The studies of partial nitrification and anaerobic ammonium oxidation(anammox) mainly focus on high ammoniacal concentration effiuents. A few research about domestic sewage of low ammonia nitrogen concentration was reported. The domestic sewage was pumped into the UASB reactor after carbon removal and partial nitrification to explore the impact of domestic sewage on mature anammox granular sludge. The results showed that the concentrations of NH4+-N and NO2--N in effluent were below 5 mg·L-1 and 1 mg·L-1

respectively when the inflow became domestic sewage. But the NO3--N concentration was higher than the theoretical value because the increased dissolved oxygen enhanced nitrification. The color of anammox sludge in UASB reactor changed from light red to dark red. The T-EPS content of sludge decreased and the PN/PS value increased from 1.13 to 3.66. The settleability of the sludge turned better. The percentage of Candidatus Brocadia bacteria in the sludge decreased from 17.7% to 14.4%. The ammonia-oxidizing bacteria and nitrite-oxidizing bacteria contents in the sludge increased. If dissolved oxygen into the UASB reactor can be reduced

the NO3--N concentration in effluent may decrease and total nitrogen removal efficiency may be higher.