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Abstract

To determine the relationship between the degree of disinfection of drinking water (infused with a bacteria culture) and varying degrees of opacity of the container

Hypothesis

The lower the degree of transparency of the plastic bottle surface, the lower the level of disinfection.

Scientific Terms

Escherichia Coli, Polyethylene terephthalate, Ultra-violet radiation

Background

What is Solar Water Disinfection (SODIS)?

Solar Water Disinfection is a method of killing unwanted microorganisms in water by exposing water in sunlight. Usually, clear plastic bottles are filled with water and then left in the sun, exposed to UV ray for hours on end.

This method is accredited by the World Health Organization because it is a cheap and efficient way to produce water safe for drinking and is currently widely used in many third world countries.

Experiments have shown that exposing polluted water to sunlight deactivates disease causing microorganisms due to the UV rays which proves to be deadly for harmful microorganisms.

What types of bottles are suitable for SODIS?

 PET, which stands for Polyethylene terephthalate bottles are used in SODIS. PET bottles are used in SODIS because they are light and hard to break. In addition, PET bottles are also easily obtained in many countries. However, certain glass bottles and specifically engineered plastic bags can also be used. 

However, over time, these PET bottles may become scratched from overuse. This would cause the plastic to lose its transparency and potentially hindering the potential effects from SODIS.
 

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Complexity level:
6
Project cost ($):
10
Time required:
6 hours for sunlight exposure, 24 hours incubation period
Material availability:
Tap water or rain water are acceptable sources of water. Agar plates are available at school biology laboratories.
Safety concerns:

Students must take personal safety steps by wearing gloves, mask and goggles before starting the experiment. Disinfectants should be available for standby in case of bacterial contamination. Teachers should be over watching students at all times during the experiment in case of any accidents. Students with respiratory problems should refrain from doing this experiment.