SUBSURFACE FLOW WETLANDS - A PERFORMANCE EVALUATION

This paper evaluates data collected by the authors as well as other individuals and agencies at operational subsurface flow constructed wetlands. The purpose of the evaluation was to identify the influence of hydraulic loading, organic loading, hydraulic residence time (HRT) on removal performance for biochemical oxygen demand (BOD), total suspended solids (TSS), nitrogen and phosphorus. The results indicate that BOD and TSS removal can be very effective at a relatively short HRT and that BOD removal exhibits a linear relationship with organic loading. Effective nitrogen removal requires a longer HRT and appears to be limited by the low oxygen availability in these systems. Phosphorus removal is also somewhat limited and ranges from 30 to 60 percent. Design models for these parameters are available or under development.