PhD Thesis, Yaiza Tejido
Title: Microalgae-based wastewater treatment processes: implementation in aquaculture sector and wwtp.
Defense Date: 28 / 07
Director: Dr. Enrique Aymerich Soler
President: Dr. Eduardo Ayesa Iturrate
Sustainable Development Goals developed by the United Nations recognize that “ending poverty must go hand-in-hand with strategies that build economic growth and address a range of social needs including education, health, equality and job opportunities, while tackling climate change and working to preserve our ocean and forests” (United Nations, 2019). This can be faced from different strategies, but a common factor to some of them deal with the use, reuse and treatment of the water in a sustainable way. Additionally, microalgae biotechnology is of increasing importance and a central application concerns the treatment of wastewater. Taken all of this together, microalgae-based processes for wastewater treatment become a research field of great interest. In this regard, the present Thesis faced this challenge from two points of view: aquaculture wastewater treatment and urban wastewater treatment plants.
The main objective of the present Thesis has been gaining deep knowledge on new sustainable technologies for wastewater treatment, developing new solutions based on microalgae. In order to achieve this objective, this Thesis is structured in two parts: a experimental part corresponding to microalgae-based aquaculture water treatment, which is described in Chapter 2 and Chapter 3; and a second part related to the development of mathematical models for enhancing the implementation of microalgae-based processes in urban wastewater treatment plants, described in Chapter 4 and 5.
The suitability of microalgae-based wastewater treatment systems in aquaculture is studied at laboratory scale, being the main objective of this study evaluate how the quality of the water taken from an aquaculture system affected the growth rate and nutrient removal efficiency of two well-known microalgae strains. Going further, a co-cultivation of these two species of microalgae was carried out also for aquaculture water treatment, to develop a more reliable and robust treatment contrasted to monocultures. This approach was tested at laboratory-scale and then compared to a co-culture at pilot-scale in an open thin-layer photobioreactor.
In order to determine the state-of-the-art of microalgae mathematical modelling a review has been carried out to define the weaknesses and strengths of current models. Amongst all models already developed, only a few number are integrated models although the integration of microalgae-based processes in plant wide models is paramount for spreading its implementation at full-scale. As a result of that, the implementation of a microalgae model in the already existing Plant Wide Model library (PWM) has been proposed. After that, a validation of the model is necessary to assure its correct use in model-based assessment of microalgae processes in WWTP.
The Thesis concludes with a chapter gathering the most significant conclusions, bibliography consulted for its development, and an appendix that includes a detailed description of the mathematical modelling methodology used.