Phosphate removal from water using alginate/carboxymethylcellulose/aluminum beads and plaster of paris

Phosphorus released in lakes due to agricultural water runoff causes eutrophication, deteriorating water quality and harming ecosystems. Two adsorbents were studied for the removal of phosphate from water: plaster of Paris powder and hydrogel beads produced using alginate, carboxymethylcellulose, and aluminum. The reaction kinetics, adsorption capacity, and ability to desorb were compared. Sorption of phosphate with either plaster of Paris or hydrogel beads was well described by the Langmuir model. In deionized water, hydrogel beads had a maximum sorption capacity of 90.5 mg  $$ /g dry bead with an equilibration time of approximately 24 hr. Monovalent anions (e.g., chloride) did not affect phosphorus sorption onto hydrogel beads, whereas divalent anions (e.g., sulfate) hindered sorption. In deionized water, plaster of Paris (POP) powder has a maximum capacity of 1.52 mg  $$ /g with an equilibrium time of less than 10 min. Sorbents can potentially be reused following phosphate desorption, and desorbed phosphate may be reused as fertilizer. At pH = 9.5, hydrogel beads desorbed up to 60% of the original amount of phosphate sorbed and lower amounts at lower pH. At pH = 2, POP powder desorbed only 35% of the initial phosphate sorbed, and desorption decreased with increasing pH. PRACTITIONER POINTS: The maximum sorption capacity of plaster of Paris is 1.52 mg  $$ /g. The maximum sorption capacity of hydrogel beads is 90.5 mg  $$ /g. Monovalent anions do not affect phosphorus sorption, and divalent anions hinder it by ≈36%. Sorption is well described by Langmuir isotherms (R²  > 0.98). Hydrogel beads desorb 60% of phosphorus at pH = 9, possibly allowing phosphorus reuse.