3. Results and discussion
3.1. Microalgae growth on swine slurry: batch vs. semi-continuous
Batch experiments were run until nutrients depletion (10 days).
The maximum biomass concentration reached 1.25 g VSS L1 and it
was attained at high NH4
þ load under favourable conditions (23 C,
14 h of illumination, Fig. 1A). On the contrary, lower microalgal
growth was observed during non-favourable conditions at high
NH4
þ load (Fig. 1A). The low temperature (15 C) applied in this
culture probably slowed down the microalgal metabolism and
consequently the growth. Biomass concentration obtained at low
NH4
þ loads was around 0.72e0.85 g VSS L1, regardless the environmental
conditions (Fig. 1B). Overall, after 10 days of cultivation,
biomass concentration was increased by 2.5e3.0 fold in all cases,
exception made for the culture at high ammonium load under
favourable conditions that increased the concentration by 4.2-fold.
In accordance with de Godos et al. [18], biomass production
increased together with increasing slurry loading rates under
favourable conditions (summer temperature and light hours) while
during winter conditions the biomass production was lower [3].
Based on the results obtained in discontinuous experiments, the
conditions at high NH4
þ load coupled with springesummer conditions
(23 C and 14 h of illumination) were selected to set up a
semi-continuous reactor treating diluted swine slurry. Microalgae
growth during semi-continuous operation was increasing with
time until steady statewas reached at approximately 0.90 g VSS L1
(Fig. 1C). No remarkable differences were evidenced when