A QUICK METHOD FOR EVALUATING THE SUITABILITY
OF ACTIVATED CARBON ADSORPTION FOR WASTEWATERS
R. S. Reimers, Assistant Professor
A. J. Englande, Associate Professor
Tulane University
Tulane Riverside Research Labs
Belle Chase, Louisiana 70037
H. B. Miles, Process Engineer
J. Ray McDermott Engineers
Singapore
INTRODUCTION
Increased consideration of activated carbon as a wastewater treatment alternative has
resulted from the enactment of the 1972 Federal Water Pollution Contrl Act (PL 92-500).
"Best available treatment technology" and discharge into "water-quality-limited segments"
have in many cases dictated an effluent quality only achievable with activated carbon as
one of the treatment operations.   The ability of activated carbon to remove contaminants
from wastewaters has to date been very empirical.   It is anticipated that a more theoretical, yet simplistic, approach can be employed in assessing the feasibility of activated carbon for removal of specific organics from wastewaters.
REVIEW OF THE LITERATURE
The first application of activated carbon to purify portable water was noted by Lips-
combe [1] in 1863.   The first study concerned with the effect of molecular structure
and solvent pH on adsorption effectiveness took place in England, when in 1929, Phelps
and Peters [2] observed that the adsorption of the lower fatty acids and simple aliphatic
amines depends on the pH of the aqueous solution and the ionic dissociation of acids and
bases.   They concluded:   (a) adsorption occurs only with the undissociated molecules;
(b) at any pH, adsorption of the acid or base will increase with the concentration of free
acid or base; and (c)the adsorptions of gasesare similar.   During the early 1940s, Cheldelin
and Williams [31 made two important observations:   (a) the adsorption of 33 amino acids,
vitamins, and related substances by activated carbon (Darco 6-60) fit Freundlich adsorption isotherms; and (b) the presence and position of polar groups and the absence of aromatic nuclei are important factors in aqueous adsorption of organics by activated carbons.
Their studies were centered around possible uses of carbon for analytical purposes such
as separations, etc.   Organic concentrations were too high to correspond to adsorption
situations for water or waste treatment.
With increased interest in pollution abatement, studies of organic adsorption onto carbon were renewed by Weber et al [4,5] and Getzen and Ward [6,7].   These investigators
studied the steric  effects of molecular branching on adsorption; the effects of adsorbate
molecular weight on the equilibrium capacitance, and kinetic uptake rates; and the quantification of ionization constant with respect to aromatic organics and pH.   The selection
of specific organics for study was based on:   (a) the relatively simple analyses of aromatics
by the U.V. spectrophotometer; (b) possible steric  and ionization constant effects of
carboxylic acids, alkyl benzenyl sulfates, nitrophenols and phenols, and (c) the organics'
competitive roles during the adsorption phenomena.   Another consideration was the similarity of aromatics to pesticides in terms of molecular structure.   Results included a reduction of capacitance with:   (a) a decrease in molecular weight of the organics; (b) an
increase in molecular branching; and (c) a decrease in the free acid or base form.   The
investigation by Weber and Morris noted an increase in the rate of organic uptake with
a decrease in the organics' molecular weight.
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