The anodic oxidation is one of the wastewater treatments most commonly used in the removal of industrial pollutants. The process can be performed individually or, thanks to its versatility, in combination with other treatments. The mechanism stimulates the release of hydroxyl radicals on the surface of the anode, which react with the contaminant molecules breaking up and/or mineralizing them. There are many studies in literature that analyse the anodic oxidation treatment, also considering the combination of the anodic oxidation and biological treatment to keep high removal rates while containing the operating costs. However, the available literature about the application of this combined treatment to effluents featuring high concentration of oils, detergents and recalcitrant organic compounds is still rather poor. This study explores the efficiency of the anodic oxidation performed in combination with the biological treatment on real wastewater containing high concentration of surfactants. Different type of anodes has been considered, but the best performance was achieved by coupling BDD (Boron-doped diamond) as anode with a stainless-steel cathode. Different operating conditions were investigated: treatment duration, current intensity, and electrolyte concentration; as a result, the optimal configuration of the cell was identified for 50-75 mA, 20 g/L of Na2SO4 as supporting electrolyte and 2 hours of treatment. With this optimal set-up, biodegradability in terms of BOD5/COD was raised for the considered effluent from 0.07 to 0.47-0.53. Similar results were also obtained for other wastewaters coming from similar industrial conditions. Furthermore, the actual application of bioremediation to the pre-treated effluent yielded an overall COD reduction of about 72%, with 2 hours of anodic treatment and 5 days of biological treatment. Hence, the combined processes could be a promising way for the efficient treatment of surfactants-rich, refractory wastewaters from industrial processes.
L’ossidazione anodica (anodic oxidation, AO) è uno dei trattamenti elettrochimici maggiormente impiegati nella rimozione di inquinanti dalle acque e risulta essere un’ottima soluzione al fine di trattare o pretrattare reflui industriali; essa, infatti, attraverso la liberazione di radicali OH* che reagiscono con le molecole inquinanti, riduce il carico inquinante e contemporaneamente rende biodegradabili molte sostanze tipicamente recalcitranti per i processi biologici. Il trattamento anodico può essere operato singolarmente oppure associato ad altri processi, tra cui il trattamento biologico (biological treatment, BT); nonostante ci siano molti riscontri nella letteratura su tale accoppiamento, esso non risulta ancora studiato per reflui ad alte concentrazioni di oli, detergenti e composti organici originariamente tossici per la biomassa. L’obiettivo di questa tesi è stato quindi quello di valutare l’efficienza di un trattamento combinato AO+BT su reflui contenenti composti organici refrattari e alte concentrazioni di tensioattivi. È stato studiato l’effetto di tipologie diverse di anodi e di elettroliti sull’efficienza di abbattimento del processo; una volta individuata la combinazione anodo-elettrolita più performante, il trattamento è stato ottimizzato rispetto ai parametri di intensità di corrente, durata di trattamento e concentrazione di elettrolita. I risultati hanno evidenziato una regione di ottimo in termini di efficienza di abbattimento nell’intervallo 50-75 mA. L’elettrolita in grado di fornire l’abbattimento maggiore è risultato essere una soluzione acquosa di Na2SO4, in concentrazione pari a 20 g/L. Selezionando i parametri ottimali è stato raggiunto un abbattimento di carico inquinante con la sola ossidazione anodica del 30% e un incremento della biodegradabilità in termini di rapporto BOD5/COD compreso tra 0.47 e 0.53, partendo da un valore iniziale di 0.07. Il trattamento biologico a valle dell’ossidazione anodica ha confermato i valori teorici ottenuti, mostrando un abbattimento complessivo del processo AO+BT del 72% di carico inquinante dopo soli 5 giorni di trattamento biologico.
Trattamento di acque di sgrassaggio industriali mediante metodi combinati elettrochimici e biologici
TRUSCELLO, MAURIZIO
2020/2021
Abstract
The anodic oxidation is one of the wastewater treatments most commonly used in the removal of industrial pollutants. The process can be performed individually or, thanks to its versatility, in combination with other treatments. The mechanism stimulates the release of hydroxyl radicals on the surface of the anode, which react with the contaminant molecules breaking up and/or mineralizing them. There are many studies in literature that analyse the anodic oxidation treatment, also considering the combination of the anodic oxidation and biological treatment to keep high removal rates while containing the operating costs. However, the available literature about the application of this combined treatment to effluents featuring high concentration of oils, detergents and recalcitrant organic compounds is still rather poor. This study explores the efficiency of the anodic oxidation performed in combination with the biological treatment on real wastewater containing high concentration of surfactants. Different type of anodes has been considered, but the best performance was achieved by coupling BDD (Boron-doped diamond) as anode with a stainless-steel cathode. Different operating conditions were investigated: treatment duration, current intensity, and electrolyte concentration; as a result, the optimal configuration of the cell was identified for 50-75 mA, 20 g/L of Na2SO4 as supporting electrolyte and 2 hours of treatment. With this optimal set-up, biodegradability in terms of BOD5/COD was raised for the considered effluent from 0.07 to 0.47-0.53. Similar results were also obtained for other wastewaters coming from similar industrial conditions. Furthermore, the actual application of bioremediation to the pre-treated effluent yielded an overall COD reduction of about 72%, with 2 hours of anodic treatment and 5 days of biological treatment. Hence, the combined processes could be a promising way for the efficient treatment of surfactants-rich, refractory wastewaters from industrial processes.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/179455