Browsing by Author "Universidad Tecnica Federico Santa Maria UTFSM QUIMICA"
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Thesis BIOELECTROCHEMICAL SYSTEMS TO INVESTIGATE THE EXOELECTROGENIC ACTIVITY OF HYDROCARBONDEGRADING BACTERIA(2017) Espinoza Tofalos, Anna Speranza; Seeger Pfeiffer, Michael; Universidad Tecnica Federico Santa Maria UTFSM QUIMICABioelectrochemistry and, more specifically, microbial electrochemistry, aretechnologies based on the connection between microbes (named asexoelectrogens or, focusing only on bacteria, electrochemically active bacteria)and electrodes. The exchange of electrons to and from the electrode has beenstudied primarily in mixed cultures but also with pure strains, mostly using modelspecies such as Geobacter and Shewanella; however, more efforts are neededto elucidate the interaction between microbes and electrode and to find newinteresting niches of application for these microorganisms. A field of application isbioelectrochemical remediation, an effective strategy in environments where theabsence of suitable electron acceptors limits classic bioremediation, and in whichbioelectrochemical systems are used for the removal of pollutants fromenvironmental matrices. Bioelectrochemical remediation of hydrocarbons withpure strains and microbial communities has been reported; however, only fewexoelectrogenic hydrocarbonoclastic bacteria have been characterized, so far.The degradative potential of several hydrocarbon-degrading strains has beenextensively studied, in terms of pollutants removal and mechanism of contaminantmineralization, but not much is known about their exoelectrogenic capacity andpossible application for bioelectrochemical remediation. Bioelectrochemistry andits application for bioremediation purposes, has primarily focused on testing thehydrocarbonoclastic capacities of already known exoelectrogenic strains. In thisstudy we took a different approach, and we aimed at studying the exoelectrogenicactivity of three strains that showed great potential for bioremediationapplications: Cupriavidus metallidurans CH34, and Pseudomonas sp. strainsDN34 and DN36. C. metallidurans CH34 is a model metal-resistant strain, whosehydrocarbonoclastic capacities have recently been individuated, andPseudomonas sp. strains DN34 and DN36 that are two hydrocarbon-degradingstrains isolated from an oil-polluted site in central Chile. By analyzing currentproduction, bacterial growth and substrate consumption in bioelectrochemicalsystems (BES), we determined that the three strains possess exoelectrogenic activity. Moreover, C. metallidurans CH34 showed the most promising results witha non-recalcitrant substrate and was selected to assess bioremediationexperiments with toluene as model hydrocarbon. We demonstrated for the firsttime that strain CH34 is able to degrade toluene under denitrifying conditions.Further experiments in Microbial Fuel Cells (MFC) linked toluene degradation tocurrent production by strain CH34, showing current peaks after toluene respike(maximum current density 0.24 mA/m2). Moreover, a Microbial Electrolysis Cell(MEC) was operated by applying an external voltage (800 mV) between anodeand cathode to stimulate microbial metabolism of strain CH34 and to observe thebehavior of the strain in terms of toluene removal and current generation. Currentoutputs increased by two orders of magnitude in comparison with MFC (up to 47mA/m2), and coulombic efficiency raised up to 77%, demonstrating that thebacterial cells adjusted progressively to the system conditions and thatelectrochemical losses were, at least partially, overcome. In order to evaluate theeffect of an electron carrier on current production, Neutral Red (NR) was selectedas external transporter and amended in a MEC containing toluene and inoculatedwith strain CH34, but no relevant effect was observed on current production norcoulombic efficiency. Hence, we concluded that NR had no influence on currentgeneration in our system and that a mediated mechanism with this electron carrieris not probable. The mechanism of extracellular electron transport (EET) is a keyfeature in BESs and the efficiency of the microorganism to exchange electronswith an electrode and to connect the EET to the cellular carbon metabolism,significantly influences the overall process performance. We demonstrated thatthe first step of the denitrification pathway is activated by nitrate reductases whenNO3- was the only electron acceptor, but we also aimed at studying whether thepathway of denitrification is still active in absence of nitrate, if a solid the anode ispotentiostetically-polarized at the same redox potential of nitrate reductase. Ourresults indicate that nitrate reductase is not involved in the transport of electronsin BES and that strain CH34 follows a different pathway of electron transport tothe anode. However, current production and cells viability demonstrated thatstrain CH34 was actively performing oxidative phosphorylation, thus that, in a mechanism that has not been elucidated yet, an extracellular electron transfertakes place, either in a direct or indirect way.Thesis SÍNTESIS DE TiO2 DOPADO CON METALES DE TRANSICIÓN POR MÉTODO SOL-GEL: CARACTERIZACIÓN Y ESTUDIO FOTOCATALÍTICO ENFOCADO A DEGRADAR COMPUESTOS FENÓLICOS(2017) Puga Martínez, Felipe Rubén; Ollino Ordenes, Mario Alberto; Universidad Tecnica Federico Santa Maria UTFSM QUIMICASe preparó una familia de nuevos fotocatalizadores dopando TiO2 con diferentes metales de transición mediante el método sol-gel. La determinación de la energía de banda prohibida (Eg) de estos nuevos materiales permitió seleccionar dos compuestos con mayor potencial para procesos fotocatáliticos: TiO2 (sin dopar) y 0,1%Cu-TiO2. Estos dos compuestos fueron caracterizados mediante microscopia electrónica de barrido, espectroscopía UV-Vis en reflectancia difusa, espectroscopía IR, difracción de rayos X, fluorescencia de rayos X y determinación de área superficial por el método B.E.T. Mediante estas técnicas se logró observar que estos compuestos poseen características físicas muy similares, siendo ambos sólidos del tipo mesoporosos, sólo presentes en la fase anatasa, con absorción en el rango de la luz visible y, con un área y tamaño promedio de 141,4 [m2/g] y 9,54 [nm] respectivamente.La actividad fotocatalítica de estas nanoparticulas se evaluó estudiando la degradación de dos compuestos fenólicos desde soluciones acuosas: catecol (CC) y ácido cafeico (AC), con irradiación de luz UV (365 [nm]) o con irradiación de luz visible, estudiando el efecto que el peróxido de hidrógeno tiene en la fotocatálisis. Ambos compuestos presentan un cierto grado de adsorción en los sólidos, el cual disminuye al adicionar H2O2. Las mejores condiciones para degradar el CC son: TiO2 como fotocatalizador, irradiación de luz UV, adición de H2O2. Las mejores condiciones para degradar el AC son: 0,1%Cu-TiO2 como fotocatalizador, irradiación de luz visible, sin adición de H2O2.Se realizaron experimentos de fotodegradación complementarios usando 3,0 [L] de solución (50 [ppm] de catecol, 25 [ppm] de ácido cafeico) en las condiciones favorables previamente determinadas para cada compuesto, usando reactores diseñados para cada caso. El diseño y fabricación de estos reactores se realizó en el Departamento de Química de la UTFSM. La fotodegradación completa de ambos compuestos fenólicos se logró en tiempos razonables. La cinética de estos procesos es de seudo-primer orden. Análisis de carbono orgánico total (COT) y demanda química de oxigeno (DQO) en muestras iniciales, intermedias y finales, permitieron determinar que la degradación completa de los compuestos orgánicos no es acompañada de una mineralización total, debido a los intermediarios generados en el proceso.
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