Removal and recovery of phosphate from municipal wastewaters using a polymeric anion exchanger bound with hydrated ferric oxide nanoparticles

A new type of ion exchange media which is highly selective for phosphate, and can be easily regenerated has been investigated. The media consists of hydrated ferric oxide nanoparticles dispersed within the pore structures of polymeric anion exchanger beads. The media combines the durability and mechanical strength of ion exchange resins with the high sorption capacity of ferric oxide for phosphate. The media was trialled in fixed bed mini column experiments with real final effluent from two UK sewage treatment works, one with treatment based on chemical precipitation with iron chloride salts into an activated sludge process (population >250,000), and one based on trickling filter treatment with no specific phosphorus removal process (population <10,000). Results show that the media has high capacity for removing phosphate, reaching capacity at 4000 and 1300 bed volumes for the chemical precipitation and trickling filter works respectively, with performance greatly exceeding that of a standard anion exchanger, Amberlite IRA-410. Also trialled was the media's ability to elute the phosphorus after breakthrough, with the aim of recovering and processing it into a useful product. A one step regenerative process using a single solution containing 4% NaOH and 2% NaCl was passed through the resin bed and the phosphorus concentration of each bed volume leaving the column analysed. 80% of the phosphorus was eluted in the first bed volume. Subsequent tests investigated the performance of the media after successive partial regenerations of one bed volume of the NaOH/NaCl solution. There was no loss of performance observed after ten regeneration cycles, and levels of eluted phosphate were consistently high. These results suggest that the media has high potential for the removal and recovery of phosphate from wastewater streams. Additionally, the small volume of regenerant required translates to a very small operational footprint.