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Developing Tools to Attenuate Emerging Contaminants in Onsite Wastewater Treatment Systems

Toor, Gurpal
University of Florida
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The overall goal of this project is to develop tools to attenuate EC from OWTS to protect drinking water supplies of rural populations. The central hypothesis of this project is that EC will respond (sorb, degrade, volatilize, mineralize, leach) differently according to their physicochemical properties, soil characteristics, and vadose zone conditions (aerobic, anaerobic); and that these properties can be manipulated to enhance EC attenuation and prevent groundwater contamination.

Specifically, the research and extension education objectives of this project are to (1) investigate the potential of current advanced treatment systems, using aerobic and anaerobic bio-filters, to remove concentrations of carbamazepine, sulfamethoxazole, estradiol, triclosan, and 1,4-dichlorobenzene in OWTS, (2) determine the fate of these EC in the vadose zone of OWTS, (3) elucidate pathways of EC transport from vadose zone to groundwater and determine the risk of groundwater contamination, and (4) provide training, education, and outreach about the risk and ways to reduce groundwater contamination by EC to stakeholders using traditional and new extension methods.

This project will provide information on potential of various media bio-filters to remove EC from onsite wastewater. Knowledge about the fate (sorption, degradation, volatilization) of EC will allow determination of the proportion of EC attenuated in the vadose zone and how different treatments can be optimized to prevent groundwater contamination.

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Non-Technical Summary:
Contamination of groundwater with a new class of contaminants known as emerging contaminants (EC) is an increasing concern as about 60,000 million liters per day or 19% of total groundwater withdrawn is used to supply drinking water for the nation's population. Another 13,000 million liters per day of groundwater is used from domestic wells for drinking purposes. Typically, homes with drinking water wells also have a septic tank system (hereafter referred to as onsite wastewater treatment system, OWTS) to dispose of household wastewater. OWTS are a sanitary necessity for rural populations, but they also create pathways for groundwater contamination with EC. Many of the EC can cause endocrine disruption in wildlife and can adversely affect human health. The impacts of EC contributed by OWTS on groundwater are poorly understood. The shallow and porous soils in the US Southeast coastal plains allow rapid percolation of wastewater and potentially EC into the groundwater. In these soils, the mechanisms such as sorption, degradation, and volatilization may not effectively attenuate EC in the shallow subsurface (vadose zone). As OWTS represent a direct source of EC to the shallow subsurface, development of tools to attenuate EC will help to protect the nation's well water and drinking water supplies. In this project, we will target five EC representing pharmaceuticals (carbamazepine, sulfamethoxazole), steroids (estradiol), antimicrobials (triclosan), and disinfectants (1,4-dichlorobenzene).

The main study site is located at the Gulf Coast Research and Education Center (GCREC) of the University of Florida in Wimauma, FL. At this site, wastewater is intercepted from graduate housing units and business units of the GCREC (daily load of ~50 people). This OWTS is a pressure dosed system with a capacity of 10,000 liters per day and includes two septic tanks (9,500 and 4,750 liters). A part of the wastewater is first carried to septic tanks passing through various media combinations. Each of the media combinations includes two connected aerobic and anaerobic media bio-filters. For Objective 1, wastewater will be collected at three points: wastewater from the facility, outlets of aerobic media bio-filters, and outlets of anaerobic media bio-filters to determine EC removal at each treatment step. For Objective 2, test areas (mounds) representative of typical OWTS will be established at the GCREC and wastewater will be dispersed in these mounds. Using installed suction lysimeters at five depths, samples will be collected and analyzed. Bench-top studies will be conducted using soil collected from mounds with onsite wastewater in both unsaturated and saturated conditions to determine sorption, degradation, and volatilization mechanisms of EC dispersal. For Objective 3, test areas will be monitored for depth of the groundwater table, gradient (i.e., water level), and groundwater quality (i.e., EC). Groundwater samples will be collected using piezometers and analyzed to determine if additional EC attenuation is achieved due to unsaturated conditions in groundwater. The collected samples will be analyzed for pH, chloride, alkalinity, BOD, COD, and five EC, using EPA or equivalent methods.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Sanitation and Quality Standards
Education and Training