Atrazine removal by ozonation processes in surface waters

Atrazine (6-chloro-N-ethyl-N'-isopropyl-1,3,5-triazinedyl-2,4-diamine) was treated with ozone alone and in combination with hydrogen peroxide or UV radiation in three surface waters. Experiments were carried out in two bubble reactors operated continuously. Variables investigated were the ozone partial pressure, temperature, pH, mass flow ratio of oxidants fed: hydrogen peroxide and ozone and the type of oxidation including UV radiation alone. Residence time for the aqueous phase was kept at 10 min. Concentrations of some intermediates, including deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine, were also followed. The nature of water, specifically the alkalinity and pH were found to be important variables that affected atrazine (ATZ) removal. Surface waters with low alkalinity and high pH allowed the highest removal of ATZ to be reached. There was an optimum hydrogen peroxide to ozone mass flow ratio that resulted in the highest ATZ removal in each surface water treated. This optimum was above the theoretical stoichiometry of the process. Therefore, to reach the maximum removal of ATZ in a O3/H2O2 process, more hydrogen peroxide was needed in the surface waters treated than in ultrapure water under similar experimental conditions. In some cases, UV radiation alone resulted in the removal of ATZ higher than ozonation alone. This was likely due to the alkalinity of the surface water. Ozonation and UV radiation processes yield different amounts of hydrogen peroxide. Combined ozonations (O3/H2O2 and O3/UV) lead to ATZ removals higher than single ozonation or UV radiation but the formation of intermediates was higher.