The inoculation and acclimatization of activated sludge (AS) is one of the vital components to provide preferably suspended aerobic growth and desired treatment mechanism for a treated wastewater using MBR. The performance of a floating media biofilter-submerged membrane bioreactor (FMB-SMBR) and a submerged membrane adsorption bioreactor (SMABR) were investigated during the acclimatization. It was observed that the duration of sludge from wastewater treatment plant in Sydney acclimated to synthetic wastewater was about 25 days for FMB-SMBR system, while SMABR took around 12 days to reach the stabilization. The acclimatized FMB-SMBR (without membrane operation) resulted in significant high dissolved organic removal of 94%. The acclimatized FMBR-SMBR system showed more than 20% TOC removal efficiency than that of the acclimatized SMABR system. Meanwhile, the results of oxygen uptake rate (OUR) measurement suggested that OUR is an accurate and simple indicator to biological process acclimatization. Membrane fouling study of the FMB-CFMF system was also carried out. The results indicate that the acclimatized FMB could be used as a pretreatment unit prior to SMBR in order to minimize membrane fouling when the FMB-SMBR system operates under sub-critical flux condition.