Page 201 - Refining Biomass Residues for Sustainable Energy and Bioproducts

170 Refining Biomass Residues for Sustainable Energy and Bioproducts

Large-scale algal biofuels production is unlikely to be viable without the use of
waste nutrients. Unfortunately, there is not enough wastewater available to significantly
replace petroleum-based fuels with microalgae-based energies. Consequently, de novo
sources of nutrientsneedtobeemployedinorder to attain an economically viable bio-
mass production at high scale. A national-scale comparison of resource demands for
algae-based biofuel production was performed for the US DOE. They compared differ-
ent biomass conversion and nutrient recycling strategies in view of land requirements,
fresh and saline water consumption, and N and P demands. The results indicated that
municipal wastewaters could potentially account for 20% of N and 49% of P demands
10
to achievea7.953 10 L/year of renewable biodiesel (Venteris et al., 2014).
The cultivation of microalgae in wastewater may require the addition of nutrients to
balance the N:P ratio. Sources of these supplements may need a pretreatment to prevent
a possible growth inhibition, such as an AD conversion. This approach was successfully
demonstrated by Olguin (2012). In her study, the effluent of a swine manure AD system
was used to cultivate microalgae. This process has the additional advantage to produce
biogas, which can be fed to the microalgae reactor as a source of inorganic carbon.
The Consortium for Algal Biofuels Commercialization, in collaboration with
Sapphire Energy, had identified commercially relevant strains that can efficiently
utilize recycled nutrients coming from HTL and oil separation steps, including
Picochlorum and Haematococcus. They also demonstrated that this process could
reduce the carbon intensity of algal biodiesel by as much as 40% (Mayfield, 2015).

7.4.3 Efficient biomass fractionation and utilization
An efficient biomass fractionation and full utilization are of absolute importance
for the sustainable development of algal biorefinery, as the production costs of the
biomass for the sole goal of fuels production would not meet market requirements.
Microalgae biomass is a rich source of several biomolecules, which makes it an
attractive feedstock for a wide range of applications. Microalgae can accumulate
significant quantities of lipids, a valuable component for the production of biodie-
sel, renewable diesel, and biocrude. Species, such as Botryococcus braunii,
Desmodesmus sp., Nannochloropsis sp., Scenedesmus SDEC-8, Nannochloropsis
sp., and Sorokiniana FCG IITG, have been reported for having the highest lipid
content ranging from 45% to 64% of dry mass (Cheng et al., 2013; Ho et al.,
2014a,b; Kumar et al., 2014; Ma et al., 2014; Nobre et al., 2013; Song et al.,
2014b; Talukdar et al., 2013). The conversion of microalgae biomass to biofuel is
an attractive venue that still faces the challenge of high energy expenditures, partic-
ularly when the drying of biomass previous to the conversion process is needed,
and when the process involves several energetically investing steps. Examples of
this are the biooil production, performed from the pyrolyzation of microalgae free
fatty acids (Chang et al., 2014), and the bioethanol production from genetically
modified cyanobacteria through a photo-fermentative route that converts sunlight
into fermentation products (de Farias Silva and Bertucco, 2016). The production of
biofuels from wet biomass has also been demonstrated. Examples are the biodiesel
production from microalgae performed by the direct conversion of wet biomass into