Novel septic system design to prevent failureEPA Grant Number: SU839288
Title: Novel septic system design to prevent failure
Investigators: Elliott, Mark
Current Investigators: Elliott, Mark , Tick, Geoff , Terry, Leigh , Mortazavi, Behzad , White, Kevin
Institution: University of Alabama
EPA Project Officer: Page, Angela
Project Period: February 1, 2018 through January 31, 2019
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2017) RFA Text | Recipients Lists
Research Category: P3 Awards , Sustainability , P3 Challenge Area - Water
Onsite wastewater treatment systems (OWTS) are used by roughly 20% of US households, including over 60% of rural households. The vast majority of these OWTS are conventional septic systems, which rely on infiltration into the subsurface to achieve adequate wastewater treatment. In some geological conditions and geographic areas septic systems tend to operate successfully, affordably treating household wastewater for many years. However, septic system failure is of particular concern in two types of geological settings: (1) areas with impermeable soils or shallow aquitards and (2) coastal areas. There are two major categories of septic system failure: (1) hydraulic failure and (2) environmental failure. Hydraulic failure is typified by wastewater surfacing in the yard or backing up into the plumbing of a home. Environmental failure, in contrast, typically does not occur on the property where it was generated; rather, inadequately treated wastewater reaches a groundwater or surface water, contaminates that water and adversely impacts use. The exposure of children and others to pathogens when untreated wastewater surfaces in the yard causes substantial health risk. There is very troubling but largely unknown evidence from Alabama that helminth (worm) infections are common among children in poor, rural areas. The last survey of helminth infections in rural Alabama was a master’s thesis project from University of Alabama at Birmingham in 1993; the study revealed that roughly 33% of children under-10 tested positive for one or more helminths (Badham, 1993).
In this P3 project, we plan to design and test a modification to a conventional septic system trench that we propose can decrease the probability of both hydraulic and environmental failure and also attenuate their consequences. Our proposed design includes a number of innovations to conventional septic system trench design; many of these innovations arise from surprising and counterintuitive research findings from co-PI Dr. Kevin White and others (e.g., White and West, 2003). We propose to both combine the characteristics of the two most popular septic system trench designs (the “pipe and gravel” trench and the Infiltrator® chamber system) and propose new innovations that we believe can further improve performance. The major shortcoming of the “pipe and gravel” trench is the presence of fine particles that wash off the gravel and cause clogging whereas infiltrator systems lack granular media to increase pressure head; both systems could benefit from more robust biological wastewater treatment in the trench. Briefly, we propose to utilize an Infiltrator®-style chamber with a high surface area plastic media and a tortuous flow path in a narrower than average, 18” trench. We believe this design will yield the following technical advantages: (1) media without fine particles prevents common failures due to clogging; while (2) the presence of media increases the pressure head leading to increased infiltration rate; (3) extended contact time with high surface area media will enhance treatment of biological and chemical contaminants; and (4) a narrower trench increases sidewall area for increased infiltration rates. These practical advantages will reduce the risk of hydraulic failure by increasing infiltration rates. They will also reduce the probability and severity of environmental failure through improved treatment, yielding higher quality effluent infiltrating into the subsurface.
An additional innovation is meant to address risk of exposure to pathogens if and when hydraulic failure does occur. We propose the addition of a pressure release and small-diameter escape pipe that would (1) alert the homeowner that the system was failing, (2) allow discharge of the partially treated effluent to a safe location where children are not exposed, and (3) incorporate a tablet chlorinator to disinfect pathogens prior to discharge. This would prevent exposure of children and other residents to infectious pathogens.
Project activities in Phase I will focus on refining the preliminary design, building lab-scale units to test the effectiveness of the design to (1) reduce hydraulic failure due to clogging and (2) reduce the concentration of bacteria, viruses, nutrients, organic matter, and pharmaceuticals prior to infiltration into the subsurface. The proposed project will incorporate people, prosperity and planet through research activities and community outreach. It addresses people through reduction of health risks from exposure to pathogens and chemical contaminants in wastewater. It contributes to prosperity by enabling an affordable OWTS solution and preventing costly failures and system replacement. It protects the planet by improving the quality of septic system effluent discharged into the subsurface and reducing hydraulic failure. This project will be incorporated into a senior-level environmental engineering lab taught each spring by Dr. Elliott.
Phase I outputs will be achieved through the design, building and testing of our labscale units. Outputs include initial and final designs, laboratory data produced, the Phase I report to EPA and Phase II proposal. Publication of findings and operation of a full-scale, permitted experimental system are planned for Phase II. While our long-term goals for this research include substantial water quality and health outcomes, measurable environmental changes are infeasible given the research focus and length of Phase I. However, throughout the design and testing phases, we plan to engage with licensed installers through our existing partners with the goal of creating a practical design that installers will want to adopt.