Removal of Ammonia by OH Radical in Aqueous Phase Li Huang Liang Li Wenbo Dong Yan Liu Huiqi Hou 10.1021/es8008216.s001 https://acs.figshare.com/articles/journal_contribution/Removal_of_Ammonia_by_OH_Radical_in_Aqueous_Phase/2904142 Many advanced oxidation technologies have been developed to remove ammonia in wastewater. All these technologies have one common characteristic, that is, the removal processes involve OH radical (•OH). In this research work, H<sub>2</sub>O<sub>2</sub> was selected as •OH precursor. The removal of ammonia under 253.7 nm irradiation from low-pressure mercury lamp in the presence of H<sub>2</sub>O<sub>2</sub> was studied to investigate the ammonia removal efficiency by •OH. Results show that the •OH, generated by H<sub>2</sub>O<sub>2</sub> photolysis, could oxidize NH<sub>3</sub> to NO<sub>2</sub><sup>−</sup> and further to NO<sub>3</sub><sup>−</sup>. Removal efficiencies of ammonia were low and were affected by initial pH value and ammonia concentration. Laser flash photolysis technique with transient absorption spectra of nanosecond was used to investigate the oxidation pathway and kinetics of ammonia oxidation by •OH. Results illustrate that •OH could oxidize NH<sub>3</sub> to form •NH<sub>2</sub> with a second-order rate constant of (1.0 ± 0.1) × 10<sup>8</sup> M<sup>−1</sup> s<sup>−1</sup> (20 °C). •NH<sub>2</sub>, the main product of •OH with NH<sub>3</sub>, would further react with H<sub>2</sub>O<sub>2</sub> to yield •NHOH. Since <sup>•</sup>NHOH could not stay stable in solution, it would rapidly convert to NH<sub>2</sub>O<sub>2</sub><sup>−</sup> and consequently NO<sub>2</sub><sup>−</sup> and NO<sub>3</sub><sup>−</sup>. The rate constants for these elementary reactions were also given. The low removal efficiency of ammonia by •OH was mainly due to the slow reaction rate constant. 2008-11-01 00:00:00 ammonia removal efficiency OH H 2O photolysis laser flash photolysis technique H 2O NHOH 253.7 nm irradiation oxidize NH 3