PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 981
waters, can be applied successfully to the treatment of sec-
ondary sewage effluent. This process consists of passing
secondary sewage-plant effluent upflow through an ion-
exchange unit filled with a weak base anion exchange resin,
Amberlite IRA-68, operated on a bicarbonate cycle. The
effluent with a pH of 6.0 is then treated with a small quan-
tity of bentonite and cationic flocculant, Prima floc C-7, fol-
lowed first by aeration to drive out carbon dioxide, and then
lime softening in proportion to its hardness concentration.
A dosage of 30 mg/l of bentonite, 3 to 5 mg/l of polyelec-
trolyte, and normal lime levels are required. The effluent
that is partially desalinated and essentially free of nitrates,
phosphates, chlorides, alkyl benzene sulfonate (ABS), and
COD can be produced. If the salinity is too high, it may be
reduced further by passing a portion of the effluent through
a weak acid cation, Amberlite IRC-84. It has been observed
that IRA-68 can remove much of the organic contents and
COD, thereby eliminating or markedly reducing the need for
carbon treatment.
Slechta and Culp (1967) tested a cationic resin, Duolite
C-25, for the removal of ammonia nitrogen from the carbon
column effluent that was containing ammonia nitrogen in
the range of 18 to 28 mg/l as nitrogen. A 100-mm-diameter
Plexiglas cylinder filled to a depth of 700 mm with the resin
served as the pilot ion-exchange column. The rate of appli-
cation of influent waste to the ion-exchange column was
0.4 m^3 /min per cubic meter of resin. Following breakthrough
of the ammonia nitrogen to 1 mg/l, the bed was backwashed
and the resin was regenerated. On the average, about 400 bed
volumes of carbon column effluent had been passed through
the ion-exchange resin prior to a breakthrough to 1 mg/l
ammonia nitrogen. However, considering the operating and
capital costs, they concluded that the ammonia-stripping
process was more efficient.
Nitrate nitrogen, present in the effluent from the acti-
vated sludge process, has been removed by anion exchange
regenerated with brine by R. Eliassen and Bennett (1967).
This ion-exchange process also removes phosphates and
some other ions; however, pretreatment by filtration is
essential. The resin is restored by treatment with acid and
methanol.
The removal of heavy metals with Mexican clinoptilo-
lite was studied by Vaca Mier et al. (2001). In this study the
interactions of lead, cadmium, and chromium competed for
the ion-exchange sites in the zeolite. The authors also stud-
ied the influence of such factors as the presence of phenol
and the pH of the solution to be treated.AdsorptionApplication of adsorption on granular active carbon, in
columns of counterflow fluidized beds, for the removal of
traces or organic pollutants, detergents, pesticides, and other
substances in wastewater that are resistant to biological deg-
radation has become firmly established as a practical, reliable,
and economical treatment (Slechta and Culp, 1967; Weber,
1967; Parkhurst et al., 1967; Stevens and Peters, 1966;
Presecan et al., 1972).Adsorption can also be accomplished with powdered
carbon (Davies and Kaplan, 1964; Beebe and Stevens, 1967),
which is mixed in wastewater, flocculated, and ultimately
settled. However, there are certain problems associated with
the use of powdered carbon. These are: (1) that large quanti-
ties of activated carbon are needed in wastewater treatment,
because it is used only on a once-through basis, and han-
dling of such large quantities of carbon also creates a dust
problem, and (2) problems in disposal of precipitated carbon
unless it is incinerated along with the sewage sludge.Carbon-Adsorption Theory Less polar molecules, includ-
ing soluble organic pollutants, are removed by adsorption
on a large surface area provided by the activated carbon.
Smaller carbon particles enhance the rate of pollutant
removal by providing more total surface area for adsorption,
partial deposition of colloidal pollutants, and filtration of
larger particles. However, it is almost always necessary to
remove finely divided suspended matter from wastewater by
pretreatment prior to its application on a carbon bed.
Depending on the direction of flow, the granular carbon
beds are either of the downflow-bed type or upflow-bed type.
Downflow carbon beds provide the removal of suspended
and flocculated materials by filtration beside the absorption
of organic pollutants. As the wastewater passes through the
bed, the carbon nearest the feed point eventually becomes sat-
urated and must be replaced with fresh or reactivated carbon.
A countercurrent flow using multiple columns in series is
considered more efficient. The first column is replaced when
exhausted, and the direction of flow is changed to make that
column the last in the series. Full countercurrent operation
can best be obtained in upflow beds (Culp and Culp, 1971).
Upflow carbon columns for full countercurrent opera-
tions may be either of the packed-bed type or expanded-
bed type. Packed beds are well suited to treatment of wastes
that contain little or no SS, i.e., turbidity less than 2.5 JTU.
However, the SS invariably present in municipal and indus-
trial wastewaters lead to progressive clogging of the carbon
beds. Therefore, expanded-bed upflow columns have certain
potential advantages in operation of packed-bed adsorbers
for treating wastes that contain SS. In expanded-bed-type
adsorbers, water must be passed with a velocity sufficient
to expand the bed by about 10%, so that the bed will be
self-cleaned.
Experiments conducted by Weber et al. (1970) have
shown that expanded-bed and packed-bed adsorption sys-
tems have nearly the same efficiency with regard to the
removal of soluble organic materials from trickling-filter
effluent, under otherwise similar conditions. The packed-
bed system was found to be more effective for removal of
SS, but the clogging that resulted from these solids required
higher pumping pressure and more frequent cleaning of
the carbon beds. Because of the time elapsed in cleaning,
the expanded-bed production was about 9% more than the
packed-bed production.
The Lake Tahoe Water Reclamation Facilities, described
by Slechta and Culp (1967), included pretreatment of second-
ary effluent by chemical clarification and filtration, therebyC016_005_r03.indd 981 11/22/2005 11:25:19 AM