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Microconstituents in Biosolids: The “New” Pollutants—An Overview of Recent U.S. Geological Survey Research and Findings

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The importance of point-source wastewater discharges of treated wastewater as sources of estrogens, pharmaceuticals, and other organic microconstituents (MCs) to surface and groundwater has been demonstrated in a number of recent studies. A comprehensive understanding of the processes controlling the transfer, transformation, or removal of these compounds in solid and liquid phases during wastewater treatment, and the subsequent fate and behavior of MCs in discharged effluent and biosolids, is only now being developed. The posttreatment fate of MCs associated with biosolids following composting and land application is less well understood and warrants additional fate- and behavior-orient research. Research conducted as part of the Toxic Substances Hydrology Program's Emerging Contaminants Project have addressed the need to develop a more comprehensive understanding of the fate and behavior of MCs in biosolids through collaborative projects that study the fate and behavior of a wide array of MCs.

One research effort focuses on the fate of MCs in solid and liquid phases as influent is processed through wastewater treatment systems typical of those in operation within the United States. The second research effort addresses the dissipation and fate of MCs at typical field application sites where biosolids are presently (2009) used as soil amendments in pasture and crop land.

In the wastewater treatment plan study, solid and liquid waste samples were collected at major treatment stages through four large municipal wastewater-treatment plants (WWTPs) that use different treatment technologies (mesophilic anaerobic digestion, mesophilic aerobic digestion, thermophilic anaerobic digestion, and lime stabilization) that are representative of WWTPs across the United States. Concentrations of pharmaceuticals, estrogens, and other MCs in these samples were determined to evaluate the efficiency of each treatment stage for removal and transfer between liquid and solid phases during treatment, and to determine instantaneous loads of individual compounds within the treatment train in these specific WWTPs.

Preliminary results suggest that most pharmaceutical, estrogen, and MC concentrations in liquidphase samples decrease substantially after activated sludge treatment, frequently by 90 percent or more. Concentrations of triclosan and the fragrances galaxolide and tonalide were high in primary unthickened sludge, decreased substantially in secondary thickened sludge, and increased through subsequent treatment processes such that the highest concentrations were present in the final digested sludge. However, concentrations of several pharmaceuticals, including diphenhydramine, miconazole, and carbamazepine, were highest in primary unthickened sludge, decreased substantially (by 50 percent or more) in secondary unthickened sludge, and remained relatively constant in subsequent sludge-treatment steps. Development of solid and liquid mass balances is underway to determine total contaminant loads in liquid and solid waste streams, which is critical to evaluating the relative importance of phase transfer and remineralization in the environmental fate of targeted MCs.

In the field application site studies, a working farm site where biosolids were applied for the first time was chosen to study the potential for MC migration through the soil column following application and followed for about 1.5 years post application, through crop production and harvest. A second experiment examined the initial mobililization of MCs in solid and liquid phase whe artificial rainfall was applied to the field following first-time biosolids application. The biosolids, produced from activated sludge secondary treatment, were applied at agronomic rates, and tillage, fallow periods, planting, and harvest were typical agricultural practice for the region.

Preliminary results from the soil column study suggest that at least four chemicals (betasitosterol, indole, cholesterol, and d-limonene) associated with the applied biosolid wre detected in the soil column to at least 41 centimeters (1.3 feet). Chemicals that were still present in the soil below 13 cm (.5 feet) 6 months after biosolids application included cholesterol and dlimonene. In the artificial rainfall study, mobilization of multiple MCs associated with the biosolid was observed, including tri(dichloroisopropyl) phosphate, triclosan, n,n-diethyl-metatoluamide (DEET), indole, and the fragrances galaxolide and tonalide. The concentrations of these MCs increased immediately upon the initiation of overland flow, and persisted throughout the duration of overland flow, suggesting that biosolids may act as a source of MCs when precipitation occurs on fields where biosolids have been recently applied.

A third component of this research program characterizes the potential for uptake of MCs from field-applied biosolids. In proof-of-concept studies conducted at biosolids application sites in Iowa and Oregon, biosolids, soils, and indigenous earthworm populations were assayed for MC content following biosolids application. Results from this study demonstrate that indigenous earthworm populations bioaccumulate and biomagnify MCs present in applied biosolids, including pharmaceuticals, synthetic fragrances, detergent metabolites, polycyclic aromatic hydrocarbons (PAHs), biogenic sterols, disinfectants, and pesticides,. For those contaminants detected in earthworm tissue and soil, bioaccumulation factors (BAF) ranged from 0.05 (galaxolide) to 27(triclosan), documenting that when MCs are present in biosolids, they can be transferred to earthworms.
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Keywords: Biosolids; Environmental Fate; Land Application; Microconstituents

Document Type: Research Article

Publication date: 2009-01-01

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