The limited number of reports in the published literature
suggests that few research groups have addressed the issue of
process hypersalinity. Yet there are clear advantages to
developing a process for treating and fermenting hypersaline
biomass, particularly in view of the extensive ongoing global
development of marine microalgal systems for producing
lipids for biofuels. Whether the end biomass is sourced from
open raceway ponds or closed PBR systems there is likely to be
an abundant supply of potentially fermentable lipid-extracted
residue marine biomass for conversion to ethanol if a sustainable
process can be developed. Even microalgal biomass with
minimal fermentable sugar mass fractions of approximately
0.10 dw could be utilised to produce significant yields of bioethanol.
However, in many instances, existing fermentation
research may not be applicable for use with a sustainable
marine or hypersaline biomass. Further investigation into
halotolerant and halophilic enzymatic hydrolysis would
address the need for more appropriate biochemical pretreatment
of hypersaline biomass for extraction of fermentable
sugars. Priority should also be given to developing improved
microbial systems for effective ethanologenic or solventogenic
conversion of hypersaline biomass, as a hypersaline fermentation
system reduces the requirement for fresh water during
production. Non-agricultural feedstock like marine microalgae
may provide a solution to sustainable biomass supply.
This review does not cover the economic feasibility of
producing bioethanol from hypersaline microalgal biomass.
Nor has it assessed the comparative costs with existing
processes that use agricultural crops. Additionally, the
process engineering challenges associated with a hypersaline
process have not been reviewed. Although the sole focus has
been on bioethanol as the end product, the principle consideration
for use of a hypersaline biomass remains the same
regardless of the eventual end product. Indeed, there is likely
significant value in other energy products such as butanol that
may be similarly converted.