Growth Characteristics Of Microalgae Biofilm And Enhancement Of Carbon Fixation Performance In Photobioreactor

The use of fossil fuels has led to the production of large amounts of greenhouse gases and energy depletion,and CO₂ contributes about half of the total greenhouse effect produced by greenhouse gases.Therefore,the technology to achieve harmonious development of energy and environment is the focus of many researchers.Based on the method of microalgae biofilm culture,the microalgae biofilm growth characteristics,carbon fixation characteristics and the enhancement of carbon fixation performance of the photobioreactor were explored.The specific research work is as follows:?1?Biofilm growth characteristics in the foam metal packed bed photobioreactor and carbon fixation characteristics were analyzed by using foamed nickel with modified surface as the immobilized microalgae cell carrier.The growth of microalgae biofilms can be divided into initial adhesion stage,proliferation and growth stage and mature and stable stage,while foam metal packed bed reduces the loss of living cells and helped to reduce the resistance of liquid film during gas-liquid mass transfer,thereby promoting the accumulation of microalgae biofilm.Properly increasing the gas flow was beneficial to increase the mass transfer rate of CO₂ from bubbles to microalgae cells.After the microalgae biofilm matures,the maximum CO₂ removal rate,CO₂ removal efficiency and protein concentration were4549.9?mol m^-3 h^-1,47.39%and 0.892 g L^-1,respectively.?2?Based on the existence of gas-liquid mass transfer resistance and the microalgae biofilm initial adsorption characteristics,a gas-liquid separation membrane with a stainless steel mesh groove was used as a gas transport and microalgae cell attachment carrier to constructed a gas-liquid separation membrane photobioreactor.The characteristics of microalgae cells adhesion,biofilm growth and carbon fixation in the gas-liquid separation membrane photobioreactor were analyzed.Compared with the bubbling gas supply method,CO₂ in the gas-liquid separation membrane photobioreactor was more easily utilized by the microalgae,and the additional stainless steel mesh grooves provided additional attachment points for the microalgae cells and allowed the microalgae biofilm to grow in a relatively stable environment.The maximum biomass yield,CO₂ removal efficiency and protein content were 31.44 g m^-2,25.53%and 10.46 g m^-2,respectively.After the microalgae biofilm matures,the maximum CO₂ removal efficiency was 65.05%.?3?Based on the gas-liquid separation membrane photobioreactor,the effect of the side fiber on the carbon fixation characteristics of the gas-liquid separation membrane photobioreactor was studied by using optical fiber as light transmission carrier.Under the appropriate high light intensity,due to the shortening of the light transmission distance,the growth and metabolism of the microalgae biofilm was promoted,and the carbon fixation performance of the gas-liquid separation membrane photobioreactor was enhanced to obtain the maximum biomass yield,CO₂ removal efficiency and nitrogen removal efficiency of37.32 g m^-2,42.24%and 49.58%,respectively.In addition,based on the gas-liquid separation membrane photobioreactor,the effect of hollow fiber membrane as gas transport carrier on the carbon fixation characteristics of gas-liquid separation membrane photobioreactor was studied.The gas entered the liquid in the form of no bubbles,which reduced the mass transfer resistance.Compared with the direct gas supply method,the biomass yield and protein content of the microalgae increased by 116%and 22%,respectively.As the gas flow increased,the gas was more easily diffused and dissolved into the medium,which enhanced the growth and carbon fixation of the biofilm in gas-liquid separation membrane photobioreactor.The maximum biomass yield and nitrogen removal efficiency were 33.33 g m^-2 and 54.67%,respectively.In this work,the growth characteristics and carbon fixation performance of microalgae biofilm in photobioreactors were explored,which is of guiding significance for further improving the carbon fixation performance and the immobilization of microalgae cells of the closed photobioreactor.