Water Purification through Adsorption

Study Notes

Adsorption is the process where contaminants adhere to the surface of activated carbon, effectively removing them from water.
Defined as the "collection of a substance onto the surface of adsorbent solids," adsorption relies on physical or chemical attraction.
Activated carbon is notable for its extensive cavernous pores, providing a vast surface area—approximately 1 gram of activated carbon has 100 m² of surface area.

Contamination starts with substances adsorbing to the exterior of carbon granules.
Substances then migrate into the pores of the carbon.
Finally, substances adsorb to the interior walls of the carbon.

Adsorption efficiency diminishes over time, necessitating the replacement or reactivation of activated carbon.
Isotherms help predict the adsorption capacity, with the Freundlich, Langmuir, and Linear being the three main types.
The Freundlich isotherm is most commonly used in drinking water treatment and is described by the equation:
- ( qe = K_F \times C_e^n ), where ( qe ) is the equilibrium concentration of adsorbate, ( C_e ) is the equilibrium concentration of solute, and ( K_F ) and ( n ) are constants.

Activated carbon is effective in removing pollutants from water, such as soluble organics, dyes, pesticides, and other odorous substances.
Its high surface area makes it beneficial for both gas and liquid treatment applications, effectively purifying water and air.
Particularly effective against organic materials, activated carbon becomes saturated, leading to a "breakthrough" of contaminants when it requires replacement or reactivation.

Use of activated carbon dates back to 1500 BC, with discoveries of medicinal applications in ancient Egypt.
Activated carbon is extremely porous and can have surface areas equivalent to up to 100 acres per pound.

Each type of granular activated carbon (GAC) has unique isotherm curves and breakthrough characteristics, aiding in understanding their adsorptive capacities.
Reactivation of carbon is essential once the breakthrough point is reached.
The Langmuir isotherm quantifies adsorption with the equation:
- ( qe = \frac{q_{max} \times K_L \times C_e}{1 + K_L \times C_e} ), where ( q_{max} ) represents maximum adsorbate concentration.

Adsorption kinetics is influenced by the diffusion of adsorbate and interactions with the adsorbent surface, which may be physical, chemical, or a combination.
Effective adsorbents need high capacity and rapid adsorption rates, characterized by models such as pseudo-first and pseudo-second order kinetics.
Factors affecting adsorption rates are crucial for understanding and optimizing the performance of activated carbon in treatment processes.