Page 188 - Refining Biomass Residues for Sustainable Energy and Bioproducts

160 Refining Biomass Residues for Sustainable Energy and Bioproducts

The addition of nutrients in digestate slurries may be required to maximize pro-
ductivities. Culture media prepared from digestates are known to be poor in phos-
phorus since precipitation of phosphates occurs at the high pH values and high
dissolved oxygen concentrations observed in digestates (Ji et al., 2014a). This also
explains the higher phosphorus-to-nitrogen removal observed in some cultures
(Koutra et al., 2018).
The highest biomass productivity (643.6 mg/L/day) found in the literature in the
present study was reported by Tan et al. (2016). The biomass, grown as feedstock
for ethanol production (containing 61.5% carbohydrates), was produced from C.
vulgaris ESP-6 grown in a 12.5% digestate diluted in water. The digestate came
from a swine anaerobic digester, and it was supplemented with P and Mg to maxi-
mize productivities.
Lizzul et al. (2014) looked at the effects of adding air containing 12% CO 2 at a
3
rate of 20 cm /min on the mixotrophic growth of C. sorokiniana. The added CO 2
promoted the growth of the microorganism, stimulated lipid production, and
achieved the complete removal of nitrogen in 96 h.
The best growths for Desmodesmus sp., P. kessleri, A. obliquus, C. vulgaris, and
C. sorokiniana were observed in the media made of 10% digestate in water.
However, lower dilutions were used to maximize the synthesis of coproducts (Ji
et al., 2014a; Koutra et al., 2018; Lizzul et al., 2014). Digestates with high pH
values and high NH 3 concentrations may require the addition of P to compensate
for P precipitation that may result from these specific conditions.

7.3.2 Domestic flows
Domestic flow refers to the sewage systems collecting municipal wastewaters from
homes, business, industries, and institutions of a locality. These wastes are normally
delivered to treatment facilities before being discharged to water bodies or land, or
being reused (EPA, 2004). These sewage systems range from unconnected simple
toilets in rural areas to modern and connected public sewage treatment plants.
The compositions of domestic flows are highly variable with various concentra-
tions of NH 3 ,NO 3 , P, and organic carbon (Table 7.3). The sewage from an individ-
ual home can be treated in a septic tank. This sewage is high in organics and
NH 3 -N (Cheah et al., 2016). On the other hand, domestic residues and effluents
from industrial processes contain large amounts of heavy metals and pesticides.
These flows require further treatment before being discharged into natural environ-
ments to avoid the eutrophication of water bodies.
The pH of the culture medium plays an important role in the availability of nutri-
ents to algae. Mahapatra et al. (2014) observed an increase in the pH from 6.3 to
8.6 after 12 days of cultivation of a consortium of algae in filtered and sterilized
municipal wastewater. The increase in the pH resulted from the algal growth and
the simultaneous increase in the photosynthetic activity and the accumulation of
2
OH ions. The increase of pH can also affect P availability to algae. Arora et al.
(2016) observed important decreases in P contents when algae (Chlamydomonas
debaryana) were grown in undiluted sewage wastewater. These decreases were