Activated carbons are substances consisting essentially of coal. Coal, of vegetable or mineral origin, becomes "active" through an activation process. This process carried out in special ovens with high-temperature steam causes the formation of tiny passages inside the coal granules, called microspores, the presence of which determines their activity. Activated carbon powder is distinguished from another by the nature of the coal (vegetable, mineral), by the average size of its porosity, by the number of the same, by the average size of the granules that constitute it (coal grain size).
Activated carbons perform their function mainly based on three mechanisms of action:
Chemical action: It is a catalysis action towards the reduction of some inorganic groups.
Chemical-physical action: The main prerogative of activated carbons is the adsorption power that is the ability to retain particular types of molecules in their porosity.
Physical action: A bed of activated carbon can perform mechanical filtration, with similar if not better results than those obtained with filtration on sand beds.
There is also the efficacy of activated carbon powder in promoting the biological processes of degradation of organic pollutants, with an action similar to that, which occurs naturally with the infiltration of water into the soil.
The applications:
A powdered carbon finds countless applications in the most varied fields, in water and air purification, in the sugar industry, in winemaking and so on.
In particular, activated carbon powder by adding water purification:
- For the removal of chlorine (exploiting the catalytic effect that favors the reduction of chlorine to chloride ion)
- For the elimination of unpleasant odors and flavors (by absorbing the organic substances that give them their origin)
- For the elimination of pollutants (by absorbing them) such as chlorinated solvents, insecticides, pesticides, detergents, etc.
- For filtration (exploiting its filtering power)
The activated carbon bed also has a mechanical filtering action similar to that of sand filters. However, it is necessary to take into account that on activated carbon filters it is better to carry out the least number of backwashes possible. It would help to avoid mixing of the bed that brings polluted coals. The saturation of porosity because of the adsorption action remains incomplete with backwashing. Saturated carbon reactivation occurs through special heat treatment.
The operating parameters for the use of activated carbon vary according to the purpose they are for. The layer height of the bed typically remains between 80 and 120 cm. In the case of de-chlorination, a minimum contact time of two minutes by increasing it is possible to obtain a longer duration of the carbon together with a lower pressure drop. In any case, with the same constitution of the filter bed, the effectiveness of the removal of pollutants increases as the water flow decreases.
A Brief History of the Use of Carbon:
The origin of the use of coal is common since ancient times.
- Charcoal is in antiquity in India by Hindus to filter drinking water
- Charred wood was used as a medical adsorbent and purification agent by the Egyptians as early as 1500 BC
- Powdered activated carbon was common as a commercial product in Europe until the 19th century, using wood as a raw material. This coal has found widespread use in the sugar industry.
- In the United States, the first production of activated carbon used as source black ash, after an accidental discovery that it is very effective for bleaching liquids. Since then activated carbon comes in handy extensively for this purpose in many industries. Specifically, it is common for the removal of organic dyes from textile wastewater.
- Documented use of activated carbon powder in a treatment application of the large-scale waters dates back to the 19th century (in England), where it has been used to remove undesirable odors and the taste.
- Activated carbon on an industrial scale only in the first mid-twentieth century from plant matter for use in sugar refining.
- Activated carbon powder is now common for a variety of purposes, including refining cane and corn sugar, gas adsorption, removal of pharmaceutical, grease, and oil scrubbing recovery products a dry, etc.