Per- and poly-fluoroalkyl substances (PFASs), due to their persistence, mobility, toxicity and resistance to degradation, pose a new challenge for the remediation of many polluted sites. The thesis paper addresses the issue of PFAS environmental contamination with the aim of providing the concepts, tools, and guidelines that environmental professionals and authorities can benefit from in dealing with such emerging contaminates, and a focus on applicable soil treatment technologies is proposed. The paper is the result of an extensive critical review of available literature, analysis of case studies, and contacts with companies, professionals, laboratories, suppliers, and the Swiss authorities that commissioned this work. The thesis deals in a practical way with the difficulty of describing the environmental behaviour of the thousands of different existing PFAS substances that affect the applicability and effectiveness of remediation processes and provides an analysis of the uncertain international regulatory framework and the presumed future guideline values, also based on the toxic equivalence of different PFASs. The analysis of the different types of contamination sources produced useful tables to guide practitioners in identifying the substances to be investigated according to the case and the types of laboratory analysis that can be used with a view to economic-environmental optimization. All potential methodologies for treating PFAS-polluted soils were subsequently screened and evaluated, and considerations for the proper design and management of the intervention were outlined for each technology. In addition, each technology was evaluated from the standpoint of stage of development, expected treatment efficiency, intervention time and cost, environmental and social impact, and possible risks of contaminant re-entry into the environment. Finally, the technologies were compared with each other in the different aspects and guidelines were produced for their optimal use according to the different situations found at the site. The low regulatory values and the recalcitrance of the compounds to degradation make the high temperatures of thermal treatment technologies (in situ/ex situ desorption, co-processing in cement plants, and incineration) the only ones capable of achieving sufficient removal efficiencies, regardless of the type of PFAS, to achieve the objectives in heavily contaminated source areas (mg/kg), at the expense of cost and high energy use. Stabilization with activated carbon-based adsorbents and eventual solidification of the matrix or surface sealing (soil capping) may be more cost-effective strategies for in situ containment of contamination, but these involve restrictions on land use and perennial post-intervention monitoring, lacking at present guarantees of long-term stability of the safeguards put in place. Soil washing allows the reuse of the gravel and sand fractions if the soil has indicatively less than 50 ug/kg initial contamination and is one of the most suitable technologies for treating soils with clay and silt amounts of less than 30 percent, outside source areas; it is also the only technology currently economically viable for treating large volumes of soil if contamination is to be removed. Finally, landfilling remains a methodology relegated to the disposal of small quantities, polluted at levels of a few units of ug/kg, often after pretreatment of the material.
Le sostanze per- e poli-fluoroalchiliche (PFAS), a causa della loro persistenza, mobilità, tossicità e resistenza alla degradazione, costituiscono una nuova sfida per il risanamento di molti siti inquinati. Il lavoro di tesi affronta la problematica delle contaminazioni ambientali da PFAS con lo scopo di fornire le nozioni, gli strumenti e le linee guida di cui i professionisti del settore ambientale e le autorità possano beneficiare nell’affrontare tali contaminati emergenti, e si propone in particolare un focus sulle tecnologie applicabili per il trattamento dei terreni. L’elaborato è frutto di un’ampia revisione critica della letteratura disponibile, dell’analisi di casi di studio e di contatti con aziende, professionisti, laboratori, fornitori e le autorità svizzere che hanno commissionato il presente lavoro. La tesi affronta in maniera pratica la difficoltà della descrizione del comportamento ambientale delle migliaia di diverse sostanze PFAS esistenti, che influenzano l’applicabilità e l’efficacia dei processi di risanamento, e fornisce un’analisi dell’incerto quadro normativo internazionale e i presumibili futuri valori guida, anche basati sull’equivalenza tossica dei diversi PFAS. L’analisi delle diverse tipologie di sorgenti di contaminazione ha prodotto tabelle utili a guidare i professionisti nella individuazione delle sostanze da indagare in funzione del caso e le tipologie di analisi di laboratorio utilizzabili nell’ottica di un’ottimizzazione economico-ambientale. Sono state successivamente sottoposte a screening e valutazione tutte le potenziali metodologie di trattamento dei terreni inquinati da PFAS e, per ogni tecnologia, sono state illustrate considerazioni per la corretta progettazione e gestione dell’intervento. Inoltre, ciascuna tecnologia è stata valutata sotto il profilo dello stadio di sviluppo, dell’efficienza di trattamento attesa, dei tempi e dei costi degli interventi, dell’impatto ambientale e sociale e dei possibili rischi di re-immissione dei contaminanti in ambiente. Le tecnologie sono state infine confrontate fra loro