Approximately 500,000 Minnesota residences rely on the use of onsite wastewater treatment
systems and >50% of these systems may be in noncompliance with state rules or are failing to
the surface. A research site at the Northeast Regional Correction Center near Duluth was
established in 1995, involving~ 50 private and public sector partners, to design, construct, and
monitor the performance of advanced onsite treatment systems. The systems were generally
designed to treat 250 gal/day of septic tank effluent from single family homes to meet secondary
treatment standards; 25 mg/L total suspended solids (TSS), 30 mg/L biochemical oxygen
demand (BOD5), and 200 cfu/lOOmL fecal coliform bacteria. In 1998, pre-engineered peat filters
(Puraflo®, Bord Na M6na, Inc.) were installed to compare the performance of a standard Irish
peat to a Bord Na M6na specified Minnesota peat. Initially, the peat filters were operated in the
recirculating mode for enhanced nitrogen removal, but were changed to single-pass mode after
ponding occurred. Hydraulic failure likely resulted due to cold temperatures (since the modules
were not insulated) coupled with high strength waste. With minor design modifications,
including foam-insulated covers, the single-pass peat filters have operated without problems. In
the recirculating mode, seasonal removal rates for both types of peat ranged 86-97% TSS, 94-
97% BOD5 96-99% fecal coliform bacteria, 6-20% total phosphorus (TP), and 31-45% total
nitrogen (TN). As single-pass filters, removal rates were comparable at 89-96% TSS, 95-98%
BOD5 >99% fecal coliform bacteria, 94-99% coliphages, 0-20% TP, and 24-37% TN for both
peat types. The module Puraflo® peat filter systems, using both the standard Irish peat and a
Minnesota peat, performed comparably and generally exceeded secondary treatment standards.
University of Minnesota Duluth, Natural Resources Research Institute, 5013 Miller Trunk Highway, Duluth, MN 55811-1442
Monson Geerts, Stephen D; McCarthy, Barbara J; Axler, Richard P; Henneck, Jerald.
Performance of Pre-engineered Modular Peat Filters for the Treatment of Domestic Wastewater at the Northeast Regional Correction Center.
University of Minnesota Duluth.
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