Phosphorus recovery from wastewater using pyridine-based ion-exchange resins: Role of impregnated iron oxide nanoparticles and preloaded Lewis acid (Cu2+ ).

Abstract

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 10µg/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 (Cu2+ ) 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, MgNH4 PO4 , a slow-release fertilizer, after addition of MgCl2 and NH4 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<6μg/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, MgNH4 PO4 (struvite), a slow-release fertilizer.