Page 177 - Refining Biomass Residues for Sustainable Energy and Bioproducts

150 Refining Biomass Residues for Sustainable Energy and Bioproducts

studies (Gupta et al., 2016; Jebali et al., 2018; Paskuliakova et al., 2018; Tan et al.,
2016). The biomass productivity and extent of the nutrients uptake in the waste-
waters are mainly dependent on microalgae species, composition of wastewaters,
and growing conditions. There are, however, common components and characteris-
tics among different waste streams that can affect the biomass production and com-
position and they are discussed in this chapter.

7.2 Factors affecting algae growth when using
wastewaters

The growing interest in renewable energies has motivated the investigation of fuel
production from various biomasses. The production of biofuels from microalgae is
considered as one of the approaches that can potentially overcome some of the chal-
lenges that alternative energies still have in front of fossil fuels. Over the years,
various approaches have been proposed to improve the economics of a microalgae-
based biorefinery. These includes genetically improved strains, new cultivation sys-
tems to improve photosynthetic efficiencies, and the use of economical sources of
nutrients, energy, and water (Ganeshkumar et al., 2018; Gao et al., 2015; Jebali
et al., 2018; Kouhia et al., 2015; Liu et al., 2013; Perin et al., 2017; Ren et al.,
2018; Shin et al., 2017; Wang et al., 2018). As such, the use of wastewaters repre-
sents a promising solution. However, the utilization of wastewaters in the formula-
tion of a culture medium to produce microalgae biomass raises several challenges
that need to be addressed, among them are the toxicity of certain components that
are present, the presence of grazers or rotifers that can affect cells reproduction and
survival, the necessity to pretreat or condition the wastewaters, and the variability
in time and place of the composition of the wastewaters (Moreno-Garcia et al.,
2017). Nevertheless, there are certain components common to most wastewaters
and known to affect microalgae cell metabolism and to influence the biomass
productivity and composition.

7.2.1 Ammonia toxicity and pH
Ammonia (NH 3 ) is produced from the decomposition of urea and from the break-
down of proteins. It is a common component found in liquid effluents coming from
landfills (Paskuliakova et al., 2018; Pereira et al., 2016) and highly present in anaer-
obic digestion (AD) slurries (digestates) (Koutra et al., 2018; Tan et al., 2016).
NH 3 has been reported as the preferred source of nitrogen to algae, but it is also
known to be toxic to them (Escudero et al., 2014; Grobbelaar, 2004; Kallqvist and
Svenson, 2003; Lin et al., 2007; Pereira et al., 2016; Sniffen et al., 2018). The most
common forms of inorganic nitrogen (N) used by algae and cyanobacteria are
1
2
2
ammonium (NH ), nitrate (NO ), and occasionally nitrite (NO ). However, there
4 3 2
2
1
is an energetic advantage of using NH rather than NO as N source by the cells.
3
4
The assimilation of NO 2 into cell material generates about 0.7 hydroxide ions
3