Method for treating seawater radioactive strontium pollution and carbon sequestration by porphyridium

Abstract

The present application relates to the technical field of bioengineering, and particularly relates to a method for treating seawater radioactive strontium pollution and fixing carbon by Porphyridium cruentum. The Porphyridium cruentum is inoculated into seawater medium polluted by radioactive strontium for treatment, and a certain content of inorganic salt and trace element solution is added, and continuous illumination is carried out, wherein the temperature, illumination intensity, sterile mixed gas ventilation rate and carbon dioxide ventilation concentration are controlled, so that the effect of treating seawater radioactive strontium pollution and fixing carbon by Porphyridium cruentum is realized, and the growth of Porphyridium cruentum is used to realize the concentration of strontium elements in seawater and the fixation of carbon dioxide. The present application combines the microalgae carbon fixation with wastewater treatment and biofuel production, has significant environmental and economic advantages, and can reduce the production cost and energy consumption to a certain extent. The method is simple in operation, low in cost and has certain universality.

Description

Technical Field

[0001] This invention belongs to the field of bioengineering technology, and specifically relates to a method for treating radioactive strontium pollution in seawater and simultaneously fixing carbon using *Porphyra yezoensis*. Background Technology

[0002] With the increasing consumption of fossil fuels, environmental degradation, and global warming, efficient and carbon-free clean nuclear power is gradually becoming an important industry worldwide. Most nuclear power plants are built near the coast, and the long-term discharge of low-level radioactive wastewater containing numerous radionuclides into the marine environment during operation increases the potential risk of marine radioactive pollution. In addition, nuclear submarines, powered ships, and other offshore nuclear-powered platforms, as well as various nuclear tests, are also potential sources of artificial radioactive pollution in the ocean.

[0003] The artificial radionuclides cesium-137 and strontium-90 in nuclear reactors and nuclear waste have half-lives greater than 20 years, requiring a long time to be purified under natural conditions. Currently used methods for treating radioactively contaminated water include adsorption, ion exchange, precipitation, membrane separation, and extraction. However, most of these methods are costly, complex to operate, and prone to causing secondary pollution, making them unsuitable for dealing with large-scale marine nuclear contamination.

[0004] Therefore, it is very important to find a way to effectively deal with marine radioactive contamination.

[0005] Microalgae are single-celled photosynthetic microorganisms that can grow rapidly in aquatic environments using light and carbon dioxide, possessing great potential to sequester carbon from the atmosphere and recover it as bioenergy. Combining microalgal carbon sequestration with wastewater treatment and biofuel production has significant environmental and economic advantages, and can reduce production costs and energy consumption to some extent.

[0006] Currently, the algae used to study the treatment of strontium pollution mainly include Nostoc commune, Chlorella vulgaris, brown algae, and copper algae, but there are no research reports on the treatment of strontium pollution in seawater by Porphyra yezoensis. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for treating strontium pollution in seawater using *Porphyra yezoensis* and combining it with carbon sequestration, offering a simple, energy-efficient, environmentally friendly, and scalable approach for treating strontium pollution in seawater.

[0008] The technical solution of the present invention is as follows:

[0009] A method for treating radioactive strontium contamination in seawater and co-fixing with *Porphyra yezoensis* includes the following steps:

[0010] The *Porphyra yezoensis* species were inoculated into radioactive strontium-contaminated seawater and cultured. Inorganic salts and trace element solutions were added, and continuous light was provided. During the culture process, the temperature, light intensity, sterile mixed gas ventilation rate, and carbon dioxide ventilation concentration were controlled. The growth of *Porphyra yezoensis* was used to concentrate strontium and fix carbon dioxide in seawater.

[0011] Preferably, the *Porphyra yezoensis* species is cultured to the end of the logarithmic growth phase.

[0012] Preferably, the inoculation amount of *Porphyra yezoensis* is 5-15% v / v (preferably 10% v / v).

[0013] Preferably, the concentration of strontium ions in the radioactively contaminated seawater that can be treated is 6–16 mg / L. This is because the concentration of strontium ions in natural seawater is relatively low. 2+ The background concentration of strontium is 6–8 mg / L, while lower concentrations of strontium promote the growth of *Porphyra yezoensis*. Therefore, the preferred initial concentration of strontium in seawater is 6–16 mg / L. Increased biomass is beneficial for improving the adsorption of strontium and carbon fixation, especially when the initial concentration of strontium in seawater is 16 mg / L.

