Simultaneous removal of NH4+-N and refractory organics through sequential heterogeneous Fenton oxidation process and struvite precipitation: kinetic study
Abstract
The aim of the present investigation was to treat wastewater containing a high concentration of NH4+-N by heterogeneous Fenton oxidation of organics and struvite precipitation. The Fenton reagent (Fe2+/H2O2-10 mM/9.8 mM) and nanoporous activated carbon (30 g L−1) as the heterogeneous matrix were used in heterogeneous Fenton oxidation (HFO) process for the destruction of refractory organic compounds present in ammoniacal nitrogen containing wastewater (ANWW). The HFO process was followed by NH4+-N removal from the ANWW as struvite crystals using MgO and Na2HPO4·2H2O. The maximum removal of NH4+-N as struvite was 96% at solution pH 9.0 and at ambient temperature after the destruction of organic compounds by a HFO process. The optimum time for struvite precipitation was 60 min and secondary crystallization time for struvite crystals was 2 h. The removal of organic impurities was confirmed through FT-IR analysis of struvite crystals formed with and without HFO treatment. The thermal stability of struvite crystals was evaluated by TGA and DTA analyses and enthalpy of formation of struvite was determined through DSC analysis. The orthorhombic crystalline nature of the struvite crystals recovered from ANWW and [ANWW]HFO was evaluated using XRD spectroscopy. The surface morphology of precipitated struvite was analysed using scanning electron microscopy.