Two science fair projects

Getting the ‘dirt’ out
Question: My 7th grade daughter has a school project which requires her to make a water filter that can clean 10 grams of dirt from 125 ml of water in 5 minutes. I don’t have a clue how to do this. What would you recommend?

Lonnie Eiseman

Answer: A simple way to accomplish this task would be to place a coffee filter in its support basket, line the bottom with one or two crushed charcoal briquettes, then cover the charcoal with a 1-2 inch layer of playground sand. (You many find that the charcoal isn’t necessary). Rinse this with clean tap water prior to testing, to wash any charcoal dust out. Add the water gently so as not to disrupt the layers. This filter will likely remove the dirt you add to the water, and the resulting water should appear clear, but this does not mean that it is safe to drink, as bacteria might still be found in the water. Many water utilities use a large version of this simple filter, but also add chlorine to disinfect microbiological organisms.

Another idea is to take a common household funnel and a paper towel to obtain 50-micron filtration and simply pour it through. A micron is 10-6 in size, which is very small. If you want to get more sophisticated, you could use filter paper, but too small a micron rating may inhibit the flow. A coffee filter may or may not be too tight to conform to the five-minute limitation. Again, a disinfection step may be necessary to ensure the water’s safety and can be accomplished by adding a few drops of chlorine. The chlorine can be removed prior to consumption by running the water through a second filtration step using the same funnel and paper towel with carbon added to it as the removal mechanism. If you have a fish tank, the type of carbon used in the filter unit will do nicely.

How do you do it?

Question: I am doing a science project on water purification. My question is how did you design your water purification systems?

Stephanie Bunch
Williamsburg, Ky.

Answer: We don’t design or sell water purification systems per se. We are a business trade magazine that publishes articles about the design and proper installation and operation of water treatment systems, primarily for residential use. These include water softeners and deionizers; undercounter reverse osmosis and filtration systems; distillation units; countertop and end-of-faucet filtration and other treatment systems; ultraviolet, ozone and chemical disinfection systems, aeration systems; well water treatment systems—as well as small municipal systems and commercial/light industrial systems that operate on roughly the same technologies, just on a larger scale. The specific design (or combination) of these systems will vary depending on the quality and chemistry of the water to be treated and its intended uses. It’s a general rule of thumb that a “multi-barrier approach” to water treatment is best as different technologies may have different strengths and weaknesses under different conditions and combining technologies can provide a more effective treatment regimen and ultimately higher quality water. In a nutshell that is not necessarily all-inclusive, that’s the function of WC&P. For more specifics, visit our website (www.wcp.net) or see the website of the Water Quality Association (www.wqa.org) or NSF International (http://www.nsf.org/programs/).

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