Growth Characteristics Of Microalgae Biofilm In A Three-dimensional Porous Light-guided Biofilm Reactor

In order to improve the energy structure and respond to the theme of"clean,low-carbon,safe and efficient"energy consumption,it is very important to seek a kind of green,clean and renewable energy.Microalgae as the third generation of biomass energy,its photosynthetic growth process can effectively fix CO2 to alleviate the global greenhouse effect,and microalgae can be processed into a variety of different types of biofuels to supply energy demand;Developing microalgae biomass energy is an effective way to reduce fossil fuel consumption,slow down carbon emissions,and promote the realization of"carbon peak,carbon neutral".Compared with suspension culture,microalgae biofilm culture has higher biomass density and better affinity for CO2.Therefore,microalgae biofilm has better carbon sequestration,emission reduction and energy conversion effect;It is more suitable for large-scale application.However,for the existing microalgae biofilm culture system,there are often the following shortcomings:low efficiency of initial biofilm formation,limited light transmission in the cultivation process,low space utilization of photobioreactor and low intelligent harvesting mode.Therefore,in order to make the microalgae biofilm culture system more efficient and accelerate the industrial application,it is necessary to put forward a universal method of strengthening the initial biofilm formation based on the existing research;Improve the space utilization efficiency of the training system;The illumination environment in the culture system was optimized;The method of collecting microalgae biofilm was simplified.Finally,the biofilm photobioreactor which can take into account the cultivation environment,space utilization and system durability is constructed.Based on the background of microalgae biofilm culture,a three-dimensional porous light guiding biofilm reactor was proposed.In the three-dimensional porous light guiding biofilm reactor,three-dimensional porous photosensitive resin with nano light guiding particles was used as the biofilm substrate.The three-dimensional porous structure of the substrate ensured high space utilization;At the same time,the light scattering effect of nano light guide particles on the surface of the biofilm can effectively optimize the uniformity of light distribution.In addition,in order to enhance the initial membrane formation of microalgae and simplify the collection method of microalgae biofilm,N-isopropylacrylamide（NIPAAm）,a temperature responsive material widely used in human tissue culture,was applied to the adsorption and desorption collection of microalgae cells in this study.NIPAAm thin film with temperature response was prepared on three-dimensional porous substrate.The unique phase transition characteristics of NIPAAm make the temperature sensitive film can enhance the initial membrane formation and the final membrane desorption of microalgae at the temperature of 32℃.On this basis,the growth characteristics of microalgae biofilm in the inner three-dimensional porous light guiding biofilm reactor were studied,The main research results are as follows:（1）For the cultivation of microalgae biofilm in three-dimensional porous light conducting biofilm reactor,the pore structure of three-dimensional substrate surface directly affects the attachment and growth of microalgae biofilm;Compared with other surface structures,the circular groove on the substrate surface is more conducive to the initial attachment of microalgae cells in the process of static sedimentation;At the same time,the high specific surface area of circular structure makes it more advantageous in the accumulation of biological value in the culture stage.On this basis,the growth characteristics of microalgae biofilm under different substrate arrangement modes and pore sizes were compared.The results showed that the highest microalgae biomass accumulation per unit area of the ground was 31.74 g m^-2 under the framework dislocation arrangement mode of circular arc biofilm with 3 mm pore diameter.（2）The thermosensitive layer which has good biocompatibility and can effectively enhance the initial membrane formation of microalgae was successfully prepared;The surface morphology of the modified substrate was verified by environmental scanning electron microscope and atomic force microscope;The changes of surface elements and functional groups of the substrate before and after grafting were proved by element analysis and Fourier transform infrared absorption spectrum.The water contact angle of the thermosensitive surface was measured at different temperatures.The results show that the water contact angle of the thermosensitive surface increases with the increase of temperature,which proves that the thermosensitive surface is temperature responsive;Finally,combined with thermodynamic adhesion prediction model and visualization experiment,it is proved that the biofilm substrate grafted with thermosensitive layer can effectively enhance the initial adhesion of microalgae biofilm.At 33℃,the total adsorption capacity of microalgae on the thermosensitive surface（base-dpa-nipaam-0.05）after polymerization of thermosensitive layer was 103.5%higher than that on the initial base surface.（3）After the thermosensitive layer was successfully grafted on the surface of three-dimensional porous substrate,the differences of the substrate surface before and after thermosensitive modification in the three major processes of microalgae cell adsorption,cell growth and culture,and desorption and harvesting were compared.The results showed that the cell biomass density of the three-dimensional porous surface modified by thermosensitive layer was 98%higher than that of the original substrate;Compared with the original unmodified surface,the total abscission rate of microalgae cells on the surface of substrate decreased by 13.3%in 12 days.At the end of the incubation period,the biomass density on the surface of the thermosensitive modified substrate was 14.43%higher than that on the original substrate.On the basis of thermosensitive modified biofilm substrate,the biomass accumulation on the surface of three position substrate was optimized by adjusting temperature and atomization flow rate;The light intensity was228μmol m^-2 s^-1;The biomass in the three-dimensional porous light conducting biofilm reactor reached the maximum of 47.12 g m^-2 in the culture period.