Combined carbon sequestration method for treating radioactive strontium pollution of seawater by porphyridium

Abstract

The invention relates to the technical field of bioengineering, in particular to a combined carbon sequestration method for treating radioactive strontium pollution of seawater by porphyridium. The method comprises the following steps: inoculating a porphyridium strain into a radioactive strontium polluted seawater culture medium for treatment, adding a certain content of inorganic salt and trace element solution, continuously illuminating, and controlling the temperature, illumination intensity, sterile mixed gas ventilation rate and carbon dioxide ventilation concentration to realize the effect of treating seawater radioactive strontium pollution by porphyridium and combining carbon sequestration. The concentration of strontium element in seawater and the fixation of carbon dioxide are realized by utilizing the growth of porphyridium. According to the method, microalgae carbon sequestration is combined with wastewater treatment and biofuel production, so that the method has remarkable environmental and economic advantages, and the production cost and the energy consumption can be reduced to a certain extent. The method is easy to operate and low in cost and has certain universality.

Description

Technical Field

[0001] The invention belongs to the technical field of bioengineering, and particularly relates to a method for treating radioactive strontium pollution in seawater by using Porphyridium cruentum and combining it with carbon fixation. Background Art

[0002] With the increasing consumption of fossil energy, environmental degradation and global warming, efficient, carbon-free and clean nuclear power has gradually become an important industry in the world. Most nuclear power plants are built near the sea. During operation, they discharge low-level radioactive wastewater containing many radionuclides into the marine environment for a long time, which increases the potential risk of marine radioactive pollution. In addition, nuclear submarines, powered ships and other offshore nuclear power platforms, as well as various nuclear tests, are also potential sources of artificial marine radioactive pollution.

[0003] The artificial radionuclides cesium 137 and strontium 90 in nuclear reactors and nuclear waste have a half-life of more than 20 years, and it takes a long time to be purified under natural conditions. Currently, the commonly used methods for treating radioactive contaminated water include adsorption, ion exchange, precipitation, membrane separation, extraction, etc. Most of them have the problems of high cost, complex operation, and easy to cause secondary pollution, making it difficult to deal with large-scale marine nuclear pollution.

[0004] Therefore, it is very important to find a method that can effectively deal with marine radioactive pollution.

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

[0006] At present, the algae that have been used in the research on the treatment of strontium pollution mainly include Closterium moniliforme, Chlorella vulgaris, Brown algae, Copper algae, etc. There are no relevant research reports on the use of Porphyridium cruentum to treat strontium pollution in seawater. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for treating strontium pollution in seawater by using Porphyridium cruentum and combining carbon fixation, which provides a simple, energy-saving, environmentally friendly and large-scale method for treating strontium pollution in seawater.

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

[0009] A method for treating radioactive strontium pollution in seawater and combining carbon fixation with Porphyridium cruentum, comprising the following steps:

[0010] The Porphyridium species are inoculated into seawater contaminated with radioactive strontium for cultivation, and inorganic salts and trace element solutions are added. Continuous illumination is applied, and the temperature, light intensity, sterile mixed gas ventilation rate and carbon dioxide ventilation concentration are controlled during the cultivation process. The growth of Porphyridium is used to concentrate strontium in seawater and fix carbon dioxide.

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

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

[0013] Preferably, the concentration of strontium ions in the radioactive strontium-contaminated seawater that can be treated is 6 to 16 mg / L. This is because Sr in natural seawater 2+ The background concentration of strontium is 6-8 mg / L, and lower concentrations of strontium will promote the growth of Porphyridium. Therefore, the preferred initial concentration of strontium in seawater is 6-16 mg / L. The increase in biomass is beneficial to improving the adsorption of strontium and carbon fixation, especially when the initial concentration of strontium in seawater is 16 mg / L, the effect is best.

[0014] Adding a certain amount of inorganic salts and trace elements to seawater can increase the biomass of Porphyridium culture and improve the effect of strontium adsorption 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, 37 mg / L (NH4)6Mo7O 24 ·4H2O.

[0015] The addition of Tris·HCl can adjust the pH in seawater to maintain relative stability. 1M Tris·HCl (pH 7.6) is used, wherein the preferred addition amount is 0 to 4 mL / L, and further preferred Tris·HCl addition amount is 0. This is because although weak alkalinity is conducive to the accumulation of Porphyridium biomass, an alkaline environment is more conducive to the adsorption of strontium.

