Residential subsurface flow treatment wetlands in northern Minnesota.
Approximately 30% of Minnesotans use on-site systems (approximately 500,000 residences) and >50% are failing or non-compliant with regulations due to restrictive soils and site conditions. Many sites occur near lakes and streams creating health hazards and deteriorating water quality. SSF CWs have been evaluated year-round at two northern sites since 1995. The NERCC CWs simulate single homes and the Grand Lake demonstration CW treats STE from a cluster of 9 lakeshore homes. Systems were generally able to achieve design criteria of 25 mg TSS/L and 30 mg BOD5/L and the NERCC CWs required only 0.3 m of unsaturated soil to achieve consistent disinfection to <200 fecals/100 mL year round. Seeding experiments with Salmonella indicated removal efficiencies of 99.8% in summer and 95% in winter. High strength (approximately 300 mg BOD/L, 95 mg TN/L) influent at NERCC probably limited system performance, particularly N-removal (mass) which was approximately 42% in summer and 20% in winter. The data indicate CW's are a viable, year-round treatment option for homeowners in terms of performance, ease of operation, and cost but require additional maintenance related to inconsistent vegetation growth, winter insulation, and meeting concentration-based regulatory standards since they were seasonally and annually variable due to rain events, partial freezing, spring snowmelt, and summer evapotranspiration.
Axler
R
R
Natural Resources Research Institute, University of Minnesota, Duluth 55811, USA.
Henneck
J
J
McCarthy
B
B
D003080:Cold Temperature; D017753:Ecosystem; D005160:Facility Design and Construction; D019983:Guideline Adherence; D006798:Housing; D008910:Minnesota; D009584:Nitrogen / Q000378:metabolism; D010944:Plants; D011786:Quality Control; D012621:Seasons; D014865:Waste Disposal, Fluid / Q000379:methods*; D014881:Water Supply
D009584:Nitrogen