Onsite septic systems are used for wastewater treatment for households not connected to sewers. There is a concern about surface and groundwater pollution when effectiveness becomes limited due to soil texture, soil temperature, neighborhood density, and distance to water resources. The goal of this study was to assess treatment performance of local soils and selected treatment media. Lab-scale column experiments were conducted using wastewater from Wastewater Reclamation Facility in Rapid City. The experiments were conducted inside and outside the lab to evaluate the effect of temperature. The columns outside the lab were subject to seasonal variation in temperature. Moisture content, temperature, and flow volume were monitored. The results indicated that higher nitrate removal was observed using redwood, biochar, and woodchips, respectively, when compared to the local soils. Average effluent nitrate concentration was 16.3 mg/L for alluvial columns followed by cedar soil (13.1 mg/L) and sand (11.3 mg/L). The performance of biochar, woodchip, and redwood was significantly higher than the local soils with an average effluent concentration of 8.5, 8.3, and 6.7 mg/L respectively. The reduction in nitrate concentration relative to alluvial columns were 20%, 31%,48%,49% and 59% respectively for cedar soil, sand, biochar, woodchips, and redwood. The performance of redwood was relatively better than biochar and woodchip. Findings from this study are useful for development of novel subsurface treatment systems, and for identifying parameters for assessing watershed-scale impacts in cold climatic regions.
Geza, Stu; Menkhaus, Todd; Li, Lianping; and Hoogestraat, Galen, "Assessment and Improvement of Performance of Septic Systems in Cold Climates (Year 1)" (2021). SDWRI Publications and Reports. 2.