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Biodiesel is a potential alternative for fossil fuel. However, its large-scale application is held up by the disadvantage of a homogenous process, the scarce availability of raw materials and the production cost, which is higher than for fossil diesel. In this work, biodiesel production was carried out using both refined and used cooking oils. The process was investigated in a batch reactor, in the presence of CaO as a heterogeneous catalyst prepared by the calcination of the natural Waste Grooved Razor Shell (GRS). Characterizations by X-Ray Diffraction (XRD) and Thermal Gravimetric (TG)/Differential Thermal Analysis (DTA) showed that the as-received GRS consists of aragonite, (i.e., CaCO3) as the main component and of water and organic matter in a lower amount. After calcination at 900 °C, CaO was formed as the only crystalline phase. The effects of several experimental parameters in the transesterification reactions were studied, and their impact on the produced biodiesel properties was investigated. The studied variables were the methanol/oil molar ratio, the catalyst weight percentage (with respect to the oil mass), the calcination temperature of the parent GRS and the recycling and regeneration of the catalyst. The physico-chemical and fuel properties, i.e., viscosity, density and acid value of used oils and of the produced biodiesel, were determined by conventional methods (American Society for Testing and Materials (ASTM) methods) and compared with the European standards of biodiesel. The optimal identified conditions were the following: the use of a 15:1 methanol/oil molar ratio and 5 wt% of CaO with respect to the oil mass. After 3 h of reaction at 65 °C, the biodiesel yield was equal to 94% and 99% starting from waste and refined oils, respectively.

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Microbial fuel cells (MFCs) are a promising technology for simultaneous electricity generation and wastewater treatment. Noble materials can offer high catalyst performance in MFCs but their high cost poses an obstacle for the practical implementation of this technology. Ferroelectric materials such as LiTaO 3 are a new generation of photocatalysts that could potentially be used for the oxygen reduction reaction in these devices. Thus, this work investigates the performance of LiTaO 3 as cathode catalyst in MFCs for the first time. The power performance of carbon cloth cathodes coated with LiTaO 3 was assessed in the presence and absence of light irradiation in MFC systems using wastewater. Prior to be tested in MFCs, the synthesized phase of LiTaO 3 was mainly characterized by XRD, particle-size distribution, TEM, and UV-vis spectroscopy analyses. The results show that the performance of the cathode coated with LiTaO 3 significantly improves under UV-vis irradiation, with a threefold increase in maximum power density compared with the results obtained in the absence of light source. Under these conditions, COD removal from wastewater reached 66% after 120 h.

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