Importance of Chain Length in Propagation Reaction on •OH Formation during Ozonation of Wastewater Effluent

During the ozonation of wastewater, hydroxyl radicals (^•OH) induced by the reactions of ozone (O₃) with effluent organic matters (EfOMs) play an essential role in degrading ozone-refractory micropollutants. The ^•OH yield provides the absolute ^•OH formation during ozonation. However, the conventional "tert-Butanol (t-BuOH) assay" cannot accurately determine the ^•OH yield since the propagation reactions are inhibited, and there have been few studies on ^•OH production induced by EfOM fractions during ozonation. Alternatively, a "competitive method", which added trace amounts of the ^•OH probe compound to compete with the water matrix and took initiation reactions and propagation reactions into account, was used to determine the actual ^•OH yields (Φ) compared with that obtained by the "t-BuOH assay" (φ). The Φ were significantly higher than φ, indicating that the propagation reactions played important roles in ^•OH formation. The chain propagation reactions facilitation of EfOMs and fractions can be expressed by the chain length (n). The study found significant differences in Φ for EfOMs and fractions, precisely because they have different n. The actual ^•OH yield can be calculated by n and φ as Φ = φ (1 + n)/(nφ + 1), which can be used to accurately predict the removal of micropollutants during ozonation of wastewater.