Analyzing Solar Pyrolysis Process of Walnut Shells: Thermal Biomaterial Behavioral Outcomes

This paper presents a new experimental method for the thermal analysis of solar pyrolysis of walnut shells. The method consists of two types of thermal experiments: (A) the pyrolysis of walnut shells, and (B) the heating-cooling of the biochar obtained during experiment A. Nutshells are a waste product from the pecan nut industry. The state of Sonora, Mexico, produces large volumes of walnuts and their residue. Likewise, this region has a considerable solar resource. The motivation of this study is to obtain biochar - a bi-product of high commercial value used for soil enhancement - using solar energy and agro-industrial waste. In this experiment, biomass pyrolysis of 50g of nutshells was carried out inside a stainless-steel reactor heated with concentrated radiation from a solar simulator. Three different heat fluxes were used: 234, 482, and 725 W. The maximum reaction temperatures were: 382, 498, and 674 °C respectively. The composition of the pyrolysis gases (H2, CO, CO2, and CH4) was measured and the biochar obtained was characterized. Finally, the performance of the solar reactor allowed us to identify and differentiate between evaporation, pyrolysis of cellulosic material, and lignin degradatio

Microbial reduction of palladium: mechanisms, modeling and applications in wastewater treatment systems

Tesis (Doctorado en Ciencias Ambientales)"El potencial metabólico que poseen los microorganismos de cambiar el estado de oxidación de los metales es ampliamente conocido y constituye una herramienta poderosa que se puede emplear en el desarrollo y aplicación de nuevas técnicas de biorremediación. En la actualidad, no sólo la recuperación de metales sino también la producción de nanopartículas metálicas es un tema de interés y las propuestas de enfoque biotecnológico han surgido como opciones prometedoras para alcanzar este propósito. El paladio (Pd) es considerado como un metal precioso con propiedades excepcionales lo cual lo hace atractivo para aplicarlo en muchas áreas de la industria, aumentando su uso y demanda. Sin embargo, su abundancia en la tierra es limitada y los esfuerzos por recuperarlo cuando se encuentra presente en efluentes y residuos es mínimo. Esta tesis se enfoca en ofrecer una solución a esta problemática, se propone un método biológico para la recuperación de Pd y producción de nanopartículas de Pd(0). Para lograr tal objetivo se evaluaron un cultivo puro de Geobacter sulfurreducens, cepa PCA y lodo granular metanogénico a fin de entender los mecanismos involucrados. G. sulfurreducens es un microorganismo con capacidades metabólicas excepcionales, se encuentra ampliamente distribuido en suelo y sedimentos, y su notable capacidad fisiológica es de gran interés desde el punto de vista biotecnológico. Los resultados obtenidos demostraron, por vez primera, que G. sulfurreducens es capaz de acoplar la oxidación de acetato con la reducción de Pd(II) y producir nanopartículas de Pd(0). Los parámetros células:Pd, composición del medio, pH, especiación, concentración de Pd(II) y la presencia de un mediador redox son de relevancia en el proceso. Se demostró que la adición de un mediador redox como la antraquinona-2,6-disulfonato (AQDS), favorece la síntesis extracelular de nanoapartículas de Pd(0), lo cual favorece la separación de las nanoparticulas, previniendo el posible envenenamiento del catalizador evitando interacciones del Pd con compuestos de azufre (por ejemplo, grupos tiol presentes en las proteínas). Hasta ahora, solo cultivos puros habían sido utilizados para la síntesis de nanopartículas, sin embargo, para aplicaciones prácticas esta condición tiene limitaciones. Por lo tanto, en este trabajo también se evaluó la capacidad de lodo granular metanogénico para reducir Pd(II) a Pd(0) mediante la adición de diferentes donadores de electrones. Los resultados obtenidos demostraron que es posible lograr la reducción de paladio y formación de nanopartículas empleando etanol como donador de electrones. Este estudió constituyó el primer reporte en el uso exitoso de un consorcio para la recuperación de Pd(II) y formación de nanopartículas de Pd(0) tanto en lote como en continuo empleando reactores tipo UASB (por sus siglas en inglés, upflow anaerobic sludge blanket). Además, la biomasa enriquecida con el Pd(0) fue utilizada en la transformación de contaminantes recalcitrantes de interés ambiental y se promovieron reacciones de deshalogenación, hidrogenación y nitro-reducción como efecto del catalizador de paladio.""The metabolic potential of microorganisms to change the oxidation state of metals is widely known and constitutes a powerful tool to develop and implement novel bioremediation techniques. Nowadays, not just the recovery of metals but also the production of metallic nanoparticles is a major issue and biotechnological approaches have emerged as promising options to accomplish this. Palladium (Pd) is considered a precious metal with remarkable properties which make it attractive to many areas in industry. However, its abundance is limited on earth and efforts for its recovery when present in effluents and residues is limited. This dissertation focuses on this problematic by proposing a biological method for the recovery of Pd and the production of Pd(0) nanoparticles. With this objective, pure cultures of Geobacter sulfurreducens, strain PCA, and methanogenic granular sludge were evaluated to understand the mechanisms involved. G. sulfurreducens is a microorganism with exceptional metabolic capacity, ubiquitous in sediments and soil, its hallmark physiological capability is of great interest from the biotechnological point of view. Results obtained demonstrated, for the first time, that G. sulfurreducens can couple the oxidation of acetate to the reduction of Pd(II) with the concomitant production of Pd(0) nanoparticles. Parameters such as cells:Pd ratio, medium composition, pH, speciation, Pd(II) concentration and the presence of a redox mediator were identified of significant relevance in the process. Extracellular synthesis of Pd(0) nanoparticles was promoted using anthraquinone-2,6-disulfonate (AQDS) as redox mediator, which represents the advantage of a simple separation method and prevention of catalyst poisoning by avoiding Pd interactions with sulfurous compounds (e.g. thiol groups of proteins from bacteria). Until now, only pure cultures of bacteria had been used for palladium nanoparticles production; however, for practical applications this condition would face limitations. Hence, in this work methanogenic granular sludge was studied for its ability to reduce Pd(II) to Pd(0) by using different electron donating substrates. Obtained results demonstrated that it is possible to achieve palladium reduction and nanoparticles production by providing ethanol as electron donor.

