Resumen de Recovery of phycobiliproteins and biogas from microalgae treating wastewater
Water is undoubtedly the most essential resource of humanity. However. supplying the human population with clean water has been a major challenge for decades. Contaminants in wastewaters endanger water bodies and the treatment of these effluents represent a high energy demand. The development of efficient wastewater treatment technologies is thus becoming increasingly important.
In the context of a circular and bio-based economy. microalgae biomass has shown its great potential to treat wastewater streams. while recovering sustainable bioproducts. However. although extensive research has been done in this field. there is still need for improvements and realistic information in order to implement these systems at large scale.
This PhD thesis aims to contribute to this quest by performing holistic studies on microalgae systems for wastewater treatment combined with different strategies for biomass valorisation. The overall content of this PhD thesis is divided in two main parts. The first part consists in experimental studies combining wastewater treatment and resources recovery using microalgae-based systems. while the second part is dedicated to the environmental analyses. through Life Cycle Assessment (LCA). of the technologies and biomass valorisation techniques investigated in this thesis.
The first part presents investigated a well-known microalgae system. high rate alga! pond (HRAP). in order to simplify its maintenance. reduce costs and the footprint. This study showed that removing the primary treatment preceding a HRAP did not significantly affect the wastewater treatment efficiency. Moreover. the co-digestion with primary sludge could significantly improve the methane yield and kinetics of microalgae mono-digestion (2382:58 ml CH4/g VS compared to 1892:25 ml CH4/g VS. Following. a second study investigated the cultivation of cyanobacteria-dominated biomass using centrate diluted in secondary effluent from the HRAP system at different ratios. Results showed that cyanobacteria dominance was stable in a mixed culture with effective treatment efficiency. In addition. biomass grown in these systems could be valorised through phycobiliproteins (up to 17 mg/g dry biomass) and biogas production (from 159 to 199 ml CH4/g VS). Lastly. a third study investigating unialgal cultivations for further phycobiliproteins recovery was carried out. Light intensity and growth medium composition were optimised. and conditions were then selected to cultivate these microalgae in food-industry wastewater. Efficient wastewater treatment and successful extraction of phycobiliproteins (up to 103 mg/g dry biomass) were achieved.
The second part of this thesis presents an overview of the environmental aspects associated with the microalgae systems and biomass recoveries focused in the previous experimental studies. A first LCA showed that. considering the most significant impact categories, HRAP system implemented in warm climate region showed to be the most environmentally friendly alternative while the biofertiliser production showed to be the most economically feasible than biogas. The second LCA indicated that a system treating industrial wastewater has lower environmental impacts than a system treating urban wastewater in most of the environmental indicators considered. Moreover, using wastewater appeared to be more environmentally friendly than using standard growth medium to cultivate microalgae.
In conclusion, the results obtained in this thesis suggested that microalgae systems seem to have a great potential to improve water quality and recover valuable resources from wastewater. Therefore. based on the results of this study and considering the increasing need for conceptual biorefineries, sustainable installations at full scale would be the next step towards a circular economy.
