Improvement of Hydraulic and Water Quality Renovation Functions by Intermittent Aeration of Soil Treatment Areas in Onsite Wastewater Treatment Systems

Abstract

Abstract:We tested intermittent aeration of the soil treatment area (STA) of onsite wastewater treatment systems (OWTS) for its ability to restore and maintain STA hydraulic flow and improve the water quality functions of conventional OWTS. Evaluation was conducted on hydraulically-failed conventional OWTS at three state-owned medical group homes in Washington County, RI, USA. Testing was conducted in two phases, with Phase I (before intermittent soil aeration (ISA)) comprising the first 6 months of the study, and Phase II (during ISA) the remaining 7 months. Intermittent soil aeration restored STA hydraulic function in all three systems despite a marked reduction in the STA total infiltrative surface. Soil pore water was collected from 30 and 90 cm below the STA during both phases and analyzed for standard wastewater parameters. Although the STA infiltrative surface was reduced-and the contaminant load per unit of area increasedafter installation of the ISA system, no differences were observed between phases in concentration of total N, NO 3 , total P, or dissolved organic carbon (DOC). Apparent removal rates-which do not account for dilution or differences in infiltrative area-for OPEN ACCESSWater 2010, 2 887 total N, total P, and DOC remained the same or improved during Phase II relative to the pre-operation phase. Furthermore, intermittent soil aeration enhanced actual removal rates -which do account for dilution and differences in infiltrative area. The effects of ISA on actual removal of contaminants from STE increased with increasing hydraulic load-a counterintuitive phenomenon, but one that has been previously observed in laboratory studies. The results of our study suggest that intermittent soil aeration can restore and maintain hydraulic flow in the STA and enhance carbon and nutrient removal in conventional OWTS.

Mechanisms of Ammonium Transformation and Loss in Intermittently Aerated Leachfield Soil

“…In previous studies we have shown that intermittent aeration of leachfield mesocosms receiving domestic STE have N removal rates ranging from 25 to 75%, depending on the soil type and dosing rates (Potts et al, 2004;Amador et al, 2007). More recently we have shown that N removal rates similar to those in the laboratory are observed in conventional OWTS under field conditions when intermittent aeration is used (Amador et al, 2010). We have hypothesized that intermittent aeration enhances N removal by promoting nitrification (during the aeration phase), followed by denitrification (as STE infiltrates and percolates through the soil), with net N losses attributed to N 2 and N 2 O produced by denitrification (Potts et al, 2004).…”

Microbial Community Structure of a Leachfield Soil: Response to Intermittent Aeration and Tetracycline Addition

“…The headspace of mesocosms was either vented to the septic system leachfield of the house to simulate a conventional leachfield atmosphere (LEACH treatment) or was aerated intermittently with ambient air (AIR treatment) using a process that has been employed successfully to rejuvenate hydraulically-failed septic systems [12]. Each treatment was replicated three times.…”