Strategic phosphate removal/recovery by a re-usable Mg–Fe–Cl layered double hydroxide

Excess phosphorus (P) in freshwater bodies is one of the major causes of eutrophication. The regulations for removing phosphate from wastewater treatment plant (WWTP) are becoming more stringent and thus the alternative technologies are sought to enhance the P removal efficiency. In this study, Mg–Fe–Cl based layered double hydroxide (LDH) compounds were synthesized and used for phosphate removal. Implementing LDH as a tertiary treatment process for the removal and recovery of phosphate is proposed. Results show that LDH dosage of 2 g/l can reduce phosphate concentration down to 0.1 mg/l from an initial value of 10 mg/l at an equilibrium contact time of 2 and 3 h, respectively. The adsorption kinetics of phosphate onto Mg–Fe–Cl LDH is well governed by the pseudo-second-order kinetic model, and adsorption data fit well to the Langmuir and Freundlich isotherms. The study on pH effect of adsorbate solution suggested that pH range between 3–7.5 is suitable for unaffected phosphate removal. The repeated use of this LDH by both batch and fixed bed column experiment showed that total phosphate reduction was about 95% and desorption percentage was about 91% through six cycles of adsorption–desorption processes. It is likely that this LDH compounds can be applied to remove and recover phosphate from secondary effluent of domestic wastewater treatment plant and thereby, to meet future stringent discharge regulations.