State Water Resources Research Institute Program

Project ID: 2008TN52B
Title: Effect of Wastewater Strength on Soil Physical Properties when using Subsurface Drip Irrigation
Project Type: Research
Start Date: 3/01/2008
End Date: 2/28/2010
Congressional District: TN Second
Focus Categories: Wastewater, Treatment, Water Quality
Keywords: Drip Dispersal, Domestic Wastewater, Decentralized Wastewater Management
Principal Investigator: Buchanan, John R.
Federal Funds: $ 25,000
Non-Federal Matching Funds: $ 50,163
Abstract: This project is a continuation of a 2008-2009 project. The focus of that project was to investigate 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.

Two subsurface wastewater drip dispersal research sites have been established and have been receiving wastewater for approximately four years. The first site is in Rutherford County, Tennessee and represents a heavy textured, poorly structured clay soil. The second site is in Blount County, Tennessee, and it is located on a silt loam soil with moderate structure. At each site, two sub-systems have been installed such that half of the site receives septic tank effluent and the other half receives secondary-quality effluent.

The primary question to be answered by the previous project was whether secondary treatment is needed before subsurface drip irrigation? For example, can the advantages of subsurface drip overcome the soil's limitation to provide renovation before the water reaches a limiting boundary (a restrictive layer)? Further, will the physical tubing serve as a limitation - will higher strength wastewater cause failure within the tubing and/or emitters? Preliminary results indicate that the uniform distribution of wastewater provided by drip irrigation does enhance the soil’s ability to renovate septic tank effluent. However, distributing septic tank effluent with subsurface drip irrigation requires the homeowner (or a maintenance provider) to provide more frequent maintenance to the drip system.

The previous project addressed the questions of renovation capacity by conducting extensive soil sampling within each of application fields, and by disinterring the sections of drip tubing. This next phase will focus on the discovery of management practices that are needed to extend the useful life of the drip tubing. The higher strength wastewater (septic tank effluent) promoted microbial growth on the interior surfaces of the tubing. This growth tends to plug the drip emitters, thus reducing the life of the tubing. A common management practice is to flush the tubing with wastewater. Tubing manufacturers promote this notion; however, preliminary evidence indicates that this practice may not be sufficient. This new project will focus on injecting chemical detergents into the flush water to restore the full functionality of the drip tubing.

Progress/Completion Report, 2008, PDF
Progress/Completion Report, 2009, PDF

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