Estudio de biodisponibilidad de una mezcla de hidrocarburos en suelo modelo
The soil is a complex porous matrix where contaminants due to human activity can be found. Hydrocarbons are highly persistant contaminants in soils and their persistancy in this environment is due to interactions between these contaminants and soil components. Bioremediation techno- logies use livin...
| Autor: | |
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| Tipo de recurso: | tesis de maestría |
| Estado: | Versión publicada |
| Fecha de publicación: | 2016 |
| País: | México |
| Institución: | Universidad Autónoma Metropolitana |
| Repositorio: | Repositorio Institucional de la UAM Iztapalapa |
| Idioma: | español |
| OAI Identifier: | oai:bindani.izt.uam.mx:pv63g030k |
| Acceso en línea: | https://doi.org/10.24275/uami.pv63g030k |
| Access Level: | acceso abierto |
| Palabra clave: | info:eu-repo/classification/LEM/Hydrocarbons -- Biodegradation info:eu-repo/classification/LEM/Biorremediación info:eu-repo/classification/LEM/Bioremediation info:eu-repo/classification/LEM/Hidrocarburos -- Biodegradación info:eu-repo/classification/cti/6 |
| Sumario: | The soil is a complex porous matrix where contaminants due to human activity can be found. Hydrocarbons are highly persistant contaminants in soils and their persistancy in this environment is due to interactions between these contaminants and soil components. Bioremediation techno- logies use living organisms capacities to eliminate contaminants and are a promising alternative for hydrocarbons degradation, its success depends on the metabolic capacities of organisms and the weakness of the interactions between soil and contaminants. There are not known studies that clearly define the difference between the total amount of hydrocarbons in a contaminated soil, the fraction that can be quantified by experimental methods ( available ) and the fraction that has low interaction with soil that can actually be degradated by an organism ( bioavailable ). Acknowledging and differentiating this fractions becomes important when working with low concentrations of con- taminants, since it implies avoiding overestimations about remediation technologies results. The main objective in this work was the evaluation of a hydrocarbon mixture bioavailability in model soil by using a biosurfactant protein produced by a biocatalyst. The target molecules were hexadecane, phenanthrene and pyrene mixed at different proportions, and the soil, where experi- ments were performed, was defined as a model soil composed by a mixture of perlite and sand. The soil was spiked with an initial concentration of hydrocarbons of 800 mg(kg) − 1 , considered as 100 %. Availability was determined by two physicochemical methods: Soxhlet and microwave assisted ex- traction. From these analyses, only 20 % of the total hydrocarbon concentration was determined as available. With the aim to find out about the possible causes for low availability, porosity (0.58) and organic matter in soil were quantified (1.3 %). Soil organic matter was also identified as organic acids (hexadecanoic and octadecanoic acids). From the last results an experimental model of hy- drocarbon sequestration in organic matter contained in the soil pores was proposed. Bioavailability was determined by the quantification of desorbed hydrocarbons after these were put in contact with a biosurfactant protein produced by the biocatalyst (fungus Aspergillus brasiliensis treated with an electric field) in liquid culture. Bioavailability was determined as 2 % of initial hydrocarbon concentration, or 10 % from available hydrocarbons, which lead to the search for conditions that allow higher bioavailability. The availability and bioavailability results, as well as the sequestra-tion model, allowed us to develop a mathematical model that describes transport and reaction of the species: protein, protein-hydrocarbon complex and oxygen. The modelling of the system was carried out using the volume averaging method and it was divided into three scales: microscopic, intermediate and experimental; mathematical model development was divided into two stages: (i) averaging from the microscopic scale to the intermediate scale , (ii) averaging from the intermediate scale to the experimental scale. Subsequently, the mathematical model was solved in the experimental scale and a parametric analy- sis was performed. The parameters analized were Thiele modulus (relationship between reaction and diffussion in the soil), Biot number (transport towards and inside the soil), changes in the diffusivity coefficient, and efectiveness factor, which allowed the definition of conditions that fa- vour contaminant’s bioavailability in the system. Regarding the Thiele modulus for the protein and protein-hydrocarbon species, it was found necesary a high value for this dimensionless number, such result implies a higher rate for reaction than for diffusion for these species since the reaction for protein supposes the production of the protein-hydrocarbon complex, this last species guarantees bioavailability in the system. On the other hand, it is necessary to have a value close to one for the oxygen’s Thiele modulus, which means a similar reaction and diffusion rates in the model soil, this last assumption is made by the premise that the biocatalyst needs the constant presence of oxygen to degrade any of the other two species. Biot number was evaluated solely for oxygen, since it is the only species present in both gas and porous medium. The results indicate the need for a high value for the Biot number, which implies that the transport rate of oxygen towards the model soil is higher than the transport rate of oxygen inside the model soil, if such thing happens, oxygen’s permanence into the model soil will remain high, a necessary condition to mantain the biocatalyst active. With respect to effectiveness factor, it was corroborated that the biocatalyst’s effectivenes is higher only in a superficial layer of the soil since this is the zone where oxygen presence is pre- dominant for aerobic microorganisms activity, as the one present in the biocatalyst. The present work can be considered as one of the first attempts to relate in a deep way both theorical and experimental methodologies, besides, it sets ground for posterior analysis of organic contami- nants’s bioavailability in model matrixes, which may help in the comprehension of bioavailability studies in natural soils. |
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