Phosphate recovery from real fresh urine by Ca(OH)2 treated natural zeolite

Abstract

Source-separation of urine can provide an alternative way for wastewater treatment and nutrients recovery by adsorbents which then can be applied in the agriculture as fertilizer. In this work, natural (NZ) and Ca(OH)2 treated zeolite (CaT-Z) were employed in batch tests for adsorption of phosphate phosphorus (P) from real fresh urine (FU). Total P removal was a simultaneous process of adsorption on NZ or CaT-Z surface and precipitation in the liquid phase as Ca-P and Mg-P containing precipitates. In the presence of CaT-Z, the contribution of adsorption on total P removal was higher than that of the liquid phase precipitation at all dilution ratios of FU with deionized water. Lower residual P concentrations in FU and more P bound on the adsorbent were observed for CaT-Z than for NZ. The sequential desorption study showed that 55.1–84.9% and 6.2–72.6% of total removed P was recovered from FU loaded CaT-Z and NZ, respectively. In less diluted FU, CaT-Z adsorbed much more P (up to 11.11 mg/g) than NZ due to the dominant contribution of inner-sphere complexation (ligand exchange). In more diluted FU, outer-sphere complexation was the major P adsorption mechanism accompanied by ligand exchange. Phosphorus removal by CaT-Z reached an equilibrium in 72–96 h. Bulk (XRD, IR-ATR) and in-situ (EPMA, SEM-EDS) analytical techniques clarified the adsorption mechanisms and confirmed the accommodation of Ca-P phases on NZ and CaT-Z. The results of the study suggested the suitable use of CaT-Z for simultaneous PO4-P and NH4-N recovery from human urine.