[0014] Adding a certain amount of inorganic salts and trace elements to seawater can increase the biomass of *Porphyra yezoensis* culture and improve its adsorption of strontium and carbon fixation. Preferably, the concentrations of the added inorganic salts and trace elements are as follows: 6.6 g / L MgSO4·7H2O, 1.6 g / L MgCl2·6H2O, 1 g / L KNO3, 0.07 g / L KH2PO4, 0.04 g / L NaHCO3, 1 mL / L 0.5 M Na2Fe-EDTA (pH 7.6), 4 mg / L ZnCl2, 60 mg / L H3BO3, 1.5 mg / L CoCl2·6H2O, 4.0 g / L CuCl2·2H2O, 40 mg / L MnCl2·4H2O, and 37 mg / L (NH4)6Mo7O. 24 ·4H2O.

[0015] Adding Tris·HCl can adjust the pH in seawater to maintain relative stability. 1M Tris·HCl (pH 7.6) is used, with the preferred addition amount being 0-4 mL / L, and even more preferably 0 mL / L. This is because although a slightly alkaline environment is conducive to the accumulation of Porphyromonas pulmonaria biomass, an alkaline environment is more conducive to the adsorption of strontium.

[0016] Preferably, the culture temperature is 25±1℃, the light intensity is 10000-15000lx (preferably 13200lx (continuous light)), and the culture period is 16-20 days (preferably 18 days).

[0017] Preferably, the sterile mixed gas is obtained by mixing air and CO2 and then filtering the mixture through a 0.22 μm sterile filter membrane to obtain a sterile mixed gas with a carbon dioxide concentration of 5% to 10% v / v (preferably 10% v / v). Under these conditions, contamination by miscellaneous bacteria during ventilation can be avoided, thus improving the growth rate and biomass yield of *Porphyra yezoensis*. The carbon dioxide in the mixed gas can also induce *Porphyra yezoensis* to fix more carbon dioxide during its growth.

[0018] Preferably, the sterile mixed gas is introduced into the seawater at a ventilation rate of 1 L / min per 0.55 L of seawater (containing *Porphyra yezoensis* species). Under these conditions, the growth of *Porphyra yezoensis* is significantly promoted, the cultivation cycle of *Porphyra yezoensis* is shortened, and the efficiency of *Porphyra yezoensis* in adsorbing strontium and fixing carbon is improved.

[0019] Preferably, after inoculating with *Porphyra yezoensis* and culturing, the algal culture is centrifuged, and the supernatant after removing the *Porphyra yezoensis* is the treated seawater; the centrifuge speed is 6000-12000 rpm.

[0020] Application of *Porphyra yezoensis* in treating radioactive strontium contamination in seawater and co-fixing carbon.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] This invention discloses a method for treating strontium pollution in seawater using *Porphyra yezoensis* and combining it with carbon sequestration. 2+ The adsorption rate can reach 24.38%, and a total of 145.17g of carbon dioxide can be fixed in 18 days. The average carbon fixation efficiency can reach 5.75g CO2 / g biomass / d, which has good environmental and economic advantages and can reduce production costs and energy consumption to a certain extent.

[0023] The method of this invention avoids the problems of difficult adsorbent synthesis and recovery, and easy secondary pollution caused by conventional adsorbent treatment of water pollution. It is simple to operate, saves raw materials, has low input cost, has the potential to treat large-scale seawater strontium pollution, and has good industrial application prospects. Attached Figure Description

[0024] Figure 1 : Trend of biomass change during the cultivation of *Porphyra yezoensis*;

[0025] Figure 2 During the cultivation of *Porphyra yezoensis*, *Porphyra yezoensis* Sr 2+ Trend graph of adsorption efficiency;

[0026] Figure 3 : Trend chart of cumulative carbon dioxide fixation during the cultivation of *Porphyra yezoensis*. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be described in detail and clearly below with reference to the accompanying drawings. Unless otherwise specified, the reagents and instruments used in the following embodiments are all commercially available products, and the experimental methods in the embodiments without specific conditions are generally performed under conventional conditions. 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.

[0028] In the embodiments of the present invention, a simulated radioactive strontium-contaminated seawater culture medium is used as the experimental object. Purple Gloy Algae is inoculated into the simulated radioactive strontium-contaminated seawater culture medium, and then a certain amount of inorganic salts and trace elements are added.

