Feasibility of using hydroponic cultivation as a pretreatment process for constructed wetland.

A pilot scale hybrid constructed wetland was employed to investigate the feasibility of using hydroponic cultivation as a pretreatment unit for the constructed wetland system treating the effluent of primary sedimentation tank in a municipal wastewater treatment plant in Xi'an.Canna indica Linn was raised both in hydroponic ditch system and constructed wetland system.Organic loading rate and the clogging risk of the constructed wetland were reduced significantly,which was due to the fact that 64.8%of COD and 88.7%of SS were removed in the hydroponic ditch system.The water depth was an important parameter for DO in the aqueous phase and pollutant removal efficiency of the hydroponic ditch system.The DO was increased from 0.75 to 2.61 mg/L when the water level decreased from 0.60 to 0.10 m.As a result,the pollutant removal performance was increased.Additionally,it was found that the pollutant removal efficiency of the hybrid constructed wetland was improved using hydroponic ditch system as pretreatment process.The concentrations of COD and SS in the effluent of hybrid constructed wetland were lower than requirement for 1B level while the concentration of NH_4~+-N and TP were reached the requirement for level 2 in the Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant.