Water Filtration

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Water Filtration

Humans need air to breathe, food to eat, and water to drink. That’s easy on Earth but difficult on the International Space Station, or any spaceship that would have humans traveling for months at a time.

To deal with the water issue, the ISS recycles water, from bathing, shaving, and even urinating. It makes sense: water is heavy and delivering it by space shuttle is expensive. NASA tested the station’s $250 million water recycling system on Earth before it was installed on the ISS in November 2008. The ISS uses physical and chemical processes to remove contaminants. The system also filters and heats the water to make sure it’s safe to drink.

The system, however, hit a snag in January: the urine clogged the filtering system. It seems astronaut urine has a high concentration of calcium, although why is a matter of debate. Does it have something to do with the bone loss associated with living in microgravity? More investigation is needed.

In the meantime, make your own low-tech water filtering unit.

Materials

• 2 tire levers (3 levers make the job easier)

• Clear Plastic bottle (two liter)

• Aquarium gravel

• Sand

• Aquarium charcoal (activated)

• Cheesecloth

• Muddy waters

• Rubber band

• Tape measure

• pH strips (optional)

Instructions

1. Cut the bottom off the bottle (use the seam as a guide).

2.Fold the cheesecloth and cut it into a square. You should have several layers of cloth.

3.Attach the cheesecloth to the mouth of the bottle with the rubber band.

4.Suspend the bottle upside-down in a wide, clear glass. (A mason jar will do, or cut off the top portion of another two-liter plastic bottle. That’s what we did.)

5.Fill the suspended bottle with the charcoal, 5 to 8 centimeters thick. Put 8 to 10 centimeters of sand on top of the charcoal. Then put 5 to 8 centimeters of gravel on top of the sand. (We used a tape measure instead of eyeballing the layers for thickness estimates.)

6.Put some water in a bucket, or empty yogurt container, and add dirt to make muddy water. Pour it into the suspended bottle. You can repeat this step several times.

7.You can also experiment with the pH strips — before pouring the water through the filter, test the pH. Do it again after you filter the water. Is there a difference?

What's Happening?

The purpose of our filter was to clean muddy water. We put so much dirt in our bucket, however, that “clean” turned out to be a relative term. You could see a big difference after just one filtering but after several uses, the filter was less efficient. It was clogged. Clogging is a real problem. Any time you try to filter anything, there comes a point at which the filter is too full of gunk, whether it’s carbon dioxide in air filters, calcium in the ISS water filters, or dirt in our low-tech water filter.

The materials we used are common water filters. Gravel caught the larger sediments and bugs that were probably present in our muddy water. Sand caught smaller solids. Filtering systems that use sand mimic nature — this is probably the oldest method of water filtration. The activated charcoal could pick up smaller sediments that get through the sand.

Activated charcoal (carbon) is charcoal treated with oxygen, which makes the charcoal more porous and allows more particles to stick to it. The particles are mostly other organic materials (composed of carbon and hydrogen) — gasoline and drugs, for example. Activated charcoal also filters chlorine (present in many municipal water systems). Eventually, however, the charcoal will absorb everything it can and should be replaced.

Even if you clean all the dirt out of your water, it would still need to be purified. Pathogens — harmful bacteria, for example — would not be filtered out with this low-tech device. Now think of designing a filtering and purifying system for a spaceship!

*About pH: we did not notice much difference. But, keep in mind that water with a higher pH absorbs less heavy metals — that’s good to know if you’re worried about old plumbing pipes.