Activated carbon is a porous substance derived from organic material (usually woody, fibrous stuff). The useful thing about activated carbon is that it can filter out contaminants from both water and air, which makes it an important substance in filtration system.
We examined a variety of methods (we considered 40+ samples to be adequate) to create activated carbon; through testing, we believe that we have found the optimal material and protocol to create the closest thing to commercial-standard activated carbon. We tried to create the easiest solution that implemented tools you already have around the household (because not everyone has a drum-steel burner on their hands).
This Instructable is meant for those DIYers with a bit of time (ok, only about two days) who aren't afraid to burn, burn, and burn. This flexible method takes all sorts of food waste and turns them into activated carbon for filtration. Use it while camping, biking, or even at home!
Our hope is that this method will eventually help impoverished areas improve overall health by providing an easy and flexible filtration option.
SO LET'S GET COOKING.
Step 1: Materials
When thinking of materials, we tried to be flexible so that you wouldn't have to go out and buy everything (that kinda defeats the purpose, doesn't it?). Here's what you need to make the carbon.
A metal container, with a lid
An oven (or something that gets hot)
A fireplace, grill or pit (something you can burn on)
A strong acid, base, or salt (we'll explain later. Some examples we have tested include 25% Calcium Chloride, Bleach, and Lemon Juice Solutions).
The food waste.
Now, picking the food waste is by far the most important step here. You want a nice, fibrous substance that already has a lot of pores. For example, commercial carbon is made with hardwood or coconut husk (that's what you see above). These are fine, but we have also tested banana peels, orange peels, nut shells, and rye husks with similar results. Feel free to explore. If you choose something with a lot of water content, you might want to dry it beforehand to prevent steam buildup.
Step 2: Char
Place the food waste into the metal container and seal/close it loosely (you could also drill a small vent hole). The priority here is to limit oxygen exposure, which causes unwanted chemical reactions, while preventing the container from becoming a pressure bomb.
Next, place the container within a VERY HOT location (aka a burning fire). We placed ours within a bed of burning coals, so this a great excuse for an impromptu BBQ party. You could place it in the center of a campfire, or in an established cooking fire. The goal here is to maintain a temperature of 400+ degrees Fahrenheit, which is when pyrolysis and charring begins. After a while, you should see steam and gas escaping from the vent holes, which should only increase the strength of the fire.
The time it takes to fully char varies depending on the material and heat, but we have found that 4 hours tends to be a good consistent number. Remove the container and let it cool before you check the insides. The material should be black and have the consistency of charcoal. Use your hand or a hammer to crush the carbon to a powder.
Step 3: Chemicals
You're going to want to make a 25% solution of any one of the following:
Calcium Chloride (a salt used in the aquarium industry)
Bleach (in our opinion, the easiest option)
Lemon Juice (you're going to need a lot of lemons. However, this is great for making food-quality activated carbon).
Online, other people have recommended more dangerous solutions (such as battery acid). We personally do not approve of using anything you wouldn't be willing to ingest (because your drinking water will be mixed with this carbon).
To remove the ash content within the carbon, you should first rinse out the carbon in the container. If you have time, let it fully dry.
Add enough of the solution to the container to fully submerge the carbon. Cover, and let rest for 24 hours.
Step 4: Cook
After the 24 hour waiting period, rinse out the solution and drain the carbon. You want to have wet carbon, but not saturated carbon. Place it back in the container.
You now want to exposure the carbon to 225-250 degrees Fahrenheit for about 3 hours. This can be done the following ways.
The easiest solution is an oven, gas or electric. The heat will dry the carbon and finish the product.
If you don't have access to an oven, we recommend placing the container above a fire, and adjusting based on the temperature. An easy way to measure temperature is to place the container next to or inside a pot of water, which will boil at 212 degrees.
A final method to cook is by creating an impromptu solar oven. This would only work in a very sunny climate, between noon and late afternoon. Seal the carbon in a BLACK metal container, and place on a reflexive surface (a tin roof, for example). To measure temperature, you may want to place wax near the container, and watch to see if it melts.
Step 5: Use!!
When used with boiling techniques and UV radiation, activated carbon can visibly improve the quality of your water.
Depending on the particle size of your carbon, it can also be used to absorb odors and improve air quality.
Finally, if all of your materials are food-grade, you can ingest it to neutralize toxins you may have accidentally consumed (we assume you accidentally ate that toxin, and we recommend this only as a last resort if you have no other option).
As you can see, these uses are vital in universally improving the quality of air and water. It's our goal to spread this method and knowledge about the uses of activated carbon to those who need it the most, especially to people in third-world countries. We thank you for reading, and we hope you will spread and improve on our methods.
Feel free to check the many other Instructables on how to use your new activated carbon!
For those interested in the full investigation we conducted to develop this method, you can visit our Google Science Fair Entry here: