In recent decades, the occurrence of contaminants of emerging concern (CEC) at trace levels in water matrixes is under investigation due to their proven or potential adverse effects on human health and the aquatic ecosystems. Amongst anthropogenic CEC, poly- and perfluoroalkyl substances (PFAS) and radioactive 137-Cesium (137Cs) have increasingly received attention due to their high solubility in water, mobility through the environment and bioavailability to terrestrial and aquatic organisms through the food chain. To date, the adsorption is deemed more cost-effective than other advanced processes and the activated carbons (ACs) are extensively recognized as the most common adsorbent materials for both organic and inorganic contaminants. However, ACs saturation is a major issue affecting full-scale treatments. As an alternative to landfill disposal, the regeneration allows the reduction of waste production and the renew of AC adsorption capacity. Microwave (MW) irradiation is currently figured out as a very effective regeneration technique for exhausted ACs due to the high dielectric nature of ACs. The overarching goal of the present research is to investigate the innovative regeneration technique based on MW irradiation for saturated ACs. Deeply, the experimental work has been conducted in order to demonstrate the efficacy of MW irradiation (performed at several irradiation power and time) in terms of AC adsorption capacity recovery and textural properties variation. With this purpose, the applicability of MW irradiation to regenerate PFAS-saturated GAC has been investigated through lab-scale experiments. The results have proven the capability of MW irradiation to desorb long-chain PFAS (i.e., perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)) from two commercially available GACs. Rapid temperature increases at short irradiation time (T>600 °C in 3 min, applying a power of 500 W), the preservation of GACs porous structure and a good regeneration efficiency throughout several regeneration cycles represent the main key findings. The results corroborate the beneficial application of the innovative regeneration technique by means of MW irradiation. Indeed, MW regeneration may allow the overcoming of several drawbacks related to currently employed techniques to manage PFAS-saturated GACs (e.g., the use of organic solvent in chemical regeneration, the costs related to landfill disposal of PFAS exhausted GAC). Based on obtained results, MW irradiation is a promising alternative regeneration technique for PFAS-saturated GACs and further investigations are still required to better understand the PFAS degradation mechanisms. A novel proof of concept based on MW regeneration coupled with permeable reactive barrier (MW-PRB) for Cs-contaminated groundwater is introduced for the first time. Batch adsorption and column experiments were performed to assess the efficacy of MW irradiation for the regeneration of Cs-saturated GAC. The noticeable Cs removal performance and the low weight loss throughout several adsorption/regeneration cycles claim that MW regeneration of Cs-saturated GAC is a potential effective treatment. A techno-economic analysis is conducted to evaluate the longevity of novel MW-PRB at different scenarios (e.g., simulated Cs field contamination and groundwater velocity) and to provide a comparison of main specific costs between new MW-PRB system and conventional one. The obtained results of techno-economic analysis revealed the MW-PRB feasibility, demonstrating its advantages also in comparison with conventional PRB systems. The main findings of this research support and promote the feasibility of MW irradiation for the regeneration of saturated ACs. They provide essential information to design and conduct the successive pilot-scale studies. Moreover, some speculations here provided could be helpful to guide the successive scaling-up and to expand the boundaries of full-scale applications.
La presenza di contaminanti emergenti (Contaminants of emerging concern, CEC) in tracce nei comparti acquatici è attualmente oggetto di studio e monitoraggio a causa dei lori effetti avversi (comprovati o potenziali) sulla salute umana e il loro impatto negativo sugli ecosistemi. Tra i CEC di origine antropica, le sostanze poli- e per-fluoroalchiliche (PFAS) e il radionuclide Cesio-137 (137-Cs) stanno ricevendo una crescente attenzione da parte della comunità scientifica e degli organi legislativi a causa della loro elevata solubilità in acqua, dispersione nell'ambiente e biodisponibilità per organismi terrestri e acquatici. Il processo chimico-fisico di adsorbimento mediante l’utilizzo di carboni attivi (Activated carbon, AC, spesso impiegati in forma granulare, Granular activated carbon, GAC) è attualmente il trattamento più utilizzato a scala reale per la rimozione di contaminanti emergenti da acque contaminate. Tuttavia, la saturazione dei AC influenza negativamente la performance a lungo termine di tale trattamento. In alternativa allo smaltimento in discarica, la rigenerazione dei carboni attivi saturi consente la riduzione della produzione di rifiuti, quindi minore impatto ambientale, e il ripristino della capacità di adsorbimento dei carboni attivi. L'irradiamento a microonde (Microwave, MW) è stato recentemente studiato come tecnica di rigenerazione alternativa al convenzionale trattamento di tipo termico conduttivo, grazie alla natura dielettrica dei AC. Obiettivo generale della presente ricerca è stato lo studio della tecnica di rigenerazione innovativa basata sull'irradiamento a microonde per GAC saturi da PFAS e 137-Cs, mediante esperimenti condotti a scala di laboratorio. I risultati hanno dimostrato la capacità delle microonde di desorbire i PFAS a catena lunga (come l’acido perfluoroottanoico (PFOA) e l’acido perfluoro-ottansulfonico (PFOS)) da due GAC disponibili in commercio e ampiamenti utilizzati negli impianti di trattamento. Il rapido incremento di temperatura in tempi di trattamento brevi (T>600 °C in 3 min, applicando una potenza di 500 W), la conservazione della struttura porosa dei GAC e una buona efficienza di rigenerazione ottenuta durante diversi cicli di adsorbimento-rigenerazione rappresentano i principali risultati ottenuti, confermando la potenziale applicabilità della tecnica di rigenerazione mediante irradiamento a microonde. Essa permette inoltre superamento di diversi inconvenienti legati alle tecniche attualmente impiegate per