Recovery of ammonium nitrogen from the effluent of UASB treating poultry manure wastewater by MAP precipitation as a slow release fertilizer

Abstract

Magnesium ammonium phosphate hexahydrate (MgNH 4PO 4·6H 2O, MAP) precipitation was studied on up-flow anaerobic sludge blanket (UASB) pretreated poultry manure wastewater in a lab-scale batch study. To recover high strength of ammonium nitrogen (NH 4 +–N = 1318 mg/L) from UASB effluent, three combinations of chemicals including MgCl 2·6H 2O + KH 2PO 4, MgSO 4·7H 2O + NaHPO 4·7H 2O, and MgO + 85% H 3PO 4 were first applied at the stoichiometric ratio (Mg 2+:NH 4 +–N:PO 4 3−–P = 1:1:1) and at different pH levels ranging from 4.45 to 11. Preliminary test results indicated that maximum NH 4 +–N removal, as well as maximum chemical oxygen demand (COD) and color reductions, were obtained as 85.4%, 53.3% and 49.8% at pH 9.0 with the addition of MgCl 2·6H 2O + KH 2PO 4, respectively. The paired experimental data obtained from batch studies were statistically evaluated by a non-parametric Mann–Whitney test and a two-sample t-test. Based on the previous results, another batch experiments were then performed at pH 9.0 using MgCl 2·6H 2O + KH 2PO 4 for different molar ratios 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). In the final step, the fertility of the MAP precipitate as struvite was also tested on the growth of three test plants including purslane ( Portulaca oleracea), garden cress ( Lepidum sativum) and grass ( Lolium perenne). Findings of this experimental study clearly confirmed the recovering of NH 4 +–N from UASB pretreated poultry manure wastewater by MAP precipitation, and also the application of recovered MAP sludge as a valuable slow release fertilizer for agricultural use.