Water Distillation in a Solar Still

An experiment was conducted using water samples spiked with Volatile Organic Compounds (VOC), which was subsequently treated in a one-stage still manufactured by Sol Aqua. This testing was performed on the south campus Engineering Research facility at New Mexico State University. Distillate samples from a solar driven still were collected, and VOC concentration measured for samples spiked with: Benzene (aromatic 75ppm); Methyl-tertbutyl ether (petroleum product 50ppm); Methylene Chloride (chlorinated VOC 100ppm); and Diethyl Phthalate (phthalate 85ppm)

These components were used in making a feedstock using de-ionized water. This solution was placed in the still on a clear, sunny day. The ambient temperature varied between 36˚C-42˚C during the duration of the test. The distillate was collected in increments of every hour. Fours hours of samples were combined to make one sample. The procedure was followed for a second sample. This experiment provided useful data in analyzing the effectiveness of the solar still, as well as demonstrated the importance of pursuing simple distillation methods for generating potable water for rural locations.

It was found that the amount of distillate (product) obtained was consistent with the volumetric flow-rate expected. This experiment is weather-dependent, with product generation increasing with warmer weather and clearer skies. The approximate flow-rate of distillate obtained in the morning hours with an ambient temperature of approximately 37˚C was 0.3225 L/hr. During the peak hours of the day an approximate flow-rate of 0.75 L/hr was observed at an ambient temperature of 42˚C. The afternoon hours saw an approximate ambient temperature of 38˚C, which provided a flow-rate of 0.4665 L/hr. A total of approximately 6 liters of distillate were collected over an eight hour period for which an average volumetric flow-rate of 0.50 L/hr was calculated.

Results obtained by an extraction of the aqueous sample into another organic phase, then analyzed by gas chromatography provided quantified decreases in the concentration for the surrogate VOC's in the distillate. Benzene had an initial concentration of 42 mg/L, and decreased in the distillate to 0.073 mg/L, Methyl-tertbutyl-ether had an initial concentration of 37 mg/L and decreased to 0.00017 mg/L. Diethyl phthalate had an initial concentration of 85 mg/L (not analytically measured). Dichloromethane had an initial concentration of 39 mg/L and decreased to 0.068 mg/L.

The concentrations in the distillate decreased significantly from the original spiked solution. The concentration for Methyl-tertbutyl-ether decreased within the minimum concentration level set by the Environmental Protection Agency (EPA). Methylene Chloride and Benzene were within 7% of the minimum concentration level set by the EPA. The decrease of VOC concentration using the one-stage distillation unit has proven to be an effective method for reducing VOC concentrations in a simple distillation method. This will provide a source of drinkable water for rural locations that may not have other cost effective methods.