Page 55 - Industrial Wastewater Treatment, Recycling and Reuse

38 Industrial Wastewater Treatment, Recycling, and Reuse

Someorganiccompounds,forexample,acetic/maleic/oxalicacids,acetone,or
chloride derivatives such as chloroform are not attacked by OH˙ radicals. In
such cases, application of AOP may not be suitable. AOPs are generally cost
intensive, mainly because of high operating cost. However, they require much
less space and many times less capital cost as compared to many of the physico-
chemical processes and biological processes. The oxidation products are gen-
erally less complex and can be treated by conventional biological methods.

1.4.7 Incineration
Toxic organic materials such as pesticides, herbicides, and chlorinated
hydrocarbons are difficult to remove by the conventional processes. Incin-
eration, by default, can be considered as an option only when the pollutants
are most difficult to degrade biologically or cannot be economically
removed by any of the physico-chemical methods (adsorption/ion
exchange/extraction/membrane separation, etc.) of separation. Because
there are strict restrictions on the levels of toxic compounds in wastewaters,
destructive methods such as incineration (thermal/catalytic) are then found
as the only techno-economically feasible technology. The organics present
in the wastewaters can be oxidized in this process along with some of the
inorganics using extremely high temperatures in the presence of oxygen.
The recommended temperatures for incineration of chlorinated hydrocar-

bons and pesticides range from 980 to 1500 C. A sustained high tempera-
ture prevents the emission of degradation products. The incinerator stack
gases generally contain HCl vapors that require the installation of scrubbers.
In general, flue gas treatment along with proper disposal or reuse for the slag/
ash produced during incineration is always required.
Incineration technology for wastewater treatment should be considered
only if there is a sufficient load of organics and inorganics for burning. Evap-
oration of water is sometimes considered for improving process perfor-
mance. For spent wash treatment, concentration followed by incineration
is one option. However, in any case, incineration is a highly energy intensive
process, and the requirement for proper technology to treat such a difficult
stream is also a challenging task, especially if the pollutant concentrations and
economics of the process cannot justify the size of the incinerator. For these
reasons, many times, design of such an incinerator facility for wastewater
treatment is highly plant specific requiring tailor-made designs. Incineration
design is usually complex and involves altogether different chemistry and
engineering when compared to the conventional methods of treatment.