Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Treatment of septic tank effluent (STE) or raw wastewater using a recirculating media filter (RMF) and an aerobic treatment unit (ATU), respectively, prior to subsurface dispersal has been shown to enhance the longevity of the dispersal system and ensure protection of ground and surface water. A field evaluation of pre-engineered RMF (three years) and ATU (two years) was conducted to determine the effluent quality produced by these systems. Effluent from the RMF (RMFE) was applied to field prototype trenches using a simulated low-pressure distribution (LPD) system while effluent from the ATU (ATUE) was applied to a raised filter bed (RFB). The LPD trenches were dosed with RMFE at rates of 2.13 and 4.26 cm d -1 from 10/97 to 6/99 and at 4.26 and 10.65 cm d -1 from 10/99 to 6/00 and STE at a rate of 2.13 cm d -1 . The RFB received ATUE generated from a single-family residence. Both the RMF and the ATU consistently produced a high quality effluent with >99.5% of the N being nitrified. The fecal coliform counts were <150 and <2000 counts 100 mL -1 and the BOD5 concentrations were < 5 and <10 mg L -1 for the RMFE and ATUE, respectively. A coliphage study in the RMF showed that phage dieoff was complete after 12 h. In both the RFB and LPD dispersal systems there was limited movement of fecal coliforms. In the RFB, there was limited P transport and N decreased with distance from the effluent application area, with almost no detectable N being present at the end of the RFB. Nitrate (NO3)-N/Cl ratios indicated that NO3 disappearance was not a result of dilution and was attributed to denitrification. In the LPD trenches, the average NO3 concentrations were >11 mg N L -1 at all sample points and P concentration increased with time. Infiltration rates in the prototype trenches have not decreased during the study where RMFE was applied at rates two and five times higher than the STE loading rate recommended in Virginia. This paper will present details of the study and complete analysis of the data along with the conclusions related to the effectiveness of pre-engineered treatment and effluent dispersal technologies for onsite systems. (Download PDF)    (Export to EndNotes)