Performance of an artificial wetlands filter treating facultative lagoon effluent at Carville, Louisiana

Abstract

ABSTRACT: Treatment plant upgrades of existing facultative lagoon systems are rapidly incorporating constructed artificial wetlands systems to control biochemical oxygen demand (BOD) and total suspended solids (TSS). Subsurface flow wetlands or artificial wetlands filters (AWF) are being installed at many facilities throughout the U.S. Most of these systems are relatively new and extensive operational experience is lacking. This study presents an examination of the performance of a system at the U. S. Public Health Service's Gillis W. Long Hensen's Disease Control Center located in Carville, Louisiana. The AWF is designed to meet effluent standards of 10 mg/L 5‐day BOD (BOD5) and 15 mg/L TSS, based on a design flow of 568 m3/d (150 000 gpd) with a 24‐hour detention time. The AWF has a 0.69‐m depth of 2–8 cm rock with a 15cm pea gravel cap and swamp potato (Sagittaria latifola) and duck potato (Sagittaria falcata) planted on 30‐cm centers. The study was initiated in the spring of 1988 and samples were collected twice a week from seven sampling stations and analyzed for BOD5, flow rates, temperature, pH, TSS, and VSS. The results indicated that the AWF was effective at controlling BOD5 and TSS within design standards over a range of hydraulic fluctuations of 163–871 m3/d (43200–230000 gpd). The AWF removed 62 and 76.5% of the influent BOD5 and TSS, respectively. Analysis of samples taken from sample wells located in the first one‐third of the filter indicated 40 and 60% removal of BOD5 and TSS, respectively. Step flow introduction of wastewater could better optimize filter bed volumes and maintain uniform plant growth. For new AWF systems designs, greater length to width ratios could achieve the same treatment while minimizing front end clogging and ponding problems.