Use of Solar Ultraviolet Irradiation as a Method of Germicidal Water Treatment

Friday, 13 February 2015
Exhibit Hall (San Jose Convention Center)
Emilie A. Wille, Plano, TX
The main cause of death among hikers is dehydration, normally a result of unexpectedly running out of water.  Stranded hikers using water straight out of lakes and streams run the risk of contracting deadly diseases from bacteria such as E.coli, salmonella, and Vibrio cholera.  While ingesting this water is sufficient for immediate survival, the future health effects can be devastating.  Water taken out of the environment must be treated in some way to ensure the stability of health. The purpose of the experiment was to discover if solar ultraviolet radiation can effectively eliminate water-borne bacteria, and if so, how long the process takes.  It was hypothesized that bacteria would be entirely eliminated by the process.  The experiment was conducted in context of a situation in which a stranded person only has an empty clear plastic water bottle and a fresh water source.  Water bottles were filled with water from a creek that contained unknown bacteria.  The water bottles were placed in a school greenhouse and exposed to sunlight for intervals of 0, 3, 7, 9, 11, and 14 hours.  Petri dishes were prepared with nutrient agar and MacConkey agar.  While nutrient agar indicates all bacteria present, MacConkey agar only reveals Gram-negative bacteria.  Most common harmful water-borne bacteria (E. coli, salmonella, and Vibrio cholera) are Gram-negative, and because it was unclear if all bacteria would be eliminated, using MacConkey agar allowed for the effectiveness of the method to be analyzed in case bacteria still remained.  After being inoculated, the petri dishes were incubated for 60 hours at room temperature before bacteria was counted.  The nutrient agar plates did not show a decrease in bacterial count over the 14 hours, while the MacConkey agar plates revealed that Gram-negative bacteria was entirely eliminated after 14 hours of exposure.  It is important to note that weather conditions varied throughout the course of the experiment.  Much of the first 7 hours ranged from overcast to partly cloudy, while the final 7 hours were mostly sunny.  Because there was a decrease in bacteria count within the first few time intervals, it is evident that there is an adequate amount of ultraviolet radiation for the method to work in cloudy skies.  However, the fall of bacteria count was more rapid while it was sunny, revealing that the treatment works more quickly when the sky is clear.  These results indicate that the method is versatile.  Not all wilderness gets constant exposure to sunlight, so it is imperative to have a water treatment method that works in a variety of places.  The hypothesis was partially supported because not all bacteria were eradicated from the water.  However, because most harmful water-borne bacteria are Gram-negative, the treatment method is effective when it comes to preventing illness.  Even though bacteria still remain, the chances of contracting disease are sharply decreased, making it safe enough for water to be consumed from the environment.  This will ensure immediate survival and future preservation of health for stranded hikers.