Ion exchange nutrient recovery from anaerobic membrane bioreactor permeate

• Published in: Water environment research 2019-07, Vol.91 (7), p.606-615
• Main Authors: Mullen, Patrick, Venkiteshwaran, Kaushik, Zitomer, Daniel H., Mayer, Brooke K.
• Format: Article
• Language: English
• Subjects: Ammonium; Ammonium compounds; Anaerobic treatment; Anion exchange; Anion exchanging; Anions; Bioreactors; Brines; Chemical precipitation; clinoptilolite; Copper; Cycles; Exchange capacity; Ferric oxide; Hematite; hydrated ferric oxide (HFO); Ion exchange; Leaching; Mineral nutrients; Municipal wastewater; Nutrient loading; Nutrient removal; Nutrients; Phosphate; Phosphates; phosphorus; Ratios; Recovery; Regeneration; Regeneration (biological); Removal; Resins; Sodium chloride; Sodium hydroxide; Struvite; Wastewater; Wastewater treatment; Water reclamation; zeolite
• ISSN: 1061-4303; 1554-7531
• DOI: 10.1002/wer.1080

Nutrient recovery from municipal wastewater was evaluated using anion exchange media loaded with hydrated ferric oxide (HFO) and copper (Cu2+) (Dow‐HFO‐Cu resin) to selectively capture phosphate, followed by clinoptilolite for ammonium removal and recovery. Nutrients were concentrated in the regenerants and recovered as precipitated struvite. Media exchange capacity after multiple ion exchange cycles was determined using permeate from an anaerobic membrane bioreactor (AnMBR) treating synthetic or actual municipal wastewater from a full‐scale water reclamation facility. Regeneration through five ion exchange cycles using relatively low concentration regenerant solution (2% NaCl and 0.5% NaOH) resulted in the highest phosphate exchange capacity and phosphate recovery. This regenerant also provided the most consistent ammonium recovery. Column tests treating AnMBR permeate were performed over five ion exchange cycles; Dow‐HFO‐Cu resin exchange capacities ranged from 1.6 to 2.8 mg PO4‐P/g dry media. A maximum of 94% of the removed phosphate was recovered during regeneration. The rate and extent of regeneration was insensitive to regenerant salt concentrations in the range investigated. Precipitation using a mixture of the spent regeneration brines from the Dow‐HFO‐Cu resin and clinoptilolite columns produced low molar ratios of Mg:NH4:PO4, suggesting that the recovered product was not pure struvite. Practitioner points Ion exchange‐precipitation for the removal and recovery of PO43− and NH4+ from AnMBR permeate is a promising technology. 2% NaCl + 0.5% NaOH regeneration solution provided the most consistent exchange performance for both phosphate and ammonium recovery. Regenerated Dow‐HFO‐Cu resin exchange capacity was consistently less than the virgin resin, likely due to copper leaching during regeneration. Molar ratios in the precipitates suggested that the precipitated material was not pure struvite. Nutrient recovery process diagram using results from lab‐scale AnMBR treating synthetic wastewater followed by ion exchange.