PHYSICAL AND CHEMICAL TREATMENT OF WASTEWATERS 983
of PACT in municipal wastewater treatment resulted from
the inability of the physical-chemical treatment process
to adequately treat wastewater. This process has been used
successfully to treat domestic wastewater from a residential
population of 30,000 in Vernon, Connecticut, and many other
plants have been under construction. Similar applications of
combined powdered-carbon and activated-sludge treatment
to various industrial wastewaters, particularly coal-gasification
wastewaters, are shown to be successful.
Miyake et al. (2003) studied the adsorption equilib-
rium isotherms of trichloroethylene (TCE) vapor stripped
from TCE-polluted waters. These results can be used for
wastewater treatment of waters with the same pollutant.
A combined Al(III) coagulation/carbon adsorption process
for the treatment of reactive dyes in synthetic wastewater
was proposed by Papic et al. (2004). This process achieved
99.9% reduction of the dyes in the wastewater as well as
95.7 and 91.3% COD reduction for the two waters used.
They conclude that the proposed process has many advan-
tages, such as high efficiency, low use of coagulant, mini-
mal sludge production, and high-quality product water with
reuse potential.Adsorption of Pollutants on Biomaterials A review of
potentially low-cost adsorbents for heavy metals was pre-
sented by Bailey et al. (1999). Minamisawa et al. (2004)
investigated the adsorption of cadmium and lead ions on
different biomaterials, concluding that this is a promising
alternative for the removal of these ions. Another review was
published in 2004 by Gardea-Torresdey et al., concluding
that Cd, Cu, Ni, Cr, and other ions have been successfully
removed from solutions using different biomaterials. Gong
et al. (2005) studied the use of peanut hull as a biosorbent
for the removal of anionic dyes in a solution, obtaining sorp-
tion capacities of between 13.99 and 15.60 mg per gram of
biosorbent for three different dyes.FlotationSurface-active contaminants, if present in wastewater, will
produce foam upon aeration. This foam rises to the surface
of the wastewater and can be separated and concentrated.
Moreover, as the foam generates and rises, certain sus-
pended impurities also get removed by entrainment. Thus,
the foam-separation process can be developed to provide a
selective removal of soluble and colloidal pollutants in vari-
ous concentrations from water or wastewater. The process
may either utilize the surface-active impurities present in the
wastewater or may require the addition of a specific surface-
active agent prior to aeration; soluble or colloidal impurities
of interest may be precipitated to improve their removal.
Factors affecting the efficiency of the process of foam
separation are:- Airflow rate/surface-active agent or airflow-rate-
to-waste-flow-rate ratio (the removal efficiency
increases when increasing the airflow rate, but
yields wetter foam)
2. Air-bubble size (fine-bubble aeration improves
the efficiency of foam separation, whereas coarse
bubbles or deck aeration are not efficient)
3. Nature and concentration of surface-active agents
4. Foam stability
5. pH of the wastewater
6. Detention period (a short aeration time, 5 minutes
or so, is considered sufficient)
7. Surface-to-volume ratio (a large surface-to-volume
area is conducive to higher efficiency)
The process of foam separation has been used successfully
in a number of waste-treatment applications. These include
(1) removal of surface-active materials such as ABS from sec-
ondary effluent sewage (Klein and McGauhey, 1963; Grieves
et al., 1964; Brunner and Lemlich, 1963; Fldib, 1963);
(2) removal of radioactive ions from dilute aqueous solutions
by the addition of anionic surface agents (Schoen and Mazella,
1961; Schoen et al., 1962; Schnepf et al., 1959); (3) removal
of specific surfactants from refining and petrochemical waste-
waters (Grieves and Wood, 1963); (4) foam fractionation of
phenol (phenolate) from aqueous solutions using a cationic
surfactant, ethyl hexadecyl dimethylammonium bromide, as
the foaming agent (Grieves and Aronica, 1966); (5) the treat-
ment of cyanide and acid chromate wastes (cyanide is precipi-
tated with ferrous ions, and the ferrocyanide precipitates are
floated with a cationic surfactant in a pH range of 5 to 7; acid
chromate is reduced and precipitated as Cr(OH) 3 , and these
precipitates are floated with an anionic surfactant [Grieves,
1972]); (6) the treatment of liquid wastes from the scrubbing
of phosphate and fluoride from air-pollution emissions of the
phosphoric-acid-manufacturing industry (these include pre-
cipitation by lanthanum (III), followed by flotation with an
anionic surfactant [Grieves, 1972]); (7) clarification of turbid
raw water supplies by microflotation-activated carbon process
(Grieves, 1972); and (8) physical separation of SS and coag-
ulated dissolved organic impurities from wastewaters. ABS
serves as activator for bubble attachment in flotation treatment
of sewage (Klein and McGauhey, 1963). Other applications
include the treatment of mine-drainage wastes combined with
secondary sewage effluents and removal of H 2 S from sour
wastes.
An overview on flotation in wastewater treatment was
published by Rubio et al. in 2002. The authors explain the
process, present conventional and emerging flotation tech-
niques and processes, and discuss the applications of the
technique to different compounds. An example of a dissolved
air flotation (DAF) process is presented in Figure 4.Chemical ProcessesAn extensive review on catalytic abatement of water pol-
lutants was published by Matatov-Meytal and Sheintuch
in 1998. In it they present the oxidation and reduction pro-
cesses involved as well as a discussion on catalyst support
and deactivation. A discussion on the use of iron for waste-
water treatment was published by Waite (2002). This article
presents the research challenges and the new possibilities inC016_005_r03.indd 983 11/22/2005 11:25:20 AM