How To Activate Charcoal To Filter Water: 10 Simple Steps

Powdered charcoal provides the maximum surface area to filter water.

Charcoal water filters are a useful filtration method that is effective, affordable and readily available. I have previously discussed the difference between activated charcoal and regular charcoal, however, can you ‘activate’ regular charcoal? What is the process to create charcoal that will purify water? These queries got me thinking and were the inspiration behind writing this article.

Activated charcoal is created by heating wood in an enclosed container, washing it in an acidic or basic solution and then reheating it to remove remaining impurities. This at-home recipe won’t completely emulate commercially produced material, but, it will be sufficiently effective for use in water filtration.

This set of instructions is designed as a simple guide to producing activated carbon for use in water filtration and/or air freshening, the ten steps are divided into two parts, creating the charcoal and then activating it! The materials suggested are all readily available at home and are designed to be as user-friendly as possible, if you already have some charcoal in your position, jump straight to Part 2. Activating the Charcoal.

Part 1. Creating The Charcoal

To create charcoal rather than ash, it is important to ‘cook’ the wood rather than burn it. When the wood is burnt in a fire it reacts with oxygen and converts to ash and carbon dioxide, whereas when the wood is ‘cooked’, the carbon remains, with the majority of impurities leaving the wood as it is heated.

This process should be undertaken outdoors over an open fire due to the fumes released from heating the wood!

1. Prepare the wood: The first step involves sourcing a saucepan or pot with a lid and loading it up with wood.

2. Start the Fire: Then you need to start a fire with sufficient wood to continue burning for a few hours and place the pot of wood on top of the fire, assuring the lid is on correctly.

3. Cook the Wood: Leave this pot to cook the wood for 3-4 hours (2-3 hours will usually suffice, but 3-4 will ensure the wood has been thoroughly cooked)

4. Cool the Charcoal: Remove the pot from the fire and when it has cooled sufficiently, empty the contents into another container to cool further.

5. Wash the Charcoal: Once cool enough to touch, rinse this charcoal under cold running water to remove ash and any other loose debris.

6. Grind the Charcoal into Powder: Using something like a mortar and pestle, grind the charcoal up into a powder and allow a day to dry out completely in an open container. You now have pure charcoal!

Part 2. Activating The Charcoal

Lemon juice contains citric acid, a natural easy option to help activate charcoal

Activating the carbon involves washing the charcoal in an acidic or basic solution to remove remaining contaminants really increases the porosity of the material, the property that makes it such a useful filter medium.

7. Prepare the Activating Solution: You have three options: Calcium chloride, Citric acid (lemon juice) or bleach. Be careful when handling these liquids as they are all reactive with skin and eyes and should not be consumed.

a. Calcium Chloride: Take caution when mixing this solution as it will get hot when dissolved in water! Available at most hardware stores, you mix approximately a 3:1 ratio with water, generally speaking, 100g of chloride mixed with 300 ml of water will suffice for most household pot-sized loads of charcoal.

b. Citric Acid/Lemon juice: A good option if you can’t source Calcium Chloride, simply use 300ml of pure lemon juice as the solution.

c. Bleach: In the same manner as lemon juice, 300ml of bleach will work fine to activate the carbon.

8. Add the Solution to the Charcoal: Intermittently add the solution of the powdered charcoal prepared in step 1, stirring until you achieve a paste-like consistency when you can stop adding additional liquid. Cover this paste and leave it for 24 hours.

9. Reheat the Charcoal: Drain any visible liquid from the paste before pouring it back into the pot, covering it with a lid and heating it over a fire for ~3 hours. This fire needs to be sufficiently hot to boil water in order to activate the carbon.

10. Make use of your Activated Charcoal: You now have activated carbon, ready for use in a water filter!

If you are wondering how to make use of your activated charcoal or how long it takes for the activated charcoal to purify water, have a quick look at my other article on the topic here.

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