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A laboratory-scale flat panel photobioreactor was operated for the continuous growth of Scenedesmus obliquus and consequent removal of nutrients in wastewater. This study develops a simple model by which biomass values in continuous operation can be predicted from kinetic growth parameters obtained from a shorter batch experiment. Based on this study, biomass concentrations and productivities in continuous operation can be successfully predicted as a function of the specific hydraulic retention time (HRT) assumed. Considerable biomass production and nutrient uptake from wastewater were achieved in the experiment. Optimum operating conditions for the reactor depend on the particular objective: the maximization of biomass production and carbon dioxide biofixation involves a HRT of 2 μ(-1) (specific growth rate), whereas efficient nutrient removal involves a HRT as close as possible to μ(-1) (as long as discharges comply fully with the parameters set); alternatively biomass intended for biodiesel or biogas production would involve a HRT > 2 μ(-1).

This study evaluates the feasibility of removing nutrients by the microalgae Chlorella vulgaris, using urban wastewater as culture medium, namely the effluent subjected to secondary biological treatment in a wastewater treatment plant (WWTP). For this, laboratory experiments were performed in batch cultures to study the effect of initial nitrogen and phosphorus concentrations on growth and reduction of nutrient performance of C. vulgaris. The microalga was cultivated in enriched wastewater containing different phosphorus (1.3-143.5 mg x L(-1) P.PO4(3-)), ammonium (5.8-226.8 mg x L(-1) N-NH4+) and nitrate (1.5-198.3 mg x L(-1) N-NO3-) concentrations. The nutrient removal and growth kinetics have been studied: maximum productivity of 0.95 g SS x L(-1) x day(-1), minimum yield factor for cells on substrate (Y) of 11.51 g cells x g nitrogen(-1) and 0.04 g cells x g phosphorus(-1) were observed. The results suggested that C. vulgaris has a high potential to reduce nutrients in secondary WWTP effluents.