Design And Performance Study Of Microalgae Biofilm Photobioreactor Coupled With Light Guide Plate

Nowadays,due to the continuous consumption of traditional primary energy sources,the energy crisis and the greenhouse effect continue to intensify.Therefore,the development and utilization of efficient,clean and renewable new energy sources is urgent.Microalgae,as the biomass source of the third generation biofuel,has the characteristics of short growth cycle,high photosynthetic carbon fixation efficiency,wide distribution range,high oil content,etc.,and microalgal biomass can be considered as a potential to replace conventional primary energy biofuels,and the large-scale and efficient cultivation of microalgae is a key link in the microalgal biomass energy industry chain.At present,large-scale industrial microalgae cultivation methods are mainly suspension culture,but suspension culture has the problems of low yield of microalgal biomass and high energy consumption for harvest,which greatly limits its further development.Recently,the cultivation of immobilized microalgae has become a hot spot for many scholars at home and abroad due to its advantages of high biomass yield,low water consumption,and simple harvesting.However,the photobioreactor for microalgae immobilized culture still faces the problems of large occupied area,low output per unit area,uneven light reception of algae cells in the reactor,etc.In view of these,this paper proposes to introduce the nano-light guide plate into the field of microalgae immobilized culture,and construct a new compact multi-layer photobioreactor employing planar waveguide.On the one hand,the light intensity distribution on the surface of the microalgae biomembrane in the reactor is more uniform by coupling the light guide plate,so as to improve the yield of the microalgae biomembrane in the reactor;On the other hand,under the same floor area,the light guide plates can be stacked in parallel along the height direction,thus improving the microalgae biomass yield per unit floor area.Through the method of experimental research,this paper first compared the performance of the new compact multi-layer photobioreactor employing planar waveguide with the traditional biofilm reactor;Subsequently,the performance of the reactor was controlled by changing the light emission spectrum of the light guide plate and changing the light intensity during the cultivation period.The main conclusions of the full text are as follows:?1?The introduction of a new multi-layer stacked light guide plate microalgae biofilm photobioreactor makes the light intensity distribution on the surface of the biofilm in the reactor more uniform,and the average light intensity on the surface of the microalgae biofilm can reach 67.84?mol m^-2s^-1,While the control group reactor is only 22.36?mol m^-2s^-1;after 9 days of cultivation,the biofilm area density in the new multi-layer stacked light guide plate microalgae biofilm photobioreactor can reach 79.35 g m^-2,the average area density is 61.35 g m^-2,while the average area density of the microalgae biofilm in the control group reactor is only 25.02 g m^-2,that is,the new multi-layer stacked light guide plate microalgae biofilm photobioreactor Compared with the control reactor,the microalgal biomass production increased by145.20%;subsequently,by changing the light intensity on the surface of the light guide plate,it was found that there was a significant difference in the growth rate of the microalgal biofilm under different light intensities.Under the condition of?mol m^-2s^-1,the growth of microalgae biofilm in the reactor is slow.With the increase of light intensity to 136?mol m^-2s^-1,the growth rate of microalgae biofilm is significantly increased.The rate reaches 12.97 g m^-2d^-1,Which is 1.39 times that of low light intensity,however,when the light intensity is further increased to 204?mol m^-2s^-1,the growth rate of microalgae biofilm decreases,and the biofilm area density yield drops to 9.28 g m^-2d^-1.This is because excessive light intensity has an inhibitory effect on the growth of algal cells,which is not conducive to the accumulation of microalgal biomass.?2?During the experiment,it was found that when CO₂was passed directly into the closed chamber of microalgae biofilm culture,the growth of the same layer of microalgae biofilm in the new multi-layer stacked light guide plate microalgae biofilm photobioreactor appeared uneven.This is because CO₂needs to be dissolved into the water environment near the biofilm before it can provide a carbon source for the biochemical conversion process of algae cells,and the amount of CO₂dissolved in the culture medium just flowed into the reactor is less,making it close to the organisms in the LED light source area.The growth of the membrane lacks the necessary inorganic carbon,which limits the growth of microalgal biofilms in this area.Based on this,this paper proposes a method of fully dissolving CO₂into the liquid culture medium in advance,thereby providing a sufficient carbon source for the growth of algal cell biofilms in different regions of the reactor.By changing the spectral structure of the light emitted from the light guide plate,it was found that under the same light intensity,the pigment content and biomass yield of the microalgae biofilm in the new multi-layer stacked light guide plate microalgae biofilm photoreactor under green light irradiation were the highest,Respectively,70.32 mg m^-2and 64.99 g m^-2,corresponding to the average yield of biofilm area density of 10.80 g m^-2d^-1.However,under blue light irradiation,the microalgae biofilm yield and pigment content were the lowest.This is due to the high energy of blue light,great damage to algae cells,and reduced algal cell activity,resulting in slow growth of microalgae biofilms.?3?The study found that at different stages of the microalgae biofilm growth phase,small changes in light intensity have a certain effect on the growth of the microalgae biofilm.Through 8 days of cultivation,it was found that when the average light intensity in the entire cultivation cycle was 150?mol m^-2s^-1,the microalgae biofilm production area under the conditions of light supply B and C,the microalgae biofilm area in the reactor The density can reach 50.07 g m^-2and 54.05 g m^-2respectively,which are 9.16%and 18.83%higher than when the light intensity is constant at 150?mol m^-2s^-1.For light supply strategy B,the light intensity is set to 60?mol m^-2s^-1on days 0 to 4 and 240?mol m^-2s^-1from 4 to 8 days;light supply strategy In terms of C,the light intensity is set to 60?mol m^-2s^-1on days 0?2,150?mol m^-2s^-1is set on days 2-6,and light is on days 6-8 The intensity is 240?mol m^-2s-1.