Abstract:Partial nitrification/anammox (PN/A) process has become one of the most innovative developments in reject water treatment in recent years. In this study, a one-stage integrated fixed-film activated sludge reactor was used to treat reject water. By inoculating partial nitrification floc sludge and anammox biofilm, gradually increasing ammonium concentration of influent and controlling DO at 0.11~0.42mg/L, the reactor was started successfully in 65days. In the stable phage, the system had a good contaminant removal performance. With influent concentration of COD and ammonium were 921mg/L and 1120.8mg/L respectively, 66.8% COD, 99.0% ammonia and 94.4% total nitrogen were removed respectively and total nitrogen removal rate reached 0.27kgN/(m3·d). The experiment showed that the start-up of PN/A process was promoted by increasing the ratio of reject water in influent gradually. Further analysis revealed that both anammox and denitrification process were present in system. The contributions to total nitrogen removal of anammox and denitrification were 67.4%~91.1% and 8.9%~32.6%, respectively.