Growth Characteristics And Performance Enhancement Of Microalgae Biofilm In The Planar Waveguide Photobioreactor

The development of renewable energy has attracted worldwide attention.As the third-generation biomass energy,microalgae have the advantages of high photosynthetic efficiency and short cultivation period.Through photosynthesis,it can fix the greenhouse gas CO₂,absorb and transform nutrients such as nitrogen and phosphorus in the wastewater,and synthesize energy oils and other high value-added organic substances.Therefore,microalgae culture and its energy utilization technology have become the focus of research at home and abroad.On the background of energy utilization of microalgae,the growth characteristics and performance enhancement of biofilm in photobioreactor were studied.The specific work is as follows:(1)The microalgae biofilms cultured in the flat panel photobioreactor were pretreated and dyed,and the morphology and structure characteristics of the microalgae biofilms were studied by scanning electron microscope and laser scanning confocal microscope.The experimental results showed that the microalgae biofilm has a large number of pore structures that allow nutrients to be transported from the pores to the biofilm.In addition,biofilm contains a large amount of EPS which makes cell to cell,cell to carrier adhesion.(2)The hollow fiber membrane arranged in a serpentine shape was used to supply the carbon source,which reduced the gas-liquid mass transfer resistance and improved the uniformity of the carbon source distribution.In addition,the planar waveguide was introduced into the biofilm culture system to homogenize the light distribution and construct a hollow fiber membrane enhanced planar waveguide photobioreactor.The effect of reactor structure,liquid flow rate,light intensity and initial NO₃^-concentration on the growth characteristics of biofilm in the reactor was carried out.The results of the study showed that compared with supplying air from above the liquid surface,the hollow fiber membrane CO₂supply method used in this experiment significantly improved the growth performance of the biofilm in the reactor,and the biomass density,protein content and chlorophyll content increased by 48%,62%and 17%,respectively.Properly increasing the liquid flow rate could enhance mass transfer and help the growth of biofilm.If the liquid flow rate is too large,biofilm is easily washed away.While,properly increasing the light intensity could increase the photosynthetic rate of the microalgae and promote the growth of biofilm.Too low or too high light intensity will cause light restriction and photoinhibition respectively,which hinder the growth of biofilm.In addition,the higher initial NO₃^-concentration provided a sufficient nitrogen source for biofilm growth.Therefore,when the liquid flow rate was 1.0 m L min^-1,the light intensity was 100?mol m^-2 s^-1,and the initial NO₃^-concentration was 12 m M,the growth performance of the biofilm in the constructed reactor was enhanced.The maximum biomass density,protein content and chlorophyll content were 47.19 g m^-2,12.27 g m^-2 and1.12 g m^-2,respectively.(3)Taking into account the adhesion characteristics of microalgae cells on the surface of the carrier,mesh substrate with rough structure on the surface was used to construct a mesh substrate enhanced planar waveguide photobioreactor.The flow field distribution in the photobioreactor was simulated.The effect of mesh pore size,mesh layer number and liquid flow rate on the growth characteristics of biofilm in the reactor was carried out.The results showed that the addition of the mesh substrate enhanced the retention of microalgae cells,weakened the flow shear,provided a larger attachment area for biofilm growth,improved space utilization,and increased the mesh pore size to enhance light transmission and nutrient transfer.While,the increase in the number of mesh layers increased the attachment area of microalgae,which strengthened the adhesion and growth of biofilms.In addition,the increase of mass transfer rate and the interception of microalgae cells by mesh substrate were beneficial to the growth of biofilm.Therefore,when the mesh pore size was3.28 mm,the number of mesh layers was 8,and the liquid flow rate was 3.5 m L min^-1,the biofilm growth performance in the photobioreactor was the best,and the maximum biomass density,protein content and chlorophyll content were 43.27 g m^-2,11.31 g m^-2 and 1.29 g m^-2,respectively.This paper contains 54 figures,5 tables and 146 references.