Effect of intracellular P content on phosphate removal in Scenedesmus sp. Experimental study and kinetic expression

• Biomass P content regulates phosphate uptake rate by Scenedesmus sp.
• Biomass with ca. 0.6% P content presented 50% of the maximum phosphate removal rate.
• Hill function successfully modeled P content influence on phosphate removal.
• Light influence in the process was successfully modeled with Steele function.

The present work determines the effect of phosphorus content on phosphate uptake rate in a mixed culture of Chlorophyceae in which the genus Scenedesmus dominates. Phosphate uptake rate was determined in eighteen laboratory batch experiments, with samples taken from a progressively more P-starved culture in which a minimum P content of 0.11% (w/w) was achieved. The results obtained showed that the higher the internal biomass P content, the lower the phosphate removal rate. The highest specific phosphate removal rate was 6.5 mgPO4–P gTSS−1 h−1. Microalgae with a P content around 1% (w/w) attained 10% of this highest removal rate, whereas those with a P content of 0.6% (w/w) presented 50% of the maximum removal rate. Different kinetic expressions were used to reproduce the experimental data. Best simulation results for the phosphate uptake process were obtained combining Steele equation and Hill function to represent the effect of light and intracellular phosphorus content, respectively.