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Evaluation of recirculating sand filter in a cold climate.
S H Christopherson1, J L Anderson, D M Gustafson
1University of Minnesota, Water Resource Center, 1985 Buford Avenue, 173 McNeal Hall, St. Paul, MN 55108, USA. heger001@umn.edu
Summary
Recirculating sand filters (RSFs) effectively treat wastewater for small flows, reducing BOD5, TSS, and nutrients. While fecal coliform reduction is significant, further treatment is needed for full environmental protection.
Area of Science:
- Environmental Engineering
- Wastewater Treatment Technologies
- Onsite Sewage Treatment
Background:
- Minnesota residents heavily rely on onsite wastewater treatment systems.
- A need exists for alternative treatment technologies for challenging sites and sensitive environments.
- Recirculating sand filters (RSFs) are increasingly used for small flow applications due to their compact footprint.
Purpose of the Study:
- To evaluate the performance of Recirculating Sand Filters (RSFs) for small flow wastewater treatment.
- To assess the effectiveness of RSFs in reducing key wastewater contaminants.
- To determine the suitability of RSFs for difficult site conditions and sensitive environmental areas.
Main Methods:
- Two RSFs were installed at a research site in southern Minnesota in 1995.
- Two additional RSFs were integrated into problematic existing residential systems in 1998.
- All RSFs utilized 0.6 meters of coarse sand, loaded at 204 L/day/m², with a 5:1 recirculation rate.
Main Results:
- RSFs effectively reduced Biochemical Oxygen Demand (BOD5), Total Suspended Solids (TSS), Fecal Coliform (FC), and nutrients (nitrogen and phosphorus).
- Secondary effluent treatment levels for BOD5 and TSS were consistently achieved.
- Median FC reduction was 90% (5.7 E4 cfu/100 mL), indicating a need for further treatment.
- Consistent removal of ≥25% Total Phosphorus (TP) and ≥40% Total Nitrogen (TN) was observed.
- RSF performance remained stable during winter months.
- RSFs receiving high-strength domestic waste showed enhanced Total Nitrogen (TN) removal due to added carbon.
Conclusions:
- RSFs are a viable alternative technology for small flow wastewater treatment, offering significant contaminant reduction.
- While effective for BOD5 and TSS, additional treatment is recommended for fecal coliform reduction to ensure public health and environmental safety.
- RSFs demonstrate consistent performance, even in colder climates, and can benefit from high-strength waste inputs for improved nitrogen removal.