Abstract: Nitrogen removal via nitrite pathway was investigated in a lab-scale modified University of Cape Town（MUCT)process treating real domestic wastewater with low C/N ratio.The experimental results of 121 d showed that nitritation was achieved at hydraulic retention time（HRT)of 8 h, dissolved oxygen（DO)of 0.3—0.5 mg·L^-1, sludge recycle ratio of 80%, anoxic recycle ratio of 120% and internal recycle ratio of 300% after startup period of 87 d.Nitritation was stabilized for 35 d with an average nitrite accumulation rate（NAR)of 62%, the highest NAR up to 80%, average ammonia removal efficiency of 65% and the highest of 87%.Mechanisms of nitritation indicated that the low DO concentrations and short HRT were really important to nitritation, whereas pH, free ammonia（FA)and free nitrous acid（FNA)had no effect on nitritation.And temperature and sludge retention time（SRT)possibly had a slightly positive effect on nitritation.The fluorescence in situ hybridization（FISH)assays demonstrated that the percentage of ammonia oxidizing bacteria（AOB)in biomass increased when the performance of MUCT reactor was converted from complete nitrification to nitritation, and the highest AOB percentage was up to 9.3%.Meanwhile, the percentage of nitrite oxidizing bacteria（NOB)decreased, and NOB were phylogenetically related to Nitrospira.Nitrogen removal via nitrite pathway saves the aeration costs and external carbon sources as compared to nitrate pathway.For the treatment of domestic wastewater, nitritation and denitritation are highly beneficial because the organic carbon source in it is typically limited.

Key words: MUCT, domestic wastewater, nitritation, ammonia oxidizing bacteria, nitrite oxidizing bacteria, fluorescence in situ hybridization

摘要： 采用MUCT工艺处理低C/N比实际城市生活污水，研究在连续流工艺中实现亚硝酸型硝化的调控措施。试验在常温下共进行了121 d，结果表明：经过87 d的启动期，最终在水力停留时间（HRT）8h，溶解氧浓度（DO）0.3～0.5 mg·L^-1，污泥回流比80%，缺氧回流比120%，硝化液回流比300%的条件下，成功启动了短程硝化，并稳定维持了35 d。 短程硝化期间，好氧区亚硝酸盐积累率平均62%，最高达到80%；氨氮去除率65%，最高达87%。短程硝化影响因素的分析表明：pH值，游离氨（FA），游离亚硝酸（FNA）对本试验短程硝化无影响；温度和污泥停留时间（SRT）影响较小；HRT和DO是短程硝化实现的控制因素。荧光原位杂交（fluorescence in situ hybridization, FISH）试验结果表明：当系统由全程硝化状态转为短程硝化状态后，氨氧化细菌（ammonia oxidizing bacteria, AOB）的比例明显提高，最高达到9.3%；亚硝酸盐氧化细菌(nitrite oxidizing bacteria，NOB)以Nitrospira为主，其所占比例明显下降。

关键词: MUCT, 生活污水, 短程硝化, 氨氧化细菌, 亚硝酸盐氧化菌, 荧光原位杂交