In every issue of The Science Reflector look for this new section including activities you can use in your classroom tomorrow. If you have activities you would like to share please email the editor.

Filtration Experiment - compare the filtering of 3 materials (sand, gravel, charcoal) used in water treatment plants.

Hurricane Ernesto - examine satellite images from the most recent hurricane to hit North Carolina.

Filtration Experiment
from Diana M. C. Rashash, Ph.D.
NC Cooperative Extension Service

In the coagulation/flocculation experiment, natural processes that remove particles from water were discussed. Filtration is a continuation of that process. Soil can be a great filter. Different soils have different characteristics, some of which make them better filters than others. People have used those characteristics to create today's water and wastewater treatment plant filters. A typical water treatment plant filter has two or three materials or “media”: either sand and charcoal or sand, charcoal, and gravel.

In a three media filter, the gravel protects the lower layers from the force of the water and traps larger materials such as twigs. The activated carbon (charcoal) has a very large surface area for its size. This surface area enables it to trap lots of particles and also remove some tastes and odors. The bottom layer of sand has small spaces between each grain. These spaces trap remaining particles from the water. Our filters have a polyester plug, which holds everything in the bottle and also traps some particles. A “real” filter is usually six or more feet deep and more than 10 feet in diameter. Ours are very small in comparison. So, how useful are they? Let's experiment!

Materials:

• settled water from coagulation/flocculation experiment
• 1-liter plastic soda bottles (works better than other sizes)
• polyester fiber (pillow stuffing or aquarium filter material)
• fine sand (play sand works well)
• coarse sand (sand-blasting sand)
• fine gravel (for aquariums)
• coarse gravel (for aquariums)
• activated charcoal (aquarium filter charcoal)
• strainers

Procedure:

Pre-rinse the sands, gravels, and charcoal to remove fine materials. Allow to drain either in the strainer or on paper towels. Mark the 1-liter bottle slightly less than halfway up the side. Cut the bottle in two at the mark. (Refer to drawing for layer placement) Remove the cap from the top portion and place a wad of polyester fiber in the opening as a plug. Then, add filter layers. Leave 1-inch free at the top for addition of the water. The layers shown in the drawing are one option. The class can try other combinations and see how they compare. Once the filter is made, add clean water as a final rinse.

When handling the filter, be careful not to squeeze it! Squeezing can cause small cracks in the layers. Although small to us, those cracks are plenty large for protozoa to pass through. Some protozoa are pathogenic and cause illnesses such as those that make campers and hikers who drink untreated water from streams sick. Protozoa are resistant to disinfection, so we rely on filters to remove them. Several cities have had large outbreaks of protozoan diseases (Giardia and Cryptosporidium) that were traced back to faulty filters.

Now that the filter is ready, slowly pour the treated water from the coagulation/flocculation experiment into the filter. Be careful not to pour in any of the sludge. How does the filtered water look compared to the original untreated water? Although the water may look a lot better than it did, it is still not safe to drink. The water still needs to be disinfected to kill any harmful bacteria that may be present. Chlorine is the most common disinfectant used in the United States. We also use ozone, chlorine dioxide, ultraviolet light, and other compounds. Not all countries treat their water the same way. Europeans for example don't like the taste of chlorine. The main disinfectant used in Europe is ozone.

Hurricane Ernesto
from John White
Meteorologist

Below are some good images of the storm, but they also illustrate some characteristics of weather satellite imagery that are good to remember.

2006.09.01 at 1145Z. Centerpoint Latitude: 35:55:29N Longitude: 77:30:04W
From http://www.nnvl.noaa.gov/cgi-bin/index.cgi?page=items&ser=111234

This first image is from 11:45Z (07:45EDT). The imager is the 4-km resolution infrared sensor on GOES-12. Post processing of the image provides the enhancements that make the land areas seem green and the water blue. The actual IR sensor doesn't detect the colors, but other sensors on board the satellite allow these to be included in the image. The satellite has sensors that are detecting specific wavelengths in the electromagnetic spectrum. Combining various wavelengths produces what is know as multi-spectral imagery (MSI).

Another example of the capability from MSI (read, in this case, "multi-spectral imaging") is the well-know water vapor imagery you see broadcast meteorologists using. The sensors that allow us to "see" the water vapor (remember, water vapor isn't visible to the naked eye -- it's the reflected light from clouds' water droplets that we see in visible imagery) because the sensors are designed to detect the specific wavelength of the energy that water vapor emits. New sensors designed for the next generation of satellites will detect many more discrete wavelengths and permit amazing analyses from these geostationary satellites that are 22,000 miles above the Equator.


2006.08.31 at 2115Z. Centerpoint Latitude: 33:48:17N Longitude: 75:45:11W.
From http://www.nnvl.noaa.gov/cgi-bin/index.cgi?page=items&ser=111229

This second image is from the late afternoon before Ernesto made landfall. The sun is low on the western horizon, and the result in this image is dark skies to the east and more texture in the scene. The shadows from the higher cumulonimbus in the rain bands to the east of the storm center are easy to pick out. The resolution of these visible images are 1 km.


2006.09.01 at 1245Z. Centerpoint Latitude: 35:55:29N Longitude: 77:30:04W.
From http://www.nnvl.noaa.gov/cgi-bin/index.cgi?page=items&ser=111235

This final image shows the same types of shadows, but now the sun is low in the east. Also note the curve of the earth in the upper edges of the image.

You can learn more about Hurricane Ernesto from the Raleigh office of the National Weather Service at http://www4.ncsu.edu/~nwsfo/storage/cases/20060831/ and weather in the classroom at http://www.erh.noaa.gov/rah/education/.

Of course, NOAA's earth observations are not limited to hurricanes. Take a peek at the imagery collection the scientists at NOAA set aside as significant on the "Operational Significant Event Imagery" page. Here you can link to many types of events that apply to almost every part of the earth science curriculum.