[0029] The seawater culture medium used in the experiment to simulate radioactive strontium contamination included seawater and strontium storage solution.

[0030] The examples use seawater as the base object, and Sr in natural seawater 2+ The background concentration was 6–8 mg / L. By adjusting the amount of strontium storage solution added, the concentration of strontium ions in the simulated radioactive strontium-contaminated seawater culture medium was controlled to 6–16 mg / L.

[0031] The strontium storage solution was a strontium chloride hexahydrate solution, containing the isotope strontium-88. Its preparation method was as follows: 2.6667 g of SrCl₂·6H₂O was weighed and dissolved in 80 mL of sterile water, then diluted to 100 mL. The solution was filtered to remove bacteria and stored in a sterile reagent bottle at 4°C. Strontium-88 was used because its chemical properties are similar to strontium-90; it is non-radioactive and can, to some extent, reduce the effects of strontium on *Porphyra yezoensis* during its cultivation.

[0032] The concentrations of inorganic salts and trace elements added to the simulated radioactive strontium-contaminated seawater culture medium are as follows: 6.6 g / L MgSO4·7H2O, 1.6 g / L MgCl2·6H2O, 1 g / L KNO3, 0.07 g / L KH2PO4, 0.04 g / L NaHCO3, 1 mL / L 0.5 M Na2Fe-EDTA (pH 7.6), 4 mg / L ZnCl2, 60 mg / L H3BO3, 1.5 mg / L CoCl2·6H2O, 4.0 g / L CuCl2·2H2O, 40 mg / L MnCl2·4H2O, and 37 mg / L (NH4)6Mo7O 24 ·4H2O.

[0033] Adding Tris·HCl can adjust the pH of seawater to maintain relative stability. Use 1M Tris·HCl (pH 7.6) and add 0-4 mL / L.

[0034] All seawater culture media simulating radioactive strontium contamination required autoclaving before inoculation with *Porphyra yezoensis* to ensure a sterile environment. Furthermore, sampling and water replenishment of the *Porphyra yezoensis* solution throughout the entire culture cycle were performed in a laminar flow hood.

[0035] The simulated radioactive strontium-contaminated seawater culture medium used for culturing *Porphyra yezoensis* contained the following components: MgSO4·7H2O, MgCl2·6H2O, KNO3, KH2PO4, NaHCO3, Tris, HCl, NaOH, Na2EDTA·2H2O, FeCl3·4H2O, ZnCl2, H3BO3, CoCl2·6H2O, CuCl2·2H2O, MnCl2·4H2O, and (NH4)6Mo7O. 24 • The purity of 4H2O was all analytical grade.

[0036] The technical effects of the present invention are demonstrated below through specific embodiments.

[0037] Example 1

[0038] The method for treating strontium pollution in seawater using *Porphyra yezoensis* and combining it with carbon sequestration includes the following steps:

[0039] (1) Inoculate the *Porphyra yezoensis* seed into a 1L Erlenmeyer flask containing 500mL of seawater culture medium at a volume of 10% v / v. Do not add strontium stock solution. At this time, the Sr content in the culture medium is... 2+ The initial concentration was 7.37 mg / L. 4 mL / L of 1 M Tris·HCl (pH 7.6) was added to seawater, and the mixture was continuously incubated under light in a light incubator. During the incubation process, the temperature was controlled at 25 ± 1℃, the light intensity at 13200 lx, the sterile mixed gas ventilation rate at 1.0 L / min, and the carbon dioxide content in the sterile mixed gas at 5% v / v. The incubation period was 18 days, with sterile water added to the initial volume every 2 days in a laminar flow hood.

[0040] (2) Throughout the entire culture period, the carbon dioxide concentration in the exhaust gas was detected daily using an Agilent 7890B gas chromatograph, the biomass of *Porphyra yezoensis* was determined every 2 days using a UV-Vis spectrophotometer, the pH value of the culture medium was measured every 2 days using a pH meter, and the remaining Sr in the culture medium was measured every 6 days using an inductively coupled plasma atomic emission spectrometer. 2+ content.

[0041] The biomass of *Porphyra yezoensis* increased from 0.28 g / L to 3.88 g / L after 18 days of cultivation in this embodiment (see Appendix). Figure 1 ), Sr 2+ The adsorption rate was 10.29% (see appendix). Figure 2 ), a cumulative total of 199.31g of carbon dioxide was fixed (see appendix) Figure 3 The average carbon sequestration efficiency was 5.59 g CO2 / g biomass / d.

