Abstract: The economy of step-feed biological nutrient removal(BNR) technology was discussed.Compared with the single stage A/O process,the step-feed BNR is efficient and cost-effective for nitrogen and phosphorous removal from municipal wastewater without mixed liquid suspended solid(MLSS) return.With the municipal wastewater at Beishiqiao Wastewater Treatment Center of Xi’an City as the treatment object,a four-stage pilot-scale step-feed BNR with useful volume of 1.2 m³ was employed and operated with 50% of return activated sludge for more than 70 days.The feed split to each tank is 40%,30%,20% and 10% of total flow rate respectively.The results obtained showed that step-feed BNR is efficient for municipal wastewater treatment,having relatively strong bearing capability against impact load.The removal efficiencies of COD_Cr,NH+4-N and TN could reach as high as 93%,95.8% and 68.5% respectively,under 7.5 hours of hydraulic retention time(HRT) and 15 days of sludge retention time(SRT).The averaged MLSS mass concentration in the reactor is about 30% higher than that of single stage A/O process.