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Obligatory anaerobic treatment of agro-industrial waste-waters releases large amounts of nutrients into receiving water-bodies. In this study, response surface methodology was employed to optimize NH4+ and PO43- recovery from anaerobic effluent of a full-scale dairy processing industry by struvite precipitation. This study also examined the residual interfering ions (Na+, Ca2+, and K+) and COD removal efficiency during struvite precipitation. Removal efficiency rates of 88.4% for NH4+ and 79.3% for PO43- were obtained at optimized conditions with pH 9.60, mixing speed 260 rpm, and Mg2+:NH4+:PO43- molar ratio of 1:1:1, respectively. The experimental data suggested that the model described the experiments well (F-NH4(+)=14.08, F-PO4(3-)=40.22, F-Table = 2.9340). According to the quadratic regression model, the linear, quadratic and interaction terms of Mg2+, PO43- and pH had significant effects on NH4+ and PO43- recovery. It was found that high concentration of Na+ in the anaerobic effluent affected the formation of struvite. The formation of struvite (MgNH4PO4(H2O)(6)), ferroalluaudite (NaFe(Fe,Mn)(2)(PO4)(3)) and sodium carbonate sulfate (Na6CO3(SO4)(2)), as products under different reaction conditions, were confirmed by XRD, SEM and EDX. Considerable COD removal was also achieved, with a maximum removal efficiency of 68.4%. |
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