No abstract

The biogas from the anaerobic digestion of wastewaters or organic solid waste represents a key renewable energy vector in order to mitigate the use of fossil fuels. Biogas upgrading is required prior use as a vehicle fuel or injection into natural gas networks. In this context, several international regulations exist setting the maximum and minimum allowed concentrations of each biomethane component depending on its final application.Multiple physical-chemical and biological technologies are nowadays commercially available in order to remove CO2 and H2S from biogas. However, most of these technologies must be sequentially implemented to remove both H2S, CO2 and trace contaminants such as siloxanes or volatile organic contaminants. In this sense, this thesis focuses on the study of new technologies supporting the simultaneously removal of H2S and CO2 from biogas in a single step process, in a sustainable manner and with low operating costs.The state-of-the-art of biogas upgrading technologies is presented in the Introduction section. The objectives, approach and strategies followed in this thesis are summarized in the Aims and Scope section.In Chapter 1, the bioconversion of biogas to biomethane coupled to centrate treatment was evaluated during summer time in an outdoors pilot scale high rate algal pond (HRAP) interconnected to an external CO2-H2S absorption column (AC) via settled broth recirculation. CO2-removal efficiencies ranged from 50 to 95% depending on the alkalinity of the cultivation broth and environmental conditions, while a complete H2S removal was achieved regardless of the operational conditions. A maximum CH4 concentration of 94%, along with a limited O2 and N2 stripping, were recorded in the upgraded biogas at recycling liquid-to-biogas (L/G) ratios in the AC of 1 and 2. Process operation at a constant biomass productivity of 15 g m -2 d -1 (controlled via settler waste) and the minimization of effluent generation supported high carbon and nutrient recoveries