Abstract
The partial nitrification (PN)–Anammox process was considered as one of the most efficient and economical method to remove ammonia from wastewater without organic carbon consumption. In this process, PN is the key step since it should provide stable effluent with suitable NO2-/NH4+ ratio for the subsequent Anammox. In this study, PN was successfully started-up during 30 d at ambient temperature (25°C) in a continuous flow membrane bioreactor (MBR), by gradually increasing ammonia-loading rate (ALR) under oxygen-limited condition. Finally, the system achieved an ammonia oxidation rate of 0.52 kg m−3 d−1 and an excellent effluent with appropriate NO2-/NH4+ ratio as 1.1–1.3. ALR was indicated as the indispensable controlling factor, and the applied alkalinity with the combination of high ALR inhibition and oxygen limitation provided the selective washout of nitrite-oxidizing bacteria (NOB) and an active aerobic ammonia-oxidizing (AerAOB) population. Techniques of fluorescence in situ hybridization and clone sequencing were utilized simultaneously to study the microbial characteristics in the stable PN system. The results demonstrated that small amounts of NOB were present and not active, while AerAOB predominated in the MBR–PN system, and Nitrosomonas-related AerAOB were considered to be responsible for the satisfactory PN performance.
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