However, ammonium load also affected the carbohydrate content
of this biomass. It can be seen in Fig. 4 that high ammonium
load resulted in slightly lower carbohydrate values. The lipids content
increased with regard to that of the biomass collected at low
ammonium load. Moreover, when the cultivation at lowammonium
load was combined with non-favourable conditions, biomass lipid
content was further enhanced up to 35e40%. In this sense, it can be
concluded that a short photoperiod and low temperature prevailed
the accumulation of lipids. These results are consistent with previous
finding showing that the lipids content of C. vulgaris increased
when decreasing the cultivation temperature from 25 to 18 C [27].
Regarding proteins, the favourable conditions (i.e. summer) promoted
the accumulation of protein in the biomass collected under
low ammonium concentration. The maximum protein content was
31% while for the rest of conditions the protein content remained in
the narrow range of 23e25%. These values were lower than the
protein content previously determined at high ammonium concentration
such as synthetic medium [28]. The protein value
calculated hereinwas low but in accordance to other report dealing
with microalgae grown in wastewater in batch mode [7].
At this point it has to be stressed out that all these results were
obtained under batch cultivation, while the cultivation of the same
microalgal biomass under semi-continuous mode exhibited a
different macromolecular profile. The analysis of the biomass
collected during the third retention time evidenced a typical
macromolecular profile in which the biomass is rich in proteins.
More specifically, the values attained for this biomass after 25 days
of semi-continuous operation resulted in 57, 28 and 15% for