Browsing by Author "Saez Navarrete, Cesar"

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    Bioremediation of contaminated mixtures of desert mining soil and sawdust with fuel oil by aerated in-vessel composting in the Atacama Region (Chile)
    (ELSEVIER SCIENCE BV, 2008) Godoy Faundez, Alex; Antizar Ladislao, Blanca; Reyes Bozo, Lorenzo; Camano, Andres; Saez Navarrete, Cesar
    Since early 1900s, with the beginning of mining operations and especially in the last decade, small, although repetitive spills of fuel oil had occurred frequently in the Chilean mining desert industry during reparation and maintenance of machinery, as well as casual accidents. Normally, soils and sawdust had been used as cheap readily available sorbent materials of spills of fuel oil, consisting of complex mixtures of aliphatic and aromatic hydrocarbons. Chilean legislation considers these fuel oil contaminated mixtures of soil and sawdust as hazardous wastes, and thus they must be contained. It remains unknown whether it would be feasible to clean-up Chilean desert soils with high salinity and metal content, historically polluted with different commercial fuel oil, and contained during years. Thus, this study evaluated the feasibility of aerated in-vessel composting at a laboratory scale as a bioremediation technology to clean-up contaminated desert mining soils (fuel concentration > 50,000 mg kg(-1)) and sawdust (fuel concentration > 225,000 mg kg(-1)) in the Atacama Region. The composting reactors were operated using live soil to sawdust ratios (S:SD, 1:0, 3:1, 1:1, 1:3, 0: 1, on a dry weight basis) under mesophilic temperatures (30-40 degrees C), constant moisture content (MC, 50%) and continuous aeration (161 min(-1)) during 56 days. Fuel oil concentration and physico-chemical changes in the composting reactors were monitored following standard procedures. The highest (59%) and the lowest (35%) contaminant removals were observed in the contaminated sawdust and contaminated soil reactors after 56 days of treatment, respectively. The S:SD ratio, time of treatment and interaction between both factors had a significant effect (p < 0.050) on the contaminant removal. The results of this research indicate that bioremediation of an aged contaminated mixture of desert mining soil and sawdust with fuel oil is feasible. This study recommends a S:SD ratio 1:3 and a correct nutrient balance in order to achieve a maximum overall hydrocarbon removal of fuel oil in the weathered and aged contaminated wastes. (C) 2007 Elsevier B.V. All rights reserved.
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    Efficacy of quinoa (Chenopodium quinoa) saponins against golden apple snail (Pomacea canaliculata) in the Philippines under laboratory conditions
    (ELSEVIER SCI LTD, 2008) Joshi, Ravindra C.; Martin, Ricardo San; Saez Navarrete, Cesar; Alarcon, John; Sainz, Javier; Antolin, Mina M.; Martin, Antonio R.; Sebastian, Leocadio S.
    A novel product for managing Pomacea canaliculata, golden apple snail (GAS), containing quinoa saponins (Chenopodium quinoa), was evaluated under laboratory conditions for the protection of newly sprouted rice seeds. Experimental methods mimicked conditions found in direct-seeded rice cultivation in the Philippines, but with a very high GAS density (90 snails/m(2)). Protection of newly sprouted seeds was directly proportional to saponin concentration in rice water. At 9 and 11 ppm saponin, seedling protection after 48 h against GAS of different sizes was 93% and 95%, respectively. Seedling recovery after 5 d with 11 ppm saponin was 93%. This value declined to 0% and 4%, for the control (untreated) and niclosamide, a synthetic chemical molluscicide, respectively. The results indicated that although niclosamide provides high efficacy against GAS (100% mortality, 24h), it has a serious detrimental effect on rice seedlings. Mean GAS mortality with 11 ppm saponin was low at 24 h (45%), but increased to 94% at 48 h. Thus, seedling protection was probably due to an almost immediate closure of the snail's opercula when exposed to saponin solutions, followed by significant death rates within 24 and 48 h. The product also exhibits ovicidal effects, particularly with 1-5 d old egg masses; older egg masses were less susceptible to the product. The use of 11 ppm saponin slightly affected shoot growth, but this effect disappeared with time and the plants attained normal development. Saponin application rates at 10 ppm saponin in the rice water correspond to ca. 6kg product/ha under cultivation conditions used in the Philippines. These results suggest that quinoa saponins may represent a commercially feasible environmentally benign alternative to synthetic chemical molluscicides against GAS, particularly in direct-seeded rice culture. (C) 2007 Elsevier Ltd. All rights reserved.
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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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    Hydrogen Productivity Analysis Using Low Concentration of TiO2-Au Nanoparticles on a Ultraviolet-LED-Based Photocatalytic Reactors
    (2021) Varas Concha, Felipe; Guzman, Diego; Isaacs, Mauricio; Saez Navarrete, Cesar
    The productivity of photocatalytic hydrogen generation via photo-reforming of organic compounds has not been studied under low concentrations of catalyst, which could lead to relevant cost savings in future real-scale applications. Herein, it uses half of the lowest concentration of nanoparticles reported of modified P25 TiO2 partially coated with gold. The nanomaterial is prepared using a non-energy intensive, chemical reduction method. Gold content on the TiO2 surface is reported (14%-surface; 9.1%-weight). Dynamic light scattering and transmission electron microscope image analyses show low agglomeration and non-homogeneous shape. Aggregates and gold nanoparticles reach average diameters of 92 and 3.8 nm, respectively. Photocatalytic experiments for hydrogen production are carried out at low concentration of nanoparticles (0.056 g L-1) in methanol-water solution (5%vol.) under 375 nm UV and visible light (20 mW cm(-2)). The system shows a catalyst productivity of 6661 mu mol h(-1) g(-1), a third of the highest reported productivity using methanol (which used a catalyst concentration 18x higher, an alcohol concentration 5x higher, and 100% anatase). The system shows an estimated reaction rate of 373 mu mol L-1 h(-1) with an apparent zero order kinetic, an overall energy conversion efficiency of 0.47%, and an apparent quantum yield of 1.03%.