Abstract:

Recovery of residual ammonium nitrogen (NH₄⁺-N) from dissolved air flotation (DAF) pretreated poultry slaughterhouse wastewater was studied by means of magnesium ammonium phosphate hexahydrate (MgNH₄PO₄.6H₂O, MAP) precipitation in a lab-scale batch study. The maximum recovery values were obtained as 80.2%, 97.1% and 53.6% with the addition of MgCl₂.6H₂O + KH₂PO₄, NaH₂PO₄.2H₂O + MgSO₄.7H₂O, and MgOHCO₃ + 85% H₃PO₄ at pH 9.5, respectively. Based on the physicochemical findings, subsequent batch experiments were conducted at pH 9.5 for eight different molar ratios (Mg²⁺:NH₄⁺-N:PO₄^3--P) applied as overdose (1.2:1:1, 1.5:1:1, 1:1:1.2, 1:1:1.5) and underdose (0.5:1:1, 0.8:1:1, 1:1:0.5, 1:1:0.8). Results indicated that the stoichiometric ratio (Mg²⁺:NH₄⁺-N:PO₄^3--P = 1:1:1) was found to be sufficient to obtain high recovery values. A detailed economic analysis of the present process demonstrated that the cost of NH4 +-N recovery was estimated as 0.297 €/m3 or 1.753 €/kg NH₄⁺-N_removed for the proposed application. The rate of reaction was found to be very fast, being completed within minutes,
and cost effective in large-scale poultry slaughterhouse facilities.