Figure 4-43: Typical Adsorption/Absorption System
Adsorption mechanisms are generally categorized as either
physical adsorption, chemisorption, or electrostatic adsorption. Weak molecular forces,
such as Van der Waals forces, provide the driving force for physical adsorption, while a
chemical reaction forms a chemical bond between the compound and the surface of the solid
in chemisorption. Electrostatic adsorption involves the adsorption of ions through
Coulombic forces, and is normally referred to as ion exchange, which is addressed
separately in the ion exchange modules. In liquids, interactions between the solute and
the solvent also play an important role in establishing the degree of adsorption.
most common adsorbent is granulated activated carbon (GAC) (Technology
Profile No. 4.46). Other natural and synthetic adsorbents include: activated alumina,
forage sponge, lignin adsorption, sorption clays, and synthetic resins.
Activated alumina is a filter media made by treating aluminum ore so that it becomes
porous and highly adsorptive. Activated alumina will remove variety of contaminants,
including excessive fluoride, arsenic, and selenium. The medium requires periodic cleaning
with an appropriate regenerant such as alum or acid in order to remain effective.
Forage sponge is an open-celled cellulose sponge incorporating an amine-containing
chelating polymer that selectively absorbs dissolved heavy metals. The polymer is
intimately bonded to the cellulose so as to minimize physical separation from the
supporting matrix. The functional groups in the polymer (i.e. amine and carboxyl groups)
provide selective affinity for heavy metals in both cationic and anionic states,
preferentially forming complexes with transition-group heavy metals.
Lignin Adsorption/Sorptive Clay
Lignin adsorption/sorptive clays are used to treat aqueous waste streams with organic,
inorganic and heavy metals contamination. The waste stream is treated due to the molecular
adhesion of the contaminants to an adsorptive surface.
Synthetic resins are more expensive than GAC, but can be designed to achieve higher
degrees of selectivity and adsorption capacity for certain compounds than activated
carbon. Resins are typically regenerated using acids, bases, or organic solvents, instead
of thermal methods, so they are better suited for thermally unstable compounds such as
explosives, and are resistant to deactivation due to the adsorption of dissolved solids.
Additionally, resins tend to be more resistant to abrasion than activated carbon,
increasing their service life.
Technologies: Field Scale Demonstration Project in North America,
of Remediation Case Studies, Volume 4, June, 2000, EPA
Battelle Memorial Institute, 1995. "ReOpt V3.1 User
Documentation", for DOE under contract DE/AC06/76RLO 1830.
Guide to Documenting and Managing Cost and Performance Information for
Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007
MTBE Treatment Case Studies presented by the USEPA Office of
Underground Storage Tanks.
N., 1995. "Forager Sponge, Technology Description",
Water Quality Association, 1994. "Treating the Water We Drink, When and
Where We Drink It.", WaterReview Technical Brief, Vol. 9, No. 4.
- EPA Demo National Lead
- Pease Air Force Base, Newington, NH
- Superfund Site:
Western Processing, WA
- Superfund Site: Rocky
Mountain Arsenal, OU 17, CO
- Superfund Site: Vally
Wood Preserving, Inc., Turlock, CA
- Superfund Site: Motor
Wheel, Lansing TWP, MI
- Superfund Site: Perham
Arsenic, Perham, MN
Points of Contact:
General FRTR Agency Contacts
Technology Specific Web Site:
Government Web Sites
Non Government Web Sites
A list of vendors offering
Ex Situ Physical/Chemical Water Treatment is available from EPA
REACH IT which combines information from three established EPA databases,
the Vendor Information System for Innovative Treatment Technologies (VISITT),
the Vendor Field Analytical and Characterization Technologies System (Vendor
FACTS), and the Innovative Treatment Technologies (ITT), to give users access to
comprehensive information about treatment and characterization technologies and
Health and Safety: