Growth And Lipid Production Characteristics Of Photoautotrophy-Heterotrophy Microalgae Biofilm

With the rapid reduction of global fossil fuels and the increasing problem of environmental pollution,the development of green renewable energy has become an important breakthrough to solve the energy and environmental crisis.Microalgae biomass as a third generation of biomass energy,from its high photosynthetic efficiency,short growth cycle,high lipid content,environmental adaptability,etc.,is a great potential for new biomass raw materials.Because of the relatively small CO2 and light transmission resistance in microalgae biofilm,the photosynthetic efficiency of microalgae is high,and the biofilm has the advantages of stable operation and convenient harvesting,which has a greater advantage than that of suspended microalgae culture.Therefore,the hydrophilic organic nylon microporous membrane as microbial biofilm attachment material,the microalgae biofilm culture.The differences of phototrophy and phototrophy-heterotrophy biofilm in the biofilm growth and the microstructure of biofilm were compared.The effects of light intensity and initial inoculation area density on the lipid-producing characteristics of phototrophy-heterotrophy biofilm were studied from the perspective of light transmission.The effects of nutrient concentration,intermittent supply of culture medium and heterotrophy time on the lipid-producing characteristics of phototrophyheterotrophy biofilm were studied from the perspective of nutrient.The main conclusions are as follows:(1)The cell diameter of the phototrophy and phototrophy-heterotrophy microalgae biofilm increased gradually with the growth.The average diameter of the phototrophyheterotrophy biofilm was 17.1% higher than that of the phototrophy biofilm.The phototrophy-heterotrophy microalgae biofilm was more porous than the phototrophy biofilm in biofilm morphology.When the agar-solidified medium was used as the nutrient substrate,the growth rate of phototrophy-heterotrophy biofilm was higher than that of phototrophy growth rate.The two-day growth rate of phototrophy-heterotrophy biofilm was 2.28 times higher than that of phototrophy.The lipid yield of phototrophyheterotrophy microalgae biofilms was 10.31 g/m2,which was 1.91 times higher than that of phototrophy.The growth rate of phototrophy-heterotrophy biofilm was higher than that of phototrophy growth rate and higher than that of curing medium,but the final biofilm area density was lower than that of solidified medium.The lipid yield of phototrophyheterotrophy biofilm was 20.12 g/m2,which was 2.22 times higher than that of phototrophy(9.08 g/m2).(2)When the agar solidified medium was used as the nutrient substrate,it was found that the light saturation point of the phototrophy-heterotrophy microalgae biofilm was 150 μmol/m2/s.The high light intensity could inhibit the microalgae biofilm.Its decomposition of the pigment so that the cell become white and biofilm density decreased.In the aspect of material transmission resistance,the phototrophy-heterotrophy microalgae cells could not absorb the nutrient with the thickness of more than 10 mm.The phototrophy-heterotrophy microalgae biofilm had the highest lipid yield(22.01 g/m2)at 4 times the inorganic salt concentration of the basal medium,indicating that the phototrophy-heterotrophy biofilm can tolerate a higher times of inorganic salts.Glucose relative to the inorganic salt ions have a greater transmission resistance,resulting in the amount of glucose transferred into the biofilm is relatively small,the biofilm microalgae heterotrophy ratio is small,and then the lipid yield is not significant.(3)When the mobile liquid medium is a nutrient base,the solid culture medium is agar-solidified,and the microflora biofilm has high water content and low light transmission ability.The saturation point of phototrophy-heterotrophy biofilm is increased to 190 μmol/m2/s.Biofilm growth initial,due to biofilm inside and outside concentration gradient,the rapid transmission of nutrients,biofilm nutrient sufficient,the growth rate is fast,resulting in the first 1 to 2 days microalgae biofilm growth rate.The initial growth rate of microalgae increased with the increase of initial inoculation area density.As heterotrophic water increased the transport resistance of biofilm,the later growth rate decreased,especially at low times(0.5 times)inorganic salt concentration low,photosynthetic intensity is relatively weak,biofilm microalgae heterotrophic ratio is large,the more water produced by heterotrophy,the more unfavorable to biofilm growth.(4)The lipid content of microalgae biofilm increased to 43.67% with heterotrophic substrate glucose concentration the increase of 1 g/L to10 g/L,and the microalgae biofilm area density increased at the same time.Simultaneous phototrophy-heterotrophy to achieve a simultaneous increase in microalgae biomass and lipid content,to solve the microalgae growth and accumulation of lipid is not contradictory problems.And because the heterotrophic metabolism of water,increase the water content of biofilm,making the material transmission resistance increased.In order to reduce the impact of the formation of water,using the first phototrophy and enrichment of a certain biofilm area density and then open the heterotrophy auxiliary method,in order to reduce the water production.It was found that when the density of phototrophy biofilm area density increased to 57.48 g/m2,the density of biofilm was up to 104.36 g/m2 and the lipid yield was up to 26.17 g/m2,also to achieve a high degree of accumulation the biomass and lipid at the same time.The intermittent supply of medium had a great effect on the growth rate of biofilm on day 1,but had little effect on the pigment and lipid compounds contents in the cells.