Thermal power plant wastewater resource utilization system and method based on microalgae technology

Abstract

The invention provides a power plant wastewater resource utilization system based on a microalgae technology, which comprises a wastewater pretreatment unit: a microalgae culture unit which is provided with a culture pond or a reactor, introduces pretreated high-concentration wastewater into the culture pond or the reactor, and inoculates microalgae for culture; the harvesting and extracting unit is used for harvesting the microalgae after the microalgae grow to a certain stage; and the wastewater reflux and reutilization unit is used for further treating the wastewater after microalgae culture, removing residual microalgae cells and metabolites, and then refluxing the wastewater to a power plant for reutilization or up-to-standard discharge. The invention aims to convert inorganic pollutants such as nitrogen, phosphorus and the like in the wastewater discharged by the power plant into valuable biomass resources.

Description

Technical Field

[0001] The present invention relates to the field of environmental protection technologies, and specifically to a system and method for resource utilization of thermal power plant wastewater based on microalgae. Background Art

[0002] For a long time, thermal power plants have been one of the main power supply units in China. During the process of generating electricity in the fuel power generation device of a thermal power plant, a large amount of wastewater is generated. If this wastewater is directly discharged into the environment, it will cause serious pollution problems. The treatment of thermal power plant wastewater has always been one of the important issues concerned by China's ecological environment protection in recent years and is of great significance to the healthy development of China's ecological environment.

[0003] With the continuous growth of energy demand and the increasing awareness of environmental protection, the problems of carbon emissions and resource utilization efficiency in power plants have become increasingly prominent. Traditional power plant equipment generates a large amount of waste gas, wastewater and waste heat during operation. These wastes not only pollute the environment but also waste valuable energy resources. Therefore, how to effectively utilize these wastes and achieve the resource utilization of power plant equipment has become an urgent problem to be solved.

[0004] Microalgae are a type of autotrophic organisms that are widely distributed on land and in the ocean, rich in nutrients and with a high photosynthetic utilization rate. Polysaccharides, proteins, pigments, etc. produced by cell metabolism make them have good development prospects in the fields of food, medicine, genetic engineering, liquid fuels, etc. As a single-celled organism, microalgae have the characteristics of fast growth rate, strong adaptability, high photosynthetic efficiency and strong carbon fixation ability. In recent years, the application research of microalgae in the fields of energy, environmental protection and biotechnology has received increasing attention. Utilizing microalgae for the resource utilization of waste gas, wastewater and waste heat discharged from power plants can not only reduce the carbon emissions of power plants but also improve the energy utilization efficiency, achieving a win-win situation of economic and environmental benefits.

[0005] Up to now, some urban sewage treatment plants (such as using Chlorella to treat domestic sewage in a certain case) and industrial wastewater treatment plants (such as treating wastewater containing heavy metals) have carried out pilot applications, adsorbing and degrading pollutants by microalgae and recovering biomass. Rural areas have tried to use microalgae to treat domestic sewage and aquaculture wastewater, achieving low-cost purification through simple facilities. The bacteria-algae symbiotic system (such as the microalgae-bacteria consortium) has demonstrated high-efficiency nitrogen and phosphorus removal ability in the laboratory, but there are still few actual engineering applications.

[0006] Microalgae that grow naturally in sewage environments usually have high tolerance to pollutants, and through long-term adaptive evolution, they are likely to form functional algal strains with efficient degradation of specific pollutants. Therefore, algal species screened in situ from sewage systems have unique advantages in the process of targeted enhanced sewage treatment. Under long-term environmental stress, endogenous microalgae in sewage systems can evolve high-efficiency degradation capabilities for polycyclic aromatic hydrocarbons / heavy metals through epigenetic regulation and metabolic pathway remodeling. Based on this, indigenous algal strains obtained through metagenomic screening and functional verification can significantly improve the ecological adaptability and treatment stability of biological enhancement processes.

[0007] Power plant wastewater contains a large amount of pollutants such as organic matter, inorganic salts, and heavy metals. If directly discharged, it will cause serious pollution to the environment. At the same time, with the increasing energy demand, it becomes particularly important to find sustainable clean energy sources. As an efficient producer of biomass energy, microalgae can use sunlight, CO2, and nutrients in wastewater for photosynthesis to synthesize high-value products such as lipids, achieving the dual effects of wastewater treatment and biomass energy production.

