Page 196 - Refining Biomass Residues for Sustainable Energy and Bioproducts

166 Refining Biomass Residues for Sustainable Energy and Bioproducts

Algae cultivation in LL can serve the double purpose of wastewater remediation
and biomass production. The composition of leachates in landfills is highly vari-
able. There are main considerations to be addressed when using LL to formulate
culture media for microalgae cultivation. One of them is the possibility of having
insufficient amounts of organic carbon and/or P. Another consideration is the toxic
effect to the cells caused by not only free NH 3 but also by volatile fatty acids, pro-
teins, carbohydrates, and hydroxylated aromatics (Lin et al., 2007; Pereira et al.,
2016; Zhao et al., 2014). In addition, high salinity and dark color of LLs are issues
that need to be dealt with to maximize algal growth (Zhao et al., 2014).

7.3.4 Treatment plants waste streams
The large-scale treatment of wastewaters generally requires three operations (EPA,
2004). The primary operation consists of the sedimentation of solid waste after the
removal of larger contaminants. The resulting sludge is then either fed into a
digester, or dewatered, yielding a wet solid and a liquid centrate. The centrate con-
tains high amounts of N (mainly in the form of NH 3 ) and P. Centrate may also con-
tain urea, organic acids, phenols, and pesticides at high concentrations. These
compounds may inhibit algae growth (Sepu ´lveda et al., 2015).
The secondary operation is a biological treatment designed to remove up to 90%
of the organic matter contained in the wastewater. The secondary treatment
involves an oxidation process to further purify the wastewater, where NH 3 can be
2
converted into NO (EPA, 2004).
3
The tertiary treatment involves the removal of heavy metals, N and P, and the
stabilization of oxygen-demanding substances. The technologies used to perform
this operation include physical chemical separation techniques (filtration, floccula-
tion/precipitation, carbon adsorption, distillation, and reverse osmosis), and can also
be extensions of conventional secondary biological treatments (EPA, 2004). During
2
this step, nitrifying bacteria are used to convert NH 3 to NO . Algae treatment to
3
wastewaters (phycoremediation) can be part of the tertiary treatment of liquid
wastes, and it allows the removal of pollutants still present in the wastewaters. The
cultivation of microalgae in different treatment plant effluents has been reported by
several authors (Table 7.5).
AlMomani and Ormeci (2016) compared the performance of three algae species
(C. vulgaris, Neochloris oleoabundans, and a mixed indigenous microalgae) to
grow and remove nutrients from primary and secondary effluents and from centrate.
21
The highest growth for C. vulgaris (0.61 day ) was observed in the primary efflu-
21
ent; for N. oleoabundans (0.35 day ) it was in the secondary effluent; and for the
21
mixed algal culture (0.41 day ) it occurred in the centrate. Centrate had the high-
est concentration of nutrients; however, only the mixed indigenous microalgae per-
formed well in this stream. The observed differences in the growth were attributed
to the concentrations of nutrients and to the C, N, and P ratios of the wastewater.
Goncalves et al. (2016) studied the synergistic effect of consortia of microalgae
and bacteria on the removal of nutrients from a secondary effluent. A 100%
removal of N was observed for the cocultivation of C. vulgaris and Enterobacter