Page 199 - Refining Biomass Residues for Sustainable Energy and Bioproducts

168 Refining Biomass Residues for Sustainable Energy and Bioproducts

asburiae. However, no N removal was detected in the cultures of E. asburiae. The
associations of microalgae and bacteria can be advantageous over axenic cultures.
This is because microalgae provide organic compounds and O 2 to heterotrophic
bacteria; and bacteria supply microalgae with CO 2 , organic growth factors, and
vitamins, required for microalgal growth (Goncalves et al., 2016).
It is commonly observed in microalgae cultures, irrespective of being performed
in wastewaters, that the optimum conditions for biomass production, coproducts
synthesis, and nutrients uptake are not the same. Sepu ´lveda et al. (2015) reported
that the maximum biomass productivity (334 mg/L NH 4 -N) was obtained in a 50%
mixture of centrate and seawater, while the maximum nitrogen uptake (95.7 mg/L
NH 4 -N) was achieved in a 20% mixture of centrate and seawater. They also
observed that proportions of centrate to seawater more than 50% had a detrimental
effect on the biomass productivity and P uptake.
2
Jebali et al. (2018) reported that a 60% centrate with 200 μE/m /s were the opti-
mal conditions maximizing the growth of Scenedesmus sp. Ge and Champagne
(2016) reported that high ratios of centrate did not translate in a better microalgae
growth or lipid production. In their study, increased concentrations of centrate
resulted in longer lag phases in their cultures of C. vulgaris due to the higher pH
value at greater centrate ratios.
A higher concentration of nutrients in wastewaters not always translates into bet-
ter biomass productivities and nutrients uptake. The ratios of C:N:P and the pH are
factors that need to be considered and often adjusted. In addition, the synergistic
effect of bacteria and microalgae on the removal of nitrogen and organic carbon
should be as well investigated.

7.4 Achieving a cost-effective microalgae biomass-based
biorefinery system

The sustainable development of algal biofuels requires not only to assure the sus-
tainable and cheap supply of enough amounts of water, energy, and quality nutri-
ents but also the colocation of the biomass production system to industries
generating these supplies as wastes. The extraction of valuable chemicals from the
biomass that can increase the whole value of microalgae biomass as an energy feed-
stock and the recycling of water and nutrients from previous harvesting and conver-
sion steps are approaches that can also significantly address the issues of
sustainability.

7.4.1 Colocation of the biomass production system to an
industry
To have an easy access to waste nutrients and energy, it is important that microal-
gae production facilities are close to where these wastes are being generated.
Lohrey and Kochergin (2012) performed a feasibility study on biodiesel production