Phosphate recovery from waste water treatment plant by commercial ion exchangers: Characterization and modelling

Abstract

In the last years were performed a huge number of research related to phosphorus removal and recovery from waste water in order to reuse this element and also to avoid eutrophication. Among the different techniques studied, adsorption is nowadays one of the most interesting alternatives. The aim of this project is to characterize the overall adsorption performance of two commercial ion exchangers, the resin Lewatit FO36 and the fibre Fiban-As (FAs), both prepared for arsenic selective adsorption but, due to their chemical similarity, can be also used for phosphate adsorption. Equilibrium and kinetics studies were performed through the batch experiments and the dynamic studies were carried out by the fixed-bed column experiments. The experimental study covered from the most simple monocomponent synthetic water (phosphate) to the complex real water from waste water treatment plant (WWTP). Equilibrium experimental data was well described by Langmuir isotherm and reported sorption capacities between 89 and 163 mg/g and the effect of interfering anions on sorption capacity was evaluated through factorial experiments concluding that both sorbents are highly selective to phosphate compared with bicarbonate, sulphate, nitrate and chloride. Furthermore, the sorption kinetic for both sorbents is controlled by the particle diffusion stage and follows a pseudo second order reaction model. The efficiency in the phosphate removal was described by Thomas, Yoon-Nelson and Bed Time Service Time model reporting capacities between 31 and 5 mg/g. Finally, the adsorbate regeneration efficiency was evaluated by five sorption cycles obtaining good results in the case of the fibre Fiban-As and a decrease of more than 60% of phosphate adsorption capacity in the first regeneration for resin FO36.