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Bacteria Affected by Ultra-Violet Light


My objective was to see what the effect was of ultra-violet light on bacteria. I
hoped that the bacteria
would get killed, and wanted to see a decrease in bacteria colonies.


I first collected water samples at Arroyo Burro Creek. I immediately took the
first sample with the water
untouched by the UV light. I exposed the water sources to the light for 24
hours, taking samples of
bacteria at 1 hour, 6 hours, 12 hours, and 24 hours. When completed, I took the
samples to the
microbiology lab of Cottage Hospital. My bacteria samples were incubated for 24
hours. I was then able
to count colonies and record my data.


The results I recieved weren't exactly what I wanted. After the first trials,
there was a slight decrease in
colonies, and then the numbers went back to even higher than the original
sample. I repeated the
experiment with a higher intensity lamp, and realized that now the colonies
continued to decrease
throughout the entire experiment.


After being unsatisfied with my results, I decided to look on the Internet to
find any information about the
methods the city was proposing to use. I found exactly what I was looking for. I
knew that I needed to
have a higher intensity lamp, and my light was only 15 watts. I knew that Energy
= Watts / Distance
squared, (E=W/D^2), so I decreased the distance between the UV lamp and the
water source. I learned
that even the slightest difference in methods could prove devestating.