Photochemical Formation of Hydroxyl Radical from Effluent Organic Matter

The photochemical formation of hydroxyl radical (HO^•) from effluent organic matter (EfOM) was evaluated using three bulk wastewater samples collected at different treatment facilities under simulated sunlight. For the samples studied, the formation rates of HO^• (<i>R</i>^{HO^•}) were obtained from the formation rate of phenol following the hydroxylation of benzene. The values of <i>R</i>^{HO^•} ranged from 2.3 to 3.8 × 10^–10 M s^–1 for the samples studied. The formation rate of HO^• from nitrate photolysis (<i>R</i>_NO₃^{HO^•}) was determined to be 3.0 × 10^–7 M_HO^• M_NO₃^–1 s^–1. The HO^• production rate from EfOM (<i>R</i>_EfOM^{HO^•}) ranged from 0.76 to 1.3 × 10^–10 M s^–1. For the wastewater samples studied, <i>R</i>_EfOM^{HO^•} varied from 1.5 to 2.4 × 10^–7 M_HO^• M_C^–1 s^–1 on molar carbon basis, which was close to HO^• production from nitrate photolysis. The apparent quantum yield for the formation of HO^• from nitrate (Φ_{NO₃–HO^•}^<i>a</i>) was determined as 0.010 ± 0.001 for the wavelength range 290–400 nm in ultrapure water. The apparent quantum yield for HO^• formation in EfOM (Φ_{EfOM–HO^•}^<i>a</i>) ranged from 6.1 to 9.8 × 10^–5, compared to 2.99 to 4.56 × 10^–5 for organic matter (OM) isolates. The results indicate that wastewater effluents could produce significant concentrations of HO^•, as shown by potential higher nitrate levels and relatively higher quantum yields of HO^• formation from EfOM