Upper left: untreated water (control)
29 March 2007
Missouri River water was collected and refrigerated
overnight, allowing it to settle. On 30 March 2007, a 110 mL
sample of the water was treated with ozone for 45 minutes. Small
samples (3 - 4 ml each) were removed after 15 min, 30 min, and 45 min
and added to agar plates. These were refrigerated for analysis
one week later. The remaining 100 mL was analyzed by the Hach
coliform/e coli test (wich gives results in 24 hours) A control
(untreated, but settled Missouri River water from the same sample was
analyzed by the Hach kit as well. Results are shown below.
The plate on the left is of the treated water showing only one red
colony of
coliform and zero colonies of
E.
coli (blue). The
plate on the right is of the untreated water showing 68 colonies of
coliform (red) and 40 colonies of
E.
coli (blue). The blue colonies were very patchy.

Laleh and Stephanie getting ready to collect a Missouri River water
sample in March, 2007
August/September,
2007. Water samples collected August 23, 2007 from Missouri
River at Omaha,
Nebraska and Carter Lake in Omaha. On August 24th, approximately
15 mL of water from each location was treated with the ozone stream
from our little generator. Samples (3 g) were removed after 5
minutes, 15 minutes and 30 minutes and placed on Nutrient agar plates
(Fisher Scientific S716931A). After 40 hours of incubation at
room temperature, the results shown above were observed. In the
top series (Missouri River) , all bacteria were killed within 5
minutes; only the untreated sample ("Missouri River t = 0 min")
produced bacteria colonies which appear as a somewhat opaque
yellow-brown discolored film across the surface. The other three
samples contained no colonies. In the bottom series (Carter
Lake), bacteria grew in the untreated sample and in the t = 5 minutes
of ozone samle, but did not grow in the t =15 minutes or t = 30 minutes
samples. The white shadows in the 15 minute and 30 minute samples
above are not bacteria and do not appear in the actual samples, only in
the photograph. They are possibly from shadows and reflections
caused by the covers being in place. Here are the same plates with the
lids off:
We repeated this experiment using time-lapsed photography. The
camera took one picture per hour for 4.5 days. This time, the
bacteria grew in clumped colonies in the untreated water (lower petri
dish) and not at all
in the sample treated with the ozone stream for 15 minutes (upper
dish.) The
sequence of photos were assembled into the following eighteen second
movie in which the bacteria can be seen to grow at about 20,000 times
faster than in the actual experiment (1 s = 6 hr.) Colonies start
appearing after 12 hours or so. (Some moisture condensation on the
cover obscures part of the viewing area.)
View a movie of this process: