Técnicas de Análisis de Riesgo para la Remediación de Suelos y Aguas Subterráneas Contaminados por Hidrocarburos

El objetivo de este proyecto es la elaboración de una herramienta de cálculo para todas las personas interesadas en la evaluación del riesgo debido a la contaminación de suelos y aguas subterráneas. La contaminación de aire y de agua por compuestos volátiles presentes en el suelo y aguas subterráneas contaminadas es un área emergente debido a la preocupación en la salud pública. La liberación de estos vapores y su incorporación a depósitos en aguas tiene lugar a través de una serie de procesos de transporte desde el suelo a ambientes tanto exteriores como interiores (ambientes industriales y domésticos). La Agencia de Protección Medioambiental de Estados Unidos (U.S. Environmental Protection Agency, EPA) ha desarrollado unas herramientas para evaluar el riesgo de la contaminación del suelo y aguas subterráneas. Estas herramientas fueron diseñadas para determinar solamente si hay un riesgo potencial inaceptable, pero no para proporcionar recomendaciones en cómo delinear el grado del riesgo o cómo eliminar el riesgo. Tomando esos problemas en cuenta y tratando el caso de contaminación por hidrocarburos se ha desarrollado una herramienta de evaluación de contaminación de aguas subterráneas y aire que permite llegar a la determinación del tipo de riesgo al que están expuestas las personas. La aplicación de modelos existentes para desarrollar y validar esta herramienta ha sido imprescindible. Los modelos más robustos como el modelo de Buscheck y Alcantar en el caso de contaminación de aguas o Johnson y Ettinger en el caso de contaminación de suelos fueron las bases de este estudio permitiendo modelizar la contaminación del agua subterránea y del suelo, en función respectivamente de la distancia de la fuente al pozo y de la altura de la fuente al edificio o emplazamiento en el que se encuentran las personas potencialmente afectadas. Una vez modelizado la dispersión de contaminante a través del suelo y del acuífero, los datos obtenidos han permitido implementar la noción de riesgo haciendo una clara diferencia entre riesgo sistémico (no cancerigeno) y riesgo cancerigeno. La implantación de una herramienta así ofrece la oportunidad, conociendo los datos referentes a un emplazamiento contaminado, de dar unas respuestas rápidas a las cuestiones sobre riesgo aceptable o inadmisible

Electrokinetic Enhanced Bioremediation of Soils Contaminated with Petroleum Hydrocarbons

Desorption of phenanthrene resulting from hydraulic flow is compared to desorption driven by electroosmotic flow with a similar flow rate. The power required for the hydraulic flow test was compared with the consumed power in the electrokinetics test. A novel approach, anode-cathode-compartment (ACC), was proposed to stabilize pH and distribute nutrients in soil in order to enhance electrokinetic bioremediation of soil contaminated with biodegradable compounds. The ACC technique was applied to investigate electrokinetic bioremediation of soil contaminated with phenanthrene. Mycobacterium pallens sp. was used to degrade phenanthrene. Solar energy was used to generate power for the hybrid technique. Three distinct bacterial strains designated as AC16, SM155, and SB53, were subjected to investigation, including ability to grow in liquid medium at different diesel fuel concentrations, identifying functional genes, and the ability to grow at different temperatures and pH. Electrokinetic bioremediation with ACC technique was conducted to mitigate soil contaminated with diesel fuel. The tests were conducted using the novel bacterial strains AC16, SM155 and SB53. The results showed that, the phenanthrene concentration in effluent samples after desorption by electroosmotic flow was found to be three to four times the concentration after desorption by hydraulic flow. The new ACC technique overcomes the shortcomings of other pH stabilization techniques by stabilizing the pH without the need for pumping or amendments. The use of solar panels as a sole source of power can reduce electricity transmission expenses and eliminate power loss in transmission lines. Diesel degradation in tests conducted with electrokinetic bioremediation was between 20 and 30%

Toxicity Assessment of PAHs and Metals to Bacteria and the Roles of Soil Bacteria in Phytoremediation of Petroleum Hydrocarbons

Petroleum hydrocarbons (PHCs) are a class of ubiquitous contaminants in the environment. PHCs impact to soil and water occur at well sites, refineries, service stations, and other facilities. Petroleum processing and consumption of petroleum products lead to the further release of other PHC pollutants such as Polycyclic Aromatic Hydrocarbons (PAHs) as well as metals. PHCs are causing serious environmental problems due to their widespread use. Hence, the central theme of this thesis addresses hydrocarbon pollutants and co-contaminating metals: their occurrence in environment, their mechanism of toxicity and their remediation via biological processes. This thesis is divided into two parts including seven chapters. The first part includes chapters 2, 3 and 4. Using bioluminescent bacterium Vibrio fischeri, a widely used bioindacator in environmental toxicology, the individual and mixture toxicities of phenanthrenequinone (PHQ), an oxyPAH, combined with copper and cadmium were assessed. PHQ is a main photoproduct of phenanthrene (PHE), a dominant PAH in the environment. Results showed that PHQ is much more toxic than its parent PAH. PHQ, alone or as mixtures with Cu and Cd, damages bacterial cells via enhancing production of reactive oxygen species (ROS). The mixture toxicity of Cu/PHQ was found to be dependent on the ratio of each chemical in the mixture. Two up-regulated genes, protein translocase subunit SecY gene and putative polysaccharide export protein YccZ precursor, were identified to be possibly response to PHQ exposure. Both genes are related to the detoxification of ROS. The second part of this thesis includes chapters 5, 6, and 7. Culture-dependent and -independent approaches were employed to evaluate the roles of bacteria as biodegraders or/and plant growth promoters during phytoremediation at a petroleum land farm (PLF) with a PHC concentration of ~130 g Kg-1. A plant growth promoting rhizobacteria (PGPR) enhanced phytoremediation system (PEP) was applied to remediate PLF soil. PEP promotes plant growth to establish dense vegetative cover. Results of both culturing and molecular methods showed that the enhanced populations and activities of soil microbes due to vigorous plant growth is a key factor in the success of PEP. Introduced PGPR could quickly establish significant populations by utilizing root exudates and dominate the PGPR population on seed coat and root surfaces at the early seedling stage of plant development, and thus modestly affected bacterial community structures at this time; thereafter, with plant growth, the effect of seed treatment on soil microbial community was masked by enhanced indigeneous microbial population. Therefore, the introduced PGPR did not exert significant influence on the indigenous microbial ecosystem. It does dramatically improve plant growth and PHC remediation. Thus, the PEP should be considered as an environmentally safe and effective approach for removing PHCs from impacted soils