[0008] Previously, through a large number of experiments, we isolated one strain of Scenedesmus, one strain of Euglena, and one strain of Haematococcus pluvialis, and determined the species through morphology, 16S rRNA sequencing, and 18S rRNA sequencing. The figure is shown in the appendix Figures 4 - 6 After the sewage co-culture experiment, the experimental results showed that all three types of algae have the ability to decompose organic pollutants in sewage, and the co-culture effect of Scenedesmus and Euglena is better than that of their separate cultures. Summary of the Invention

[0009] To solve the above problems, the present invention discloses a microalgae-based resource utilization system and method for power plant wastewater, aiming to convert inorganic pollutants such as nitrogen and phosphorus in the wastewater discharged from power plants into valuable biomass resources.

[0010] A microalgae-based resource utilization system for power plant wastewater includes Wastewater pretreatment unit: Microalgae culture unit: Set up a culture pond or reactor, introduce the pretreated high-concentration wastewater into it, and inoculate microalgae for cultivation; Harvesting and extraction unit: After the microalgae grow to a certain stage, harvest them; Wastewater reflux and reuse unit: Further treat the wastewater after microalgae cultivation to remove residual microalgae cells and metabolites, and then reflux it to the power plant for reuse or discharge up to standard.

[0011] A microalgae-based resource utilization method for power plant wastewater specifically includes the following steps: including: Step 1: Pretreat the wastewater for the preliminary treatment of power plant wastewater, remove suspended solids and heavy metal impurities, and adjust the pH value and nutrient salt content of the wastewater to meet the growth requirements of microalgae; filter the wastewater through a reverse osmosis membrane system to obtain high-concentration wastewater; Step 2: Cultivate microalgae, set up a culture pond or reactor, introduce the pretreated high-concentration wastewater into it, and inoculate microalgae for cultivation; Step 3: Harvest the microalgae and extract the microalgae obtained from the cultivation in Step 2; Step 4: Further treat the wastewater after microalgae cultivation, remove residual microalgae cells and metabolites, and then recycle it to the power plant for reuse or discharge up to the standard.

[0012] Experimental condition setting: Determine the optimal light intensity and temperature for each type of algae through preliminary experiments, measure the number of algal cells every day, and select the cultivation day with the highest algal density. Measure various data such as the algal cell density and Fv / Fm of microalgae, and the conductivity and TDS of the water body, aiming to explore the growth conditions of different microalgae in wastewater. Fv / Fm is the maximum photochemical absorption of photosystem II of chloroplasts, which can reflect the photosynthesis intensity of algal cell chloroplasts to a certain extent.

[0013] Furthermore, in Step 2, Scenedesmus is used as the microalgae variety, and a tubular photobioreactor is designed as the culture container; cultivate for 7 days under the conditions of a light intensity of 5000 Lx and a temperature of 25 °C, the Scenedesmus biomass reaches 2.0 g / L, and the lipid production rate is 15 mg / L·d. The harvested Scenedesmus is extracted for lipids through crushing and centrifugation, and the wastewater is further treated and recycled to the power plant for use as cooling water.

[0014] Furthermore, in Step 1, the wastewater discharged from the thermal power plant is treated by coagulation sedimentation to remove suspended solids, and chemical precipitation is used to remove heavy metal ions, and then the pH value is adjusted to 6.0 - 7.5, and reverse osmosis is concentrated 2 - 4 times or membrane filtration is used to remove suspended solids and colloidal substances.

[0015] Furthermore, in Step 2, Euglena is selected as the microalgae variety, and a tubular photobioreactor is designed as the culture container; cultivate for 5 days under the conditions of a light intensity of 4000 Lx and a temperature of 30 °C, the Euglena biomass reaches 1.8 g / L, and the Euglena polysaccharide production rate is 20 mg / L·d; the harvested Euglena is extracted for polysaccharides by water extraction, and the wastewater is further treated and discharged up to the standard to the environment.

[0016] Further, in Step 2, mixed microalgae, a mixture of Scenedesmus and Euglena, are used as the algal species; the pretreated wastewater is introduced into the microalgae cultivation unit, and the mixed microalgae are inoculated for cultivation; under the conditions of a light intensity of 6000 Lx and a temperature of 28 °C, cultivation is carried out for 6 days, and the biomass of the mixed microalgae reaches 2.2 g / L, while the lipid and protein contents are produced; after harvesting, the lipid and protein are extracted from the mixed microalgae by solvent extraction, and the wastewater can be used as boiler make-up water after further treatment.

[0017] Further, in Step 2, Haematococcus pluvialis is used as the algal species. Under the conditions of a light intensity of 6000 Lx and a temperature of 28 °C, cultivation is carried out for 6 days, and the biomass of Haematococcus pluvialis reaches 2.5 g / L, while astaxanthin is produced; after harvesting, astaxanthin is extracted from Haematococcus pluvialis by solvent extraction, and the residue is sold to feed mills as feed raw materials, and the wastewater can be used as reclaimed water after further treatment.

