A laboratory study on nitrification of high-strength source-separated urine was conducted by means of sequencing batch reactors (SBR) and membrane bioreactors (MBR). The highest influent ammonia concentration for SBR and MBR reached more than 2,400 and 1,000 mg N/L, while the maximum pH was about 9 and 8.9, respectively. The ammonia oxidizing efficiency in both SBRs and MBRs was around 50%, which was restrained mainly by the deficiency of alkalinity in bulks. Meanwhile, the nitrite accumulation did also dominate in these two systems, and the major factor to inhibit the nitrite oxidization was thought to be the high free ammonia and free nitrous acid content in bulks. Hence, an ammonia nitrite solution was achieved with concentration ratio of 1:1; after that ammonia oxidation was restrained owing to the deficiency of alkalinity in urine. The temperature and influent ammonia content have no great influence on the nitrification process in both kinds of bioreactors. The nitrification can be progressed under a solids retention time (SRT) longer than 30 d; however, termination of ammonia oxidization was observed as the SRT fell below 20 d. The nitrifier biomass showed an excellent settleability, such that the suspended solids (SS) in effluent was of a low average, about 60 mg/L. This study on the stabilization of human urine will be useful to understand the process of urine separation from source.

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