An Orbal process model which volume is 330 liters was used to treat the urban sewage, and the phenomenon of simultaneous nitrification and denitrification (SND) was investigated. The result revealed that by means of controlling the DO level in the out lag can the SND be achieved without inner recycle and external carbon added:t he nitrogen removal ratio could reach up to 86 %. It is believed that the key factor influencing the SND occurred in the Orbal process is the concentration and distribution of the dissolved oxygen. At the same time, the process of SND is straightly affected by the COD/TN of the influent; the oxidation-reduction potential (ORP) could be a controllable factor to the SND. It is feasible to apply the SND to realize the biological nitrogen removal in urban wastewater treatment plant at low cost.%采用有效容积为330L的氧化沟模型,以城市污水为研究对象,研究了Orbal氧化沟中的同时硝化反硝化生物脱氮现象.实验结果表明,在不投加外碳源和不设硝化液内回流的条件下,通过控制氧化沟溶解氧浓度及分布,可以实现氧化沟外沟道内的同时硝化反硝化生物脱氮,TN去除率最高可达86％.分析认为,溶解氧浓度及分布是氧化沟同时硝化反硝化的决定因素;进水COD/TN直接影响总氮去除率；氧化还原电位(ORP)可以作为同时硝化反硝化的控制因素.利用同时硝化反硝化原理实现城市污水处理厂的低能耗脱氮运行是可行的.
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