New Solar Pond Distillation System
Researchers at the University of Nevada, Reno are developing a solar technique that will take care of the ecosystems of terminus lakes around the world. This new solar distillation system will help in removing the salinity of the lake water. This will be possible with the help of a specialized low-cost solar pond and patented membrane distillation system deriving power by renewable energy. Francisco Suarez is a doctoral student in hydrological sciences at the University. He is of the view, “These lakes — hundreds worldwide — such as the Great Salt Lake, the Salton Sea, the Aral Sea and Walker Lake here in Nevada, see a decline in water levels and an increase in salinity from both human and natural processes. The high levels of salinity are dangerous and unsustainable for aquatic life.”
He presented a portion of his solar pond research at the annual Fall AGU (American Geophysical Union) Conference in San Francisco that was attended by 16,000 geophysicists from around the world. A paper on his project will be published in the International Journal of Heat and Mass Transfer in early 2010.
Currently Suarez is working on a mechanism to create an artificial salt-gradient stratification process. This stratification process entraps solar heat at the bed of the solar pond and utilizes the collected energy to power the membrane distillation system. This system is patented by the University. The aim of developing such a system is to maintain the ecosystems of the closed water bodies. There is no system for an outflow of water. But the processes of nature such as evaporation still occur in these closed water bodies. This leads to high concentration of minerals and salts in the closed-basin regions.
The hot salt water is present in the lower storage zone of a pond. This temperature of this bottom area of a pond can rise up to more than 195 degrees Fahrenheit. This heat can be utilized for heating, thermal desalination, or for other low-temperature thermal applications.
Suarez explained about his experiments, “Our model results show that in a two-week period, the temperature in the bottom of the solar pond increased from 68 to 126 degrees Fahrenheit and, even though the insulating layer is being eroded by double-diffusive convection, the solar pond remained stable.”
The whole experiment was met with a roaring success in the laboratory on a small level. They carried out the 400-gallon tank. They had put the dissolved solids and installed a precise fiber-optic temperature sensor. The temperature sensor keeps tabs on the process as desalination of the water. Creating a low-temperature desalination system that works in an open environment on a demonstration scale is going to be the next pilot project of Saurez and the research team.
Suarez is working on this project in collaboration with Civil and Environmental Engineering Department Professor and Chair Amy Childress and Professor Scott Tyler of the Department of Geological Sciences and Engineering. Childress and colleagues woked on the patented membrane distillation system and Tyler put his energies on the development of the distributed temperature sensing system. The temperature sensing system consists of a laser and fiber-optic cable to record temperatures in the solar pond.
Tyler shares his enthusiasm, “We’re working on funding and permissions to build a system at Walker Lake where dissolved solids have increased by a factor of five to an unhealthy level for aquatic life, and water levels have dropped 140 feet in the past 100 years.”
The icing on the cake is the cost related to run this system. Actually it is negligible because it uses the renewable energy of the sun, trapped as heat in the bottom, to power most of the system.
Suarez said, “This can operate 24 hours a day using the stored energy. Very little electricity would be used. For every surface acre of solar pond we can make three acre-feet of freshwater in about one year. The major advantages of this system are that renewable energy is used, the system is low maintenance and the stratification process that helps drive the process uses the salts from the lake itself.”