Simultaneous sorption of orthophosphate and phosphonate from RO concentrate by kaolin/lanthanum carbonate composites: Experimental investigation and multi-objective artificial neural network modeling

Abstract

Orthophosphate and phosphonate are the main phosphorus (P) species in membrane concentrate, and they should be removed before discharge to prevent eutrophication in the aquatic environment. A variety of factors affect orthophosphate and phosphonate removal performance, while their contribution to the sorption process in the complex environment was not clear. In this study, the novel kaolin/lanthanum carbonate (KLC) composites were prepared for the simultaneous sorption of phosphate and phosphonate, and their surface morphology and crystal structure were characterized. The sorption kinetics and isotherms results indicated the competitive sorption of orthophosphate and phosphonate on the surface of KLC. The two phosphorus species’ maximum sorption capacities were both achieved at the equilibrium pH around 4.9, and the ionic strength showed negligible effect on their sorption capacity. The sorption capacities and rates were applied to explore the effects of sorbent dosage, pH and co-existing ions on the sorption process. To predict the simultaneous orthophosphate and phosphonate removal performance under different conditions, a multi-objective artificial neural network (ANN) model was established based on seven input variables (dosage, reaction time, pH, and concentrations of SO42-, HCO3-, Ca2+ and Mg2+). The model was trained with experimental data, and could well predict the orthophosphate and phosphonate removal efficiency. In addition, the relative significance of these variables was also evaluated. This study provides a reliable ANN model to predict simultaneous orthophosphate and phosphonate removal, and insights into factors for phosphorus removal by Lanthanum-based sorbent.