[0018] Advantages of the present invention: 1. The resource utilization of the wastewater discharged from the power plant can be realized; 2. Water resources are saved: Using the wastewater as the water source for microalgae cultivation can save precious water resources and reduce the treatment cost of wastewater.

[0019] 3. Economic benefits are generated: As a high-value biomass resource, microalgae can be applied in multiple fields to generate significant economic benefits.

[0020] 4. Co-removal of pollutants: Microalgae absorb COD, ammonia nitrogen, and phosphate in the power plant sewage through photosynthesis (the removal rates of TN and TP can reach 50%-95%), and adsorb heavy metal ions (copper, lead, cadmium) and organic pollutants (such as antibiotics and pesticide residues) to achieve the synchronous purification of multiple pollutants.

[0021] 5. Carbon emission reduction and oxygen increase benefits: Microalgae photosynthesis can fix the carbon dioxide emitted from the power plant (the carbon sequestration potential reaches 1.8-2.5 kg CO 2 / m·d 3 ), while releasing oxygen to increase the dissolved oxygen in the water body (DO≥4 mg / L).

[0022] 6. Low cost and resource utilization: Compared with the traditional activated sludge method, the energy consumption of the microalgae system is reduced by 30%-50% (no mechanical aeration is required), and the biomass can be converted into biodiesel (lipid content reaches 27%), feed protein (protein content >50%) or biofertilizer, realizing a "pollution treatment-resource utilization" closed loop, and the nitrogen and phosphorus removal efficiency can be increased from 70% of the traditional sludge method to more than 85%.

[0023] 7. For the pretreatment, only reverse osmosis concentration is required, and then the concentrated water is used to cultivate algae. The water can be reused or directly discharged. If the screened algal species are directly cultured, no additional nutrient salts are needed. Description of the Drawings

[0024] Figure 1 The system flowchart of the present invention; Figure 2 、 2 Cell density of Haematococcus pluvialis in the concentrated water of 2-fold concentration and 4-fold concentration; Figure 3 、 2 Cell density of Euglena gracilis in the concentrated water of 2-fold concentration and 4-fold concentration; Figure 4 、 Conductivity change of Euglena gracilis in 96 hours; Figure 5 、 TDS change of Euglena gracilis in 96 hours; Figure 6 、 Microscopic examination diagram of Scenedesmus sp.; Figure 7 、 Microscopic examination diagram of Euglena gracilis; Figure 8 、 Microscopic examination diagram of Haematococcus pluvialis. Detailed Embodiment

[0025] The present invention will be further clarified below in conjunction with the drawings and detailed embodiments. It should be understood that the following detailed embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the drawings, and the words "inside" and "outside" respectively refer to the directions towards or away from the geometric center of a specific component.

[0026] As Figure 1 shown, a power plant wastewater resource utilization system based on microalgae technology in this embodiment includes: Wastewater pretreatment unit: used for preliminary treatment of power plant wastewater, removing impurities such as suspended solids and heavy metals, and adjusting the pH value and nutrient salt content of the wastewater to meet the growth requirements of microalgae. The wastewater is filtered through a reverse osmosis membrane system to obtain high-concentration wastewater, so as to improve the treatment efficiency.

[0027] Microalgae culture unit: set up a culture pond or reactor, introduce the pretreated wastewater into it, and inoculate microalgae for cultivation. By controlling conditions such as light, temperature, and stirring, the growth environment of microalgae is optimized. All the microalgae are obtained by separating water samples collected in the wild.

[0028] Harvesting and extraction unit: after the microalgae grow to a certain stage, they are harvested. High-value products such as lipids and proteins in the microalgae are extracted by methods such as centrifugation, pressing, or solvent extraction.

[0029] Wastewater reflux and reuse unit: The wastewater after microalgae cultivation is further treated to remove residual microalgae cells and metabolites, and then refluxed to the power plant for reuse or discharged up to the standard.

[0030] A method for resource utilization of power plant wastewater based on microalgae technology, including: Example 1: Scenedesmus was selected as the microalgae species, and a tubular photobioreactor was designed as the cultivation container. The wastewater discharged from the thermal power plant was treated by coagulation sedimentation to remove suspended solids and by chemical precipitation to remove heavy metal ions, and then the pH value was adjusted to about 7.0 and reverse osmosis was used for 4-fold concentration. After pretreatment, it was introduced into the reactor and inoculated with Scenedesmus for cultivation. It was cultivated for 7 days under the conditions of light intensity of 5000 Lx and temperature of 25 °C, and the Scenedesmus biomass reached 2.0 g / L, and the lipid productivity was 15 mg / L·d. After harvesting, the Scenedesmus was broken and centrifuged to extract lipids, and the wastewater was further treated and then refluxed to the power plant for use as cooling water.

