The aim of this study was to evaluate the effect of light intensity and phosphorus concentration on biomass growth and nutrient removal in a microalgae culture and their effect on their competition. The photobioreactor was continuously fed with the effluent from an anaerobic membrane bioreactor pilot plant treating real wastewater. Four experimental periods were carried out at different light intensities (36 and 52 μmol s−1 m−2) and phosphorus concentrations (around 6 and 15 mgP L−1). Four green algae – Scenedesmus, Chlorella, Monoraphidium and Chlamydomonas– and cyanobacterium were detected and quantified along whole experimental period. Chlorella was the dominant species when light intensity was at the lower level tested, and was competitively displaced by a mixed culture of Scenedesmus and Monoraphidium when light was increased. When phosphorus concentration in the photobioreactor was raised up to 15 mgP L−1, a growth of cyanobacterium became the dominant species in the culture. The highest nutrient removal efficiency (around 58.4 ± 15.8% and 96.1 ± 16.5% of nitrogen and phosphorus, respectively) was achieved at 52 μmol s−1 m−2 of light intensity and 6.02 mgP L−1 of phosphorus concentration, reaching about 674 ± 86 mg L−1 of volatile suspended solids. The results obtained reveal how the light intensity supplied and the phosphorus concentration available are relevant operational factors that determine the microalgae species that is able to predominate in a culture. Moreover, changes in microalgae predominance can be induced by changes in the growth medium produced by the own predominant species.

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