The dilute nature of microalgae culture requires that the biomass be concentrated and dried so that oil extraction can be achieved without water. About 30% of biomass production cost goes to harvesting and dewatering while 84.9% of process energy is expended on harvesting and drying of microalgae. Two ways of improving the energy balance are: use of low energy drying methods or the complete avoidance of the drying steps by carrying out oil extraction on the wet biomass.

 

The combination of extraction and conversion to biodiesel of vegetable oil is known as reactive extraction and has formed the principle behind most processes that attempt the use of wet algae biomass for biodiesel production. However, the reactive extraction process consumes a large amount of alcohol, leading to additional cost required to recover over 94% excess methanol albeit the excess methanol allows for a more water tolerant process compared to conventional transesterification. Foam fractionation or flotation has the ability to combine harvesting with oil extraction if the cell lysing and solid separation capacity of surfactants is combined with solvent extraction by a solvent either within the column or at the top of it.