Thermal analysis of green algae for comparing relationship between particle size and heat evolved

The thermal properties affected by particle size of microbial cell were investigated by the simultaneous thermogravimetry (TG) and differential thermal analysis (DTA). The particle size, which could affect the heat evolved, occurred from the combustion of the microbial cells. The model microorganism used in this study is Nostoc, a genus of flamentous, heterocystous, and cyanobacteria, known as a freshwater microalga, which can accumulate a large amount of lipid in the cell. As a result, the marked difference in heat energy between the different particle sizes of microbial sample was detected in the temperature range from 310 to 351 °C. So, the two-step linear temperature program is used for resolving the overlapping exothermic peaks in the DTA curves in the temperature range from 310 to 315 °C. The heat evolved from 45 μm-sized particle sample in this temperature range was 3.78 ± 0.19 kJ/g which was 1.1- to 1.4-fold greater than those from the other particle size samples. The heat evolved occurred in 310–351 °C was inversely proportional to the particle size of dried microbial cells. In conclusion, exothermic heat per dry sample mass (kJ/g) in the temperature range from 310 to 351 °C is highly dependent on the particle size of dried microbial cell.