[0042] Example 2

[0043] The difference between Example 2 and Example 1 is as follows:

[0044] The amount of strontium stock solution added was 1 mL / L (at which point the Sr in the culture medium was...). 2+ The initial concentration was 15.52 mg / L.

[0045] The biomass of *Porphyra yezoensis* increased from 0.27 g / L to 4.34 g / L after 18 days of cultivation in this embodiment (see Appendix). Figure 1 ), Sr 2+ The adsorption rate was 1.81% (see appendix). Figure 2 ), a total of 142.52g of carbon dioxide was fixed (see appendix) Figure 3 The average carbon sequestration efficiency was 3.54 g CO2 / g biomass / d.

[0046] Experimental results show that, compared to Example 1, the Sr in the culture medium 2+ The increase in initial concentration caused *Porphyromonas purpureus* to enter its premature death phase. Cellular death and fragmentation caused the strontium accumulated by *Porphyromonas purpureus* to re-precipitate into the culture medium, resulting in a significant decrease in adsorption rate on day 18, and a corresponding reduction in cumulative carbon fixation and efficiency. This is because *Porphyromonas purpureus* has a lag phase, a logarithmic growth phase, a stationary phase, and a death phase. While a certain amount of strontium promotes the growth of *Porphyromonas purpureus* and increases its biomass, it also accelerates its growth, causing it to enter the death phase prematurely.

[0047] Example 3

[0048] The difference between Example 3 and Example 1 is as follows:

[0049] (1) The amount of strontium storage solution added was 1 mL / L (Sr in the culture medium). 2+ The initial concentration was 15.52 mg / L.

[0050] (2) The carbon dioxide content in the sterile mixed gas is 10% v / v.

[0051] The biomass of *Porphyra yezoensis* increased from 0.27 g / L to 3.93 g / L after 18 days of cultivation in this embodiment (see Appendix). Figure 1 ), Sr 2+ The adsorption rate was 3.10% (see appendix). Figure 2 ), a total of 193.53g of carbon dioxide was fixed (see appendix) Figure 3 The average carbon sequestration efficiency was 5.34 g CO2 / g biomass / d.

[0052] Experimental results show that, compared to Example 1, the Sr in the culture medium 2+ The increase in initial concentration caused the purple algae to enter the death phase earlier. The death and breakage of cells led to a significant decrease in the adsorption rate on day 18. However, higher concentrations of carbon dioxide induced an increase in the ability of the purple algae to fix carbon dioxide, so the cumulative carbon fixation amount and carbon fixation efficiency did not decrease significantly.

[0053] Example 4

[0054] The difference between Example 4 and Example 1 is as follows:

[0055] Without adding Tris·HCl; at this time, the Sr in the culture medium 2+ The initial concentration was 7.37 mg / L;

[0056] The biomass of *Porphyra yezoensis* increased from 0.24 g / L to 3.58 g / L after 18 days of cultivation in this embodiment (see Appendix). Figure 1 ), Sr 2+ The adsorption rate was 25.41% (see appendix). Figure 2 ), a cumulative total of 96.87g of carbon dioxide was fixed (see appendix) Figure 3 The average carbon sequestration efficiency was 2.93 g CO2 / g biomass / d.

[0057] Experimental results showed that, compared to Example 1, without the addition of Tris·HCl, the pH of the culture medium increased with the increase of the extracellular polysaccharide content of *Porphyra yezoensis*, and alkaline conditions were more favorable for Sr. 2+ Adsorption occurs, but the decrease in biomass leads to a decrease in the cumulative carbon sequestration.

[0058] Example 5

[0059] The difference between Example 5 and Example 1 is:

[0060] (1) Do not add Tris·HCl;

[0061] (2) The amount of strontium storage solution added was 1 mL / L (Sr in the culture medium). 2+ The initial concentration was 15.52 mg / L.

[0062] The biomass of *Porphyra yezoensis* increased from 0.25 g / L to 4.08 g / L after 18 days of cultivation in this embodiment (see Appendix). Figure 1 ), Sr 2+ The adsorption rate was 21.05% (see appendix). Figure 2 A total of 61.68g of carbon dioxide was fixed (see appendix). Figure 3 The average carbon sequestration efficiency was 1.63 g CO2 / g biomass / d.

