5. Conclusion
Chlorella and Scenedesmus are capable of adjusting the N and P
concentration in their biomass to the N and P supply in the
wastewater, which is important to achieve simultaneous
removal of both N and P in wastewaters with a variable N and
P loading. The degree to which both species adjusted the P
concentration in their biomass, however, depended on the N
concentration in the biomass. Microalgae can accumulate
more P when N concentrations are high but P uptake is
reduced when N concentrations are low. This implies that a
sufficiently high N concentration in the wastewater is a prerequisite
for effective P removal. Scenedesmus can accumulate
more P in its biomass compared to Chlorella, while Chlorella can
accumulate more N than Scenedesmus. Because microalgae
adjust the N and P concentration in the biomass, the biomass
yield varies relatively little with differences in wastewater
nutrient concentration. The biochemical composition of the
biomass, on the contrary, is strongly influenced by the
wastewater nutrient concentration, with a two-to four-fold
increase in lipids or carbohydrates when the wastewater N
concentration is low.