Multilayer partially saturated vertical flow wetlands for advanced small community wastewater treatment

Abstract

This study evaluated the performance of four types (zeolite, gravel, complete woodchip, and vertical shaft) of pilot-scale partially saturated vertical flow wetlands for treating domestic wastewater. The zeolite-woodchip PSVF design achieved a mean total nitrogen removal of 80 % and also performed best in terms of ammonium-N removal (99 %). The complete woodchip design also achieved a similar mean reduction in TN but by having better nitrate removal. The corresponding changes in alkalinity and nitrogen species measured above and below the unsaturated zones of the PSVF suggest that classical nitrification and denitrification are the main mechanisms involved in nitrogen removal. All four systems achieved >95 % removal for biochemical oxygen demand and total suspended solids. Phosphorus removal was 55 % for zeolite, gravel and vertical shaft, and 37 % for the complete woodchip system. The elimination of E. coli ranged between 1.7 and 2.8 log₁₀ in all four systems, with the complete woodchip PSVF delivering the highest reduction. PSVF wetlands can provide effluent quality equivalent to multistage hybrid systems while occupying a significantly lower footprint without additional power requirements.