With the aim of optimizing the management of a Granular Activated Carbon (GAC) adsorption step, the removal of chloroform and tetrachloroethylene from groundwater by means of GAC filters has been studied using the Homogeneous Surface Diffusion Model, calibrated by adsorption isotherms, Short Bed Adsorber tests and kinetic batch tests. This has also allowed to compare the efficacy of various methods proposed in literature. Two types of GAC have been studied: a coal-based carbon and a coconut-shell carbon. Experimental results, validated by comparison with breakthorugh (BT) profiles observed on real scale filters, showed good predictive ability for chloroform only, characterized by a fast BT, very close to the ideal profile (average deviation between real and simulated profile from 22 to 41%). The best management method of GAC filters operating in parallel was searched evaluating EBCT (Empty Bed Contact Time) and filtration velocity (vF) values and replacement strategy, with the aim of minimizing operating costs and environmental impacts. The optimal configuration calculated for chloroform in terms of number and size of filters, is related to the feasible EBCT minimum values and vF maximum values; vice versa for tetrachloroethylene, representative of pollutants with long BT profiles. It was observed a reduction in costs, environmental impacts and time between two consecutive replacements by reducing the number of filters replaced simultaneously. At last, the presence of an air stripping step before GAC filters was assessed, proving economic benefits due to the increase of operating GAC life (reduction in operating costs up to 84%).
Ai fini dell’ottimizzazione gestionale di una sezione di adsorbimento su carbone attivo granulare (GAC, Granular Activated Carbon), è stato simulato il profilo di breakthrough (BT) di filtri GAC per la rimozione di cloroformio e tetracloroetilene da acqua di falda attraverso il modello Homogeneous Surface Diffusion Model, calibrato con isoterme di adsorbimento, Short Bed Adsorber tests e prove cinetiche in batch. Ciò ha anche permesso di confrontare l’efficacia delle varie metodologie proposte in letteratura. Sono stati utilizzati due tipi di GAC, rispettivamente di origine vegetale e minerale. I risultati sperimentali, validati per confronto con profili di BT osservati su filtri a scala reale, hanno evidenziato buona capacità previsionale per il solo cloroformio, caratterizzato da un profilo di BT ripido e prossimo all’ideale (scostamento medio tra profilo reale e simulato dal 22 al 41%). È stata inoltre ricercata la migliore metodologia di gestione operativa dei filtri GAC operanti in parallelo, in termini di valori di EBCT (Empty Bed Contact Time), velocità di filtrazione (vF) e strategia di sostituzione, in modo da minimizzare costi di esercizio ed impatti ambientali. Per il cloroformio, la configurazione ottimale per numero e dimensione dei filtri è legata ai minimi valori di EBCT ed alle massime vF consentite; viceversa per il tetracloroetilene, rappresentativo di inquinanti con profili di BT allungati. È stata osservata una diminuzione dei costi, degli impatti ambientali e dei giorni compresi tra due sostituzioni consecutive al diminuire del numero di filtri sostituiti contemporaneamente. È stata infine valutata la presenza di una fase di strippaggio a monte dei filtri GAC in relazione all’estensione della vita utile del GAC, evidenziando benefici economici (fino all’84% in meno dei costi di gestione).
Adsorbimento su carbone attivo granulare di microinquinanti organici : simulazione di processo e ottimizzazione delle prestazioni
CRIPPA, FEDERICO
2014/2015
Abstract
With the aim of optimizing the management of a Granular Activated Carbon (GAC) adsorption step, the removal of chloroform and tetrachloroethylene from groundwater by means of GAC filters has been studied using the Homogeneous Surface Diffusion Model, calibrated by adsorption isotherms, Short Bed Adsorber tests and kinetic batch tests. This has also allowed to compare the efficacy of various methods proposed in literature. Two types of GAC have been studied: a coal-based carbon and a coconut-shell carbon. Experimental results, validated by comparison with breakthorugh (BT) profiles observed on real scale filters, showed good predictive ability for chloroform only, characterized by a fast BT, very close to the ideal profile (average deviation between real and simulated profile from 22 to 41%). The best management method of GAC filters operating in parallel was searched evaluating EBCT (Empty Bed Contact Time) and filtration velocity (vF) values and replacement strategy, with the aim of minimizing operating costs and environmental impacts. The optimal configuration calculated for chloroform in terms of number and size of filters, is related to the feasible EBCT minimum values and vF maximum values; vice versa for tetrachloroethylene, representative of pollutants with long BT profiles. It was observed a reduction in costs, environmental impacts and time between two consecutive replacements by reducing the number of filters replaced simultaneously. At last, the presence of an air stripping step before GAC filters was assessed, proving economic benefits due to the increase of operating GAC life (reduction in operating costs up to 84%).File | Dimensione | Formato | |
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https://hdl.handle.net/10589/120084