An evaluation of pollutant removal from secondary treated sewage effluent using a constructed wetland system

Pilot scale investigations were carried out to examine the pollutant removal efficiency of a constructed wetland receiving secondary treated sewage effluent. Four constructed wetland cells were established, three of them planted with either Schoenoplectus validus, Juncus ingens or both species of macrophytes, and the fourth serving as an unvegetated control cell. Although there was a significant improvement in the effluent quality during the initial ten month period of monitoring, results to date have not indicated any overall trend for pollutant removal by a particular plant species. Biochemical oxygen demand and chemical oxygen demand removals averaged between 71-75% while suspended solids removals were around 85% in the macrophyte cells. Ammonia reductions were in the range 17-24% but better nitrate reductions between 65-80% were obtained. Phosphorus removal has been low (13%) in all four of the wetland cells and bore hole samples have shown no groundwater contamination with nitrogen or phosphorus from the wetland system to date.