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

[0017] Preferably, the sterile mixed gas is obtained by the following method: after mixing air with CO2, the obtained carbon dioxide concentration is 5% to 10% v / v (preferably 10% v / v) of the sterile mixed gas filtered through a 0.22 μm sterile filter membrane. Under this condition, the growth rate and biomass yield of Porphyridium cruentum can be increased while avoiding the contamination of bacteria during the ventilation process to affect the growth of Porphyridium cruentum, and the carbon dioxide in the mixed gas can induce Porphyridium cruentum to fix more carbon dioxide during growth.

[0018] Preferably, the sterile mixed gas is introduced into the seawater at a ventilation rate of 1 L / min for every 0.55 L of seawater (containing the Porphyridium species). Under this condition, the growth of Porphyridium is significantly promoted, the culture period of Porphyridium is shortened, and the efficiency of Porphyridium adsorption and carbon fixation is improved.

[0019] Preferably, after inoculating and culturing Porphyridium, the algae liquid is centrifuged in a centrifuge, and the supernatant after removing the Porphyridium is the treated seawater; the speed of the centrifuge is 6000-12000 rpm.

[0020] Application of Porphyridium cruentum in treating radioactive strontium contamination in seawater and combining it with carbon fixation.

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

[0022] The method for treating seawater strontium pollution by using Porphyridium crusgalli combined with carbon fixation disclosed in the present invention combines treating seawater strontium pollution by using Porphyridium crusgalli with carbon fixation. 2+ The adsorption rate can reach 24.38%, and 145.17g of carbon dioxide can be fixed cumulatively in 18 days. The average carbon fixation efficiency can reach 5.75g CO2 / g biomass / d. It has good environmental and economic advantages and can reduce production costs and energy consumption to a certain extent.

[0023] The method of the present invention avoids the problems of adsorbent synthesis, difficult recovery, and easy secondary pollution faced by conventional adsorbents in treating water pollution. It is simple to operate, saves raw materials, has low investment cost, has the potential to treat large-scale seawater strontium pollution, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 :The biomass variation trend of Porphyridium cruentum during cultivation;

[0025] Figure 2 :Sr in Porphyridium cruentum during the culture period 2+ Variation trend of adsorption efficiency;

[0026] Figure 3 : Trend of cumulative fixed carbon dioxide mass during Porphyridium cultivation. DETAILED DESCRIPTION

[0027] In order to make those skilled in the art better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be described in detail and clearly in conjunction with the accompanying drawings. Unless otherwise specified, the reagents and instruments used in the following examples are commercially available products, and the experimental methods in the embodiments without specifying specific conditions are generally in accordance with conventional conditions. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the art without making creative work are within the scope of protection of the present invention.

[0028] The embodiment of the present invention uses a seawater culture medium simulated with radioactive strontium contamination as an experimental object, inoculates Porphyridium cruentum into the seawater culture medium simulated with radioactive strontium contamination, and then adds a certain amount of inorganic salts and trace elements.

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

[0030] The example is based on seawater. 2+ The background concentration is 6-8 mg / L. By adjusting the amount of strontium storage solution added, the concentration of strontium ions in the seawater culture medium simulating radioactive strontium contamination is controlled to 6-16 mg / L.

[0031] The strontium storage solution is a hexahydrate strontium chloride solution, and the strontium in the storage solution is the isotope strontium 88. The preparation method is as follows: weigh 2.6667g SrCl2·6H2O and dissolve it in 80mL sterile water, finally make the volume to 100mL, filter and sterilize, and store it in a sterilized reagent bottle and store it in a refrigerator at 4°C. The reason why the isotope strontium 88 is used is that it has similar chemical properties to strontium 90 and is not radioactive. It can reduce the effect of strontium on Porphyridium to a certain extent during the cultivation of Porphyridium.

[0032] The concentrations of inorganic salts and trace elements added to the seawater culture medium simulating radioactive strontium contamination 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, 37 mg / L (NH4)6Mo7O 24 ·4H2O.

[0033] The addition of Tris·HCl can adjust the pH in seawater to keep it relatively stable. 1M Tris·HCl (pH 7.6) is used, and the addition amount is 0-4mL / L.

[0034] The seawater culture medium simulating radioactive strontium contamination needs to be sterilized by high pressure before inoculating Porphyridium to ensure a sterile environment. And the sampling and water replenishment of Porphyridium liquid during the entire culture cycle are carried out in a clean bench.

