RGBI Researchers Spend Time in Prison
Graywater versus well water study in El Paso
Naomi Assadian and other researchers have been going to Rogelio Sanchez State Prison in El Paso, Texas, not serving time, but spending time exploring the potential for safe and beneficial uses of graywater for irrigation.
“We have been interested in wastewater reclamation to conserve fresh water supplies and realized little work had been done with graywater in far West Texas,” said Naomi Assadian, associate research scientist at the El Paso Agricultural Research and Extension Center. “We also wanted to do something at the state prison because a prison crew helps us at the Research Center. One crew is assigned to work at our Research Center three-quarters time and they assist and get trained in maintenance projects. A different crew maintains our research plots located at the prison.”
Assadian decided to use the prison grounds to construct a field test and study how graywater irrigation affects crop yields versus using salty groundwater. The prison provided a non-traditional site on a desert mesa of shallow, loamy sand underlain by caliche, receiving less than 10 inches of rain during the growing season. Graywater, diluted wastewater coming from showers, kitchens and laundry, comprises 68 percent of total domestic wastewater. At the prison, 11 loads of laundry are washed per day going through two wash cycles, two rinse cycles and one sour bath/bleach cycle, using 3,500 gallons of water daily.
“Using laundry water was an excellent choice because in most households and in the prison, laundry consumes vast amounts of water,” Assadian said.
The prison’s only source of landscape irrigation up to this point was salty groundwater. The researchers decided that reusing the laundry wastewater provided an alternative to using potable water or the salty groundwater.
Prior to planting, two moisture sensors were placed 5 and 8 inches below the soil surface and connected to above-ground data loggers. Vegetable seedlings were purchased from a local nursery and transplanted to the plots on May 3, 2005. Tomatoes, long green chilies and bell peppers were the vegetables chosen for this study because they are very susceptible to salinity.
“If we could grow high maintenance veggies with poor water, we knew we could grow almost any crop,” Assadian said. “We also wanted to verify that pathogen contamination may be little to none under a hot and dry desert environment in spite of potential waterborne pathogens.”
Bell pepper mortality was highest, suggesting more sensitivity to environmental change and salinity than tomatoes or long green chilies.
“Hot temperatures in May followed by a cool, moist winter and spring flushed leaf hopper populations from the fringe of the desert onto the plots,” Assadian said. “Leaf hoppers were vectors that transmitted curly leaf virus to the vegetable plants. About 30 percent of all plants were infected with the virus by June 10, 2005.”
Evidence of infection increased and affected overall plot production, she said. Insecticide application alone did not control the transmission of disease. However, in spite of the infection, all vegetables grew well in all plots.
The most challenging issue was establishing a water delivery system to the demonstration plots, Assadian said.
“Security prevented construction of a continuous pipe system from the laundry trap inside the prison to the field test site outside of the prison,” she said. “As a consequence, water was pumped and transferred from a mobile reservoir to a stationary one. The 250-gallon capacity of the stationary water tanks and the tedious pumping process dictated irrigation volumes for each application.”
Shallow, salty groundwater was pumped from a well, hauled and placed in a 900-gallon stationary tank. Water delivery from the tanks to the blocks was via a 2-inch diameter PVC pipe using gravitational flow. The PVC delivery pipe was connected to a perforated PVC pipe laid perpendicular to the nine rows in each plot, so that water was distributed uniformly to each furrow (see Figure 1).
The plots were irrigated every two to three days, and soil moisture was measured by the moisture sensors. Salinity, soil moisture, E. coli and vegetable data were collected regularly. E. coli was not found in laundry water collected directly from the subsurface laundry water trap. Both the laundry water and well water were tested for salinity, and the laundry water was less saline than the well water. Soil moisture data was collected for each plot at time intervals from 1 minute to 15 minutes and this data was downloaded every other week.
Researchers originally thought that salty well water may be a superior irrigation source to laundry water. Instead, laundry water irrigation significantly increased vegetable production relative to well water irrigation.
Preliminary results suggest that the reuse of laundry water for irrigation may be beneficial and safe even for salt sensitive crops like vegetables, she said. Vegetable data results suggest laundry water had no detrimental affect on early transplant stress and plant growth. Irrigation with laundry water actually increased fruit yields, fruit size and the number of fruits harvested from selected plants relative to those receiving well water irrigation, Assadian said. Average yields from the three plants irrigated with laundry water were almost four times greater than those from well water plots. Tomatoes produced the highest yields, followed by bell peppers and long green chilies.
“Our field observations indicate that long green chilies and bell peppers were more salt sensitive than tomatoes,” Assadian said. “Salts decreased long green chili pods to the size of jalapeno peppers.”
“We are now entering year two of a three year project, and we are hoping to gather more data on potential salt accumulation in the soil, the persistence of E. coli in soil and on mature fruits, and the yield performance of relatively salt sensitive crops,” Assadian said. “RGBI contributes to this project in a tremendous way. I use RGBI support for labor, chemical analysis and supplies. Without RGBI funds, this project would be reduced to a show and tell project without any data.”
Additional funds for this project are received from the U.S. Bureau of Reclamation (BOR). Collaborators are Woody Irving with BOR and Sergeant Gibson, Officer Barnes and offenders at Rogelio Sanchez State Prison. Critical support is also provided by co-PI Dr. Zhuping Sheng, Dr. Wesley Brown, Joshua Villalobos and Elizabeth Gonzalez from the Texas A&M El Paso Research Center.
“Water reclamation is not an easy task and often is more challenging than using good water supplies,” Assadian said. “However, this project demonstrates that a multiple-agency, multiple-team effort can successfully work toward a common, but challenging goal to beneficially use every drop of precious water.”
