Phosphate Removal Through Nano-Zero-Valent Iron Permeable Reactive Barrier; Column Experiment and Reactive Solute Transport Modeling

Abstract

This study investigates the efficacy of nano-zero-valent iron (nZVI) permeable reactive barriers (PRBs) as an in situ phosphate removal method. Batch equilibrium experiments were conducted to determine maximum adsorption capacity of nano-iron particles for phosphate to be 54.34 mg-P/g-Fe. Short-term experiment was performed for a period of a month through three sandy soil columns with different configurations of nZVI reactive layers. Initial concentration of 25 (PO4–P) mg/L was introduced to the columns, while effluent samples were collected for analysis. Numerical model was developed to simulate the 1-D advective–dispersive reactive transport of phosphate through the porous media in the three columns. Sensitivity analysis of model parameters was performed, expressed by the change in the effluent concentration with respect to variation in the value of model critical parameters. Optimization of transport process in columns was based on minimizing the sum of squared error values between measured and predicted effluent concentration. Phosphate breakthrough curves implied that Column 2 (C2) with two reactive layers showed a slight better performance in phosphate removal than Column 1 (C1) with maximum efficiency of 98.9% after only 17 h from the beginning of the experiment, whereas phosphate concentration in Column 3 (C3) reached the full saturation by the 9th day. The model verification with experimental data showed a reasonable agreement with a correlation coefficient (R2) ranging from 0.97 to 0.99. The results in this study confirmed that such presented model can be used for the promotion of the preliminary design of PRBs.