Page 202 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Biorefinery of microalgae biomass cultivated in wastewaters 171

biodiesel through a microwave-assisted transesterification (Cheng et al., 2014) and
the HTL process, where the whole microalgae biomass is decomposed and con-
verted into a hot and compressed water matrix (Hietala et al., 2016). AD of micro-
algae biomass yields biogas, containing methane and carbon dioxide as main
constituents (Klassen et al., 2016). Biogas production can be performed from the
whole microalgae biomass, thus significantly reducing energy inputs. However, the
lower C:N ratios found in microalgae biomass compared to lignocellulosic feed-
stocks cause a favored production of ammonia over methane, a toxic component to
bacterial communities responsible for the conversion of the biomass into biogas.
In addition to its energy content, microalgal biomass can contain considerable
amounts of bioactive molecules, such as carotenoids (astaxanthins, β-carotenes, and
xanthophylls), omega 3 fatty acids, polysaccharides, and proteins, which can be used
in several applications as colorants, pharmaceuticals, food and feed, and as bioplastics
(Nobre et al., 2013; Urreta et al., 2014; Zhang et al., 2014). The principal use given
to microalgae biomass is a source of proteins. The protein content in microalgae cells
can reach 70%. Species, such as Arthrospira maxima, Synechococcus sp., Chlorella
vulgaris, Scenedesmus obliquus,and Anabaena cylindrical, are among the ones with
the highest protein content reported (Becker, 2007; Harun et al., 2010). Applications
of algal proteins include enzymes, antibodies, hormones, antibacterial proteins, anti-
oxidants, chelator proteins, mineral binding, and animal feed. Enterprises engaged in
the commercialization of algae proteins include Triton Algae Innovations, Subitec
GmbH, Cellana Inc., RAE, Earthrise Nutritional, Algae Scientific Corporation,
TerraVia Holdings Inc., Sapphire Energy Inc., among others. According to a report
released by Market Research entitled “Algae Market, By Application, By Cultivation
Technology, and Geography-Global Industry Analysis, Size, Share, Growth, Trends,
and Forecast—2016 2024,” in the year 2015, almost 54% of the total algae market’s
revenue came from protein sales and pharmaceutical applications. This market is
expected to expand at a compound annual growth rate of 6.5% from 2016 to 2024.
Other-than-fuel coproducts, opportunities have yet to be fully explored for eco-
nomic trade-offs. It was demonstrated that, from an economic and energy standpoint,
higher incomes and better net energy ratios are related to greater quantities of copro-
ducts and to more types of coproducts produced, respectively (Soratana et al., 2014).
There is actually a strong market demand for selected microalgal high-value products,
such as carotenoids, fatty acids, and phycobiliproteins. However, production costs are
still too high to meet requirements for larger volumes at lower prices. Also, the alter-
native sources for these products are available at lower costs, which limit the poten-
tial of microalgae products. Technological innovation is important for microalgae
transformation in terms of process improvement and lower cost production.

7.5 Conclusions

The production of biofuels from microalgae does not represent a significant share
in the worldwide liquid fuel supply. Large-scale production of microalgal biofuels