The rate of NH4+ removal in all batch cultures increased at higher temperatures and longer photoperiods (p < 0.05)(Table 2).
NH4+ and PO43 were not removed in batch cultures at 5 C (B5–6 and B5–12). This is in agreement with the absence of
at 70 h and then decreased, presumably due to further nitrite assimilation by the microalgae. Comparing the nitrite concentration profile for the illuminated cultures at 25 C (Fig. 1b) and the cultures in obscurity (Fig. 4c), one can expect nitrite uptake by microalgae to occur after ammonium exhaustion under illuminated conditions.
The nitrate concentration remained approximatelyconstant and low (about 2 mgN L1) over the entire experiment (data not shown).
Its consumption due to denitrification was unlikely to occur under aerobic conditions and increasing dissolved oxygen concentration in the culture.
On the other hand, data obtained for the cultures in obscurity (Fig. 4c) suggest no nitrification by conversion of nitrite to
nitrate after ammonium exhaustion.