Operación robusta de un biorreactor discontinuo secuencial con membranas sumergidas para el tratamiento de efluentes tóxicos

Operación robusta de un biorreactor discontinuo secuencial con membranas sumergidas para el tratamiento de efluentes tóxico

Review of Constructed Wetlands for Acid Mine Drainage Treatment

The mining industry is the major producer of acid mine drainage (AMD). The problem of AMD concerns at active and abandoned mine sites. Acid mine drainage needs to be treated since it can contaminate surface water. Constructed wetlands (CW), a passive treatment technology, combines naturally-occurring biogeochemical, geochemical, and physical processes. This technology can be used for the long-term remediation of AMD. The challenge is to overcome some factors, for instance, chemical characteristics of AMD such a high acidity and toxic metals concentrations, to achieve efficient CW systems. Design criteria, conformational arrangements, and careful selection of each component must be considered to achieve the treatment. The main objective of this review is to summarize the current advances, applications, and the prevalent difficulties and opportunities to apply the CW technology for AMD treatment. According to the cited literature, sub-surface CW (SS-CW) systems are suggested for an efficient AMD treatment. The synergistic interactions between CW components determine heavy metal removal from water solution. The microorganism-plant interaction is considered the most important since it implies symbiosis mechanisms for heavy metal removal and tolerance. In addition, formation of litter and biofilm layers contributes to heavy metal removal by adsorption mechanisms. The addition of organic amendments to the substrate material and AMD bacterial consortium inoculation are some of the strategies to improve heavy metal removal. Adequate experimental design from laboratory to full scale systems need to be used to optimize equilibria between CW components selection and construction and operational costs. The principal limitations for CW treating AMD is the toxicity effect that heavy metals produce on CW plants and microorganisms. However, these aspects can be solved partially by choosing carefully constructed wetlands components suitable for the AMD characteristics. From the economic point of view, a variety of factors affects the cost of constructed wetlands, such as: detention time, treatment goals, media type, pretreatment type, number of cells, source, and availability of gravel media, and land requirements, among others

Biochar-Assisted Bioengineered Strategies for Metal Removal: Mechanisms, Key Considerations, and Perspectives for the Treatment of Solid and Liquid Matrixes

Biochar has drawn the scientific community’s attention during the last few years due to its low production value and unique physicochemical properties, which are helpful for numerous applications. The development of biotechnological processes for the remediation of heavy metal environmental pollution is one central research avenue in which biochar application has shown promising results, due to its positive effect on the bacteria that catalyze these activities. Biochar stimulates bacterial activity through adsorption, adhesion, electron transport, and ion exchange. However, before biochar implementation, a complete understanding of its potential effects is necessary, considering that those interactions between biochar and bacteria may help improve the performance of biological processes designed for the remediation of environmental pollution by metals, which has been historically characterized by limitations related to the recalcitrance and toxicity of these pollutants. In this review, the key biochar–microorganism interactions and properties of unmodified biochar with the potential to improve metal bioremediation in both solid (mine tailings, polluted soils) and liquid matrixes (metal-laden wastewaters) are summarized. Knowledge gaps regarding the mechanisms involved in remediation strategies, the effect of long-term biochar use and the development of improved biochar technologies and their combination with existent remediation technologies is summarized. Additionally, an up-to-date summary of the development of biochar-assisted bioengineered strategies for metal passivation or removal from solid and liquid matrixes is presented, along with key perspectives for the application of biochar-based biotechnologies at full scale during the treatment of mining effluents in the real scale