Marx, Kurt. 1999. Nutrient removal efficiency of a Pacific Northwest treatment wetland receiving sewage lagoon effluent. M.S.
In 1993, the City of Stanwood, Washington constructed a free water surface wetland to demonstrate the effectiveness of treatment wetland technology. The pilot wetland system treats approximately 18,000 gallons per day (approximately 7% of total plant flow). This project investigated the nutrient removal efficiency, design and operational parameters of a Pacific Northwest treatment wetland receiving primary sewage lagoon effluent.
Primary effluent from a partial-mix pond was fed to four parallel wetland cells in a flow ratio of 1:2:3:4. Each cell consists of a marsh area, followed by a wet meadow area. The marshes contained predominately Scirpus acutus (hard-stem bulrush). Vegetation in the wet meadows consisted mainly of Juncus effusus (soft rush), Phalaris arundinacea (reed canary grass), and Typha latifolia (cattail). Water quality, flow rate, and weather parameters were monitored for 12 months. Nutrient removal efficiencies quantified included ammonium (NH4+), nitrate (NO3), and total phosphorus (TP). Weekly BOD and TSS were also measured. Finally, a lithium tracer study was conducted to determine the actual hydraulic retention time of each cell.
Annual ammonium mass removals ranged from 11% to 87%. Total phosphorus reduction ranged from 14% to 66%. Nutrient removal was found to be primarily a function of loading rate, retention time, temperature, and vegetation patterns. Wetland effluent BOD and TSS concentrations were generally below current discharge limits. Actual retention times were from 31% to 77% lower than theoretical retention times.
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