Browsing by Author "Baraza, Xavier"

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    Evaluation of Aspergillus flavus Growth on Weathered HDPE Plastics Contaminated with Diesel Fuel
    (2025) Valenzuela, Juan; Sáez-Navarrete, César; Baraza, Xavier; Martínez, Fernando; Márquez, Bastián
    Plastic containers used for diesel storage represent an underexplored but significant environmental challenge due to hydrocarbon retention and prolonged weathering. This study evaluates the capacity of Aspergillus flavus to colonize and grow on high-density polyethylene (HDPE) surfaces contaminated with weathered and fresh diesel residues. Circular plastic samples from HDPE tanks exposed to environmental conditions for over two years (weathered) and for less than two months (non-weathered) were inoculated with A. flavus and incubated at 20 °C, 25 °C, and 30 °C. Growth kinetics were assessed through radial expansion and halo formation, quantified via digital imaging and ImageJ analysis. Results showed the most robust fungal growth occurred on weathered diesel-contaminated gray plastics at 30 °C, with colony areas exceeding 350 mm2 and halos over 3000 mm2. Conversely, white HDPE with fresh diesel showed limited and inconsistent growth, likely due to the presence of volatile hydrocarbons and polymer additives. These findings underscore the critical role of diesel aging and polymer characteristics in shaping fungal adaptability, providing a foundation for the development of environmentally sustainable bioremediation strategies targeting diesel-contaminated HDPE plastics.
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    HYDROGEN KINETICS LIMITATION OF AN AUTOTROPHIC SULPHATE REDUCTION REACTOR
    (UNIV NAC COLOMBIA, FAC NAC MINAS, 2012) Saez Navarrete, Cesar; Rodriguez Cordova, Leonardo; Baraza, Xavier; Gelmi, Claudio; Herrera, Leandro
    Sulphate-reducing bacteria (SRB) are microorganisms that can be used as removal agents in polluted water sources. The use of inorganic substrates in SRB systems could reduce the cost and simplify operation. However, the use of H-2 as an energetic substrate and the production of H2S as a metabolic product could produce kinetic limitations. The aim of this study was to assess the extent to which the kinetics of a sulphate reduction bioreactor was limited by its gas transfer capacity. Reactor kinetics were monitored by total pressure kinetics without sulphate limitation. It was concluded that the bioreactor design should be based on transfer properties. The uptake rate of H-2 reached a maximum of 10(-4) M/min, equivalent to a sulphate reduction rate of 3.4 g.L-1.d(-1). The hydrogen mass transfer rate required a k(L)a of 1.48 min(-1) at 1.2.10(9) cells/L in order to avoid limitation by H-2 bio-availability (1.23.10(-9)L.min(-1).cell(-1))(,) which is a relevant value for scaling-up purposes.
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    Laser-Induced Surface Vitrification for the Sustainable Stabilization of Copper Tailings
    (2025) Sáez Navarrete, César; Baraza, Xavier; Ramos Grez, Jorge; Sans, Carmen; Arauzo Ayre, Claudia Maria; Coca, Yoandy
    This study introduces CO2 laser surface vitrification as an innovative method for managing copper mining tailings, offering a sustainable solution to critical challenges in mineral processing. This technique transforms tailings into a stable and impermeable layer, immobilizing hazardous metals contained within them. By achieving vitrification at the surface level and operating at temperatures around 1200 °C, the process significantly reduces energy consumption compared to traditional vitrification methods, making it suitable for large-scale applications in remote mining sites. Detailed geochemical and mechanical analyses confirmed the formation of a dense vitreous matrix with high hardness (7.19–7.48 GPa) and reduced permeability, ensuring compliance with stringent environmental regulations. However, the brittle nature of the vitrified layer underscores the need for further research to enhance mechanical resilience. This work positions CO2 laser vitrification as a transformative approach for integrating energy-efficient technologies into mineral processing, addressing key environmental concerns while advancing the sustainable management of mining waste.