"This study delivers a comprehensive analysis of the integration of renewable energy sources for a self-sustaining organic wastewater treatment operation. The increase in human population and the continuous expansion of residential and industrial activities in the last decades has elevated the generation of wastewater that can irreversibly damage the environment. The current technologies to treat wastewater require significant amounts of energy to operate, and most of them use non-renewable energy sources (fossil-based fuels are the main energy sources), which implies that current treatment technologies are not completely sustainable. The goal of this study is to integrate solar energy into the process of wastewater treatment synergistically. The first stage of this study evaluates the two options to generate electricity (Rankine and Brayton cycles for steam and gas turbines, respectively) using biogas as a sub-product of anaerobic digestion (the first stage in the proposed wastewater treatment) and incorporating solar energy to balance the thermal energy requirements. The results indicate that a steam turbine is the most convenient technology for the integration into a solar-bio concept, although its thermal-to-electrical energy conversion efficiency is lower than that for gas turbines. The second stage studies the steam turbine energy generation system to provide electricity for the wastewater treatment plant (anaerobic and aerobic digestion), considering two options for solar-bio hybridization: concentrated solar power (CSP) and photovoltaics (PV). Results show that PV requires a smaller collection area and biomethane volumetric storage capacity to support the electricity needs. The third stage evaluates the geometrical and operational parameters for a CSP system using refractive Fresnel lenses, as an alternative to parabolic reflectors. The solar concentration ratio and absorber area were the parameters studied to calculate the change in the absorber temperature. The parameters were evaluated using a small bench-scale unit with an accurate solar tracking system using an astronomical algorithm. The results indicate that the absorber area affects the maximum temperature in the solar receiver to a greater degree than the concentration ratio. The last stage involves the design of two solar thermal receivers for a refractive Fresnel lens. The first design is a single path receiver with a conical absorber; the second is a cavity receiver with a spiral groove for multi-path flows. Both receivers were simulated using computational fluid dynamics, obtaining the fluid outlet temperature under different scenarios. The analysis showed that the cavity receiver exhibited higher efficiencies than the conical receiver, but its application is limited to low concentration ratios."--Pages ii-iii.
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