In What Way Does Activated Charcoal Purify Water?

Nov 24 09:23 2009 Thelma Oliver Print This Article

A charcoal filter is a common part of most gravity fed and many force-fed water filters. Charcoal is the product of the destructive distillation of wood. This process yields wood alcohol, acetic acid, several burnable gases, and a few other products. The solid residue that results from this process is what we know as charcoal.

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,Guest Posting several burnable gases, wood alcohol, and some other products.

Charcoal is a black, brittle solid that is very porous. It is also odorless and tasteless. Though denser than water, charcoal can float! It does this because it is able to adsorb solids and gases so well. When charcoal has the opportunity to adsorb enough gases, they make it float.

Activated charcoal, coal, or carbon is charcoal that has been processed to make it extra porous. Because of this, just one gram of activated carbon has a surface area of approximately 500 m2 but this could be as much as 1500 m2! Considering that it takes 454 grams to make a pound and that a tennis court has 260 m2, it is easy to see just how porous it is! This increased surface area means that more impurities will touch the charcoal as they pass by.

Charcoal is able to filter because of its ability to adsorb. What is adsorption (note: not absorption)? "Adsorption is the concentration of a gas, liquid, or solid on the surface of a liquid or solid with which it is in contact." To show how good charcoal is at this, consider the fact that one cubic centimeter of charcoal can adsorb 90 cc of ammonia gas. It adsorbs other substances even 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."

Though this is very technical, it can be summarized by saying molecular forces bind some compounds to the charcoal. Activated carbon does not bind all chemicals equally well. It does not do as well with ammonia, alcohols, strong acids and bases, glycols, metals and most inorganics, such as fluorine, lithium, iron, sodium, lead, arsenic, and boric acid.

In one sense this is good. For example, our bodies need the minerals in water and we wouldn't want them filtered out. Some who live in cities where the water if fluoridated want it left in the water for family dental health. But other substances on the list are clearly unwanted and the filter must contain other adsorbers 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.

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Thelma Oliver
Thelma Oliver

The best line of activated charcoal filter we are aware of is the Berkey Filter. Whether you choose their Fluoride 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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