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- Physicochemical Characterisation of Olive Mill Wastewaters Based on Extraction Methods and Filtration LevelsPublication . Afonso, Inês Santos ; Duarte, Cristina; Afonso, Maria João A.P.S.; Ribeiro, António E.; Amaral, Joana S.; Sousa, Patrícia C.; Lima, Rui A.; Ribeiro, João E.Olive mill wastewaters (OMWW) generated during olive oil extraction represent a significant environmental challenge due to their high organic matter content, acidic pH, phenolic content, and toxicity. Their composition varies widely depending on the extraction method and remains difficult to treat, particularly for small-scale producers lacking access to complex infrastructure. This study evaluates the combined effect of the extraction system (traditional vs. three-phase continuous) and filtration level (single vs. double) on the physicochemical and biological properties of OMWW. The methodologies employed included the analysis of water content, density, fatty acid composition, acidity, pH, total solids, chemical and biochemical oxygen demand, and biodegradability. The results indicate that traditional systems consistently produced OMWW with higher organic matter and phenolic loads, while filtration moderately reduced antioxidant potential and acidity, especially in traditional systems. The use of simple, low-cost filtration materials proved effective in improving effluent clarity and could serve as a practical pre-treatment option. This approach offers an accessible strategy for small producers aiming to valorise OMWW or reduce environmental impact. However, the study was conducted at the laboratory scale, and the long-term behaviour of filtered OMWW under real operating conditions remains to be evaluated.
- Progress in Nanofluid Technology: From Conventional to Green Nanofluids for Biomedical, Heat Transfer, and Machining ApplicationsPublication . Cardoso, Beatriz D.; Souza, Andrews; Nobrega, Glauco; Afonso, Inês Santos ; Neves, Lucas Boniatti; Faria, Carlos; Ribeiro, J.E.; Lima, Rui A.Nanofluids (NFs), consisting of nanoparticles (NPs) suspended in base fluids, have attracted growing interest due to their superior physicochemical properties and multifunctional potential. In this review, conventional and green NF technology aspects, including synthesis routes, formulation, and applications, are discussed. Conventional NFs, involving NPs synthesized using physical and chemical approaches, have improved NP morphology control but are likely to cause environmental and safety concerns. In contrast, green NFs that are plant extract, microorganism, and biogenic waste-based represent a sustainable and biocompatible alternative. The effect of key parameters (e.g., NP size, shape, concentration, dispersion stability, and base fluid properties) on the performance of NFs is critically examined. The review also covers potential applications: in biomedical engineering (e.g., drug delivery, imaging, theranostics, and antimicrobial therapies), in heat transfer (e.g., solar collectors, cooling electronics, nuclear reactors), and precision machining (e.g., lubricants and coolants). Comparative insights regarding green versus conventionally prepared NFs are provided concerning their toxicity, environmental impact, scalability, and functional performance across various applications. Overall, this review highlights the new promise of both green and conventional NFs and provides key opportunities and challenges to guide future developments in this field.
- Thermal performance evaluation of pure PDMS and PDMS composites heat exchangersPublication . Souza, Reinaldo; Nobrega, Glauco; Afonso, Inês Santos ; Pereira, José; Cardoso, Elaine; Marques, Filipe; Vilarinho, Cândida; Moita, Ana; Lima, Rui A.This study investigates the heat transfer performance of three types of heat exchangers: one made of pure polydimethylsiloxane (PDMS), another incorporating recycled graphite (PDMS + Graphite 30 mass%), and a third using commercial aluminium nanoparticles (PDMS + Aluminium 30 mass%). Thermal performance was evaluated by measuring the thermal conductivity of the materials, analysing experimental convection tests with deionized water in a single-phase regime and using a thermal camera to obtain temperature profiles of the different surfaces. The results revealed that the composites formed with PDMS matrix and recycled graphite showed elevated thermal conductivity, approximately 2.7 times higher than pure PDMS. The heat transfer coefficient performance was 2.5 times superior to that of the heat exchanger made with commercial aluminium nanoparticles and up to 5 times higher compared to pure PDMS. The thermal analysis highlighted the benefits of the composites, showing a more uniform temperature distribution both in the serpentine channel and along the sides of the PDMS. The study aimed to provide an economical alternative that also contributes to waste valorisation. These findings validate the effectiveness of recycled particles in improving heat transfer performance in heat exchangers made from a combination of PDMS matrix and recycled, economical materials.