Solar Disinfection for Water PurificationBy 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 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.

Results

Oxygen level pH Temperature8.37 mg/L 8.34 24.8˚CTable 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.

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

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

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

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)

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.

AcknowledgmentsResearch 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.