Activated Carbon and Some Applications for the Remediation of Soil and Groundwater Pollution

by Jason Philip Pope

Introduction to Activated Carbon and Its Uses

Activated carbon is remarkable, highly adsorbent material with a large number of applications in the remediation of contaminated groundwater. Its properties and uses have been known for centuries, but modern applications involving water and wastewater treatment have expanded the understanding of its nature and potential.

Activated carbon is an effective absorbent primarily due to its extensive porosity and very large available surface area. The chemical nature of the carbon's adsorptive surface is also important but is usually considered much less significant. The specific properties of an activated carbon are the result of both the raw material used to produce it and the activation process, which boosts its adsorbent qualities.

A variety of raw materials, including wood and coal, are used in activated carbon manufacture, making it plentiful, relatively inexpensive, and versatile. It is generally manufactured as either granular activated carbon (GAC) or powdered activated carbon (PAC). In the most popular granular form, activated carbon is used as a filter medium through which contaminated water or air is passed. The powdered form is mixed into wastewater to react with contaminants and later filtered or settled from the mixture. These two forms may be applied to a variety of treatment systems.

Activated carbon is used in water and wastewater treatment primarily as an adsorbent for the removal of relatively low levels of organic and inorganic contaminants via transfer from the dissolved phase to the solid carbon surface. While its adsorbent nature also makes it useful for the filtration of contaminated air, only its use in water treatment will be considered in this document.

Most forms of activated carbon are non-polar in nature, so they have the greatest affinity for other non-polar substances. As a result, they are most effective in the removal of a variety of organic contaminants, including trihalomethanes, pesticides and herbicides, and polyaromatic hydrocarbons. However, activated carbon may also be used for the removal of trace metals such as cadmium and lead, and it has also been effective in removing some polar organics as well. On the other hand, activated carbons do not effectively remove contaminants of high solubility or inorganic salts like nitrates.

In remediation systems, activated carbon is almost always used as a component in some form of pump-and-treat system. Commonly, it is used as a sorptive filter medium through which contaminated water is passed before it is re-injected or routed to a stream or sewer. In these applications, activated carbon is most commonly used as a tertiary step, in which low concentrations of contaminants are removed from partially treated water.

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