Sistemes basats en microalgues per a l'eliminació de microcontaminants, la recuperació de recursos y la producció de bioenergia amb un enfoc de bioeconomia circular
- Autores: Cintia Romina Avila Mazzieri
- Directores de la Tesis: Maria Teresa Vicent Huguet (dir. tes.), Paqui Blánquez Cano (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2021
- Idioma: catalán
- Tribunal Calificador de la Tesis: Aurora Seco Torrecillas (presid.), Xavier Font i Segura (secret.), Maria Dolors Balaguer Condom (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencia y Tecnología Ambientales por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Microalgae-based technologies offer a promising solution to shift the focus from wastes and wastewater treatment, toward energy and resource recovery. In these systems, microalgae remove nutrients from wastewater and produce oxygen useful for bacteria to biodegrade organic matter. This has been fully demonstrated in urban wastewater treatment, but in increasingly industrialised cities and agricultural environments, the challenge is to determine if microalgae-based systems can degrade organic micropollutants such as pesticides.
Microalgae biomass can be further valorised for the production of biofuels and valuable bioproducts. Anaerobic digestion is one of the most established technologies to convert organic wastes into renewable energy in the form of biogas. Another opportunity is the simultaneous anaerobic co-digestion of two or more bio-wastes, contributing to overcome the drawbacks of mono-digestion and boosting energy production in anaerobic digestion plants. Nonetheless, microalgae anaerobic digestion is generally hindered by the recalcitrancy of their cell walls, which lead to low methane potential.
The present thesis assesses different processes included in the microalgal biorefinery concept: utilisation of algae for micropollutant degradation, energy production by algal anaerobic digestion, co-digestion with other nearby wastes, and utilisation of waste streams as fertilizers.
First, it was studied the individual degradation of three polar and three hydrophobic pesticides frequently found in surface waters by a mixed-microalgae culture. Different conditions were studied to determine the main degradation mechanisms. Biodegradation plus photodegradation contributed to the removal of propanil (100%), acetamiprid (100%), oxadiazon (55%), chlorpyrifos (35%), and cypermethrin (14%) while more than 60% of chlorpyrifos and cypermethrin were removed by bio-sorption. Transformation products generated by the active microalgae were identified for chlorpyrifos, acetamiprid, and propanil. The performance of an outdoor pilot-photobioreactor operated at a HRT of 8 days in the treatment of synthetic wastewater containing a mixture of selected pesticides was assessed. During the steady-state, degradation capacity was evaluated by quantifying nutrients and pesticides removal, and transformation products were detected. Nitrate and ortophosphate removal efficiencies were 24 and 94%, respectively. Propanil and acetamiprid were effectively removed (99 and 71%, respectively) mainly by algal-mediated biodegradation as confirmed by the transformation products detected. The anaerobic digestion of the algal biomass was not inhibited by the retained pesticides.
To enhance the solubility and the anaerobic digestibility of algal biomass, different mild pretreatments were assessed. Formerly, microalgal harvesting was tested by different cost-effective techniques: sedimentation, coagulation-flocculation, and pH-induced flocculation. The pretreatments were applied before the anaerobic co-digestion of microalgae with sludge. The effect of thermal pretreatments at low temperature were evaluated for microalgae and sludge mixtures. Additionally, the effect of enzymatic pretreatments on microalgae cell wall solubilisation was investigated. In both cases, the effect of the pretreatment in the biogas yield was tested. Results indicate that algal biomass solubility increased and led to a higher methane yield. Nonetheless, in the co-digestion of sludge and algal biomass, even when biomass solubility was enhanced after the pretreatment, biogas production did not increase.
Furthermore, this thesis assesses a case study for the integration of a microalgae-based system into the industrial wastewater treatment plant of a winery company looking for a circular approach for nutrients and bioenergy recovery from wastewater and sludge. Tertiary wastewater treatment by microalgae efficiently removed ammonium (97%) and phosphate (93%). Algal biomass was co-digested in a 50 L pilot anaerobic digester with sludge obtaining a yield of 225.8 NL CH4 kg VS-1. The digester was operated in SBR mode showing adaptations to substrate variability over time. The valorisation of the generated bio-wastes for fertilization indicate that mono- and co-digestion digestates and dry algal biomass improved plant biomass accumulation (growth indexes of 163, 155 and 121% relative to those of the control -commercial amendment-).
