Environmental Engineering Reference
In-Depth Information
Table 7.3
Characteristics of textile dying mill wastewater [8,11].
pH
7.0-12
BOD, Biochemical Oxygen Demand (mgL
-1
)
80-6000
COD, Chemical Oxygen Demand (mgL
-1
)
150-12000
TOC, Total Organic Carbon (mgL
-1
)
130-1120
TSS, Total Suspended Solids (mgL
-1
)
15-8000
TDS, Total Dissolved Solids (mgL
-1
)
2900-12500
Chloride (mgL
-1
)
1000-1600
TKN, Total Kjeldahl Nitrogen (mgL
-1
)
70-80
Color (Pt-Co)
50-12500
nanofiltration, all of which are indeed phase transfer operations that
remove dissolved and suspended solutes from the aqueous to the solid
phase, thus generating large volumes of hazardous sludge. As such, these
processes need to be modified to satisfy the strict regulations on sludge
treatment/disposal and/or adsorbent regeneration/replacement, which are
all costly operations [20,21]. The above challenges to destroy dye residuals
in biotreated wastewater effluents seem to be resolved by the introduction
of advanced oxidation processes (AOPs), whereby highly reactive hydroxyl
radicals are generated chemically, photochemically and/or by radiolytic/
sonolytic means. Hence, AOPs not only offer complete decolorization of
aqueous solutions without the production of huge volumes of sludge, but
also promise considerable degrees of mineralization and detoxification of
the dyes and their oxidation/hydrolysis byproducts.
7.2
Sonication: A Viable AOP for Decolorizing/
Detoxifying Dying Process Effluents
Advanced oxidation processes (AOPs) are powerful methods of destroy-
ing recalcitrant compounds in water, and ultrasound is a unique AOP
that is particularly effective in decolorizing intensely colored solutions
[5,17,22-29]. The potential of ultrasound as an AOP is based on cavitation
phenomenon, i.e., the formation, growth and implosive collapse of acous-
tic cavity bubbles in water and the generation of local hot spots with very
extreme temperatures and pressures. Hence, cavitation is a source of high-
energy microreactors, where water vapor and volatile gases such as N
2
and
O
2
are thermally fragmented to produce highly reactive oxidizing spe-
cies as hydroxyl (HO ), peroxyl (HO
2
-
) and superoxide (O
2
-
) radicals.
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