Page 192 - Refining Biomass Residues for Sustainable Energy and Bioproducts

Biorefinery of microalgae biomass cultivated in wastewaters 163

37.5% content of MUFAs in lipids produced from Chlamydomonas sp. grown in
municipal domestic sewage at 25%, while He et al. (2013) obtained a 17.45% con-
tent of MUFAs for C. vulgaris grown in septic and secondary sedimentation tank
effluents.
Microalgae are able to use organic carbon from primary municipal wastewater
as the sole carbon source (Ebrahimian et al., 2014). However, the incomplete
removal of organic carbon has been observed (Arora et al., 2016; Mahapatra et al.,
2014). This most likely resulted from light inhibition or from the presence of refrac-
tory carbon/algal polysaccharide secretions, inhibiting cell growth.
It is known that among domestic flows, there are significant differences not only
in their nutrients’ contents but also in the ratios of their elemental compositions.
Optimum N/P and C/N ratios are needed to maximize nutrients removal by the
cells. Arora et al. (2016) obtained better nutrient removal in a medium consisting of
a mixture of dairy and domestic wastewaters by C. debaryana, compared to the one
in a medium made with sewage and paper wastewaters. They attributed this differ-
ence to an optimum N/P ratio of 5:1 in domestic wastewaters, as opposed to the 2:1
ratio found in sewage and paper wastewaters.
Cultivating algae in domestic wastewater effluents is an efficient and attractive
way to reduce wastewater nutrient loads, to leverage the currently existing infra-
structure of treatment plants, to provide oxygen for biological organic matter oxida-
tion and nitrification, and to produce biomass as feedstock for biofuels production
(Peccia et al., 2013).

7.3.3 Landfill leachates

Landfills are currently one of the most common ways of solid waste management.
LLs are waste liquids seeping out of landfill sites. They are considered a burden
because of their large content of nutrients. These nutrients can be of great value to
grow algae. Nitrogen in the form of NH 3 is a key element for algae growth, and it
is largely present in LLs.
The composition of LLs varies widely and depends on the local climate, precipi-
tation volume, and management techniques. The NH 3 content and the pH in LLs
mainly depend on the age of the landfill. Young landfills often have acidic pH and
a relatively low NH 3 content. The pH of LLs increases as AD of the organic acids
takes place, producing methane (CH 4 ) and CO 2 gases (Edmundson and Wilkie,
2013). The high level of NH 3 in LLs is the result of the decomposition of the large
proportion of organic nitrogen (proteins, amino acids, or urea) found in municipal
solid wastes (Lin et al., 2007). This concentration increases with landfill age and is
considered as a long-term issue for its management.
Several studies have reported on the cultivation of microalgae in LLs
(Table 7.4). Edmundson and Wilkie (2013) cultivated Scenedesmus cf. rubescens in
100% LL stream from a closed, methanogenic-stage landfill under pH-controlled
conditions. They observed similar growths in LL and in the control group cultivated
in BBM (specific growth rates of 0.83 day 21 in LL and of 0.91 day 21 in BBM).