Thesis title: Processi di risanamento chimico-fisici combinati con sistemi di manipolazione idraulica della falda
This doctoral thesis, framed within the "Industrial Doctorates" program, presents a comprehensive research journey that seamlessly integrates advanced academic research with its practical application in the industrial sector of environmental remediation. Conducted in collaboration with IEG Technologie GmbH, the work is structured into two distinct yet interconnected pillars, addressing both the optimization of field-installed technologies and the development of a novel laboratory-scale process.
Chapter 1 is dedicated to the advanced management and optimization of remediation systems in real-world, complex field conditions. It underscores a paradigm shift towards a data-driven approach, where high-resolution site characterization (HRSC) and 3D hydrogeochemical modeling are pivotal for designing targeted and effective strategies. This chapter is articulated through two extensive case studies. The first, at the SIN Livorno site, involved a decommissioned thermoelectric plant plagued by a persistent Trichloroethylene (TCE) plume. Through an integrated approach using membrane interface probe (MIP) screening and 3D geomodeling, a previously unidentified secondary contamination source was delineated. To intercept the plume migrating from this source, a pioneering virtual hydraulic barrier was designed and installed, comprising three Groundwater Circulation Wells (GCWs). This system created overlapping ellipsoidal recirculation cells perpendicular to the groundwater flow. The results were decisive: the GCW barrier achieved a mass removal of 3360 g of TCE over four months, outperforming the existing Pump-and-Stock (P&S) system by a factor of 30, while simultaneously eliminating groundwater extraction and waste generation, thus demonstrating superior effectiveness and sustainability.
The second case study, at the SIN Gela site, involved a pilot-scale investigation of a GCW's ability to remediate a coastal aquifer historically contaminated with high concentrations of Arsenic (As). Over a rigorous 550-day monitoring period, the GCW operated in a complex hydrogeological setting influenced by a saline wedge. The system successfully mobilized approximately 120 kg of As, with the above-ground treatment plant achieving a 66% removal efficiency, equating to about 53 kg of As per year. Crucially, integrated monitoring with multi-level sampling wells provided direct physico-chemical evidence of the recirculation cell's development, showing homogenization of As concentrations and electrical conductivity across the aquifer's vertical profile. This demonstrated the GCW's unique capability to flush contaminants from low-permeability layers and interact with saline-water dynamics, offering a sustainable alternative to conventional Pump-and-Treat for such challenging scenarios.
Chapter 2 transitions to the domain of process innovation within the academic laboratory, focusing on the development of a novel in-situ technology for groundwater remediation: an Injectable Permeable Reactive Barrier (IPRB) based on a biochar-biopolymer composite. The research first identified and characterized pine wood biochar (BC), a waste product from biomass gasification, as a sustainable and high-performance adsorbent. A key challenge was stabilizing the hydrophobic BC in an aqueous suspension for effective subsurface delivery. Through systematic screening, sodium carboxymethylcellulose (CMC) was identified as the optimal biopolymer to produce a colloidally stable BC@CMC suspension. The research (Chapter 2.4) then extensively characterized this composite, evaluating its stability under varying pH and ionic strength conditions and optimizing its injectability by controlling the particle size distribution via pre-filtration to prevent well clogging.
The final and critical phase of this research involved a complete simulation of the IPRB process. A reactive zone was first created within a column packed with glass beads by successfully distributing the optimized BC@CMC suspension, achieving a biochar retention of 0.22% w/w of the porous medium. Subsequently, this biochar-packed column was used in continuous-flow adsorption tests with synthetic groundwater contaminated with Toluene (TOL) and Perchloroethylene (PCE). The composite demonstrated remarkable adsorption capacities, with Freundlich isotherm parameters comparable to, and in the case of PCE nearly identical with, a commercial activated carbon. The continuous flow tests yielded high experimental retardation factors (144 for TOL and 360 for PCE), validating the process's efficacy in significantly delaying contaminant breakthrough and confirming the potential of this sustainable, low-cost biochar-based composite as a viable technology for in-situ groundwater remediation.