Study On Gas Exchange Technology Of Space Microalgae Culture Based On Hydrophobic Membrane

It is an important direction of manned space bioprotection technology to develop efficient space microalgae photobioreactor and to construct a complete controlled ecological bioprotection system.At present,for the microgravity environment in space,the method of hydrophobic permeable membrane to solve the gas-liquid two-phase gas exchange in the process of microalgae culture is a more appropriate technical means.However,in the process of microalgal culture,the membrane will be corroded by the medium and polluted by algal liquid,which will change the surface properties of the membrane material,and may lead to the blockage or even rupture of the membrane hole.In view of this,this thesis aims to screen out a kind of diaphragm that can be used for long-term culture of microalgae,and finally realize long-term and efficient culture of Spirulina,and lay a foundation for subsequent on-orbit verification research and application.The main conclusions are as follows:（1）The experimental study on the permeability,hydrophobicity and tolerance of the film shows that the thickness of the film material has no significant effect on the gas penetration flux.Monolayer diaphragm is changeable,so non-woven fabric should be added to improve the mechanical strength of the diaphragm,among which mesh non-woven fabric has little influence on the permeability of the diaphragm.To ensure long diaphragm life,a three-layer diaphragm must be selected with an aperture of no greater than 2μm.In addition,by studying the influence of algal liquid and lye liquid on the membrane in long-term use,it is found that the permeability of different membranes in algal liquid decreases to different degrees,while lye liquid has no significant effect on the permeability of the membrane.（2）By studying the effects of blue light intensity,cyclic speed and CO₂ concentration on microalgae growth,it was found that T-AOC and carotenoid gradually increased with the increase of blue light dose,and the contents of flavonoids,V_Cand V_Ewere significantly increased by blue light supplement.With the increase of rotational speed,the contents of chlorophyll-a and phycyanin increased gradually,and the content of protein increased firstly and then decreased,while the content of carotenoid was not significantly affected by rotational speed.With the increase of CO₂ concentration,the content of chlorophyll-a in spirulina cells showed an increasing trend,while the contents of cyanin and protein showed a trend of first increasing and then decreasing.The complete exchange of O₂ and CO₂ could be realized by the culture of microalgae based on hydrophobic membrane.The growth rate of Spirulina was the fastest at T3（R:B:60:15）and 100 RPM,and the concentration of dissolved oxygen in the medium was kept within the range of 11 mg/L.（3）A long-term culture experiment of Spirulina was carried out based on hydrophobic membrane photobioreactor.Spirulina was cultured for 30 days in the interval feeding culture mode.During the experiment,300 m L of algal liquid was collected every 6 to 7 days,and 300 m L of fresh medium was added to the control group,while the experimental group was supplemented with the medium without Na HCO₃.The long-term culture results of spirulina showed that compared with the air control group,the experimental group not only grew faster,but also had higher content of photosynthetic pigment and protein under the condition of CO₂ concentration of 3%,and the p H value of the medium was maintained between 8 and 9.The above results show that this study selected a kind of microalgae for space optical bioreactor cultivation and gas exchange of hydrophobic membrane material the key components,and master a set of better micro algae cultivation method,for the next step to carry out the space micro algae bioreactor engineering design of light and space orbit validation laid a good foundation.