1. Solar Disinfection for Water Purification
By Amanda M. Icazatti Burtell, Fernando Pacheco Ocasio, and RISE Program University
of Puerto Rico-Cayey Campus
Abstract
It is a well-known fact that a great percentage of the population of the planet does not posses access to
potable water. Water is a quintessential part for the surviving of all living beings. Contaminated water can
lead to a great number of deceases that have only one outcome: death. Diarrhea is the second cause of death
in children five years and under. The SODIS Method (Solar Disinfection for Water Purification) is a
technique developed by scientist to clean water and reduce the chance of acquiring deadly bacteria by
consuming dirty water. It consists of exposing any PET bottle filled with water to the sun for 6 hours
straight. The exposure to the UV rays is supposed to kill all if any bacteria and contaminants that may be in
the water. In this experiments we are going to reproduce the SODIS method in a controlled environment
and measure the concentration of colipaghes if any on the water after a certain time exposed to UV light to
study the effect and relation the UV light has on the decrease of biological pathogens.
Key words: SODIS Method, biological pathogens, PET bottles, UV Light, Escherichia coli, coliphages,
apoptosis.
Introduction
Water quality is critical to human health.
Many human diseases, especially in
developing countries, are caused by poor
water quality. Several kinds of pollutants
raging from biological and chemical
contaminants can be disposed to water
supplies. Biological pathogens, such as
viruses and bacteria, thrive in drinking
water primarily when human or animal
waste is dumped into bodies of water.
(Tro 2011)
Scientists have developed a technique
for treating water for drinking in the aid
to this problem. The method is called
Solar Disinfection for Water
Purification; better know for its
acronyms in English, SODIS Method.
This technique consists of a very simple
and affordable procedure. To perform
the SODIS Method a PET bottle is
cleaned and/or disinfected. Then, the
bottle is filled with water and placed in
sunlight for six (6) full hours. After this
period, the water is disinfected and is
safe to drink.
The use of fecal coliforms as indicators
of recent fecal contamination of waters
is based on the assumption that
Escherichia coli (the target organisms in
these analyses) cannot survive for
extended periods of time in the
environment. It is generally accepted
that the fecal coliforms, as the name
implies, can only originate from fecal
(human or any warm-blooded animal)
sources. (Toranzos et al. 1987). Since,
bacteriophages are viruses that infect
bacteria (Snustad and Simmos 2012) and
coliphages are viruses that infect
specifically the bacteria Escherichia
Coli, they are used for this experiment as
indicators to help detect the presence of
bacteria or pathogens other than E. coli
and to study the effect of sunlight in
reducing the contamination in water.
In addition of using coliphages as an
indicator for fecal pollution, a variation

2. was made to the materials used to
perform the experiment. The weather
conditions were not favorable to use the
sunlight as a method of disinfection in
order to obtain accurate results,
therefore, a Ultra Violet Light Machine
(UV light Machine) was used to simulate
the effect the UV Rays from sunlight
would have.
Materials and Methods
Study site. The water samples were
taken from Rio La Plata, Cayey in the
University of Puerto Rico-Cayey
Campus. A single site was chosen for the
collection of the water sample.
Sampling Procedures. The oxygen
levels, pH, and temperature of the study
site were measure with a Multimeter.
With a sterilized probe, 800- mL of
water were collected from a place were
there was a water stream. The 800-mL
water sample was placed between iced in
a dark container that did not allow the
passage of light while it was transported
to the laboratory.
Laboratory Procedure and
Techniques. Sixteen (16) PET bottles
were cleaned with Lysol and sterilized
for 15 minutes in the UV Lights
Machine. Sixty-four (64) petri dishes
were identified for the study (4
repetitions per control and experimental
group). Sixteen (16) medium broth and
E. coli bacteria were prepared for the
water sample mixture. The 800-mL
water sample was divided equitably in
50-mL for each bottle (800 mL / 16 PET
bottles). (Important: Every time the
800-mL water sample is taken for its
distribution, it has to be shaken to
stabilize the concentration of pathogens
present in the mixture). Eight (8) PET
bottles were used as the control group, in
which bottles were coated with
aluminum foil paper. The other eight (8)
bottles were used as the experimental
group, which did not require to be
covered with aluminum foil paper. All of
the bottles were placed at the same time
in the UV Light Machine for ten (10)
minutes and every minute and a half
(00:01:30) a control and experimental
bottle was taken from the UV Light
Machine in order to begin preparing the
mixture for the analysis.
The medium broth was taken from the
water-bath, mixed with 2-mL of the host
bacteria (E. coli) and the 50-mL of water
were added (Important: the mixture
should be constantly shaken to prevent
solidification). The mixture was evenly
distributed thought all of the four (4)
petri dishes. The same procedure was
repeated for all control and experimental
water samples. The methodology was
taken from a scientific paper, but the
measurements were altered in order to
fix our experiment necessities (Toranzos
2010)
A period of time of approximately
fifteen (15) minutes was waited for the
mixture to solidify. After the necessary
period of time, the petri dishes were
placed in an incubator at 37˚C. for
twenty-four 24 hours.
Data analyses. The petri dishes were
analyzed after four (4) hours of
incubation, nineteen and a half (19 ½) of
incubation, and finally after twenty-four
(24) hours of incubation to study how
the contamination concentration
decreases over time.

