Methyl-, Ethyl-, Propyl-, Butyl-, & Benzyl-paraben degradation is investigated by combination of ZnO-based photo-catalysis and ozonation in a batch cylindrical photo-reactor to evaluate the influence of ZnO concentration, ozone dose, and pH. The results reveal that parabens removal increases by rising the ozone dosage up to 1.8 g/h and ZnO loading climb up to 1 g/L. Optimum pH value for parabens removal is 9, in 1 g/L of ZnO and 1.1 g/h of ozone dose in 20 min reaction time, which leads to complete removal of methyl-paraben by the combined photocatalytic ozonation (O-3/UV/ZnO). (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.