Kinetic model-based optimization in electro-activated sulfite system for carbamazepine degradation: Aeration and multiple dosages of sulfite

Abstract

Electro-activated sulfite system (E-SO32−) was an emerging advanced oxidation technology, but its kinetics and process optimization have been overlooked. This study developed a first-principle kinetic model to investigate carbamazepine (CBZ) degradation and optimized this process by aeration and multiple dosages of SO32−. A low aeration rate (140 mL/min) remarkably accelerated sulfate radical (SO4•−) generation because of the enhanced rate of sulfite radical (SO3•−) reacting with oxygen. Thus, the degradation efficiency of CBZ improved from 71 % to 84 % and the electrical energy per order (EE/O) decreased from 4.55 to 2.32 kWh/m3/order at current density of 103 A/m2 and initial dosage of SO32− of 4 mM. However, further increasing the aeration rate diminished the enhancement of SO4•− generation rate due to the limited SO3•− generation, and excessive aeration resulted in decreased degradation efficiency and increased cost of aeration due to the direct oxidation of SO32− by oxygen. Consequently, matching of SO32− concentration, current density and aeration rate was crucial to maximize the generation rate of SO4•−. The most optimal strategy was at current density of 75 A/m2, aeration rate of 100 mL/min and SO32− concentration of 1.1 mM with multiple dosages. 95 % of CBZ was removed in 20 min, 18 % higher than that in single dosage. Finally, the optimal strategy for CBZ degradation was successfully applied in different water matrixes and real wastewater and well predicted by the kinetic model. Furthermore, degradation pathways of CBZ, including hydroxylation and deamidation, were elucidated from density functional theory and LC-MS detection. The toxicity of most intermediates decreased, while some intermediates possessed higher toxicity than CBZ. Overall, the firstly proposed combined strategy of aeration and multiple dosages of SO32− significantly facilitated the application of E-SO32− system in contaminants degradation.