Ion exchange columns. A promising technology for nitrogen and phosphorus recovery in the main line of a wastewater treatment plant.

Abstract

Anaerobic membrane bioreactor (AnMBR) technology has great advantages for treating urban wastewaters, but, when irrigation cannot be applied and the effluent is discharged in a sensitive zone, a post-treatment of this effluent is needed for nitrogen and phosphorus removal. Under this scenario, ion exchange processes represent one of the most promising technologies for treating this effluent. Ion exchange technology allows to meet discharge limits and to recover these nutrients in a highly concentrated stream. In this work, the technical feasibility of using a commercial resin for phosphorus recovery and a natural zeolite (clinoptilolite) for nitrogen recovery was evaluated. Purolite FerrIX A33E resin removed phosphate from the AnMBR permeate within 500 Bed Volumes (BVs) with a maximum adsorption capacity (q_max) of 2,1 mg P-PO₄/g resin. Regeneration of the resin (2% NaOH 2% NaCl) recovered over 95% of the phosphorous retained, achieving a concentration of 316,7 mg P-PO₄/L in the regeneration solution. In the absence of a long-term study, the resin showed a stable adsorption capacity during 16 cycles of saturation-regeneration. Clinoptilolite removed nitrogen within 139 BVs obtaining a q_max of 3,68 mg N-NH4/g zeolite. 97 % of the retained N-NH₄ was recovered in the regeneration stage (0,8% NaOH) with an average concentration of 577 mg N-NH₄/L. Continuous exposure of the zeolite to alkaline solutions led to reduction of 50% of the adsorption capacity after 17 cycles.