Oil to alcohol ratio, time, temperature are the significant factors influencing biodiesel production.

Water presence both in methanol (or other alchool used) or in the fat material itself is the main factor which quench transesterify reaction, which otherwise proceeds steadily at temperatures higher than 20 Celcius. The glycerol phase formation also quenches the reaction.

Hi Benavides,

Regarding biofuels from microalgae (third generation biofuels), harvesting is one of the major bottlenecks to its commercial expansion.

Microalgae are unicellular and microscopic organisms, ranging from 2 to 200 µm in diameter, achieve low densities even in high production systems as photobioreactors (< 5 g/L). Also, they have negative surface charge and low sedimentation rates, forming stable suspensions. These characteristics make microalgae hard to be concentrate.

Nowadays, commercial microalgae harvesting is achieved by centrifugation, though large scale application is problematic due to increased power consumption, being only justified for high value products.

http://pubs.rsc.org/en/Content/ArticleHtml/2014/CS/c4cs00189c