Abstract:Two stages Multi-soil-layering (MSL) systems filled zeolite in permeable layer was designed for purifying domestic wastewater polluted river water. Because the absence of denitrification negatively influenced the nitrogen removal of MSL system, the step feed method, which added the organic carbon to the second stage without aeration, was applied to MSL systems to improve TN removal efficiency. The results indicated that after the step feed applied to MSL system, the TN removal of MSL system increased by 26% . In addition, appropriate ratio of wastewater is also a equally vital factor to balance the nitrification and denitrification. When the average C/N ratio of wastewater increased from 0.8 to 2.5, the TN removal rate of MSL system increased from 53.7% to 89.4%. Moreover, the step feed had no negative but positive effect to organic matter and phosphorous removal efficiency, and the COD and TP removal rates increase by about 10% after step-feed.