NH4+and PO43 were not removed in batch cultures at 5C (B5–6 and B5–12). This is in agreement with the absence of
biological activity in those cultures. Neither biomass production nor nitrification was observed in these conditions (Fig. 4).
A linear correlation between chlorophyll and ammonium concentration in the culture was observed for the experiments
at 15 C and 25C (Fig. 5a).
The pattern suggests that the consumption of this compound was associated with microalgal growth, nevertheless,ammonium may have been also depleted by abiotic phenomena such as stripping related to the high pH levels induced by the photosynthetic activity (see later) and respired by nitrifying bacteria.
The slopes of the graphs were dependent on the conditions tested (Fig. 5a). The maximal slope was found for the B25–12 test (25C and 12 h photoperiod) which suggested that microalgaerelated ammonium depletion is temperature dependent. The slope of ammonium depletion at 25 C seems to be additionally influence by bacterial nitrification as demonstrated by our experiments performed in the dark (Fig. 4c).
At 15C, ammonium depletion was expected tobe only related