Photochemical Formation of Hydroxyl Radical from Effluent Organic Matter: Role of Composition

The photochemical formation of hydroxyl radical (HO•) from effluent organic matter (EfOM) depends upon the chemical properties of this heterogeneous mixture. In this study, two EfOM samples collected from wastewater treatment plants (WWTP A and B) were fractionated by both hydrophobicity (bulk and non-humic) and apparent molecular weight (AMW). The apparent quantum yield for HO• formation (ΦHO•) and the maximum fluorescence quantum yield (ΦF) were subsequently measured for each subfraction. The formation rates of HO• (considering only the hydrogen-peroxide-independent pathways) for the bulk waters were 4.8 × 10–10 and 9.6 × 10–11 M s–1 for WWTP A and B, respectively. For the AMW fractions, the values of ΦHO• increased as the AMW of the material decreased. For the WWTP A sample, the ΦHO• increased from 2.54 × 10–4 (bulk water) to 6.29 × 10–4 for the <1 kDa fraction, and for the WWTP B sample, the value of ΦHO• increased from 6.50 × 10–5 for bulk water to 3.45 × 10–4 for the <1 kDa fraction. In the case of ...