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ONSITE TREATMENT OF SEPTIC TANK EFFLUENT IN MINNESOTA USING SSF CONSTRUCTED WETLANDS: PERFORMANCE, COSTS AND MAINTENANCE
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: Pp. 649-661 in On-Site Wastewater Treatment, Proc. Ninth Natl. Symp. on Individual and Small Community Sewage Systems (11-14 March 2001, Fort Worth, Texas, USA), ed. K. Mancl., St. Joseph, Mich. ASAE 701P0009.(doi:10.13031/2013.6070)
Authors: J. Henneck, R. Axler, B. McCarthy, S. Monson Geerts, S. Heger Christopherson, J. Anderson, J. Crosby
Keywords: Constructed wetlands, wastewater, alternative technologies, cold-climate
About 30 % of Minnesotans use on-site systems for wastewater treatment (~500,000 residences). Unfortunately, 55-70 % are failing or out of compliance with state standards. Homeowners and small businesses require cost-effective options in locations with restrictive soil and site conditions. In particular, many sites occur near lakes and streams creating a health hazard and deteriorating water quality. Constructed wetlands (CWs) are one option being evaluated and this paper addresses CWs as a viable wastewater treatment option in Minnesota based on experiences at three research sites, encompassing 5 subsurface flow wetlands from 1995-2000. These are small flow (<1000 gpd) subsurface flow gravel beds located at the Northeast Regional Correction Center (NERCC), Grand Lake, and Lake Washington, MN. Performance monitoring shows that CWs are a viable, year-round onsite treatment option. The systems were generally able to achieve design criteria of 30 mgBOD5/L, 25 mgTSS/L and 200 fecal cfu/100mL, although the NERCC CWs required 30 cm. of unsaturated soil to achieve consistent disinfection. High strength (~300mgBOD/L and 100mgTN/L) influent at NERCC probably limited system performance, particularly N-removal which was ~40% in summer and ~20% in winter (mass-based). Declining P-removal at the oldest sites suggest substrate saturation. Although CWs remain a viable option for homeowners in terms of performance, ease of operation, and cost, other issues relate to inconsistent vegetation growth (affecting performance and freezing), and meeting concentration-based regulatory standards since they may exhibit substantial variability due to rain events, partial freezing, spring snowmelt, and summer evapotranspiration.(Download PDF) (Export to EndNotes)