The expertise in plant-based waste processing systems generated during the past 15 years as part of the KSC/Advanced Life Support missions has been leveraged to solve terrestrial concerns with wastewater treatment. Leach fields used to treat septic tank effluent can lead to contamination of groundwater and surrounding surface water, particularly in sites with limited land area and either impermeable or overly porous soils. Nutrient leaching is a significant concern in the Florida Keys where increased development has been associated with decreasing water quality in the near-shore areas. These coastal areas can no longer use stand-alone septic tanks because of capacity limitations; therefore, the wastewater must be treated prior to its being released directly to the groundwater. Current treatment methods are time-consuming and costly. The objective of this project is to evaluate a cost-effective method using a conventional septic tank “front end” followed by a subsurface flow “garden” designed for zero-discharge (uptake of wastewater by plants that transpire clean water to the atmosphere).

The concept employs a closed plant bed for evapotranspiration treatment of all blackwater effluent. The goal of the project is to develop a system that is simple to operate, requires no pretreatment other than the septic tank, minimizes or eliminates moving parts, and is low-maintenance. An ancillary goal is to ensure the system is a desirable landscape element using common landscaping plants to capitalize on the landowner’s interest in gardening/horticulture. The landscape plants were selected in relation to transpiration rates, nutrient removal capacity, maintenance issues, and salt tolerance for use in the subsurface “flow” garden. The first-generation trials evaluated the water processing rates and plant growth responses of four 50-square-foot test beds planted with 4 common tropical horticultural species.

Each bed is receiving 5 gallons of septic tank effluent per day or about a half-person estimated toilet flow. The septic tanks used an ersatz blackwater composed of urine salts analog and vegetarian dog food to simulate feces. After 105 days of testing, plant growth appears vigorous and plants show no acute phytotoxic responses. Plant evapotranspiration rates were approximately 40 percent of projected average yearly levels, which is consistent with expected transpiration during winter months and early plant establishment.

Key accomplishments:

• Completed the first-generation system design.
• Deployed and performed proof-of-concept testing of system at experimental onsite location.
• Performed 105-day experiment.
• Completed analysis of system performance.
• Monitored water quality.
• Evaluated acute phytotoxicity issues.
  

Key milestones:

• Modification of design for optimization.
• Long-term operation testing (6 to 9 months) of second-generation design.
• Deployment of system in Florida Keys (Phase III).
  

Contact: Dr. J.C. Sager (John.Sager-1@ksc.nasa.gov), YA-E4, (321) 476-4270
Participating Organizations: Dynamac Corporation (J.L. Garland, N.C. Yorio, P.A. Fowler, and V.J. Krumins), Azurea Inc., and Childs Enterprises (P. Childs)