[Nitrogen Removal Effect and Conversion Characteristics of Nitrous Oxide in Single-stage and Multi-stage A/O Processes].

The single-stage A/O and multi-stage A/O processes were simulated by sequencing batch reactors (SBRs) with alternate stirring and aeration. The removal efficiency of nitrogen and the release mechanism of NO were studied under the identical conditions of influent quality, hydraulic retention time (HRT), sludge retention time(SRT), temperature and anoxic/oxic (A/O) retention time ratio. Experimental results showed that COD or ammonia-nitrogen removal had no significant difference between the single-stage and the multi-stage A/O processes for the influent quality equivalent to municipal wastewater. However, TN removal efficiency of the former was better than the later with 72.1% and 52.2%, respectively. In the conversion of total nitrogen, during the typical cycle in the single-stage A/O and multi-stage A/O processes, the yields of NO were 16.95 mg and 3.95 mg, respectively. The conversion rate, which is the ratio of NO yield and TN removal, was respectively 11.47% and 4.11%. NO production and emission occurred mainly in aerobic (nitrification) phase while there was little NO emission in anoxic (denitrification) phase. Although the dominant species of AOB was both in the single-stage A/O and the multi-stage A/O processes under the same operating conditions, it was more conducive to the growth of nitrifying bacteria (AOB, NOB) in the single-stage A/O process with the greater abundance of . Meanwhile, the type and abundance of NOB in the single-stage A/O process were significantly more than in the multi-stage A/O process too. Therefore, it is more competitive to deal with the high-strengthening ammonia-nitrogen wastewater in the single-stage A/O process. In the actual operation of wastewater treatment, using appropriate partitions of A/O or oxygen-supplying modes can not only result in better nitrogen removal but also decrease the secondary pollution caused by NO to the atmosphere.