Page 204 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Biorefinery of microalgae biomass cultivated in wastewaters 173

extra nutrients must be taken carefully, as this can increase cultivation times to
meet the legal emission limits desired in a scale-up phycoremediation process.
Also, the supplementation of wastewaters with nutrients signifies polluting the
wastes that are being treated and increasing the operational expenses of the waste-
water cleaning process. Mixing different wastewater streams can be done to achieve
an appropriate composition to successfully grow microalgae. The proportions of the
streams in the mixture must follow the intended purpose of the cultivation, that is,
to lower nutrient levels in the cultures, to produce lipids for biofuel, or to produce
value-added coproducts.
Costs of biomass production can be reduced by fitting the cultivation to the site-
specific conditions, considering the available sources of nutrients and designing a
coproduct scenario according to the best environmental, energy, and marketing
standpoints.
There are many technologies to produce biofuels from microalgae. The most
favorable ones, in terms of energy return of investment, are those produced through
thermochemical processes from wet biomass: the biodiesel obtained from the direct
extraction and conversion of microalgae oil, the biocrude obtained from an HTL
process, and the biogas made from the whole microalgae biomass. Any strategy
that includes the drying of the biomass will convey a big investment in operational
costs.
The exploration of novel coproducts is an important aspect to improve the eco-
nomics of any biofuel production system from microalgae. Many of the components
contained in the biomass have been proven to have valuable properties. The market
of the microalgae coproducts is expected to flourish as the technologies for identifi-
cation, extraction, and purification of these products come to hand. Strict govern-
ment regulations on carbon emissions are forcing several companies to shift to
biodegradable products, an example of this is bioplastics derived from microalgae.
The global algae market is projected to reach US$1.143 B by 2024, expanding at
a compound annual growth rate of 7.39%. With more than 91.3% of the overall
algae market in 2015, Algenol, Solazyme Inc., and Sapphire Energy Inc. are the
leaders in this industrial sector. Their success can be attributed to the expansion of
their facilities and to the commercialization of their cultivation technologies, as
well as their targeting of government and private investments for technological
developments on projects oriented to minimize carbon emissions. These three
industries, together with Chevron Corporation, are investing, researching, and actu-
ally producing biofuels from microalgae biomass (Transparency Market Research,
2015). Up to date, however, the majority of the biomass produced is destined to the
commercialization of nonenergy products. Nonetheless, the future of large-scale,
sustainable microalgae biofuel production is promissory.
The National Alliance for Advanced Biofuels and Bioproducts, with the support
of the US DOE, has developed a technology that has the potential to reduce the
cost of algae-based biocrude from $240 to $7.50 per gallon. This technology is
based on new strain developments, an improved cultivation process, a cost-effective
harvesting technology, and a high-yield extraction conversion process (NAABB,
2014).