First-year performance evaluation of a cold climate constructed wetland for wastewater treatment
Date
1999
Authors
Andre, Mary DeMartini, author
Ward, Robert C., advisor
Albertson, Maurice, committee member
Klein, Donald, committee member
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Abstract
A unique, subsurface flow (SF), constructed wetland pilot study was carried out at Highlands Presbyterian Camp located near Allenspark, Colorado. This site is located in a cold climate region at an elevation of 2530 m (8300 ft). The Highlands treatment system, designed for enhanced removal of suspended solids, biochemical oxygen demand, nutrients, and fecal conforms, was constructed in the late summer of 1996 and monitored from October 1996 through September 1997. The Highlands treatment system is a multiple-unit, passive treatment train with a 1.9 m3/d (500 gpd) capacity located in between a standard septic tank and leachfield. The septic tank effluent flows sequentially through an upflow anaerobic filter with a dosing siphon, a vertical flow aerobic filter, a constructed SF wetland, and another automatic siphon dosing chamber to dose a subsurface disposal field. Water quality monitoring of the system involved measuring physical, chemical, and biological variables at four sampling ports, which isolated each treatment unit. These variables included flow, water temperature, pH, total dissolved solids (TDS), specific conductance, dissolved oxygen (DO), oxidation-reduction potential (ORP), 5-day biochemical oxygen demand (BOD5), total suspended solids (TSS), total organic carbon (TOC), ammonia/ammonium (NH3/NH4+), nitrites/nitrates (N02-/N03-), total phosphorus (TP), and fecal coliforms (FC). Water quality monitoring was performed approximately biweekly for one year. Monitoring results for the system’s first year of operation showed a reduction in BOD5, TSS, TP, and FC. However, the removal efficiencies are generally less than those presented in the literature for more established systems. As the literature indicates, the consistency and magnitude of removal efficiencies are expected to improve with maturation of the wetland plants and establishment of microbial communities. Seasonally, the removal efficiencies for TSS, TP, and FC were more consistent and of higher magnitude in the warmer months than in the colder months. The removal efficiency for NH3/NR4+-N was negative in the colder months (indicating an increase through the system) and positive in the warmer months. The lower hydraulic wastewater loading during the winter months due to lower attendance levels at the camp provided a longer hydraulic residence time and compensated for the reduced treatment capability of the wetland at colder temperatures. The effluent from the system did not meet secondary treatment standards for BOD5 and TSS consistently. In addition, the observed removal efficiencies of BOD5 and TSS for the SF wetland were significantly lower than those predicted by first-order kinetic models and regression models from the literature. However, the influent wastewater was consistently at least twice typical domestic wastewater strength. The development of full wetland treatment potential is expected to take several growing seasons. Further monitoring is necessary to document nitrogen reduction and pollutant removal trends with respect to seasonal variation and system maturation.
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Subject
Constructed wetlands
Sewage -- Purification -- Biological treatment
Sewage disposal in the ground