Application of electrochemical oxidation in cold climate regions – Effect of temperature, pH and anode material on the degradation of Bisphenol A and the formation of disinfection by-products

This study assessed the feasibility of electrochemical oxidation (EO) for the removal of organic compounds in cold climate regions. A two-level full factorial design was used to test the effect of three factors, temperature (6/20 °C), anode material (Pt/BDD) and pH (7/10) on the degradation of Bisphenol A. Due to the use of a chloride electrolyte, the formation of the disinfection by-products, perchlorate and trichloromethane was assessed too. The 90 % removal of the initial Bisphenol A concentration took up to 71 % (30 min) longer and up to 46 % more power input was required at 6 °C than at 20 °C. At pH 10, degradation and formation kinetics of Bisphenol A and trichloromethane were faster due to the higher oxidation power of OCl- than HOCl (pKa = 7.5) and the formation of bisphenolate ions (pKa = 9.6), which are more prone to electrophilic attack than Bisphenol A. Temperature and anode material were the two factors that significantly affect the trichloromethane formation. Trichloromethane was formed up to 45 % faster at 20 °C than at 6 °C and up to 23 % faster on Pt than on BDD anodes. However, higher trichloromethane concentration were reached on BDD anodes, but were formed at slower rates. The anode material was the only factor, which had a statistically significant influence on for the formation of perchlorate. On BDD anode up to 89 % more perchlorate was formed than on Pt anode. The present study shows that the application of EO for organic pollutant removal in regions with low average temperatures is a feasible treatment step although it is associated with higher energy demand and consequently higher costs. The formation of unwanted disinfection by-products in chloride containing waters could not be avoided, but it was shown in this study, that it can be limited by an adequate choice of treatment time, pH and anode material.