[0063] Experimental results showed that, compared to Example 1, without the addition of Tris·HCl, the pH of the culture medium increased with the increase of the extracellular polysaccharide content of *Porphyra yezoensis*. Alkaline conditions and increased initial strontium concentration were both beneficial to Sr. 2+ Adsorption; however, under alkaline conditions, dissolved CO2 mainly exists as HCO3-. - The low concentration of dissolved CO2 mainly reduces the cumulative carbon fixation of *Porphyra yezoensis*, and also greatly reduces its carbon fixation efficiency.

[0064] Example 6

[0065] The difference between Example 6 and Example 1 is:

[0066] (1) Do not add Tris·HCl;

[0067] (2) The amount of strontium storage solution added was 1 mL / L (Sr in the culture medium). 2+ The initial concentration was 15.52 mg / L.

[0068] (3) The carbon dioxide content in the sterile air is 10% v / v.

[0069] The biomass of *Porphyra yezoensis* increased from 0.26 g / L to 2.81 g / L after 18 days of cultivation in this embodiment (see Appendix). Figure 1 ), Sr 2+ The adsorption rate was 24.38% (see appendix). Figure 2 ), a total of 145.17g of carbon dioxide was fixed (see appendix) Figure 3 The average carbon sequestration efficiency was 5.75 g CO2 / g biomass / d.

[0070] Experimental results show that, compared to Example 1, when Tris·HCl was not added, the increase in the extracellular polysaccharide content of *Porphyra yezoensis* led to an increase in the pH of the culture medium. Alkaline conditions and an increase in the initial strontium concentration were all beneficial to Sr. 2+ Adsorption; Although the low concentration of dissolved CO2 under alkaline conditions reduces the cumulative carbon fixation of Porphyra yezoensis, the increased carbon dioxide concentration greatly improves the efficiency of carbon dioxide fixation by Porphyra yezoensis.

Claims

1. A method for treating radioactive strontium contamination in seawater and simultaneously fixing carbon using *Porphyra yezoensis*, characterized in that, Includes the following steps: The *Porphyra yezoensis* strain was inoculated into radioactive strontium-contaminated seawater and cultured. Inorganic salts and trace element solutions were added, and continuous light was provided. The culture temperature, light intensity, sterile mixed gas aeration rate, and carbon dioxide aeration concentration were controlled. The growth of *Porphyra yezoensis* was used to concentrate strontium and fix carbon dioxide in the seawater. When the *Porphyra yezoensis* strain was cultured to the end of the logarithmic growth phase, the algal culture was centrifuged, and the supernatant after removing the *Porphyra yezoensis* was the treated seawater. The inoculation amount of *Porphyra yezoensis* was 10% v / v; the concentration range of strontium ions in the radioactively contaminated seawater was 16 mg / L; the treatment temperature was 25 ± 1℃, the light intensity was 13200 lx, and the treatment cycle was 18 days. The sterile mixed gas was obtained by mixing air and CO2 and then filtering it through a 0.22 μm sterile filter membrane; the carbon dioxide concentration in the sterile mixed gas was 10% v / v. The concentrations of the added inorganic salts and trace elements are as follows: 6.6 g / L MgSO4·7H2O, 1.6 g / L MgCl2·6H2O, 1 g / L KNO3, 0.07 g / L KH2PO4, 0.04 g / L NaHCO3, 1 mL / L 0.5 M Na2Fe-EDTA (pH 7.6), 4 mg / L ZnCl2, 60 mg / L H3BO3, 1.5 mg / L CoCl2·6H2O, 4.0 g / L CuCl2·2H2O, 40 mg / L MnCl2·4H2O, and 37 mg / L (NH4)6Mo7O. 24 ·4H2O.

2. The method as described in claim 1, characterized in that, A sterile mixed gas was introduced into the seawater at a rate of 1 L / min per 0.55 L of seawater, and the seawater contained the species of *Porphyra yezoensis*.

3. The method as described in claim 1, characterized in that, The centrifuge speed for centrifuging algae liquid is 6000-12000 rpm.

4. The application of *Porphyra yezoensis* in the treatment of radioactive strontium contamination in seawater and its combined carbon sequestration, characterized in that... The method described in any one of claims 1-3 shall be used.

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