When you burn something with a high amount of carbon in it, like bamboo, coconut shell, willow peat, wood, coir, lignite, coal or petroleum pitch, you get carbon.
To activate it you then have to treat it either with temperatures over 600 °C and oxygen or use chemical activation. Chemical activation works at much lower temperatures when used with certain acids and bases.
The result is charcoal with a huge amount of tiny pores and a much larger surface area than before. Just image, one gram of activated charcoal has a surface area of 500 to 1,500 square meters.
Activated carbon water filters are made of granular activated carbon (GAC), bead activated carbon (BAC) or a carbon block.
In reverse osmosis systems, activated carbon is used in pre- and post filter elements.
How does activated carbon work to clean water?
Water and gas can pass through a activated carbon water filter and the material adsorpts certain contaminants.
Adsortion - not to confuse with absorption - is a process, where molecules connect with the outside of another compound through so called Van der Waals forces.
The activated carbon has a slightly positive chemical charge. This positive charge attracts contaminants with neutrally charged molecules, and they cling to the carbon.
What can an activated carbon filter remove from water?
Activated carbon filters remove
- Some drugs
- Hydrogen sulfide
- some odor causing volatile compounds
It is less effective, and will only reduce smaller amounts of iron, mercury and chelated copper and other metals.
Which factors influence the effectiveness of activated charcoal (ac) filters?
How effective your ac water filter is depends on a lot of different factors. Most of them are out of your control, like the source material for the filter or the the activation process used.
Activated charcoal water filters work better when the water is in contact with the filter material for a longer time. If your filter works with gravity, there is little you can do. In case you have a faucet filter, slowing the water flow may help.
Temperature and pH level of the tap water you use also determines the kind and amount of contaminants it can remove.
And lastly the form of the activated carbon - wether it is BAC, GAC or Carbon Block - plays a role too.
What are the Pro' s and Cons of activated carbon water filters?
healthy minerals stay in the water
improves the flavor
easy to maintain
- Pathogens or microorganisms may stay in the water.
- Small AC filters can not remove fluoride effectively.
- If not used for some time, bacteria may grow inside the filter.
NSF standards for activated carbon water filters
There are several NSF standards that may apply to activated charcoal water filters.
The NSF/ANSI 42 standard covers the reduction of aesthetic impurities such as chlorine and taste/odor.
NSF/ANSI 53 relates to the reduction of contaminant with a health effect. U.S. Environmental Protection Agency (EPA) and Health Canada Health define these.
Water filters that meet this standard reduce PFOA and PFOS in drinking water. Additionally they have to meet the definition of material safety and structural requirements of the NSF/ANSI 53 standard.