[0031] Example 2: Euglena was selected as the microalgae species, and a tubular photobioreactor was designed as the cultivation container. The wastewater discharged from the thermal power plant was treated by coagulation sedimentation to remove suspended solids and by chemical precipitation to remove heavy metal ions, and then the pH value was adjusted to about 6.5 and reverse osmosis was used for 2-fold concentration. After pretreatment, it was introduced into the reactor and inoculated with Euglena for cultivation. It was cultivated for 5 days under the conditions of light intensity of 4000 Lx and temperature of 30 °C, and the Euglena biomass reached 1.8 g / L, and the Euglena polysaccharide productivity was 20 mg / L·d. After harvesting, the Euglena was extracted for polysaccharides by water extraction method, and the wastewater was further treated and then discharged up to the standard to the environment.

[0032] Example 3: A mixed microalgae (a mixture of Scenedesmus and Euglena) was used as the algal species. The wastewater pretreatment unit used membrane filtration to remove suspended solids and colloidal substances, and then the pH value was adjusted to about 7.2 and appropriate amounts of inorganic salts and trace elements were added. The pretreated wastewater was introduced into the microalgae cultivation unit and inoculated with the mixed microalgae for cultivation. It was cultivated for 6 days under the conditions of light intensity of 6000 Lx and temperature of 28 °C, and the mixed microalgae biomass reached 2.2 g / L, and at the same time, it had relatively high lipid and protein contents. After harvesting, the mixed microalgae was extracted for lipids and proteins by solvent extraction, and the wastewater was further treated and could be used as boiler make-up water.

[0033] Example 4: Haematococcus pluvialis was used as the algal species. The wastewater pretreatment unit used membrane filtration to remove suspended solids and colloidal substances, then adjusted the pH value to about 7 and concentrated it 2 times by reverse osmosis. The pretreated wastewater was introduced into the microalgae culture unit and inoculated with mixed microalgae for cultivation. Under the conditions of a light intensity of 6000 Lx and a temperature of 28 °C, after 6 days of cultivation, the biomass of Haematococcus pluvialis reached 2.5 g / L, and at the same time, a relatively high astaxanthin content was produced. The harvested Haematococcus pluvialis was used to extract astaxanthin by solvent extraction, and the residue was sold to feed mills as feed raw materials. The wastewater could be used as reclaimed water after further treatment.

[0034] Combined with the analysis of Figure 2 Haematococcus pluvialis, the algal cells of Haematococcus pluvialis showed a rapid growth trend in the first 5 days, which was consistent with the growth trend of Haematococcus pluvialis in the second experiment with reverse osmosis water. The density in 4-fold concentrated reverse osmosis water was slightly higher than that in 2-fold concentrated reverse osmosis water, but the difference was small. In the cultivation cycle after 5 days, the density of Haematococcus pluvialis algal cells showed a stable state. Combining with the observation of the pictures, it was found that when the density of Haematococcus pluvialis was stable, the color of the algal liquid began to deepen and turn red. The experimental data proved that when Haematococcus pluvialis was cultivated in concentrated reverse osmosis water, it would gradually consume all the nutrients after 5 days and start to accumulate astaxanthin, and the rate was similar to the time when Euglena turned yellow mentioned above. Combining with the pictures, it was found that the time for 2-fold concentrated reverse osmosis water to induce astaxanthin was slightly faster than that of 4-fold concentrated reverse osmosis water. In the later stage of the experiment, obvious red wall-hanging substances appeared on the bottle wall, proving that Haematococcus pluvialis continuously accumulated astaxanthin.

[0035] Combined with the analysis of Figure 3 、 Figure 4 and Figure 5 the experimental data of algal cell density, considering the medium cost and microalgae biomass output, when cultivating Euglena with reverse osmosis water, the medium should be inoculated once. In addition, the growth of Euglena is also affected by the inoculation density. The appropriate density is higher than too low or too high density. In the experiment, the density of Euglena with 25 w / mm inoculated in reverse osmosis water was the best.

[0036] The experiment proved that 2-fold concentrated reverse osmosis water triggered astaxanthin synthesis earlier than 4-fold concentration (about 12 - 24 hours earlier), and the astaxanthin production increased by 15 - 20%. It was determined that "2-fold concentration" was the optimal economic concentration for inducing Haematococcus pluvialis to transfer from the proliferation stage to secondary metabolism (the cost was reduced by 70% compared with the traditional BG11 medium), breaking through the inertial thinking of blindly using high-concentration osmotic pressure induction in the existing technology.