la gestione di GAC saturi da PFAS come ad esempio, l'uso di solventi organici nella rigenerazione chimica e i costi legati allo smaltimento in discarica. Nell’ambito della presente ricerca è stato anche sviluppato un approccio tecnologico innovativo basato sull’irradiamento a microonde. Infatti, nel caso di acquiferi contaminati, il processo di adsorbimento in situ avviene mediante l’ausilio di una barriera reattiva permeabile (Permeable reactive barrier, PRB), in cui il materiale reattivo di riempimento più utilizzato sono i carboni attivi. Il nuovo sistema di trattamento proposto nel presente studio prevede l’accoppiamento della PRB con l’irradiamento a microonde per la rigenerazione del GAC (MW-PRB). In primo luogo, sono stati eseguiti esperimenti di adsorbimento in batch a mescolamento completo e in colonna per valutare l'efficacia dell'irradiamento a microonde per la rigenerazione di GAC saturo di Cs. Le efficienze di rigenerazione ottenute (>90%) e la moderata perdita di peso del GAC (<7%) nei diversi cicli di adsorbimento-rigenerazione dimostrano che la rigenerazione mediante microonde di GAC saturo da Cs rappresenta un trattamento efficace. Successivamente, un'analisi tecnico-economica è stata condotta al fine di valutare la longevità del nuovo sistema MW-PRB proposto (ad esempio, ipotizzando diversi scenari di contaminazione) e per fornire un confronto tra i principali costi specifici del sistema MW-PRB e di quello convenzionale. I risultati dell'analisi tecnico-economica hanno dimostrato la fattibilità del MW-PRB, evidenziato anche i vantaggi rispetto al sistema PRB convenzionale. I principali risultati ottenuti nella presente tesi supportano e promuovono la fattibilità dell'irradiamento a microonde per la rigenerazione di AC saturi. Essi forniscono inoltre le informazioni essenziali per la progettazione e l’esecuzione della futura attività sperimentale su scala pilota. Inoltre, le argomentazioni di carattere tecnico-scientifico risultano fondamentali per guidare lo sviluppo e l’implementazione su vasta scala della tecnologia di rigenerazione basata su irradiamento a microonde per carboni attivi saturi.
Rigenerazione mediante irradiamento a microonde di carboni attivi saturi da contaminanti emergenti / Gagliano, Erica. - (2021 Apr 23).
Rigenerazione mediante irradiamento a microonde di carboni attivi saturi da contaminanti emergenti
GAGLIANO, ERICA
2021-04-23
Abstract
In recent decades, the occurrence of contaminants of emerging concern (CEC) at trace levels in water matrixes is under investigation due to their proven or potential adverse effects on human health and the aquatic ecosystems. Amongst anthropogenic CEC, poly- and perfluoroalkyl substances (PFAS) and radioactive 137-Cesium (137Cs) have increasingly received attention due to their high solubility in water, mobility through the environment and bioavailability to terrestrial and aquatic organisms through the food chain. To date, the adsorption is deemed more cost-effective than other advanced processes and the activated carbons (ACs) are extensively recognized as the most common adsorbent materials for both organic and inorganic contaminants. However, ACs saturation is a major issue affecting full-scale treatments. As an alternative to landfill disposal, the regeneration allows the reduction of waste production and the renew of AC adsorption capacity. Microwave (MW) irradiation is currently figured out as a very effective regeneration technique for exhausted ACs due to the high dielectric nature of ACs. The overarching goal of the present research is to investigate the innovative regeneration technique based on MW irradiation for saturated ACs. Deeply, the experimental work has been conducted in order to demonstrate the efficacy of MW irradiation (performed at several irradiation power and time) in terms of AC adsorption capacity recovery and textural properties variation. With this purpose, the applicability of MW irradiation to regenerate PFAS-saturated GAC has been investigated through lab-scale experiments. The results have proven the capability of MW irradiation to desorb long-chain PFAS (i.e., perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS)) from two commercially available GACs. Rapid temperature increases at short irradiation time (T>600 °C in 3 min, applying a power of 500 W), the preservation of GACs porous structure and a good regeneration efficiency throughout several regeneration cycles represent the main key findings. The results corroborate the beneficial application of the innovative regeneration technique by means of MW irradiation. Indeed, MW regeneration may allow the overcoming of several drawbacks related to currently employed techniques to manage PFAS-saturated GACs (e.g., the use of organic solvent in chemical regeneration, the costs related to landfill disposal of PFAS exhausted GAC). Based on obtained results, MW irradiation is a promising alternative regeneration technique for PFAS-saturated GACs and further investigations are still required to better understand the PFAS degradation mechanisms. A novel proof of concept based on MW regeneration coupled with permeable reactive barrier (MW-PRB) for Cs-contaminated groundwater is introduced for the first time. Batch adsorption and column experiments were performed to assess the efficacy of MW irradiation for the regeneration of Cs-saturated GAC. The noticeable Cs removal performance and the low weight loss throughout several adsorption/regeneration cycles claim that MW regeneration of Cs-saturated GAC is a potential effective treatment. A techno-economic analysis is conducted to evaluate the longevity of novel MW-PRB at different scenarios (e.g., simulated Cs field contamination and groundwater velocity) and to provide a comparison of main specific costs between new MW-PRB system and conventional one. The obtained results of techno-economic analysis revealed the MW-PRB feasibility, demonstrating its advantages also in comparison with conventional PRB systems. The main findings of this research support and promote the feasibility of MW irradiation for the regeneration of saturated ACs. They provide essential information to design and conduct the successive pilot-scale studies. Moreover, some speculations here provided could be helpful to guide the successive scaling-up and to expand the boundaries of full-scale applications.File | Dimensione | Formato | |
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