Abstract
Conventional onsite wastewater treatment system design relies on a septic tank and soil treatment unit (STU) for treatment of wastewater and integration of the final effluent into the environment. Organic water contaminants (OWCs), chemicals found in pharmaceutical drugs, detergents, surfactants, and other personal care and cleaning products, have been observed in septic tank effluent and the environment. Sorption of OWC mass to soil is a key mechanism in the removal and retardation of many of these chemicals in effluent as it travels through an STU. The primary purpose of this study was to investigate the relationship between the fraction of organic carbon of soil and the equilibrium sorption partitioning coefficient of a selected group of relevant and diverse OWCs. A secondary goal is to evaluate current methods of modeling the sorption of selected OWCs in soil. Five point Freundlich isotherms were constructed from equilibrium sorption batch tests for target OWCs with four different soils. For soils with organic carbon fraction between 0.021 and 0.054, Kd values were calculated between 60 and 185 for 4-nonylphenol, 75 to 260 for triclosan, 115 to 270 for bisphenol-A, 3 to 255 for 17β-estradiol, 40 to 55 for 17α-ethynylestradiol, and 28 to 70 for estrone. An empirically derived, direct relationship between foc and Kd may be a useful approach to estimating sorption for a soil based on organic carbon content.
Highlights
One fifth of the US population is served by onsite wastewater treatment systems (OWTSs), which are a significant and growing means of wastewater treatment in the US [1]
Sorption to soil is a key process in the fate and transport dynamics of Organic wastewater contaminants (OWCs) as they infiltrate through soil
The Kd value is used to characterize sorption in fate and transport models that consider the advection-dispersion equation incorporating solute transport and, generally, model output is highly sensitive to the magnitude of this parameter
Summary
One fifth of the US population is served by onsite wastewater treatment systems (OWTSs), which are a significant and growing means of wastewater treatment in the US [1]. Endocrine disrupting chemicals (EDCs) are a subclass of OWCs that can impair reproductive development and hormone production in some organisms This effect has been well documented in fish and amphibians, with some populations experiencing skewed gender ratios and/or feminization of males [4]. Antimicrobial OWCs may contribute to the evolution of resistant strains of bacteria [7,8,9] Given these potential adverse impacts and the large and growing fraction of US wastewater treated by STUs, an accurate understanding of the factors controlling the removal of OWCs in STUs is needed. This knowledge will aid in the understanding, design and operation of STUs so as to minimize environmental impacts
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