[0035] MgSO4·7H2O, MgCl2·6H2O, KNO3, KH2PO4, NaHCO3, Tris, HCl, NaOH, Na2EDTA·2H2O, FeCl3·4H2O, ZnCl2, H3BO3, CoCl2·6H2O, CuCl2·2H2O, MnCl2·4H2O, (NH4)6Mo7O in the simulated radioactive strontium-contaminated seawater medium used for culturing Porphyridium 24 ·4H2O purity is analytical grade.

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

[0037] Example 1

[0038] The method for treating strontium pollution in seawater and combining carbon fixation with Porphyridium cruentum comprises the following steps:

[0039] (1) The Porphyridium cruentum was inoculated into a 1 L conical flask containing 500 mL of seawater culture medium at an inoculation volume of 10% v / v. No strontium storage solution was added. At this time, the Sr content in the culture medium was 2+ The initial concentration was 7.37 mg / L, 4 mL / L of 1M Tris·HCl (pH 7.6) was added to the seawater, and the cells were cultured in a light incubator under continuous illumination. During the culture process, the temperature was controlled at 25±1°C, the light intensity was 13200 lx, the ventilation rate of the sterile mixed gas was 1.0 L / min, the carbon dioxide content in the sterile mixed gas was 5% v / v, the culture period was 18 days, and sterile water was added to the initial volume in the clean bench every 2 days;

[0040] (2) During the entire culture period, the carbon dioxide concentration in the exhaust gas was detected every day using an Agilent 7890B gas chromatograph, the biomass of Porphyridium cruentum was measured every 2 days using a UV-visible spectrophotometer, the pH value of the culture medium was measured every 2 days using a pH meter, and the residual Sr in the culture medium was measured every 6 days using an inductively coupled plasma emission spectrometer. 2+ content.

[0041] It was measured that the biomass of Porphyridium cruentum 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 is 10.29% (see Appendix Figure 2 ), cumulative fixed carbon dioxide 199.31g (see attached Figure 3 ), with an average carbon fixation efficiency of 5.59 g CO2 / g biomass / d.

[0042] Example 2

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

[0044] The amount of strontium storage solution added is 1mL / L (at this time, Sr in the culture medium 2+ The initial concentration was 15.52 mg / L).

[0045] It was measured that the biomass of Porphyridium cruentum 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 is 1.81% (see Appendix Figure 2 ), cumulative fixed carbon dioxide 142.52g (see attached Figure 3 ), with an average carbon fixation efficiency of 3.54 g CO2 / g biomass / d.

[0046] The experimental results show that compared with Example 1, the Sr 2+ The increase in initial concentration caused the Porphyridium to enter the decay phase ahead of time. The decay and fragmentation of cells caused the strontium adsorbed and enriched by the Porphyridium to precipitate back into the culture medium, resulting in a significant decrease in the adsorption rate on the 18th day, and a corresponding decrease in the cumulative carbon fixation amount and carbon fixation efficiency. This is because the growth of Porphyridium has a retardation period, a logarithmic growth period, a stable period, and a decay period. A certain amount of strontium will promote the growth of Porphyridium and increase its biomass, but it will also accelerate the growth of Porphyridium and cause it to enter the decay phase ahead of time.

[0047] Example 3

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

[0049] (1) The amount of strontium storage solution added is 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 introduced is 10% v / v.

[0051] It was measured that the biomass of Porphyridium cruentum 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 is 3.10% (see Appendix Figure 2 ), cumulative fixed carbon dioxide 193.53g (see attached Figure 3 ), with an average carbon fixation efficiency of 5.34 g CO2 / g biomass / d.

[0052] The experimental results show that compared with Example 1, the Sr 2+ The increase in initial concentration caused Porphyridium to enter the decay period ahead of schedule, and the cell decay and fragmentation resulted in a significant decrease in the adsorption rate on the 18th day. However, higher concentrations of carbon dioxide induced an increase in Porphyridium's ability to fix carbon dioxide, resulting in no significant decrease in the cumulative carbon fixation amount and carbon fixation efficiency.

[0053] Example 4

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

[0055] No Tris·HCl was added; at this time, Sr 2+ The initial concentration was 7.37 mg / L;

[0056] It was measured that the biomass of Porphyridium cruentum 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 ), cumulative fixed carbon dioxide 96.87g (see attached Figure 3 ), with an average carbon fixation efficiency of 2.93 g CO2 / g biomass / d.

