In situ groundwater remediation treatments : natural denitrification study and nano zero valent iron production
Freshwater is a scarce resource, threatened by an ongoing pollution, global climate change and industrialization. Among other freshwater sources, groundwater is by far the most important source of usable freshwater but due to the intrinsic nature of aquifers; low flow rates and a complex matrix comp...
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| Tipo de recurso: | tesis doctoral |
| Fecha de publicación: | 2017 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/107957 |
| Acceso en línea: | https://hdl.handle.net/2117/107957 https://dx.doi.org/10.5821/dissertation-2117-107957 |
| Access Level: | acceso abierto |
| Palabra clave: | Aigües subterrànies -- Depuració Aigües residuals -- Depuració -- Desnitrificació Desnitrificació Bioremediació Àrees temàtiques de la UPC::Enginyeria civil |
| Sumario: | Freshwater is a scarce resource, threatened by an ongoing pollution, global climate change and industrialization. Among other freshwater sources, groundwater is by far the most important source of usable freshwater but due to the intrinsic nature of aquifers; low flow rates and a complex matrix compared to superficial waters, attempts to remove contaminants are more complex and slow. The aim of this thesis is to increase the knowledge of two remediation technologies: first, nitrate and nitrite removal based on natural occurring bioremediation and second, the production, reactivity and agglomeration of nano Zero Valent Iron (nZVI) particles. Natural occurring denitrification is a promising and partially implemented remediation approach but concerns about its performance out of the lab are justified. The following studies were carried out: evaluation of denitrification potential of wetlands from two sites in Denmark, soil characteristics and composition impact on denitrification highlighting the role and vertical distribution of organic matter, assessment of the Dissimilatory Nitrate Reduction to Ammonium (DNRA) importance as a denitrification competitor and effect of the seasonal variations. Regarding seasonal fluctuations, results showed that Heterotrophic Denitrification (HD) is an Arrhenius temperature dependant process. Although, observing that HD is a very resilient process, being dominant under all tested conditions, the importance of DNRA arose in dried and frozen soils, in addition a nitrite increase was observed. Concerning to organic matter studies, heterotrophic denitrification was only present in a very narrow superficial zone where Organic Matter (OM) was abundant. DOC and LOI could not express by themselves an absolute correlation with HD, however high amounts of DOC ensured enough quantity and quality of OM. DNRA was important only in the very superficial samples where an excessive content of OM could trigger it. On the other hand, nZVI is a very promising in situ new technology which can achieve the degradation of a broad range of contaminants, some being reluctant to previous remediation and bioremediation approaches. The purpose is to help to overcome some of the challenges that limit a widespread implementation of this technique, such as: the lack of a cost -effective- straightforward production method, uncertainness on the reactivity governing factors including the passivating oxide shell in commercial particles and the agglomeration driving factors. After replicating the previous milling methods in literature (where the iron ductility if using inert media was an insurmountable barrier to reach a nanoscale size), the need to break the iron flakes was stated. Several approaches were tested, finally the addition of micronized alumina produced nanoscale particles. Abrasion of the grinding media and breakage of flakes were the main mechanisms for the nZVI production. The physicochemical properties of the obtained particles were: a mean particle diameter of 0.16 µm (by SEM) and a specific surface area of 29.6 m2·g-1 and a reactivity toward Cr (VI), trichloroethylene and tetrachloroethylene higher than commercial nZVIs. In reference to the work performed assessing the effect of a passivation oxide layer on a commercial nZVI (NANOFER STAR, nanoIron s.r.o.) it was concluded that the oxide shield of surface-passivated nZVI particles significantly decreases the performance. A process to weaken the oxide shield was tested, it consisted in exposing the passivated nZVI to water for 36 hours at w iron / w water concentration of 0.2, just before the reaction with the pollutants. The results show that this activation process increases the effectiveness of the remediation and simplifies the overall handling of the nZVI. |
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