Page 200 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Biorefinery of microalgae biomass cultivated in wastewaters 169

where a 530 Ha algae production facility and a 10,000 t/day sugar cane mill were
colocated on the same site. The results indicated that the plant could produce up to
5.8 million L of biodiesel/year, that the mill CO 2 emissions would be reduced by
15%, and that fossil fuel would no longer be needed for the plant operation.
The colocation approach allows to grow microalgae biomass outdoors reducing
the sensitiveness to seasonal changes. The waste energy of the industrial plant can
be potentially used to control the temperature of the reactor and the reduction in
irradiance during the winter months can be mediated by moving to a heterotrophic
production system. Another strategy to mitigate the effect of seasonal changes
would be to dry part of the biomass produced during the hot summer months for
later use in the low session. Additional advantages of a colocation system are the
possibility of using energy and coproducts locally; the creation of new partnerships
with local businesses, industrial plants, and wastewater treatment plants; and the
cousage of the available industrial equipment for the harvesting and conditioning of
the biomass.
BioProcess Algae LLC and Green Plain’s joint venture is an example of a colo-
cation integrated system that enables the conversion of light and CO 2 into microal-
gae biomass. The CO 2 produced as a by-product by the Green Plain’s ethanol plant
(Iowa, United States) is used to grow algae biomass with the potential to be used
for biofuel, high-quality animal feed, nutraceuticals, pharmaceuticals, and/or bio-
mass for energy production.
Another example of a colocation is a venture started in 2011 by the industries
Pond Biofuels and Marys Cement Plant. The 25,000 L photobioreactor in the pilot
scale algal biorefinery utilizes waste CO 2 and energy by the cement plant to grow
algae biomass. The harvested biomass is then dried using waste heat and burned as
a fuel inside the plant.

7.4.2 Nutrients recycling
When using wastewater as a medium for biomass cultivation, the addition of N
and/or P may be needed to achieve the proper ratio. At early cultivation stages,
large quantities of fixed nitrogen would be required to achieve high biomass pro-
ductivities. To be sustainable, it is necessary to incorporate a nutrient recycle sys-
tem to the biomass production system. Potential sources of recycled nutrients are,
for example, the fuel-extracted algal residues and the aqueous phase from previous
conversion processes. Trials performed by Lo ´pez Barreiro et al. (2015) revealed
that C. vulgaris and Nannochloropsis gaditana can be grown in a medium prepared
by replacing 75% of the nutrients from the standard formulation with nutrients
recovered from a hydrothermal liquefaction (HTL) conversion. Scenedesmus acutus
was able to use extracellular proteinaceous nitrogen from algal biomass residuals
after fuel extraction (Gu et al., 2015). The needs of nutrients recycling have to be
assessed for each case scenario as its success depends on the ability of the strain to
assimilate the nitrogen contained in amino acids, yeast extracts, and proteinaceous
algal residues. Moreover, it should be considered that metal catalysts and NH 1
4
present in the recycled media could be toxic to the strain.