3. Results
Oxygen level pH Temperature
8.37 mg/L 8.34 24.8˚C
Table 1. Data given by the Multimeter
The control and experimental group
were analyzed after four (4), nineteen
and a half (19 ½), and twenty-four (24)
hours of incubation at 37˚C. A total of
sixty-four (64) petri dishes were used
(Image 1). After four (4) hours of
incubation no coliphages where present
in any of the petri dishes. Instead, a large
amount of bubbles in all petri dishes was
appreciated (Image 2). This is an
indicator that the E.coli is working in
optimum conditions. At the nineteen and
a half (19 ½) hours of incubation the
petri dishes were revised again. This
time the presence of phages was visible
in all of the petri dishes (Image 3, 4, 5,
& 6). Both the control and experimental
group showed an equal quantity of phage
plaques. In addition, all of the petri
dishes showed a great quantity of
contamination. Not even a small
diminishment was appreciated from the
plates at zero (0) minutes to the plates
exposed for the longest time, which was
a total of ten (10) minutes under UV
light exposure. At the twenty-four (24)
hours of incubation the results did not
change that much (Image 7 & 8). The
quantity of coliphages and
contamination were almost identical as
the 19 and a half (19 ½) hour mark
(Graph 1).
Image 1. Sixty-four (64) Petri dishes. Image 2. Bubbles after four (4) hours of incubation.

4. Image 3. Control: 0 minutes (19 ½ hours)
Image 4. Control: 10 minutes (19 ½ hours)

5. Image 5. Experimental: 0 minutes (19 ½ hours) Image 6. Experimental: 10 minutes (19 ½ hours)

6. Figure 1. Results of coliphages concentration per 150-ml of water after
24 hours of incubation.
Discussion
Due to the lack of proper weather for the
SODIS method to be performed
effectively, the UV Light Machine was
used as a substitute. It is know that
Ultraviolet light has the capacity of
destructing cell membranes. The
exposition for extended periods of time
to Ultraviolet light would cause a
mutation in the genetic material of the
bacteria and the cell would choose for
apoptosis (Snustad and Simmons 2012)
Therefore, the bacteriophage function
would be inhibited and no organism
growth is expected in the experimental
samples after the UV light exposition.
However, the results did not show a
decrease in the contamination or
coliphages concentrations.
Qualitative and Empirical evidence
support analyses. By observing and
counting the contamination and
Image 7. Control: 10 minutes (24 hours)
Control Experimental
Image 8. Experimental: 10 minutes (24 hours)

7. coliphages present in the petri dishes,
respectively, was concluded that the
SODIS Method did worked effectively.
In addition, all the data collected though
the experiment (concentration of
coliphages) was graph (Figure 1) in
order to have a visual perspective of the
results obtained. It was expected for the
graph to have a negative slope, since
coliphages concentrations decreases but
instead, a positive slope was obtained.
The lineal regression was calculated and
the coefficient of correlation (R2
) gives
us more details about how to interpret
the slope.
Exist the possibility that the intensity of
the UV Light Machine was not as high
as expected or was damaged. It could
also be that more exposition time to the
UV light was needed for the water to
diminish the contamination. Compared
to the sun, the heat factor that may also
play a role in the effective kill of
bacteria in the water.
Acknowledgments
Research supported by the RISE
Program.
Special thanks to Dr. Javier Arce,
Jennifer Paredes (TA), and Giovanni
Cruz (TA).
References
Rivera S., Hazen T., and Toranzos G.
(1988) Isolation of Fecal Coliforms in
Pristine Sites in a Tropical Rain Forest.
American Society of Microbiology 54:
513-517.
Bonilla N., Santiago T., Marcos P.,
Urdaneta M., Santo Domingo J.,
Toranzos G (2010) Enterophages, a
group of pahges infecting Enterococcus
faecalis, and their potential as alternate
indicators of human faecal
contamination. Water Science and
Technology 61.2: 293-300.
Snustad and Simmos (2012) The
Genetics of Viruses. Principles of
Genetics: 165.
Tro N. (2011). Chemistry in the
Environment: Water Pollution.
Chemistry: A Molecular Approach: 488.