[0057] The experimental results show that, compared with Example 1, when Tris·HCl is not added, the pH of the culture medium increases with the increase of the extracellular polysaccharide content of Porphyridium, and alkaline conditions are more conducive to the growth of Sr 2+ However, the decrease in biomass leads to a decrease in the cumulative carbon fixation.

[0058] Example 5

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

[0060] (1) No Tris·HCl was added;

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

[0062] It was measured that the biomass of Porphyridium cruentum 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 is 21.05% (see Appendix Figure 2 ), cumulative fixed carbon dioxide 61.68g (see attached Figure 3 ), with an average carbon fixation efficiency of 1.63 g CO2 / g biomass / d.

[0063] The experimental results show that, compared with Example 1, when Tris·HCl is not added, the pH of the culture medium increases with the increase of the extracellular polysaccharide content of Porphyridium cruentum. The alkaline condition and the increase of the initial strontium concentration are beneficial to the growth of Sr 2+ adsorption; however, the dissolved CO2 under alkaline conditions is mainly in the form of HCO3 - Mainly, low concentration of dissolved CO2 causes the cumulative carbon fixation of Porphyridium to decrease, and the carbon fixation efficiency is also greatly reduced.

[0064] Example 6

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

[0066] (1) No Tris·HCl was added;

[0067] (2) The amount of strontium storage solution added is 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] It was measured that the biomass of Porphyridium cruentum 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 ), cumulative fixed carbon dioxide 145.17g (see attached Figure 3 ), with an average carbon fixation efficiency of 5.75 g CO2 / g biomass / d.

[0070] The experimental results show that, compared with Example 1, when Tris·HCl is not added, the increase in the extracellular polysaccharide content of Porphyridium leads to an increase in the pH of the culture medium. The alkaline conditions and the increase in the initial strontium concentration are beneficial to the growth of Sr 2+ adsorption; although the low concentration of dissolved CO2 under alkaline conditions caused the cumulative carbon fixation of Porphyridium to decrease, the increase in carbon dioxide concentration induced a significant increase in the efficiency of Porphyridium in fixing carbon dioxide.

Claims

1. A method for treating radioactive strontium pollution in seawater by using Porphyridium cruentum combined with carbon fixation, characterized in that: The following steps are involved: The Porphyridium species are inoculated into seawater contaminated with radioactive strontium for cultivation. Inorganic salts and trace element solutions are added. Continuous illumination is applied. The culture temperature, light intensity, sterile mixed gas ventilation rate and carbon dioxide ventilation concentration are controlled. The growth of Porphyridium is used to concentrate strontium and fix carbon dioxide in seawater.

2. The method according to claim 1, characterized in that The Porphyridium algae species were cultured to the end of the logarithmic growth phase.

3. The method according to claim 1, characterized in that The inoculation amount of Porphyridium algae species is 5-15% v / v (preferably 10% v / v).

4. The method according to claim 1, characterized in that The concentration range of strontium ions in radioactive strontium-contaminated seawater that can be treated is 6 to 16 mg / L (preferably the initial concentration of strontium in seawater is 16 mg / L).

5. The method according to claim 1, characterized in that 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, 37 mg / L (NH4)6Mo7O 24 ·4H2O.

6. The method according to claim 1, characterized in that The treatment temperature is 25±1°C, the light intensity is 10000-15000lx (preferably 13200lx), and the treatment period is 16-20 days (preferably 18 days).

7. The method according to claim 1, characterized in that The sterile mixed gas is obtained by the following method: air and CO2 are mixed and then filtered through a 0.22 μm sterile filter membrane; the concentration of carbon dioxide in the sterile mixed gas is 5% to 10% v / v (preferably 10% v / v).

8. The method according to claim 1, characterized in that Sterile mixed gas was introduced into seawater at a ventilation rate of 1 L / min for every 0.55 L of seawater (containing Porphyridium species).

9. The method according to claim 1, characterized in that After the inoculation with Porphyridium, the algae solution is centrifuged in a centrifuge, and the supernatant after removing the Porphyridium is the treated seawater; the speed of the centrifuge is 6000-12000rpm.

10. Application of Porphyridium cruentum for treating radioactive strontium pollution in seawater and combining carbon fixation, characterized in that: The method according to any one of claims 1 to 9 is adopted.

Images