Microplastics (MPs) pollution has emerged as one of the most prominent environmental issues over the last decade. Wastewater treatment plants (WWTPs) are one of the pathways through which MPs migrate from the terrestrial to the aquatic environment through effluent discharge. MPs removed from wastewater are mostly accumulated in sludge. This research is focused on studying the fate and removal of MPs in WWTPs and investigate the effects of advanced oxidation processes (AOPs) on MPs as a pretreatment before anaerobic digestion. In this study the concentrations and removal mechanisms of MPs in WWTPs are investigated through the integration and statistical analysis of a database containing information from 488 WWTPs reported in literature. WWTPs achieve median removal efficiencies of 51%, 84% and 94% with respect to the influent through primary, secondary and tertiary treatments, respectively. Ozonation batch tests were performed on deionized water and synthetic sludge samples spiked with LDPE, PA 6,6 and PP MPs. For water samples, 1 L of deionized water containing 100 mg of MPs was exposed to ozone doses of 5, 10, 25 and 50 g O3/g MPs. Ozonation tests on synthetic sludge were conducted on 1 L of synthetic sludge spiked with 100 mg of MPs, with doses of 25 and 50 g O3/g MPs. Although O3 did not cause a mass reduction of MPs, it determined a change in their chemical structure by initiating a degradation process on MPs surface. FTIR (Fourier Transform Infrared spectroscopy) analysis showed increasing intensity of the carbonyl (C=O) band, leading to increased values of the carbonyl index (CI). Differential scanning calorimetry (DSC) revealed a decrease in the crystallinity of polymers after ozonation, possibly determining reduced mechanical resistance of MPs.
L'inquinamento da microplastiche (MP) è emerso come uno dei problemi ambientali più rilevanti nell'ultimo decennio. Gli impianti di depurazione (ID) delle acque reflue rappresentano una delle vie attraverso le quali le MP migrano dall'ambiente terrestre a quello acquatico tramite lo scarico degli effluenti. Le MP rimosse dalle acque reflue si accumulano principalmente nei fanghi. Questa ricerca è incentrata sullo studio delle MP negli ID e sulla comprensione degli effetti dei processi di ossidazione avanzata (AOP) sulle MP come pretrattamento dei fanghi prima della digestione anaerobica. In questo studio, le concentrazioni e i meccanismi di rimozione delle MP negli ID sono stati indagati attraverso l'integrazione e l'analisi statistica di un database contenente informazioni da 488 ID riportati in letteratura. Gli ID raggiungono efficienze mediane di rimozione del 51%, 84% e 94% rispetto all'influente attraverso i trattamenti primari, secondari e terziari, rispettivamente. Le prove di ozonizzazione in batch sono state eseguite su campioni di acqua deionizzata e di fango sintetico addizionati con MP di LDPE, PA 6,6 e PP. Per i campioni d'acqua, 1 litro di acqua deionizzata contenente 100 mg di MP è stato esposto a dosi di ozono di 5, 10, 25 e 50 g O3/g MP. I test di ozonizzazione su fango sintetico sono stati condotti su 1 litro di fango addizionato con 100 mg di MP, con dosi di 25 e 50 g O3/g MP. Sebbene l'ozono (O3) non abbia causato una riduzione di massa delle MP, ha determinato un cambiamento nella loro struttura chimica avviando un processo di degradazione sulla superficie delle MP. L'analisi FTIR (spettroscopia infrarossa a trasformata di Fourier) ha mostrato un aumento dell'intensità della banda carbonilica (C=O), portando a valori crescenti dell'indice carbonilico (CI). La calorimetria a scansione differenziale (DSC) ha rivelato una diminuzione della cristallinità dei polimeri dopo l'ozonizzazione, determinando una potenziale diminuzione della resistenza meccanica delle MP.
Analysis of removal processes and effects of ozonation on microplastics in wastewater treatment plants: experimental and statystical results
Vicari, Ilaria
2023/2024
Abstract
Microplastics (MPs) pollution has emerged as one of the most prominent environmental issues over the last decade. Wastewater treatment plants (WWTPs) are one of the pathways through which MPs migrate from the terrestrial to the aquatic environment through effluent discharge. MPs removed from wastewater are mostly accumulated in sludge. This research is focused on studying the fate and removal of MPs in WWTPs and investigate the effects of advanced oxidation processes (AOPs) on MPs as a pretreatment before anaerobic digestion. In this study the concentrations and removal mechanisms of MPs in WWTPs are investigated through the integration and statistical analysis of a database containing information from 488 WWTPs reported in literature. WWTPs achieve median removal efficiencies of 51%, 84% and 94% with respect to the influent through primary, secondary and tertiary treatments, respectively. Ozonation batch tests were performed on deionized water and synthetic sludge samples spiked with LDPE, PA 6,6 and PP MPs. For water samples, 1 L of deionized water containing 100 mg of MPs was exposed to ozone doses of 5, 10, 25 and 50 g O3/g MPs. Ozonation tests on synthetic sludge were conducted on 1 L of synthetic sludge spiked with 100 mg of MPs, with doses of 25 and 50 g O3/g MPs. Although O3 did not cause a mass reduction of MPs, it determined a change in their chemical structure by initiating a degradation process on MPs surface. FTIR (Fourier Transform Infrared spectroscopy) analysis showed increasing intensity of the carbonyl (C=O) band, leading to increased values of the carbonyl index (CI). Differential scanning calorimetry (DSC) revealed a decrease in the crystallinity of polymers after ozonation, possibly determining reduced mechanical resistance of MPs.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/223676