The use of constructed wetland systems for wastewater treatment : nitrogen transformation and indicator bacteria removal

Increasing demands for improved water quality in receiving waters, effluent reclamation and reuse have prompted wide interest in the use of wetlands for the treatment of wastewater. Over a four year period, domestic sewage effluent was treated using a range of gravel based, subsurface flow constructed wetland systems. Weekly samples at inlet and outlet points were assayed for suspended solids, biological oxygen demand, organic carbon, total kjeldahl nitrogen, ammonium, nitrate/nitrite, phosphorus, dissolved oxygen, temperature, pH and faecal coliform levels. The wetland system received secondary treated effluent for three years and primary settled effluent for one year. The potential of constructed wetland systems for nitrogen removal and potential pathogen reduction was investigated. Nitrogen removal was characterised by estimation of potential nitrification and denitrification rates within the system. Disinfection performance of the wetland system was assessed by enumeration of faecal indicator bacteria in the system influent and effluent, as well as with distance along the length of the system. The removal rate was estimated, considering influent and effluent faecal coliform concentrations as well as system hydraulic retention time and temperature