Kinetics of photocatalytic reduction of nitrate in synthetic and real effluent using TiO2 doped with Zn as photocatalyst

BACKGROUND The main industries that contribute to the presence of nitrate in water are the production of fertilizers, explosives, pulp and paper, and food products. Nitrate removal by filtration and advanced biological processes can be costly and generate unwanted waste. The catalytic photoreduction of nitrate to N2 has recently been proposed. However, most studies do not address the kinetic aspects of the reactions. RESULTS The kinetics model of Langmuir–Hinshelwood for nitrate photoreduction in the presence of formic acid in aqueous solution and in real industrial effluent using ZnO-TiO2 as the photocatalyst was proposed and adjusted to the experimental data obtained for a synthetic effluent (R2 = 0.991; apparent constant of the reaction was k′R = 0.226 mg N (mg C min)−1). After adaptation the model was used to predict the reaction time required to remove a given concentration of nitrate from the effluent produced by a slaughterhouse (k″R = k′R/2). CONCLUSION The proposed kinetic model can be applied to any type of effluent, promoting the possibility of production of high quality reuse water, reduction of fresh water consumption, reduction of discharge of pollutants discharged in water bodies, hence promoting the preservation of the environment. © 2014 Society of Chemical Industry