Research Activities

1. Screening and evaluation of characteristic oleaginous microalgae species
Microalgae specie is one of the most key technologies of microalgae biofuel, not only influences the cost of energy product but also usually dominates the success or failure of mass cultivation. Conventional oleaginous microalgae species are almost focused on the unicellular species, which is very tiny in size. Such tiny unicellular specie is very difficult to be harvested to account for 20-30% of the total costs of microalgae biomass production. Most importantly, tiny unicellular algal cells are usually palatable for grazers to usually cause the crash of mass cultivation. Microalgae species with industrial characteristics such as robustness to grazers phagocytosis and ease to be harvested without any auxiliary additives would have more potentials to settle down above problems. We have firstly obtained six Tribonema sp. species and evaluated their potentials as for microalgae biofuel production. The cell size are very big to around 0.2~3mm. 5.0g/L biomass density and around 45~60% lipid oil content, of which more than 80% are TAG, have been approached by 12 days bubbling column cultivation. 99% biomass can be harvested by filtration or dissolved air flotation without adding any flocculants. More than one year mass cultivation practices in 500m2 ponds demonstrated their robustness to any Protozoa. More interestedly, These species have distinguished biochemical response to nitrogen that the lipid accumulation does not dominated by nitrogen starvation, but usually for conventional unicellular algal species, stress of nitrogen starvation is essential indispensable .

Fig.1 Cellular morphologies of tested strains. a, T.vulgare24.94. b, T.aequale 200.80. c, T.aequale 880-1. d, T.ulotrichoides 21.94. e, T.ultriculosum22.94. f, T.minus 880-3

Fig. 2. Dynamics of cellular components, protein (A), lipid (B), soluble sugar (C) and insoluble sugar (D) in Tribonema minus in response to 0N, 0.05N, 0.1N and 1N-BG11 medium.

2. Attached mass cultivation technology for microalgae and its pilot practices

Attached cultivation of microalgae in biofilm is potential cultivation method of microalgae which has variety of advantages including high biomass productivity, less medium consumption, economical harvesting and ease to scale-up. We have proposed and constructed this attached cultivation technology and has demonstrated its feasibility of efficient cultivation for variety of microalgae species. Systematic investigations on the cultivation conditions including inoculum density, attached substratum, medium composition, CO2 concentration and medium addition method have been carried out. The principle of attached cultivation photobioreactor design based on the dilution of solar light intensity has been proposed to boost the utilization efficiency of solar light and then produce dramatic high biomass of around 40~100gm-2d-1. A pilot cultivation photobioreactor of curtain structure in array with 200m2 scale has been constructed, and continuous cultivations lasting more than one month for both oleaginous specie of Tribonema minus and Spirulina sp. have been finished.  More than 10% of solar photosynthesis efficiency (to optical spectrum), or maximum 40gm-2d-1 biomass productivity has been approached.

Fig.3 Attached mass cultivation of oleaginous Tribonema minus in 200m2 pilot scale