Phosphorus recovery from wastewater using pyridine‐based ion‐exchange resins: Role of impregnated iron oxide nanoparticles and preloaded Lewis acid (Cu 2+ )

Inputs of P into receiving water bodies are attracting increasing attention due to the negative effects of eutrophication. Presently available P treatment technologies are unable to achieve strict P discharge limits from wastewater treatment plants (WWTPs) that may be as low as 10 µg/L as P. Moreover, P is a nonrenewable resource and needs to be recycled in a closed‐loop process for environmental sustainability. This article provides details of a process where a pyridine‐based polymeric ion exchanger is modified with a combination of impregnated hydrated ferric oxide (HFO) nanoparticles and a preloaded Lewis acid (Cu 2+ ) to effectuate selective P removal from wastewater and its recovery as a solid‐phase fertilizer. Three such ion exchangers were studied: DOW‐HFO, DOW‐Cu, and DOW‐HFO‐Cu. Each of these materials displays selective phosphate affinity over competing anions chloride and sulfate, and also has the ability to be regenerated upon exhaustion to strip off the P in a concentrated solution. The P in concentrated regenerant can be recovered as struvite, MgNH 4 PO 4 , a slow‐release fertilizer, after addition of MgCl 2 and NH 4 Cl. Results of equilibrium and kinetic studies and column experiments with synthetic solutions and a real WWTP effluent are discussed. Practitioner points Fixed‐bed columns with DOW‐HFO, DOW‐Cu, or DOW‐HFO‐Cu—can selectively remove phosphorus over competing anions. Fixed‐bed columns of above‐listed ion exchangers can produce an effluent P < 6 μg/L. DOW‐Cu fixed‐bed column ran for ≈500 Bed Volumes before breakthrough when fed Dartmouth WWTP secondary effluent. Regeneration of the exhausted DOW‐Cu column resulted in ≈90% recovery of the phosphorus. Regenerant solution was used to generate high‐purity crystals of magnesium ammonium phosphate, MgNH 4 PO 4 (struvite), a slow‐release fertilizer.