P07402: UV-Tube Water Disinfection Project
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Test Product Concept(s)

Filter Concept Testing

The effectiveness of the sand filter and different filter materials was tested. Flour was suspended in tap water to simulate turbidity. The same concentration was first run through just a layer of felt, and then a layer of canvas fabric. It was shown visually that the canvas performed much better than the felt at removing the flour. A photo of the canvas vs. felt results may be viewed here:

canvas vs. felt results

The sand filter was then constructed with washed play sand and the canvas fabric placed in a 2 gallon bucket. Increasing the depth of the sand resulted in more turbidity removed from the water. It was also determined that the sand must be washed and "conditioned" before use, by running water through several times. The ideal amount of conditioning and depth of sand will be determined during the product testing phase. A photo of the sand depth results may be viewed here:

sand depth results 1 (control, 4 inches unconditioned, 4 inches conditioned)

sand depth results 2 (4 inches, 5 inches, 6 inches conditioned)

Tube Material Testing

The single most expensive component of the current UV Tube design is the stainless steel sheet, and bending this metal was also one of the most difficult parts of the process. The team wanted to investigate using aluminum instead of stainless for the body of the tube. Aluminum is generally more ductile than steel, is cheaper, and is easy to obtain.

Unfortunately, exposure to high levels of aluminum has been linked to the development of Alzheimer's disease, as well as bone, respiratory, and neurological problems. There is not, however, any conclusive evidence that ingesting aluminum leads to these conditions. Aluminum ingested with drinking water is absorbed faster by the body than in other forms. Aluminum levels are not regulated for drinking water, but the EPA suggests secondary maximum containment levels of 0.05 mg/L in drinking water.

There has been very little research done regarding the interaction of aluminum with UVC radiation and water. In order to test this, two set-ups were constructed with an enclosed aluminum trough and UV germicidal bulb suspended over the water. The troughs were filled with water, and the bulbs were left on continuously for 10 days. One of the aluminum samples was a plain 5052 aluminum sheet, and the other was a piece of commercial aluminum roof flashing which had been sanded and cleaned to remove any coatings.

At the end of ten days, the bulbs were turned off and the covers removed, to reveal that the aluminum looked like the following:

Aluminum testing picture 1 - 5052 aluminum

Aluminum testing picture 2 - aluminum flashing

A substantial amount of water had evaporated from the heat of the light bulb in both set-ups, but there was more remaining in the one made from the 5052 aluminum. The water was removed from the tube and brought to the Monroe County Pure Waters Environmental Lab where it was tested for aluminum content. It was found that this sample had 3.18 mg/L of aluminum, which is much higher than the EPA recommended amount.

From this testing, it was decided that aluminum is not an ideal material to replace the stainless steel, due to uncertain health effects and potentially very high levels.

References:

http://www.atsdr.cdc.gov/tfacts22.pdf

http://www.hc-sc.gc.ca/ewh-semt/water-eau/drink-potab/aluminum-aluminium_e.html