Pretreatment of ammonium removal from landfill leachate by chemical precipitation

Chemical precipitation is a useful technology to remove ammonium (NH4+) from landfill leachate. In this paper, the removal of ammonium from landfill leachate was studied. The objective of this study was to investigate optimum pH, optimum molar ratio, and different kinds of chemicals combinations for magnesium ammonium phosphate (MAP) precipitation. Furthermore, the kinetics of MAP formation and surface characterization were analyzed. The results indicated that ammonium in landfill leachate could be removed with the optimum pH of 9.5. The Mg2+:NH4+:PO43− molar ratio was practically controlled at 1.15:1:1 to remove ammonium effectively and avoid higher concentration of PO43− in the effluent. Highest salt concentration was generated by using MgCl2·6H2O plus Na2HPO4·12H2O. Compare to MgCl2·6H2O and Na2HPO4·12H2O, adding MgO and 85% H3PO4 could significantly minimize the salt concentration, although ammonium removal ratio was 9 percents lower. The lowest ammonium removal ratio was generated by adding Ca(H2PO4)2·H2O and MgSO4·7H2O. Moreover, the kinetics experiment shown that the rate of reaction was closer to the first-order kinetic model. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis indicated that MAP was the main composition of the precipitates. Scanning electron microscopy with energy dispersive X-ray (SEM-EDX) analysis indicated that the unshaped crystal was coarse and its size was irregular, the surface composition of the precipitates contains a great deal of O, P, Mg and trace of C, K, Na, Cl.