A lab-scale membrane aeration bioreactor (MBR) system was developed for treating synthetic ammonium-rich wastewater to yield an appropriate NO2-/NH4+ mixture as a pretreatment for anaerobic ammonium oxidation (Anammox). The effluent with a suitable NO2-/NH4+ ratio (1: 1 to 1: 1.3) was obtained in 24 h using the developed MBR system under suitable conditions. Additionally, the control of bulk dissolved oxygen (DO) level under a desired condition (anoxic condition) was easier and more economical than traditional aeration systems. An optimal initial alkalinity of 1500 mg CaCO(3)l(-1) was necessary for achieving 50% partial nitrification of wastewater with an initial ammonium concentration of 510 mg NH4-Nl(-1) within 24 h. Furthermore, there is no need for pH adjustment by adding a base or an acid throughout the reaction if the initial alkalinity is appropriately controlled. Both the appropriate NO2-/NH4+ ratio and the low DO level make this MBR system an ideal system for Anammox.