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 (O 3 ) 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 )/( n φ + 1), which can be used to accurately predict the removal of micropollutants during ozonation of wastewater.