How Does Activated Charcoal Cleanse Water?

Many force fed water filters and most gravity fed water filters use a charcoal filter. What is charcoal? It is the solid residue resulting from the process of the destructive distillation of wood. This process also yields acetic acid, several burnable gases, wood alcohol, and some other products.

Charcoal is an odorless and tasteless solid, porous, black, and brittle.  Charcoal is normally too dense to float in water, yet sometimes it does. How can this be? It is because charcoal has the remarkable ability to adsorb solids and gases. Charcoal does this so well that it can adsorb enough gases to make it float.

The filters usually use activated charcoal, coal, or carbon. This means the charcoal has been processed to make it extra porous. The result is that just one gram of activated carbon has a surface area of between 500 m and 1500 m! When you consider that it takes 454 grams to make one pound and that a tennis court has 260 m, you can see it is very porous! The fact is, the greater the surface area, the more likely it is that impurities will touch the charcoal as they pass by.

The secret of charcoal’s filtering ability is in the fact that it is so good at adsorbing (not absorbing). “Adsorption is the concentration of a gas, liquid, or solid on the surface of a liquid or solid with which it is in contact.” Just one cubic centimeter of charcoal is able to adsorb 90 cc of ammonia gas though it adsorbs other substances far better.

Pollutants that are dissolved in the water as it passes through the filter come in contact with the activated charcoal. These substances are actually attracted to the charcoal by van der Waals forces. Wiki explains these forces this way. “In physical chemistry, the van der Waals force is the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules.”

Putting it simply, molecular forces bind some compounds to the charcoal. Not all substances are equally attracted to the activated carbon. Substances such as alcohols, glycols, ammonia, strong acids and bases, metals and most inorganics, such as boric acid lithium, sodium, iron, arsenic, lead, and fluorine are not filtered as well.

This is good in some ways. The minerals in water are needed in the body; drinking distilled water all the time would deplete the body of needed substances. So it is good that they are not filtered out. Also, some do not want fluorine removed from the water because of claims that it aids in dental health. However, others of these chemicals are unwanted and the filters must have other substances in them to remove these.

In conclusion, water and contaminants pass through the activated charcoal filter and, because of the filter?s porosity, the substances will likely come in contact with the carbon. The van der Waals forces will cause the substances to be attracted to the charcoal where they will remain until the filter is washed or replaced. For the contaminant, it is dead end road. For the person drinking the water, it is refreshing and healthy.

The best line of activated charcoal filter we are aware of is the Berkey Filter. Whether you choose their Berkey Light Water Filter or another model, each set of filters they ship with can be re-cleaned to purify up to 6,000 gallons of water.

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