the relative humidity of the outlet mixed gas stable between 80% and 95%.

5. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 1, characterized in that, The thermodynamic state of the reconstructed mixture specifically includes: The outlet dew point temperature and outlet dry bulb temperature of the mixed gas after passing through the constant temperature saturation chamber are collected simultaneously, and the difference between the two is calculated as the saturation deviation. The saturation deviation is compared with the preset allowable fluctuation range. If the deviation exceeds the range, the cooling power of the previous condenser is adjusted in reverse. Repeat the sampling and adjustment steps until the relative humidity and temperature of the outlet mixed gas simultaneously meet the inlet requirements of the culture system.

6. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 1, characterized in that, The process for obtaining the real-time decay curve of dissolved carbon dioxide is as follows: The rate of change of dissolved oxygen concentration was continuously monitored within the culture system, and the rate of increase of dissolved oxygen was used as an indirect characterization of the intensity of photosynthesis. When the rate of increase of dissolved oxygen is less than 30% of that in the previous period, the dissolved carbon dioxide in the culture system is determined to have entered the decay phase. Starting from the determination time, the dissolved oxygen concentration value is recorded at fixed time intervals, and the recorded value is converted into carbon dioxide consumption rate. The consumption rates at each time point are connected in series to form a real-time decay curve.

7. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 1, characterized in that, The injection volume and injection frequency of each pulse gas cloud are adaptively modulated based on the real-time decay curve of dissolved carbon dioxide in the culture system, specifically including: The slope of the real-time decay curve is used as the modulation reference. The larger the absolute value of the slope, the faster the carbon dioxide is consumed. The injection volume of the next pulse gas mass is dynamically adjusted based on the slope value, so that the injection volume is proportional to the absolute value of the slope. The interval between two adjacent pulses was inversely correlated with the injection volume; the larger the injection volume, the shorter the interval, thus maintaining a stable fluctuation in the dissolved carbon dioxide concentration within the culture system.

8. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 1, characterized in that, The feedback correction process for the dynamic mixing ratio pair specifically includes: The carbon dioxide concentration at the inlet and outlet of the culture system were measured separately, and the difference between the two concentrations was calculated as a characterization value of carbon absorption efficiency. The carbon absorption efficiency characterization value is compared with the preset benchmark efficiency range. If the characterization value is lower than the lower limit of the benchmark range, it is determined that the carbon dioxide supply in the mixture is excessive. The dynamic mixing ratio is adjusted by reducing the flue gas flow rate by 5% for every unit deviation of the characterization value from the lower limit, until the carbon absorption efficiency characterization value returns to the benchmark range.

9. The method for constructing a gas path for microalgae cultivation under waste incineration flue gas conditions according to claim 1, characterized in that, The feedback correction process for pulse modulation parameters specifically includes: The residual concentration of nitrogen oxides in the exhaust gas from the outlet of the culture system was detected and compared with the initial concentration of nitrogen oxides at the inlet to calculate the relative removal rate of nitrogen oxides. When the relative removal rate is lower than the preset tolerance threshold, it is determined that the current pulse air mass injection frequency is too high, resulting in the inhibition of microalgal metabolism. The pulse modulation parameters are adjusted sequentially by reducing the pulse injection frequency by 2% for every percentage point the relative removal rate falls below the threshold, until the relative removal rate recovers to above the threshold.

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