nei diversi aspetti e sono state prodotte linee guida per il loro impiego ottimale a seconda delle diverse situazioni riscontrabili in sito. I bassi valori previsti dalla normativa e la recalcitranza dei composti alla degradazione rendono le alte temperature delle tecnologie di trattamento termico (desorbimento in situ/ex situ, co-processamento in cementificio e incenerimento) le uniche in grado di ottenere efficienze di rimozione sufficienti, a prescindere dalla tipologia di PFAS, per raggiungere gli obiettivi in zone sorgente fortemente contaminate (mg/kg), a discapito di costi ed elevato uso di energia. La stabilizzazione con adsorbenti a base di carbone attivo e l’eventuale solidificazione della matrice o l’impermeabilizzazione della superficie (soil capping) possono essere strategie più economiche di contenimento in situ della contaminazione, che comportano però restrizioni all’uso dei terreni e monitoraggi perenni successivi all’intervento, mancando al momento garanzie di stabilità a lungo termine dei presidi messi in opera. Il soil washing permette il riutilizzo delle frazioni di ghiaia e sabbia se il terreno ha indicativamente una contaminazione iniziale inferiore ai 50 ug/kg ed è una delle tecnologie più adatte per il trattamento dei terreni con quantità di argilla e limo inferiore al 30%, fuori dalle aree sorgente; è anche l’unica tecnologia al momento economicamente sostenibile per il trattamento di grandi volumi di terreno se si vuole rimuovere la contaminazione. Infine, il conferimento in discarica rimane una metodologia relegata allo smaltimento di piccoli quantitativi, inquinati a livelli di poche unità di ug/kg, spesso previo pretrattamento del materiale.
Sviluppo di linee guida per il risanamento di terreni contaminati da sostanze per- e poli-fluoroalchiliche (PFAS)
Ciabattoni, Eugenio
2023/2024
Abstract
Per- and poly-fluoroalkyl substances (PFASs), due to their persistence, mobility, toxicity and resistance to degradation, pose a new challenge for the remediation of many polluted sites. The thesis paper addresses the issue of PFAS environmental contamination with the aim of providing the concepts, tools, and guidelines that environmental professionals and authorities can benefit from in dealing with such emerging contaminates, and a focus on applicable soil treatment technologies is proposed. The paper is the result of an extensive critical review of available literature, analysis of case studies, and contacts with companies, professionals, laboratories, suppliers, and the Swiss authorities that commissioned this work. The thesis deals in a practical way with the difficulty of describing the environmental behaviour of the thousands of different existing PFAS substances that affect the applicability and effectiveness of remediation processes and provides an analysis of the uncertain international regulatory framework and the presumed future guideline values, also based on the toxic equivalence of different PFASs. The analysis of the different types of contamination sources produced useful tables to guide practitioners in identifying the substances to be investigated according to the case and the types of laboratory analysis that can be used with a view to economic-environmental optimization. All potential methodologies for treating PFAS-polluted soils were subsequently screened and evaluated, and considerations for the proper design and management of the intervention were outlined for each technology. In addition, each technology was evaluated from the standpoint of stage of development, expected treatment efficiency, intervention time and cost, environmental and social impact, and possible risks of contaminant re-entry into the environment. Finally, the technologies were compared with each other in the different aspects and guidelines were produced for their optimal use according to the different situations found at the site. The low regulatory values and the recalcitrance of the compounds to degradation make the high temperatures of thermal treatment technologies (in situ/ex situ desorption, co-processing in cement plants, and incineration) the only ones capable of achieving sufficient removal efficiencies, regardless of the type of PFAS, to achieve the objectives in heavily contaminated source areas (mg/kg), at the expense of cost and high energy use. Stabilization with activated carbon-based adsorbents and eventual solidification of the matrix or surface sealing (soil capping) may be more cost-effective strategies for in situ containment of contamination, but these involve restrictions on land use and perennial post-intervention monitoring, lacking at present guarantees of long-term stability of the safeguards put in place. Soil washing allows the reuse of the gravel and sand fractions if the soil has indicatively less than 50 ug/kg initial contamination and is one of the most suitable technologies for treating soils with clay and silt amounts of less than 30 percent, outside source areas; it is also the only technology currently economically viable for treating large volumes of soil if contamination is to be removed. Finally, landfilling remains a methodology relegated to the disposal of small quantities, polluted at levels of a few units of ug/kg, often after pretreatment of the material.| File | Dimensione | Formato | |
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Descrizione: Tesi di Laurea Magistrale di Eugenio Ciabattoni
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https://hdl.handle.net/10589/223792