The use of electrochemical oxidation methods has attracted interest over the years due to its high degradation efficiency of a wide variety of organic pollutants and its environmental compatibility. In this thesis work, the degradation of gallic acid and two surfactants, genapol X80 and cocamide DEA, through electrochemical anodic oxidation is studied using a boron-doped diamond layer deposited on a titanium substrate as the working electrode. The pollutants degradation, with a starting concentration of 100 ppm, was evaluated during two hours of treatment under different operating conditions, namely by varying the concentration of Na2SO4 (chosen as electrolyte) in the range 16-20 g/l and by applying different currents (30-50 mA), using a potentiostat-galvanostat device connecting a reference electrode (Ag/AgCl) and steel plate counter electrode. HPLC analysis of the treated solutions evidenced that, at the end of the degradation, the maximum removal rates of gallic acid, cocamide and genapol which are respectively of 55%, 79.6% and 87.2%, are reached with the lowest electrolyte concentration of 16 g/l and by applying a current of 50mA. According to these initial results, further degradation of the three pollutants was performed to evaluate the trend of chemical and biochemical oxygen demand, pH and conductivity. The analyses carried out with COD and BOD kits showed that gallic acid provided the highest COD and BOD reduction compared to those of the two surfactants, despite having a lower removal yield. Regarding the pH and conductivity, the variation during degradation is evaluated with respect to untreated solutions. It was shown that conductivity is essentially unaffected during the treatment, while pH is reduced during gallic acid oxidation, probably due to the formation of more acidic intermediates. These results suggest that a biological treatment is possible and desirable downstream the electrochemical process to achieve a higher purification of the wastewater and to minimize operating costs, considering the high energy consumption that would occur using only the electrochemical process.
L’utilizzo dei metodi di ossidazione elettrochimica ha suscitato interesse negli anni a causa della sua alta efficienza di degradazione di un’ampia varietà di inquinanti organici e della sua compatibilità ambientale. In questo lavoro di tesi viene studiata la degradazione dell’acido gallico e di due tensioattivi, genapol X80 e cocammide DEA, mediante ossidazione anodica elettrochimica, utilizzando diamante drogato con boro depositato su substrato di titanio come elettrodo di lavoro. La degradazione degli inquinanti, con concentrazione iniziale di 100 ppm, è stata valutata durante due ore di trattamento a diverse condizioni operative: variando la concentrazione di Na2SO4 (scelto come elettrolita) nell’intervallo 16-20g/l e applicando correnti differenti (30-50mA), utilizzando un dispositivo potenziostato-galvanostato collegante un elettrodo di riferimento (Ag/AgCl) e un controelettrodo in acciaio. L’analisi HPLC delle soluzioni trattate ha evidenziato che, al termine della degradazione, le massime percentuali di abbattimento del gallico (55%), cocammide (79.6%) e genapol (87.2%) vengono raggiunte con la concentrazione di elettrolita più bassa e applicando una corrente di 50mA. In base a questi primi risultati, è stata eseguita un’ulteriore degradazione dei tre inquinanti per valutare l’andamento della domanda chimica e biochimica di ossigeno, pH e conducibilità. Le analisi effettuate con kit di COD e BOD hanno evidenziato che il gallico ha fornito la più alta riduzione di COD e BOD, rispetto a quelle dei due tensioattivi, pur avendo una percentuale di abbattimento inferiore. Per il pH e la conducibilità, viene valutata la variazione durante la degradazione rispetto alle soluzioni non trattate. È stato dimostrato che la conducibilità è inalterata, mentre il pH si riduce durante l’ossidazione del gallico, probabilmente a causa della formazione di intermedi più acidi. Questi risultati suggeriscono che un trattamento biologico è auspicabile a valle del processo elettrochimico per ottenere una maggiore depurazione dei reflui e per minimizzare i costi operativi, considerando l’elevato consumo energetico che si verificherebbe utilizzando solo il processo elettrochimico.
Degradation of organic pollutants and surfactants through electrochemical anodic oxidation processes
Regazzi, Francesca
2019/2020
Abstract
The use of electrochemical oxidation methods has attracted interest over the years due to its high degradation efficiency of a wide variety of organic pollutants and its environmental compatibility. In this thesis work, the degradation of gallic acid and two surfactants, genapol X80 and cocamide DEA, through electrochemical anodic oxidation is studied using a boron-doped diamond layer deposited on a titanium substrate as the working electrode. The pollutants degradation, with a starting concentration of 100 ppm, was evaluated during two hours of treatment under different operating conditions, namely by varying the concentration of Na2SO4 (chosen as electrolyte) in the range 16-20 g/l and by applying different currents (30-50 mA), using a potentiostat-galvanostat device connecting a reference electrode (Ag/AgCl) and steel plate counter electrode. HPLC analysis of the treated solutions evidenced that, at the end of the degradation, the maximum removal rates of gallic acid, cocamide and genapol which are respectively of 55%, 79.6% and 87.2%, are reached with the lowest electrolyte concentration of 16 g/l and by applying a current of 50mA. According to these initial results, further degradation of the three pollutants was performed to evaluate the trend of chemical and biochemical oxygen demand, pH and conductivity. The analyses carried out with COD and BOD kits showed that gallic acid provided the highest COD and BOD reduction compared to those of the two surfactants, despite having a lower removal yield. Regarding the pH and conductivity, the variation during degradation is evaluated with respect to untreated solutions. It was shown that conductivity is essentially unaffected during the treatment, while pH is reduced during gallic acid oxidation, probably due to the formation of more acidic intermediates. These results suggest that a biological treatment is possible and desirable downstream the electrochemical process to achieve a higher purification of the wastewater and to minimize operating costs, considering the high energy consumption that would occur using only the electrochemical process.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/170939