Optimization Of High Efficiency Culture For Microalgae In Municipal Sewage

The fossil energy crisis and water eutrophication problem are increasing, microalgae can effectively removed nitrogen and phosphorus in municipal sewage, while harvested algal cells can be extracted algae oil for biodiesel production, it can partially replace fossil energy. In this paper, we used Chlorella sp. as research subjects and municipal sewage as a culture medium. By controlling the culture conditions such as sterilization conditions, ventilation, initial inoculation density, we analyzed the effects of these environmental conditions on biomass and fatty acid composition of Chlorella, studied removal law of nitrogen and phosphorus in municipal sewage. We designed a uniform experiment to comprehensive study the effects of these environmental conditions on Chlorella biomass and total fatty acid production, and Optimized of Microalgae culture conditions in Municipal Sewage to increase biomass and total fatty acid production. The main results were as follows:(1) Chlorella could grow normally in the sewage which completely unsterilized, but the growth was slow, and the total fatty acid production was relatively low. Sterilization of Municipal Sewage was beneficial to the growth and biomass accumulation of Chlorella, the group of high-temperature steam sterilization had the highest biomass accumulation, the biomass was 0.2181g/L. Ventilation could increase the contact area between the algal cells and nutrients in municipal sewage, which was conducive to the growth of Chlorella; compared with no ventilation cultured, the biomass accumulation of Chlorella under ventilation conditions increased significantly. When the ventilation was 2L/min, Chlorella had the highest biomass of 0.2413g/L. Increasing the seeding density and adding trace elements are conducive to growth and biomass accumulation of chlorella.(2) The content of C16:0, C18:1, C18:2 and C18:3 was relatively high in Chlorella cells. Environmental conditions had a certain impact on fatty acid composition of Chlorella. The more stringent sterilization conditions, the more conducive to the accumulation of unsaturated fatty acids, especially polyunsaturated fatty acids algal cells. When the algal cells after high-temperature steam sterilization, The content of unsaturated fatty acids and polyunsaturated fatty acid were the highest, they were respectively accounting for 62.68% and 25.74% of the total fatty acids content. The Chlorella with ventilation had higher the unsaturated fatty acid content than the Chlorella without ventilation. When the ventilation was 1L/min, the algal cells had the highest unsaturated fatty acids and polyunsaturated fatty acids content. However, saturated fatty acid content would increase, unsaturated fatty acids and polyunsaturated fatty acid content would decrease with the increasing of the amount of ventilation. the saturated fatty acid content is a rising trend, unsaturated fatty acids and polyunsaturated fatty acids is a downward trend with the increasing the seeding density. After adding trace elements, algal cells were more abundant species of fatty acids, but the content of saturated fatty acids, unsaturated fatty acids and polyunsaturated fatty acids would decrease.(3) Chlorella had a good purification effect in municipal sewage. Sterilization, increasing ventilation, increasing inoculum concentrations and adding trace elements could improved the removal efficiency on COD, NH4+-N, TN, TP. The purification of COD by Chlorella basically completed in three days, the COD removal efficiency could reach more than 55%. The purification of TN and NH4+-N throughout the entire culture process. The content of TN and NH4+-N would declined with increasing culture time, eventually the content would stabilized at a certain level. Chlorella purification of TN and NH4+-N basically completed in 72h, and ultimately,TN and NH4+-N removal rates were as high as 83.6% and 80%. The purification of TP by Chlorella generally showed that rapid decline in the first, and then picked up and stabilize. Within 24h, the purification of TP was fastest, TP content decreased linearly, the removal rate reached a maximum and could reach 73% in this time. Then TP levels rebounded and fluctuated and basically stabled at a certain level, the final removal rate of TP could also reach more than 47.5%.(4) Optimal culture conditions for chlorella with multifactor and determine optimal culture conditions: ventilation was 2L/min, seeding density was 2.1×106cells/ml, not add trace elements. The theoretical value of the fatty acid was 42ug/mg, the actual measured value was 37.8ug/mg, relative error of 10%.