In a number of studies, it has been assumed that the biodiesel production from algal oil should be conducted using the same approach as for vegetable oil. This requires the drying of the algal biomass to 90% solids by mass (Sazdanoff 2006; Lardon et al., 2009; Batan et al., 2010; Yang et al., 2011). Typically, belt or drum drying is used, with energy provided by natural gas. This may represent the major or a significant portion of the energy demand of the process. Sander and Murthy (2010) estimated that 89% of the energy requirement of their “well-to-pump,” raceway — based algal biodiesel system was required for drying the intermediate product prior to conversion to biodiesel, using a natural gas powered dryer. Razon and Tan (2011) attributed 48% of their energy requirement (310 MJ per tonne biodiesel) to drying, following production of 1 kg FAME and 1.5 m3 biogas using a raceway pond. Drying of the biomass is only feasible where natural resources (e. g., solar drying) can be used while preventing lipid oxidation (Lardon et al., 2009).

Furthermore, the requirement of cell disruption for product recovery has also been considered. Razon and Tan (2011) demonstrated that the energy input to the bead mill for disruption of Haematococcus pluvialis formed the greatest contribution to the process energy required (>30%). Stephenson et al. (2010) estimated cell dis­ruption by high-pressure homogenization to account for approximately 5 GJ tonne-1 biodiesel formed and 320 kg CO2 eq tonne-1 biodiesel in GWP. The need for cell disruption is a function of both the flowsheet selected and the algal species.

In a comparison of the hypothetical wet and dry processing routes for the trans­esterification to biodiesel, the benefit of developing an effective wet processing route for which a discrete cell disruption step and rigorous drying are not essential is clearly demonstrated (Lardon et al., 2009). The energy requirement was reduced to 70% to 75% of the dry processing route while the energy recoverable through further processing of the oil cake increased by 67% to 115%. Overall, the additional energy recoverable was 0.6 to 1.1 MJ per 1 MJ biodiesel. Direct esterification in the presence of water has been demonstrated under analytical conditions (Griffiths et al., 2010) and requires further optimization for large-scale use.