Resumen:
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The carboxylate platform arises as a potential technology to produce bio-based chemicals from renewable resources. Anaerobic digestion (AD), traditionally employed for biogas production, can be shortened to the fermentative stages (anaerobic fermentation AF, acidogenesis and acetogenesis) to produce volatile fatty acids (VFAs) or carboxylates. In this manner organic acids namely acetic, propionic, (iso)butyric, (iso)valeric and caproic acids are produced. The main interest of these compounds, currently obtained petro-chemically, lies in their added value with respect to biogas and the wide range of applications in the chemical industry. Concurrently, the use of microalgae to treat wastewater can decrease the energy cost associated to aeration in traditional systems. The biomass grown constitutes a potential residue to valorize via AF. Notwithstanding, this biomass requires pretreatments prior digestion due to the hard cell wall of certain strains (Publication I). Even though this biomass has been lately studied for biogas production, the operational conditions and anaerobic microbiome remains unknown when it comes to VFAs production. The novelty of this work, including the use of microalgae biomass as feedstock for VFAs production, is the operational conditions optimization focusing on methanogenic inhibition to avoid VFAs consumption (Publication II and III). Archaea inhibition is of outmost importance since these species contribute to VFAs degradation. The main objective was to evaluate microalgae biomass (Chlorella sp.) as feedstock for VFAs production via AF. The employed proteolytic pretreatment responded to the high protein content of the microalgae as well as to avoid any hydrolytic barrier and fully focus on the acidogenic stage. Two approaches were followed, namely shaping the inoculum via pretreatments and tuning operational parameters in order to maximize VFAs production by decreasing archaea activity...
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