On the role of Graphene Oxide/Titania catalyst, visible LED and ozone to remove mixtures of pharmaceutical contaminants from water and wastewater
A mixture of eight contaminants of emerging concern (CECs), most of them of pharmaceutical origin: Acetaminophen, Antipyrine, Caffeine, Hydrochlorothiazide, Sulfamethoxazole, Ketorolac, Metoprolol, and Diclofenac have been treated with some advanced oxidation processes (AOP) involving ozone, visible LED radiation and a graphene oxide/titania catalyst (GO/TiO2). Variables that affect the process rate: visible LED radiation fluency, catalyst concentration and percentage of graphene oxide on the catalyst were optimized through a factorial design taking TOC as objective function. These variables were found to be: 303 W m-2, 0.4 g L-1, 1.5% GO loading, respectively, and tested in CEC doping wastewater. Application of gas-liquid absorption kinetics allows the kinetic regime of ozone reactions and the relative importance of mass transfer and chemical reactions be determined. Two reaction periods were observed: an initial one of less than 20 minutes where contaminants are removed mainly through direct reactions with ozone and a second one, where free radical oxidation predominates. In this second period, hydroxyl radical concentrations for ozonation and photocatalytic ozonation were found to be 1.1 and 3.2 x 10-13 M, respectively.