The landfill leachate in Hong Kong usually contains quite high NH4+-N concentration, which is well known to inhibit nitrifica-tion in biological treatment processes. A common pre-treatment for reducing high strength of ammonium (NH4+-N) is by an air-stripping process. However, there are some operational problems such as carbonate scaling in the process of stripping. For this reason, some technical alternatives for NH4+-N removal from leachate need to be studied. In this study, a bench-scale experiment was initiated to investigate the feasibility of selectively precipitating NH4 +