Wastewater Treatment by Artificial Wetlands

This report describes studies of artificial wetlands at Santee, California which demonstrate the capacity of these systems for integrated secondary treatment (BOD and suspended solids removal) and advanced treatment (nitrogen removal) of municipal wastewater effluents. When receiving a blend of primary (1°) and secondary (2°) wastewaters at a blend ratio of 1:2 (6 cm per day 1° : 12 cm per day 2° ), mean removal efficiencies for a complete year of operation from July, 1982 through July, 1983 were 80% for total nitrogen (TN) and 80% for total inorganic nitrogen, with the mean inflow TN level of 21.5 mgl⁻¹ reduced to a mean value of 4.3 mgl⁻¹ in the wetland effluent. The BOD and suspended solids removal efficiencies were 93% and 88% respectively. The mean wetland effluent values for both BOD and suspended solids were below the 10/10 mgl⁻¹ standard for advanced secondary treatment. When primary effluent was the sole source of inflow to the artificial wetlands, BOD and suspended solids levels approaching the quality of a secondary treated effluent (30/30 mgl⁻¹) could be attained at an application rate of 6-8.3 cm per day. In this case, mean BOD and suspended solids removal efficiencies for the complete year from July, 1982 through August, 1983, were 78% and 80% respectively, with the effluent levels reduced to mean values of 33 mgl⁻¹ for BOD and 10 mgl⁻¹ for suspended solids. At the application rate of 6 cm per day, our study shows that only 16 acres (6.5 ha) of constructed wetlands would be required to treat 3785 m³ of primary wastewaters to secondary treatment levels. Data on capital and O&M cost show that artificial wetlands are competitive with other treatment technologies available to small to medium sized communities.