Influence of Molecular Size on the Electrochemical Oxidation of Fractioned Cork Boiling Wastewater

Abstract

The performance of electrochemical oxidation (EO) using a boron doped diamond (BDD) anode was assessed for cork boiling wastewater (CBW) molecular size fractions of > 100 kDa, 50-100 kDa, 20-50 kDa, 10-20 kDa and < 10 kDa, obtained through sequential use of ultrafiltration (UF) membranes. The best EO results were found in the experiments performed with no addition of supporting electrolyte and at the lowest applied stirring speed, the more economical and environmentally friendly conditions. The highest EO treatment efficiency was observed for the fraction > 100 kDa, which presented also the highest organic load. EO treatment led to an increase in the biodegradability of the fraction > 100 kDa and to a decrease in the biodegradability of the fraction < 10 kDa. Moreover, samples toxicity was not affected by the EO process, suggesting that the treated samples can be forwarded to biological posttreatment processes. UF fractionation showed to be advantageous in combination with EO, since it enables the selective use of EO where it is more effective regarding biodegradability and current efficiency.be considered non-toxic, since the obtained values were 1.50 TU for F1 and 1.47 TU for F5. After the 8-h EO treatments, the toxicity was similar, with an LC 50 of 68.0 % (1.47 TU) for both fractions, F1 and F5.According to Canizares et al., [37] EO with BDD anodes allows the toxicity of aqueous wastes polluted with phenolic compounds to be reduced significantly, in spite of the variation of the toxicity with time be strongly dependent on the nature of the phenolic compounds, and especially on the substituent groups of the phenol molecule. In this work, this decrease in toxicity was not observed, mainly due to the molecular complexity of the fractions and, also, due to the existence of chloride in the initial samples. In fact, despite the low chloride concentration presented by the CBW fractions, perchlorate was formed during the EO assays, being its concentration after 8 h treatment, at 70 mA cm À 2 , of approximately 160 mg L À 1 , for both fractions F1 and F5. Chlorate ion was not detected after 8 h treatment and chloride concentration was below 1 mg L À 1 , meaning that organochloride compounds may have been formed. 4 5 6 7 8