COMBINING GEOCHEMICAL AND NUMERICAL MODELING FOR CHLORINATED SOLVENTS GROUNDWATER CONTAMINATION
Tesi di Dottorato
Data di Pubblicazione:
2023
Citazione:
COMBINING GEOCHEMICAL AND NUMERICAL MODELING FOR CHLORINATED SOLVENTS GROUNDWATER CONTAMINATION / G. Casiraghi ; tutor: D. Pedretti, G.P. Beretta ; coordinatori: M.I. Spalla, F. Camara Artigas. Dipartimento di Scienze della Terra Ardito Desio, 2023 Jul 25. 35. ciclo, Anno Accademico 2022.
Abstract:
Chloroethenes represent a serious risk to aquatic ecosystems and human health on a worldwide scale. Chloroethenes contamination is difficult to solve due to the different optimal redox conditions needed to obtain efficient degradation of each chloroethene. The more chlorinated ones such as tetrachloroethene (PCE) and trichloroethene (TCE) are better degraded via reductive dechlorination (RD) under anaerobic conditions, while the less chlorinated compounds such as dichloroethene (DCE) and vinyl chloride (VC) are better degraded via oxidation (OX) under aerobic conditions. Thus, sequential bioremediation systems (SBSs) able to stimulate anaerobic and aerobic biodegradation are preferred over traditional bioremediation systems targeting single degradation pathways.
Assessing the efficiency of SBSs is a challenging task that requires a multidisciplinary approach, spanning from hydrogeology, organic geochemistry and microbiology. While expert knowledge and laboratory analyses provide initial inputs for the design of SBS, field monitoring data are needed to evaluate if and how bioremediation is carried out.
Reactive transport models (RTMs) are suitable tools to assist decision makers when designing and monitoring bioremediation efficiency. To date, no applications to SBSs have been reported, possibly owing to the relative novelty of SBS and to the additional modeling challenges (e.g., more complex parameterization) that sequential systems pose over traditional bioremediation systems. RTMs have the capability to integrate and harmonize multiple data and, when properly tailored, to make useful predictions about a system’s behavior when different remediation set-ups are tested in order to optimize the cleanup operations.
The general objective of this thesis was to develop methodologies for the evaluation of the efficiency of SBSs applied to chloroethenes aquifer contamination. As case study, we investigated one the largest SBS currently implemented in a polluted alluvial aquifer in Italy. The SBS is about 800 m-long and was created to remediate organic pollutants such as chloroethenes and petroleum hydrocarbons (PHCs). The SBS is made up of a hydraulically upgradient anaerobic (AN) biobarrier, where a reducing substrate is injected to stimulate RD of higher chloroethenes (PCE, TCE), and downgradient aerobic (AE) biobarrier, where OX of lower chloroethenes (DCE, VC) is stimulated through nutrients and oxygen injection. In addition, P&T wells are active downgradient of the two biobarriers in order to intercept the remaining contaminants exfiltrating from the SBS.
The first part of the thesis evaluates the initial characterization activities propaedeutic to the installation of the operational (full) scale SBS: Microcosm experiments and in situ tests were carried out to assess the biodegradation potential of the autochthonous microbial communities in the laboratory and in the site under both natural and biostimulated conditions. Both investigations showed a satisfactory efficiency of aerobic and anaerobic degradation only after biostimulation, proving the feasibility as well as the necessity of the full-scale SBS for the cleanup of the site. The analysis of these data constitutes an improvement of the current state of the art in the design and implementation of large-scale SBS.
The second part of the thesis is dedicated to the analysis of time series of chloroethenes concentrations and environmental parameters observed during periodic monitoring of groundwater in the site piezometers of the full-scale SBS. Carbon compound-specific isotopic analysis (C-CSIA) were carried out on chloroethenes PCE, TCE, cis-DCE and VC in samples acquired along a flow path crossing both biobarriers. Target chloroethenes concentrations and isotopic compo
Tipologia IRIS:
Tesi di dottorato
Keywords:
chloroethenes ; enhanced bioremediation ; sequential bioremediation system ; anaerobic organohalide respiration ; aerobic oxidative biodegradation ; landfill ; compound-specific stable isotope analysis; reactive transport model ; PHREEQC ; RT3D.
Elenco autori:
G. Casiraghi
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