The rapid development of the biofuels production technologies from differ­ent biomass types has given rise to the biomass and food markets as it was aforementioned. Besides the use of residual biomass, research and in par­ticular biotechnology has moved forward into seeking alternative biomass production technologies that will offer higher yields per hectare as well as lipids and carbohydrates, which are not part of the human and animal food — chain, avoiding competition between food/feed and energy crops. Targeted research efforts have offered a promising solution by the selection of unicel­lular microorganisms for the production of biofuels [48][49]. Micro-algae are photosynthetic microorganisms that can produce lipids, proteins and car­bohydrates in large amounts over short periods of time.

Micro-algae are currently considered a prominent source of fatty acids, which offers large yields per hectare with various fatty acid foot-prints from each strain. In fact, there are certain strains that offer fatty acids of in­creased saturation (small content of unsaturated fatty acids) and of smaller carbon-chain length such as Dunaliellasalina, Chlorella minutissima, Spi — rulina maxima, Synechococcus sp. [50] etc. Another advantage of algal oils is that their fatty acid content can be directed to small carbon-chain mol­ecules either genetically or by manipulating the aquaculture conditions such as light source and intensity [51], nitrogen starvation period [52], nutrients and CO2 feeding profiles [53].

Micro-algae and their products formulated the so called 3rd generation biofuels, as they incorporate various characteristics, which render them superior over other biofuels and biomass types. Micro-algae can also be produced in sea water [54] or even waste water, while they are biodegrad­able and relatively harmless during an eventual spill. Furthermore, their yield per hectare can reach 3785-5678lit, which is 20-700 higher over the conventional energy crops yield (soy, rape and palm). The lipids contained in most micro-algal oils have a similar synthesis with that of soy-bean oil, while they also contain some poly-saturated fatty acids with four double bonds. As a result catalytic hydrotreating of micro-algal oil is the most promising technology for converting it into biofuels.