Nutrient Recovery from Anaerobic Membrane Bioreactor Permeate Using ion Exchange

Phosphorus is a common element in wastewater streams and traditional treatment processes are often designed remove it to achieve low effluent limits. Such processes often do not often consider the potential value of the nutrient. Currently, production of phosphate fertilizers has dramatically risen causing concern for the depletion of phosphate rock reserves, bringing about exploration into alternative sources of phosphorus for agricultural use. Combining the needs of phosphorus removal from wastewaters and securing alternate sources of the nutrient provide an opportunity for recovery. This project evaluated a nutrient recovery process through ion exchange with beneficial recovery as precipitated struvite using novel anion exchange media loaded with hydrated ferric oxide (HFO) and copper (Cu2+) known in literature as Dow-HFO-Cu. Previous work has not defined the exchange capacity of the media through multiple exchange cycles nor has it been tested in permeates from anaerobic membrane bioreactors (AnMBR). Batch tests were done to determine the exchange capacity of the Dow-HFO-Cu media using different regeneration solutions. Regeneration using less alkaline solutions (pH=11) provided the highest overall exchange capacity of phosphate (PO43-) through 5 ion exchange cycles, with a regeneration solution of 2% NaCl + 0.5% NaOH providing the highest overall recovery. Column tests treating permeates from a lab-scale AnMBR were performed over 5 ion exchange cycles, resulting in exchange capacities of the Dow-HFO-Cu media to ranging from 1.6 to 2.8 mg PO4-P/g media. From the removed portion, recovery of PO4-P achieved 94% and 79% of the mass of PO4-P was recovered during regeneration for column tests using permeate from an anaerobic membrane bioreactor treating synthetic wastewater and real primary effluent, respectively. Ammonium (NH4+) ion exchange using the natural zeolite clinoptilolite in batch tests demonstrated that more dilute sodium chloride regenerant concentrations could achieve similar performance to higher concentration solutions. Column tests of NH4+ removal showed decreased performance compared to batch tests as influent wastewater characteristics such as organic matter likely reduced exchange capacity. Precipitation tests using the regeneration eluate from anion and cation columns produced low molar ratios of Mg:NH4:PO4 with the best resulting ratio of 0.8:0.1:0.9, suggesting that the recovered product may not be struvite