3.2. Microalgal biomass concentration and biomass
composition
The final dry weight microalgal biomass yield was about 10%
higher for Scenedesmus than for Chlorella when compared
pairwise for each nutrient combination (paired t-test,
p ¼ 0.03). The final microalgal biomass yield varied between
245 and 475 mg L1 for Chlorella and between 304 and
564 mg L1 for Scenedesmus. For Chlorella, the final biomass
yield decreased in a quadratic way with the N supply in the
medium and was reduced by about 40% at the lowest N supply
level (Fig. 4, Table 1). The final biomass yield was also significantly
reduced at lower P supply in the medium, but only by
about 20%. The final biomass yield of Scenedesmus was unaffected
by the medium composition. This is due to the relatively
large measurement error on the dry weight biomass
measurement for Scenedesmus (standard error is 56 mg L1
, i.e.
more than 10% of the mean, Table 1). In contrast to Chlorella
cells, Scenedesmus formed small flocs. This complicated subsampling
of the cultures and resulted in higher variability
between replicate biomass measurements.