Isolation, identification and outdoor cultivation of thermophilic freshwater microalgae Coelastrella sp. FI69 in bubble column reactor for the application of biofuel production

Identifying a suitable microalga, which has the attributes of optimal growth characteristics, preferable biofuel profile and high-value product accumulation capability, is necessary for a feasible microalgal cultivation process. In this regard, the objective of this present study comes under the topic called phyco-prospecting, which is identification of appropriate microalgae for a specified task. With this, the aim of the study is to molecularly identify an interest of organism to conduct outdoor cultivation, biomass production and biofuel evaluation. Concerning this, environmental samples were collected from a dry lake at summer time to isolate thermophilic microalgae using traditional isolation techniques. The isolated microalgae was identified as species of Coelastrella based on 18 s rRNA gene analysis, and tested specifically for its thermo-tolerant competency at an outdoor pilot scale cultivation facility. Based on the desirable growth performance of the species, it was further cultivated in series of bubble column reactors aerated at a higher rate of 4.4 vv−1 m−1 of 0.04%, 1.5% and 5% CO2 (vv−1) enriched air. Improved growth was observed in 1.5% CO2 aeration, whereas slightly inhibited growth was found biomass productivity, and produced 3.5 g L−1 of dry biomass from 0.05 g L−1 of initial concentration within 9 days of cultivation. The biomasses had ~18% (ww−1) of total lipids, and the fatty acid profile of lipids shows higher presence of C18:1, which is desirable for biodiesel conversion. The energy content biomass was about 21 MJ kg−1, and the reddish pigment accumulation characteristic of the species was considered as beneficial.