Applications of Hybrid Anion Exchanger containing Hydrated Fe(III) Oxide Nanoparticles for Simultaneous Nitrate and Phosphate Removal in a Recirculating Aquaculture System

Abstract

Biofloc technology (BFT) is environmentally friendly aquaculture technology due to the reduction of wastewater discharge. However, to control the Biofloc concentration, there is still considering amount of wastewater being discharged typically 20% per week. In this study, the hybrid polymeric anion exchanger impregnated with hydrated Fe(III) oxide (HFO) nanoparticles, HA520E-Fe, was used for removal of nitrate and phosphate in a Biofloc system, resulting zero waste discharge (ZLD) for the BFT processes. HA520E-Fe contains two functional groups; quaternary ammonium (R₄N⁺) selective for nitrate removal and HFO specifically adsorbed trace phosphate. The fixed-bed column run shows that the HA520E-Fe has a high nitrate and phosphate removal capacity approximately 47.27 mgNO₃^-/g and 45 mgPO₄^3-/g, respectively. Moreover, the HA520E-Fe can also partially remove organic matter. The exhausted material can be reused for many cycles by using mixed regenerant solution containing 10% w/v MgCl₂ and 5% w/v KOH solution. The high nitrate and phosphate recovery were achieved at 93.72 and 99.61 %, respectively. The regenerant solution composes of Mg²⁺, NO₃^- , K⁺ and PO₄^3- , which are essential nutrients for plants and can be further converted into slow-release fertilizers such as K-struvite (magnesium potassium phosphate: MPP) and NH₄-struvite magnesium ammonium phosphate: MAP).