Page 509 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

464 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

15.1.4 APPLICATIONS
TABLE 15.2
For engineered systems, activated carbon is the adsorbent of
Organic Compounds Amenable to Adsorption by GAC
choice in most situations in which organic carbon is an issue.
Class Examples
Such situations include the following: (1) NOM occurs in
Aromatic solvents Benzene, toluene, xylene ambient waters (see Appendix 2.A) and reacts with chlorine
Polynuclear aromatics Naphthalene, biphenyl (and other halogens). (2) Organic carbon residuals in munici-
Chlorinated aromatics Chloro benzene, PCB’s, endrin, toxaphene, pal wastewaters may impede reuse unless removed. (3) Syn-
DDT thetic organic carbon (SOC) compounds discharged into
Phenolics Phenol, cresol, resorcinol, nitrophenols, ambient freshwaters are a health hazard in potable water and
chlorophenols, alkyl phenols must be removed. (4) In some cases, e.g., the Love Canal,
Aromatic amines and high Aniline, toluene, diamine SOCs are a health hazard with respect to various forms of
MW aliphatic amines
exposure possibilities. (5) Industrial process waters often have
Surfactants Alkyl benzene sulfonates
exacting specifications, which require removal of any organics.
Soluble organic dyes Methylene blue, textile dyes
(6) Industrial wastewaters may need pretreatment prior to
Fuels Gasoline, kerosene, oil
discharge into municipal sewerage systems in order to meet
Chlorinated solvents Carbon tetrachloride, perchloroethylene
standards for acceptance to a municipal wastewater treatment
Aliphatic and aromatic acids Tar acids, benzoic acids
plant; if discharged to an ambient water, effluent discharge
Pesticides=herbicides 2.4-D, atrazine, simazine, aldicarb,
standards must be met.
alachlor, carbofuran
Source: Adapted from Groeber, M.M., Granular Activated Carbon
15.1.5 HISTORY
Treatment, Engineering Bulletin EPA-540=2-91=024, Office of
Research and Development, U.S. Environmental Protection The use of wood chars and bone chars in medicine dates to
Laboratory, Cincinnati, OH, October, 1991. 1550 BC (Hassler, 1974). Their use in modern industry started
in the early years of the nineteenth century to purify sugar.
The development of modern activated carbons is dated to
patents in 1900. The first commercial production (Kornegay,
15.1.3.1.1 Adsorbable Categories of Compounds 1979, p. 1) was in 1913 by the Industrial Chemical Company
Compounds not amenable to adsorption are those that have (later, in 1979, the company became the Chemical Division,
low MW and high polarity (Groeber, 1991, p. 2); examples Westvaco Corporation). The first municipal use of activated
include low MW amines, nitorsamines, glycols, and certain carbon was at the Hackensack Water Company, Milford, New
ethers. The readily adsorbed compounds include pesticides, Jersey in 1930 when PAC was used for taste and odor control.
polynuclear aromatic hydrocarbons, phthalates, phenolics, By 1943, 1200 water treatment plants were using PAC
and substituted benzenes (Dobbs and Cohen, 1980, p. 3). (Baker, 1948, p. 454). PAC was favored over GAC because
Examples of absorbable substances within different categories of the relatively low cost for storage and feed equipment and
of organic compounds are given in Table 15.2. the flexibility in operation.
As a unit process, GAC adsorption emerged in 1960 as a
part of the Advanced Water Treatment Research Program
15.1.3.2 Natural Organic Matter (AWTR) of the U.S. Public Health Service (Anon., 1962).
Natural organic matter (NOM) is quantified, in general, by The groundwork for this program was the survey of organics
total organic carbon (TOC), and if filtered, the TOC measure in ambient surface waters in the late 1950s that used the CCE
is dissolved organic matter (DOC) (see Appendix 2.A). (carbon chloroform extract) method of sampling and analysis.
Humic and fluvic acids comprise 0.4–0.9 fraction of DOC Based on the findings of this survey, the AWTR program was
(Karanfil et al., 1996a, p. 2187). Adsorption of humic matter initiated in 1960 and authorized by Congress in the 1961
is governed largely by molecular size with lower MW frac- amendments to the Federal Water Pollution Control Act, i.e.,
tions being removed preferentially. Public Law 87-88. The mandate was to search for new tech-
In treatment trains for drinking water, GAC reactors are nologies that could treat secondary effluents such that the
located, as a rule, after coagulation and filtration. The latter product was suitable for further uses (Morris and Weber,
processes reduce ambient DOC concentrations 0.1–0.9 frac- 1962, p. iii).
tion, with about 0.3 removal expected. Generally, the higher The AWTR program sponsored extramural research in
MW compounds are removed by coagulation=filtration activated carbon adsorption, which included pilot plant stud-
removals; thus the influent to the GAC reactors is mostly the ies, demonstration scale plants, and one full-scale plant (South
lower MW compounds (Karanfil et al., 1996b). If synthetic Lake Tahoe) built during the 1960s. The program paved the
organic compounds (SOCs) are to be treated at the same time, way for the use of granular carbon beds as a unit process in a
the ‘‘preloading’’ of DOCs will preempt the removal of the ‘‘tertiary-treatment’’ train. Tertiary treatment became the
SOCs (Carter and Weber, 1994; Müller et al., 1996). means to use effluent streams from municipal wastewater