WATER RESOURCES RESEARCH GRANT PROPOSAL
Project ID: 2004TN14B
Title: In-Field Comparison of Drip Distribution Dosed with Septic Tank Effluent vs. Secondary Quality Effluent
Project Type: Research
Focus Categories: Non Point Pollution, Water Quality
Keywords: drip dispersal, domestic wastewater, decentralized wastewater management
Start Date: 03/01/2004
End Date: 02/28/2005
Federal Funds: $24,000
Non-Federal Matching Funds: $136,011
Congressional District: TN2
John R. Buchanan
The University of Tennessee Center for Decentralized Wastewater Management (CDWM) is under contract with the Tennessee Valley Authority (TVA) to investigate the use of drip irrigation technology to disperse wastewater into the subsurface soil. This contract (hence known as the TVA-Drip contract) will be conducted at a housing development served by Consolidated Utility District of Rutherford County. Because this research will be conducted at one location, in one soil series, and with one wastewater stream, the data will not provide information about the natural variability that will occur when using this technology at different locations. The TN-WRRC funding requested by this proposal will supply the necessary resources to replicate the above-mentioned investigation in an East Tennessee location. This replication will allow the effects of the experimental treatments to be observed with a different wastewater source, a different soil type, and a different climate. Having replicate data from different locations greatly strengthen the value of this research effort.
The focus of this project is the use of drip irrigation technologies for the dispersal of domestic wastewater to the subsurface soil. Applying domestic wastewater to the subsurface soil has three basic goals: (1) the soil is a highly-reactive media that provides final treatment of wastewater, (2) the soil minimizes human contact with the potential pathogens in wastewater, and (3) the soil disperses renovated water back into the hydrologic cycle. Drip irrigation is known to provide a uniform water application at a rate that minimizes both temporal and spatial saturated soil conditions. Most conventional methods of applying wastewater to the infiltrative soil surface create long-term saturated zones. Saturated soils are anaerobic and anaerobic microorganisms cannot provide bio-chemical oxidation of the organic compounds contained within wastewater. Although anaerobic microbes thrive on the wastewater and convert some of the organic compounds into new cells, a residual of dead cells clog the pores within the saturated zone. This residual formation is called biomat. Biomat has both positive and negative aspects. Clogged soil pores limit the flow of water through the soil matrix. This limits the volume of water that can be expected to flux through the infiltrative soil surface. The positive aspect of biomat is that it is important for pathogen removal from the wastewater. Biomat creates a hostile environment for human pathogens and scientists are concerned that a system that does not create a biomat will allow pathogens to travel further in the subsurface soil.
The objective of this project is to determine whether wastewater applied by an appropriately-designed drip system must receive secondary treatment before dispersal. A great cost savings will result if secondary treatment is determined to be unnecessary. The null hypothesis is that when using a properly designed drip system, the soil water quality below the infiltration area is not dependent on whether the applied wastewater was septic tank effluent or secondary-quality effluent quality. In other words, the soil will provide sufficient renovation of the wastewater without additional pre-treatment. Statistical analysis will be performed on the data to verify this hypothesis.