Filter B: Coconut active charcoal Filter
Activated carbon pre-filters are most common in water purifiers. Large internal surface area of activated carbon makes it a very good adsorbent for many contaminants in drinking water. The sources of activated carbon are mostly , coal (anthracite, bituminous, lignite), coconut shells, peat and petroleum based residues.
Most carbonaceous materials do have a certain degree of porosity and internal surface area in the range of 10-15 meter2 / gram (m2/g). Activation of carbon, which consists of a process in which controlled oxidation of carbon atoms is done by steam at high temperature, enhances, the internal surface of the carbon to 1000-1200 m2/g.
The activation process generates a network of minute openings (pore or cavities) of different diameters on the carbon surface which become the path for water to access the extended internal surface created by the activation. The pore diameters are usually grouped as follows:
Micro-pores < 4 nm
Meso-pores 4-500 nm
Macro-pores > 500 nm (typically 500-2000 nm)
nm is nanometre. It is one billionth (10-9 ) of a meter
Adsorption of a contaminant from the water on the activated carbon surface may result from hydrophobicity of the molecule. Most organic contaminants in drinking water are hydrophobic in nature. They bind very well with the non-polar carbon surface within pores. Activated carbon can remove organic contaminants, including many VOCs, pesticides and herbicides, disinfection by-products like Tri halo methane etc.
Why Coconut shell activated carbon is the most preferred choice in the industry
Activated carbon from coconut shell has predominantly pores in micro pore range. Almost 85-90% surface area of coconut shell activated carbon exists as micro-pores. These small pores match the size of contaminant molecules in drinking water and therefore are very effective in trapping them.
Peat and wood activated carbon has mostly meso and macro-pores which suit trapping of bigger molecules. The pore structure of coal carbons falls between coconut shell and wood based carbons.
Macro-pores are considered as an access point to micro-pores. Meso-pores do not usually play an important role in the adsorption unless the surface area of these pores is large, 400 m2/g or more.
The predominance of micro-pores in coconut shell carbon gives it tight structure and provides good mechanical strength and hardness and also high resistance to resist attrition or wearing away by friction.
Some of other features which carbon industries, see as a great advantage in favour of coconut carbon are as follows:
- Coconut is a renewable source of carbon
- Coconuts grow throughout the year, with harvesting generally occurring 3-4 times in a year
- Coconut tree can be preserved for many years
On the whole, activated carbon plays a very critical role in drinking water purification as described.
To summarize, carbon key points as follows:
- Adsorbs disinfection by-product like THM
- Adsorbs VOCs
- Adsorbs pesticide and herbicide
- Removes halogens from water
- Improves appearance of drinking water
- Improves taste of water