Cyclic Batch Subsurface Wetland for Treating Rural Sewage with Low Carbon-to-Nitrogen Ratio

A novel vertical flow constructed wetland system,named cyclic batch subsurface wetland(CBW),was developed by modifying the operation of the constructed wetland.The treatment efficiencies of CBW and conventional constructed wetlands operated under high and low water level conditions were compared.Among the three operation modes,CBW achieved the highest TN and TP removal rates,30.85% and 52.59% respectively.The removal rates of NH+4-N and COD by CBW were 80.75% and 70.14% respectively,only lower than those by constructed wetland operated under low water level condition.The optimal hydraulic loading of CBW for treating rural sewage with low carbon-to-nitrogen ratio was 0.1 m3/(m2·d).Stable performance of the CBW system continued for two months.The effluent concentrations of NH+4-N and COD met the second criteria specified in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant(GB 18918-2002).