[0037] The experiment verified that 25 w / mm was the optimal inoculation density for the growth of Euglena in reverse osmosis water. The biomass yield increased by 30% compared with the traditional process (10 - 15 w / mm), and the competitive inhibition caused by high density (>40 w / mm³) was avoided.

[0038] Among them, such as Figure 6 , the microscopic examination diagram of Scenedesmus; Figure 7 , the microscopic examination diagram of Euglena; Figure 8 , the microscopic examination diagram of Haematococcus pluvialis.

[0039] The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features.

Claims

1. A power plant wastewater resource utilization system based on microalgae technology, characterized by: include Wastewater pretreatment unit: Microalgae cultivation unit: a cultivation pool or reactor is set up, high-concentration wastewater after pretreatment is introduced into it, and microalgae are inoculated for cultivation; Harvesting and extraction unit: After the microalgae grows to a certain stage, it is harvested; Wastewater return and reuse unit: The wastewater after microalgae cultivation is further treated to remove residual microalgae cells and metabolites, and then returned to the power plant for reuse or discharge in compliance with standards.

2. A method for resource utilization of power plant wastewater based on microalgae technology, characterized in that: The specific steps include: Step 1: Pre-treat the wastewater to preliminarily treat the wastewater from the power plant, remove suspended solids and heavy metal impurities, and adjust the pH value and nutrient content of the wastewater to meet the growth needs of microalgae; filter the wastewater through a reverse osmosis membrane system to obtain high-concentration wastewater; Step 2: Cultivate the microalgae, set up a cultivation pool or reactor, introduce the pretreated high-concentration wastewater into it, and inoculate the microalgae for cultivation; Step 3: harvesting the microalgae and extracting the microalgae cultured in step 2; Step 4: The wastewater after microalgae cultivation is further treated to remove residual microalgae cells and metabolites, and then returned to the power plant for reuse or discharge in compliance with standards.

3. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 2 is characterized by: In the step 2, Scenedesmus is used as a microalgae variety, and a pipeline photosynthetic reactor is designed as a culture container; the culture is carried out for 7 days under the conditions of a light intensity of 5000Lx and a temperature of 25°C, and the Scenedesmus biomass reaches 2.0 g / L and the oil yield is 15 mg / L·d; the harvested Scenedesmus is crushed and centrifuged to extract lipids, and the wastewater is further treated and then returned to the power plant for use as cooling water.

4. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 2, characterized in that: In step 1, the wastewater discharged from the thermal power plant is subjected to coagulation sedimentation to remove suspended solids, chemical precipitation to remove heavy metal ions, and then the pH value is adjusted to 6.0-7.5, and reverse osmosis is used to concentrate 2-4 times or membrane filtration is used to remove suspended solids and colloidal substances.

5. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 2, characterized in that: In the step 2, euglena is selected as the microalgae species, and a pipeline photosynthetic reactor is designed as a culture container.

6. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 5, characterized in that: After culturing for 5 days under the conditions of light intensity of 4000 Lx and temperature of 30℃, the biomass of euglena reached 1.8 g / L and the polysaccharide yield of euglena was 20 mg / L·d. The polysaccharides were extracted from the harvested euglena by water extraction, and the wastewater was further treated and discharged into the environment after meeting the standards.

7. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 2, characterized in that: In step 2, mixed microalgae are used as algae species, i.e., a mixture of Scenedesmus and Euglena; the pretreated wastewater is introduced into a microalgae culture unit, and the mixed microalgae are inoculated for culture.

8. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 7, characterized in that: After culturing for 6 days under the conditions of light intensity of 6000 Lx and temperature of 28℃, the biomass of the mixed microalgae reached 2.2 g / L, and the oil and protein content was also produced. After harvesting, the mixed microalgae were extracted with solvent to extract lipids and proteins, and the wastewater could be used as boiler feed water after further treatment.

9. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 2, characterized in that: In step 2, Haematococcus pluvialis is used as the algae species.

10. The method for resource utilization of power plant wastewater based on microalgae technology according to claim 9, characterized in that: After 6 days of cultivation under the conditions of light intensity of 6000 Lx and temperature of 28℃, the biomass of Haematococcus pluvialis reached 2.5 g / L, and astaxanthin was produced at the same time. After harvesting, astaxanthin was extracted from the harvested Haematococcus pluvialis through solvent extraction, and the residue was sold to feed factories as feed raw materials. The wastewater can be used as reclaimed water after further treatment.

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