Inhibition by dissolved organic matter of the degradation of purine compounds by the sulfate radical.

Dissolved organic matter (DOM) has been known to inhibit the degradation of compounds in advanced oxidation processes but quantitative understanding is lacking. Given the variable concentrations and properties of DOM in real aquatic systems, the concentration-dependent kinetics of compounds degradation were systematically investigated in the presence of 8 DOM isolates separately during UV/peroxydisulfate (UV/PDS) process. Due to the ubiquitous presence of purine compounds in aquatic environments, guanine was selected as a model purine compound. The concentration-dependent kinetics of guanine degradation exhibit consistent across all 8 DOM. The inhibition percentage (IP) exhibited an initial rapid enhancement with increasing DOM concentrations from ∼0 to 1.0 mg L⁻¹, following by a gradual rise at higher DOM concentrations (∼2.0-5.0 mg L⁻¹) among 8 DOM isolates. The elaborated kinetics model including radical oxidation and reverse-reduction process was then applied in this study, which successfully quantifies the contribution of guanine degradation. During UV/PDS process, the sum of [Formula: see text] and [Formula: see text] decreased with increasing DOM concentration among 8 DOM isolates. It shows minimal variation across different types of DOM at specific DOM concentrations. The contribution to (lack of) guanine degradation by reverse-reduction process (k) shows an initial significant increase followed by a gradual decrease with increasing DOM concentrations. The k values were found to differ significantly among 8 DOM isolates. The concentrations of DOM ([DOM]) at which the reverse reduction ratio is 50% were in the range of 0.14-0.88 mg L for 8 tested DOM. [DOM] values show negative correlations with specific absorbance at 254 nm (SUVA) (R = 0.70) or total antioxidant capacity (TAC) (R = 0.92), indicating that the overall reactivity between guanine's intermediate and DOM is mainly attributed to the aromatics and antioxidant moieties in DOM. The research findings have significant guiding implications for predicting the degradation rates of compounds in actual water and improving compounds removal efficiency.