5.1 Sorption and Desorption

Sorption is the result of a number of processes by which one substance becomes chemically or physically attached to another. In the case of DOC in groundwater, aquifer solids of varying compositions (e.g., quartz sand, limestone, granites) form the solid material to which DOC molecules in aqueous solution can attach. There are many possible kinds of sorption processes for DOC, but they fall into three loosely defined categories of physical, chemical, and electrostatic. Physical sorption processes involve dipole attraction between sorbate and sorbent molecules. The relatively weak bonds associated with physical sorption are often amplified in the case of hydrophobic molecules by their tendency to leave the aqueous phase. Chemical interactions involve covalent bonds and hydrogen bonds that attach DOC to aquifer solids. Finally, electrostatic interactions involve ion-ion and ion-dipole forces that attach DOC to aquifer solids. In the case of DOC, sorption typically reflects the simultaneous contribution of two of more of these mechanisms because the nonpolar or polar character of DOC can vary depending on the source material and the degree of biodegradation to which it has been subjected.


Dissolved Organic Carbon in Groundwater Systems Copyright © 2022 by Francis H. Chapelle. All Rights Reserved.