High lipid productivity is not the only factor that should be considered early during strain selection. Outdoor cultivation should determine wheth­er the selected microalgae are robust enough to withstand variable local climatic conditions and whether they can dominate a culture. This is par­ticularly important for open pond systems where other algae strains, graz­ers or viruses may easily contaminate the culture. For this purpose, many phycologists recommend the use of local dominant species, even if their lipid productivity may not be as high as other species [43].

Harvesting capability is another important feature of microal­gae with biodiesel potential. Harvesting or dewatering can be best achieved through settling, flocculation or froth flotation [49,50]. For example, many microalgae settle under adverse conditions, and this can be tested under small scale conditions [51]. Lipid extraction ef­ficiency from microalgae is dependent on residual water content after drying and in particular the structure of their cell wall. For example, Nannochloropsis sp. is regarded a highly productive microalga with strong potential for large-scale biodiesel production [43], but ideally requires pretreatment to open up the highly rigid cell walls for higher lipid extraction efficiency.

9.3 CONCLUSIONS

Development of biodiesel production from microalgae presents an im­portant move to address the limitations posed by current first generation biodiesel crops. Microalgae, once developed for commercial biodiesel production, may offer many economical and environmental advantages. Current biodiesel production from microalgae is in the research phase, but is being developed to commercial scale in many countries. Finding promising microalgae for commercial cultivation is multi-facetted and challenging because particular microalgae strains have different require­ments in terms of nutrients intake, environmental and culturing condi­tions and lipid extraction technology. However, diversity of lipid-pro­ducing microalgae species is one of the major advantages of this group of organisms that is likely to lead to selection of suitable algae crops to achieve algal biodiesel production in different regions. A combination of conventional and modern techniques is likely the most efficient route from isolation to large-scale cultivation (Figure 2). Careful initial analy­ses and far-sighted selection of microalgae with a view towards down­stream processing and large-scale production with potential value-add products, is an important prerequisite to domesticate and develop algae crops for biodiesel production.