Section Four
PROCESSES-A. SORPTION
35    SELECTING ACTIVATED CARBON FOR ADSORPTION
TREATMENT
Wei-chi Ying, Scientist
Michael E. Tucker, Staff Technician
Occidental Chemical Corporation
Grand Island Technology Center
Grand Island, New York 14072
INTRODUCTION
The use of activated carbon for adsorption treatment was first recorded more than two hundred
years ago.1 Carbon adsorption is now commonly employed for product purification (sugar refining,
food processing, production of water) and pollution control (water and wastewater treatment,
removal of volatile organics). Because activated carbon has a very large specific area (up to more than
2000 m2/g), It is a powerful adsorbent, capable of adsorbing most organic impurities and/or contaminants. The criteria for determining whether to use carbon treatment is often the cost of the adsorption
process relative to alternative treatment processes, such as ion-exchange, oxidation, biodegradation,
which can accomplish the same treatment objectives. The most important cost factor in applying
adsorption treatment is the carbon exhaustion rate or the amount of carbon required to treat a given
quantity of feed.1,2
The carbon exhaustion rate is dependent both on adsorptive capacities of carbon for the compounds to be removed and on environmental and operating conditions under which the adsorption
process is applied for treatment.3,4 The capacities of carbon for organic compounds dependent on the
type of activated carbon (raw material, manufacturing processes) as well as the type of adsorbate
(molecular size and structure, solubility, vapor pressure). The environmental and operating factors
affecting carbon requirements include: pH, ionic strength, initial concentration, competitive adsorption, adsorber size and configuration.
It is important to recognize mass transport limitations in designing carbon adsorbers for removing
organic contaminants, consisting of high molecular weight compounds. Because of the large molecules, these contaminants diffuse slowly into the carbon pores where they are adsorbed, and in fact,
they may be too large to go into some of the smaller pores.5 At one of Oxychem silicate plants, almost
immediate color breakthrough was observed in a study on carbon treatment of groundwater using a
small adsorber containing 200 lb of cecarbon 30, the best carbon for removing organic constituents of
leachate.6 Other carbons, less effective in treating leachate, performed much better in removing the
color agents of the groundwater. Furthermore, only small fractions of the isotherm capacities for
color agents were utilized in the carbon column breakthrough runs.
The objectives of this investigation were to develop simple procedures for selecting the best carbon
and to identify the optimum environmental and operating conditions for a particular adsorption
treatment application. Established carbon characterization parameters —the phenol value, the iodine
number, the methylene blue number, and the tannin value7,8— were employed to rank activated
carbon for color removal and other applications. Three carbon adsorption treatment cases— color
removal for a silicate plant groundwater, purification of phosphoric acid, and polishing treatment for
biotreated phenolic wastewater—are presented to illustrate the methods for selecting carbon and
enhancing adsorber performance.
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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