In the recent years, global warming becomes more serious problem due to the increasing carbon dioxide (CO2) accumulated in the atmosphere, The plant steel for industry plays the important role in releasing flue gas which is CO2-rich. Microalgae is the candidate to solve the problem by photosynthesis, which use sun light as energy source to convert water and CO2 into biomass, and it can consume CO2 to reduce the CO2 emission. We utilized these mutant microalgae to reduce the CO2 in flue gas aerated from coke oven of a steel plant and produce microalgae biomass which can extract oil to produce FAME. Furthermore, we cultivate microalgae combined with response surface methodology to get the optimized cultivation condition under the specific initial density, aeration rate, and flue gas ratio.
To investigate the effect of flue gas ratio, there were 0, 12.5, 25, 50, and 100 % flue gas ratio gases utilized to study the effect of flue gas ratio in microalgae cultivation. The
microalgae Chlorella sp. TT-1 aerated with 25 % flue gas had more biomass production, which is 1.284 g/L, than the other microalgae cultivations, and its biomass productivity were 0.421 g/L/day. Lipid content of Chlorella sp. TT-1 cultures with 12.5, 25 % flue gas ratio aeration were 41.55 % and 40.23 %. By all accounts, Chlorella sp. TT-1 cultivated in 25 % had the most lipid quantity due to biomass production and lipid content. In the part of FAME, there was no difference between the FAME content of Chlorella sp. TT-1 cultivated with different flue gas ratios, but lipid enhancement will increase the FAME content in microalgae cell simultaneously.
The aeration rate of 0.1, 0.2, and 0.3 vvm were aerated in microalgae culture to study the effect of aeration rate with flue gas. The biomass production of Chlorella sp. TT-1 at 0.1, 0.2, and 0.3 vvm aeration rate were 0.775,0.842, and 0.897 g/L, and the biomass productivities were 0.270, 0.279, and 0.286 g/L/day, respectively. The lipid contents of Chlorella sp. TT-1 with 0.1, 0.2, and 0.3 vvm aeration rates were 36.12, 37.61, and 39.90 % respectively, and the result of the experiment was obtained that the biomass production and lipid content in
microalgae cells increased with the increasing aeration rate. The experimental result of FAME content showed the contents of FAME compositions slightly increase with high aeration rate, and the variance was 4~5 %.
In order to investigate whether the illumination is necessary in microalgae culture aerated with flue gas, Chlorella sp. TT-1 was cultivated under full and half illumination. The
biomass production of Chlorella sp. TT-1 in full and half illumination were 1.116 g/L and 0.517 g/L respectively. The microalgae cultivation with flue gas under full illumination was obviously better than half illumination, the biomass of Chlorella sp. TT-1 cultivated with flue gas under half illumination even reduced during the microalgae aerated with flue gas was shielded from irradiation. In summary, the better irradiation time is full illumination for microalgae cultivation, and the light should be devised when the microalgae cultivated with flue gas. The lipid content of Chlorella sp. TT-1 under full and half illumination were 36.90 % and 14.53 %, and the lipid production were 0.412 g/L and 0.083 g/L respectively. Obviously, the lipid in microalgae cell under full illumination was all more than it cultivated under half illumination. The saturated fatty acid (C16:0) accounted for the most part in Chlorella sp.
TT-1 cultivated under half illumination, while the microalgae had more long and unsaturated fatty acid (C18:1, C18:2, and C18:3) under full illumination.
Instead of enormous experiments to test, we cultivate microalgae Chlorella sp. TT-1 combining response surface methodology which can reduce the experiment times to diminish the cost, and simulate the experiment formula to get the optimum condition for microalgae cultivation. In my experiment, initial density, aeration rate, flue gas ratio, and irradiation time these factors were discussed to study the effect to biomass productivity, lipid content, and lipid composition. The optimized biomass productivity of Chlorella sp. TT-1 is 0.4864 g/L/day when the initial density of 0.37 g/Laerated with 75 % flue gas ratio at 0.30 vvm aeration rate; the optimized lipid production of Chlorella sp. TT-1 is 0.2164 g/L when the initial density of 0.35 g/Laerated with 75 % flue gas ratio at 0.24 vvm aeration rate; the optimized FAME production of Chlorella sp. TT-1 is 0.1568 g/Lwhen the initial density of 0.37 g/Laerated with 74 % flue gas ratio at 0.25 vvm aeration rate. The optimum condition was utilized to cultivate microalgae culture in practice, and the predicted value and
experimental productivity are shown in Figure 3-15.
In order to investigate whether the enhancement of the illumination is necessary in microalgae culture aerated with flue gas under the optimum microalgae cultivation condition and the effect of different illumination density for microalgae cultivation, the illumination of 300, 500, and 700 μmol/m2/s were utilized and irradiated for the microalgae cultivation with flue gas. The microalgae cultivation cultivated with 500 μmol/m2/s had the most microalgae biomass production 1.015 g/L while the biomass productivity was 0.390 g/L/day. The illumination of 500 μmol/m2/s could enhance the lipid accumulation, and it could obtain the
lipid content of 48.68 %. Furthermore, the culture irradiated under 500 μmol/m2/s had more C16:0 content, and it means higher illumination would induce microalgae to synthesize the saturated carbon compound of shorter chain like C16:0 which high levels of saturated fatty acids tend to increase the stability of FAME.