Demonstration of ion exchange technology for phosphorus removal and recovery from municipal wastewater

Abstract

• HAIX removed 90% of the PO 4 -P for 430 BV at 5 min EBCT. • HAIX removed 26% of the COD but it resulted in progressive fouling of the resin. • A regeneration with NaCl 5% is needed to maintain high adsorption capacity. • NaOH 2% can be used as regenerant solution for eight consecutive times. • Around 95% of the P was recovered from saturated NaOH as hydroxyapatite. Orthophosphate (PO 4 -P) removal and recovery from municipal wastewater were investigated in a 10 m 3 /day hybrid anion exchanger (HAIX) demonstration plant. To date, HAIX resins have been investigated for PO 4 -P removal at laboratory scale with promising results but there is a need to investigate the application of the technology at larger scale, over extended operation whilst establishing an efficient regenerant management solution. The HAIX removed an average of 6 mg PO 4 -P /L to > 0.3 mg PO 4 -P/L, within 430 bed volumes, with a capacity of 4.1 mg PO 4 -P/g resin. To manage the regenerant (NaOH 2%) efficiently, this was reused up to 8 times, reaching 785 mg PO 4 -P/L, but the adsorption capacity was compromised, and it decreased to 1.5 mg PO 4 -P/g resin. By adding calcium hydroxide to the saturated NaOH, 95% of the PO 4 -P was recovered as hydroxyapatite, and at the same time the regeneration effectiveness was re-established, as < 0.3 mg PO 4 -P/L was reached again in the effluent. The treated NaOH was reused as regenerant solution, ensuring high effluent quality of < 0.2 mg PO 4 -P/L. This study confirmed the capability of HAIX technology to remove and recover PO 4 -P from wastewater offering a solution which ensures both a high effluent quality and a circular economy approach.