In chemistry, a substance is said to be activated if it it has undergone some process to facilitate a chemical reaction, while remaining essentially the same substance. For example, activated charcoal has been cracked to present a very large surface area for burning or other reactions. Activated charcoal is frequently used in filtration systems. Once is is saturated with contaminants, charcoal can be regenerated by heating and re used. The contaminants are burned in the regeneration process, making CO2 . Alternatively, the contaminated charcoal could be used to create soil, but the presence and nature of the contaminants needs to be evaluated before such a solution is adopted.