Residential subsurface flow treatment wetlands in northern Minnesota

Abstract

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.

Effect of alternative on-site wastewater treatment on the viability and culturability of Salmonella choleraesuis

“…Further details about the treatment systems and their seasonal performance for removing the model pathogen, Salmonella choleraesuis, may be found in Pundsack (2000) and Pundsack et al (2001). Details regarding the overall design, construction, operation and performance of the treatment systems may be found in McCarthy et al (1997McCarthy et al ( , 1998McCarthy et al ( , 1999 and Axler et al (1999Axler et al ( , 2001. (Hicks et al 1992;DeLong 1993;Amann et al 1995;Pommepuy et al 1996).…”

Seasonal virus removal by alternative onsite wastewater treatment systems

“…McCarthy et al (1997,1998,1999) and Axler et al (2001) showed significant decreases in the reduction of nitrogen, phosphorus and BOD 5 in winter relative to summer.…”

“…These viruses, including polio virus, hepatitis, norwalk virus, rotavirus and others, can easily reach water sources and become a serious human health concern. This problem is accentuated in communities in northern Minnesota due to lack of centralized wastewater treatment, small lot size, close proximity to water sources, poor or thin soils, and a long, severe winter during which performance may decrease dramatically (Crosby et al 1998;McCarthy et al 1998McCarthy et al , 1999Axler et al 2001;Henneck et al 2001;Pundsack et al 2001;Kadlec et al 2003). In Minnesota, nearly 30% of the population is dependent on onsite treatment systems with more than 500,000 individual onsite treatment systems in use state-wide (MPCA 1996).…”

“…fecal coliforms and E. coli). Recently, demonstration projects performed near Duluth, Minnesota, at a cluster CW treatment system at Grand Lake and at replicate residential sized systems at the North East Regional Correction Center (NERCC) research site showed them to be effective in removing fecal coliforms year round, but with reduced efficiency in the winter (McCarthy et al 1998(McCarthy et al , 1999Axler et al 2001;Henneck et al 2001;Monson-Geerts et al 2001;Pundsack et al 2001Pundsack et al , 2005. Traditional bacterial indicators have come under intense scrutiny as indicator organisms for human pathogens because of their lack of correlation with levels of enteric viruses and their low survivability in aquatic environments (Goyal & Gerba 1983;Stetler 1984;Havelaar et al 1993;Ferguson et al 1996;Calci et al 1998;Leclerc et al 2001).…”

“…nominal retention time of 13 days and areal loading rate of 2.6 g BOD per m 2 day 21 . The first cell of each wetland was planted with cattail species, Typha latifolia and Typha angustifolia, and was designed to achieve a 6.5 day hydraulic retention time (HRT) and achieve the level of secondary treatment based on best available design information (details inAxler et al 1996Axler et al , 2001Kadlec & Knight 1996;McCarthy et al 1997).The second cells of each constructed wetland were designed to enhance nutrient removal by doubling the HRT of the wetlands to 13 days to improve nitrogen removal (see Axler et al 2001). These cells were planted with greenhouse raised soft-stem bullrush, Scirpus taebermontani, also intended to aid in N-removal.…”