Soil Clogging During Subsurface Wastewater Infiltration as Affected by Effluent Composition and Loading Rate

Abstract

AbstractThe soil clogging effects of wastewater effluent composition and loading rate were investigated in pilot‐scale infiltration cells installed in situ in the structured silty clay loam subsoil of a Typic Argiudoll (fine‐silty, mixed, mesic). Over a 70‐month period domestic septic tank effluent (DSTE), graywater septic tank effluent (GSTE) and tapwater (TW) were intermittently applied in an average of 5.2 doses/d to yield daily loading rates of 1.3, 2.6, and 5.2 cm/d. Soil clogging was negligible in all TW treatments and in the GSTE treatments at 1.3 and 2.6 cm/d. In the GSTE treatments at 5.2 cm/d and in all DSTE treatments, severe soil clogging led to continuous ponding of the soil infiltrative surfaces. A logistic model fit to the experimental data confirmed that soil clogging development was highly correlated with the cumulative mass density loadings of total biochemical oxygen demand and suspended solids. After 62 and 70 months of loading, soil properties were determined with depth. Clogged infiltrative surface zones exhibited significant accumulations of organic materials at the infiltrative surface and within the first few millimeters of the soil matrix. This field study demonstrated that higher quality wastewater effluents can be discharged to subsurface infiltration systems at hydraulic loading rates in excess of those utilized for DSTE without stimulating soil clogging development.