Synthetic lepidocrocite for phosphorous removal from reclaimed water: optimization using convex optimization method and successive adsorption in fixed bed column

The batch and column experimental studies on the adsorption of phosphate onto synthetic lepidocrocite from reclaimed water are presented. A second-order polynomial model in the batch study is successfully applied to describe phosphate immobilization performance using the response surface methodology. The model proposed is further linked with the convex optimization method to determine the optimal variables for maximum phosphate uptake since convex method is a global optimization method. Consequently, under optimal parameters determined as pH of 3.88, an initial P concentration of 0.66 mg/L, and a dosage of 0.15 g, the corresponding phosphate removal efficiency can reach up to 97.4%. Adsorption behavior is further revealed by X-ray photoelectron spectroscopy observation and FTIR spectra. A comparative column study indicates that co-existing competing anions in artificial reclaimed water do not significantly interfere with P adsorption under the neutral condition. The experimental results highlight that synthetic lepidocrocite is an excellent absorbent for sustainable P removal from reclaimed water.