Nutrient removal from septic effluents as affected by soil thickness and texture

Abstract

This study evaluated the effectiveness of soils with different textures and thickness to treat BOD, N and P eluted from household septic effluent. The assessments were accomplished by leaching undisturbed soil monoliths of 30, 45 and 60 cm thickness and 25 cm in diameter, representing the four different textural groups and hydraulic loadings recommended by the Kentucky Health Department, with domestic wastewater effluent collected regularly from a household septic system. Effluent concentrations were monitored daily over a 15d period for biochemical oxygen demand (BOD), total-N, NH4-N, NO3-N and total-P concentrations. The results of the study indicate an alarming frequency of failure to comply with EPA criteria for BOD, total-N and NH4-N concentrations when using a 30 cm vertical separation distance between the bottom of the drain field and a limiting soil interface. The treatment performance was particularly poor in coarse-textured soils, apparently due to insufficient reactive surface area. Although biomat development over time is expected to improve the treatment for some of these parameters, the high influent levels of BOD pose great concerns for surface and groundwater contamination during the early stages of operation. Fine-textured soils generally provided better treatment efficiency and more consistent compliance with EPA standards for BOD, total-N, NH4-N and total-P, as well as greater nitrification/denitrification potential. Treatment efficiency and compliance usually improved with increasing soil depth, with the 60 cm thickness providing the most consistent performance and compliance with MDL requirements. Considering that increasing soil thickness requirements may be impractical in many marginal soils, complementary or alternative treatment technologies should be adopted to improve treatment efficiency and prevent further deterioration of the quality of water resources.

Controls on groundwater nitrogen contributions from on-site wastewater systems in coastal North Carolina

“…Karathanasis et al (2006) that found finer textured soils (clay loams and clays) were more efficient at reducing NH 4 , total N and BOD than coarse textured soils, due to more reactive surface areas and greater nitrification/ denitrification potential.CONCLUSIONSOSWWS in soil groups I and II were less effective at DIN removal as compared to systems in soil group III.OSWWS installed in soil groups II with 30 cm of separation distance and in soil group I with 45 cm of separation distance consistently contributed septic effluent with elevated NH 4 þ -N concentrations to the shallow groundwater. The shallow groundwater in coastal North Carolina is connected to the adjacent surface waters and such pollutant loading may contribute to eutrophication and fish kills.…”

Meteorological Influences on Nitrogen Dynamics of a Coastal Onsite Wastewater Treatment System

“…Although numerous studies have focused on the effects of soil type and groundwater depth on OWTS N treatment (Cogger and Carlile 1984; Karathanasis et al 2006; Humphrey et al 2010a) few studies have focused on the effects of meteorological conditions on OWTS N treatment in coastal settings. Arnade (1999) looked at the effects of increased summer rainfall patterns and shallow water tables on groundwater NO 3 − -N concentrations in Palm Bay, FL.…”

Groundwater Quality

“…Soil texture and depth also were also determined to be important for removal of fecal bacteria from septic effluents (Karathanasis et al, 2006b). The recommended separation of 30 cm between the bottom of the drain field and a limiting soil interface was generally inadequate for removing coliforms, especially for coarser soils.…”