Analyzing the productivity values reported in Table 1, one can
observe that, for a given R value, the cultivation took shorter
time when using lower tf value, hence increasing cell productivity
(Px). ANCOVA demonstrated that such an effect was
significant (p < 0.001, Table 2) and particularly evident in run 7
(R = 0.80 and tf = 6 d), which exhibited an average productivity
(Px =219±13mg L−1 d−1) about 70% higher than those obtained
at longer tf values (runs 8 and 9) and about 90% higher than
those reported by Rangel-Yagui et al. [12] and Danesi et al. [36]
for fed-batch supply of urea with exponential increasing feeding
rate at 5.0–5.6 klx (60.0–67.2mol photonsm−2 s−1) and less
starting biomass levels. Besides, it was higher than when using
either lower R values (0.20–0.50), because of light limitation, or
higher R value (0.95), owing to photoinhibition [7] along with lower
growth rate associated to less initial cell concentration. As far as
the cultivation cycle is concerned, the quite high p-value reported
in the same table (0.475) does not point out any statistically significant
effect of this parameter on cell productivity, which means
that the repeated fed-batch process using urea as nitrogen source
could keep stable throughout several successive cycles, and then
it could be successfully employed in long-term A. platensis cultivations