The core of microalgal biofuel production is to obtain a large number of microalgal biomass through large-scale cultivation robustly at low cost. To date, almost all oleaginous microalgae species used for biofuel are unicellular. However, all the used unicellular oleaginous microalgae species are very tiny in size around 1-10microns, which are nutrient rich and palatable for grazers during cultivation. As a result, mass cultivation is usually crashed away by the swallowing of grazers in the outdoor culture. And also the recovery of unicellular microalgae with tiny size is difficult and costive for harvesting. Therefore, those species with industrial characteristics having high oil content, large size, robustness to contamination, etc would be preferable for the developing of microalgae biofuel.

In view of above problems, Energy Algae Resource Group in Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, changed the attention on the filamentous microalgae neglected previously. Lots of filamentous microalgal species were evaluated and a strain of Tribonema sp. with the size of 0.5-3mm in length was focused.

The total lipid of Tribonema sp. was over 60% of dry weight and neutral lipids accounted for 80% of the total lipid when it was cultured in bubbling columns in laboratory after 12 days. Afterwards, the filamentous microalgae were cultivated for 21 days in 40L glass panel, microalgae biomass reached 3.14g/L and total lipid was 50.23% (Fig.1). Recovery rate around 95.57% by dissolved air flotation without any flocculants was obtained (Fig.2). Subcritical ethanol extraction for lipid followed with the two-step catalytic conversion was adopted for biodiesel production. The main fatty acid compositions of the biodiesel was C16:0 and C16:1 and the properties satisfied the Chinese National Standard BD-100. Moreover, the pollution by grazers has seldom happened in one year mass cultivation outside, revealing the good characteristic of pest resistant of this filamentous species.

This work may provide a new train of thought oleaginous microalgae screening. The research work has been supported by the projects of the national High Technology Plan and the Solar Initiative Plan by Chinese Academy of Sciences.

Fig.1 Morphology of Tribonema sp.

Fig.2 Dissolved air flotation of Tribonema sp. without any flocculants

Table3 Composition of fatty acid in the biodiesel by Tribonema sp.

Reference: Hui Wang, Lili Gao, et al. Integration process of biodiesel production from filamentous oleaginous microalgae Tribonema minus (Bioresource Technology, 2013, 142:39-44 Contact: Prof. LIU Tianzhong Email: liutz (AT) qibebt.ac.cn