Effects of nutrients variability on green microalgae kinetics in a continuous flow photobioreactor

Recently, different studies have suggested the application of green microalgae for wastewater treatment, highlighting their ability to take up nitrogen and phosphorus producing valuable biomass. Among the others, Valverde-Pérez (2015) proposed an innovative full biochemical resource recovery process (TRENS), where the tertiary treatment is done through the cultivation of microalgae in photobioreactors. This thesis aims to take forward Valverde-Pérez (2015) work, focusing on the understanding of the effects of the influent wastewater variation on the photobioreactors operation. In particular, the consequences caused by the variation of the influent N-to-P ratio are investigated studying green microalgae culture stability in terms of composition and contamination and the effects on the kinetics of the processes involved. With this aim, laboratory experiments were carried out and a model-based approach was used to analyze the experimental data. From the results, green microalgae seem to be not greatly affected by the variation of the N-to-P ratio in the influent and no relevant effects of the culture history on the kinetics have been underlined. However, the overall removal of nitrogen results enhanced by 20%, which means that there may be a possibility to increase the efficiency of the treatment by subjecting green microalgae to cycles of nutrients limitation. Finally, a new images analysis method to quantify the microbial community is also described.