ENHANCEMENT OF NITROGEN REMOVAL IN SUBSURFACE FLOW CONSTRUCTED WETLANDS EMPLOYING A 2-STAGE CONFIGURATION, AN UNSATURATED ZONE, AND RECIRCULATION

Constructed wetland technology is currently evolving into an acceptabl e, economically competitive alternative for many wastewater treatment applications, Although showing great promise for removing carbonaceous materials from wastewater, wetland systems have not been as successfu l at, nitrification. This is primarily due to oxygen limitations. Nitr ification does occur in conventional wetland treatment systems, but ty pically requires long hydraulic retention times. This paper describes a study that first evaluated the capability of subsurface flow constru cted wetlands to treat a high strength seafood processor wastewater an d then evaluated passive aeration configurations and effluent recircul ation with respect to nitrogen treatment efficiency. The first stage o f a 2-stage wetland treatment system exhibited a relatively short hydr aulic retention time and was designed for BOD removal only. The second stage wetland employed an unsaturated inlet zone and effluent recircu lation to enhance nitrification. Results indicate that organic loading , and thus BOD removal, in the first stage wetland is key to optimal n itrification. Passive aeration through an unsaturated inlet zone and r ecirculation achieved up to 65-70 per cent ammonia nitrogen removal at hydraulic retention times of about 3.5 days. Inlet zone configuration and effluent recirculation is shown to enhance the nitrogen removal c apability of constructed wetland treatment systems.