The present study investigated the kinetics and formation of hydroxylated and chlorinated intermediates during electrochemical oxidation of salicylic acid (SA). A chloride (NaCl) and sulfate (Na₂SO₄) electrolyte were used, along with two different anode materials, boron doped diamond (BDD) and platinum (Pt). Bulk electrolysis of SA confirmed the formation of both hydroxylated and chlorinated intermediates. In line with the density functional theory (DFT) calculations performed in this study, 2,5- and 2,3-dihydroxybenzoic acid, 3- and 5- chlorosalicylic acid and 3,5-dichlorosalicylic acid were the dominating products. In the presence of a chloride electrolyte, the formation of chlorinated intermediates was the predominant oxidation mechanism on both BDD and Pt anodes. In the absence of a chloride electrolyte, hydroxylated intermediates prevailed on the Pt anode and suggested the formation of sulfonated SA intermediates on the BDD anode. Furthermore, direct oxidation at the anode surface only played a subordinate role. First order kinetic models successfully described the degradation of SA and the formation of the observed intermediates. Rate constants provided by the model showed that chlorination of SA can take place at up to more than 60 times faster rates than hydroxylation. In conclusion, the formation of chlorinated intermediates during electrochemical oxidation of the organic model pollutant SA is confirmed and found to be dominant in chloride containing waters.

This study investigated the applicability of electrochemical oxidation for landfill leachate treatment in climate areas, where cold temperatures prevail (like Northern Norway). Experiments were completed with pre-treated (coagulation/flocculation and separation) landfill leachate at 6 and 20 °C in order to assess the temperature influence on the degradation of the organic pollutant Bisphenol A and the fate of the ordinary wastewater parameters COD and nitrate. Furthermore, two different anode materials (Ti/Pt and Nb/BDD) and three different current densities (10, 43 and 86 mA cm⁻²) were compared. Additionally, the formation of the two groups of disinfection by-products, trihalomethanes and perchlorate, was monitored. A 99% removal of Bisphenol A was confirmed at 6 °C on both tested anode materials, but a current density of at least 43 mA cm⁻² must be applied. Removal rates were on average 38% slower at 6 °C than at 20 °C. For comparison, Bisphenol A removal in clean electrolyte disclosed faster degradation rates (between 50 and 68%) due to absent landfill leachate matrix effects. The energy consumption for 99% Bisphenol A removal was 0.28 to 1.30 kWh m⁻³, and was on average 14% higher at 6 °C compared to 20 °C. Trihalomethanes were mainly formed on Pt anodes in the ppb range, while perchlorate was primarily formed at BDD anodes in the ppm range. Formation of disinfection by-products increased with increased applied current and temperature. Electrochemical oxidation was found to be a suitable treatment process for landfill leachate in cold climate areas by successfully meeting treatment goals. Graphic