Phosphorus removal and recovery from secondary effluent in sewage treatment plant by magnetite mineral microparticles

This study investigated the applicability and chemical stability of magnetite mineral microparticles (Mag-MM) (average particle size: 34 mu m) for phosphorus (P) removal and recovery from actual secondary effluent (SE) of a sewage treatment plant. The maximum P adsorption capacity of Mag-MM was 0.52-0.83 mg P/g at 5-45 degrees C. The values of three thermodynamic parameters, standard entropy Delta S degrees (137.74-138.04J/(K mol)), standard enthalpy Delta H degrees (7.32 kJ/mol), and standard Gibbs free energy Delta G degrees (-30.97 to -36.57 kJ/mol), indicated that P adsorption on Mag-MM was endothermic and spontaneous in nature and involved both physisorption and chemisorption. The coexisting cations, anions, and dissolved organic matter in the actual SE had little or no effect on P adsorption on Mag-MM. Approximately >40 g/L Mag-MM and >200 g/L Mag-MM were individually required to produce quality effluent (<0.1 mg P/L) from the actual SE of anaerobic-anoxic-oxic (1.0-2.0 mg P/L) and conventional activated sludge (similar to 8 mg P/L) processes, respectively. During 30 adsorption-regeneration cycles, the amount of reloaded P Mag-MM varied over a range of 0.023-0.039 mg P/g, which stably produced quality effluent from the actual SE. The P in exhausted regeneration solutions was finally recovered as a precipitate of calcium phosphate by the addition of CaCl2, with an optimum Ca/P (mol ratio) of 2.0. Compared with NaAc solutions, other alkaline regeneration solutions (i.e., NaOH, KHCO3 or Na2CO3) can produce quality effluent with lower P or organic concentration. These results demonstrated that Mag-MM has a remarkable potential for cost-effective P removal and recovery from actual SE. (C) 2016 Elsevier B.V. All rights reserved.