Performance evaluation, comparison and modeling of passive wastewater treatment systems

The objectives of this research were to evaluate and compare five configurations of wastewater treatment for on-site or communal applications in various climate conditions: a peat filter, a sand filter, a subsurface flow constructed wetland cell, a peat filter followed by a wetland cell, and a sand filter followed by a wetland cell. Oxygen demand, nitrogen and phosphorus compounds, temperature, and indicator bacteria of the influent and effluent of each treatment stage were monitored over a period of 17 months. The sand and peat filters achieved over 98% reduction in carbonaceous biochemical oxygen demand (CBOD5) to <1 mg/L (below detection limits) in most samples. The filters also reduced all indicator bacteria parameters to low levels. Phosphorus removal through the sand filter consistently exceeded 98% but declined rapidly after 14 months, likely due to saturation. Phosphorus reduction in the peat filter averaged 47% with an additional 58% provided by the wetland cell (total 78%); no saturation trend was apparent by the 17th month. The total nitrogen reductions were low initially but improved over time in both filters. The wetland cell provided low to moderate treatment efficiencies for CBOD5 (49%), phosphorus (33%), indicator bacteria (similar to 2 log reduction), and total nitrogen (31%).