Page 122 - Industrial Wastewater Treatment, Recycling and Reuse

96 Industrial Wastewater Treatment, Recycling, and Reuse

formulation strategy. Figure 2.5 highlights changes and range modifications
that can occur using a formulation of inorganic and organic coagulants viz.
PAC and poly DADMAC for reactive blue dye removal with high effi-
ciency. Analysis of data using a PAC concentration of 200 ppm and varying
the concentration of poly DADMAC from 20 to 100 ppm shows significant
modification in the operating pH range. This may be attributed to the con-
tribution of an organic coagulant in the formulation. As mentioned earlier,
the combined formulation works better with wider pH range than that with
individual coagulants. This aspect is further supported by the fact that when
PAC or poly DADMAC alone is not effective, the formulation of PAC and
poly DADMAC works effectively.
The inorganic+organic coagulant formulation strategy can be further
developed in the form of two or more inorganic and organic coagulants.
This is demonstrated in Figure 2.6. A formulation of PAC, alum, and
poly DADMAC (100 ppm inorganic and 60 ppm of poly DADMAC) only
slightly modifies the color removal behavior. However, a little higher con-
centration of alum (500 ppm) changes the color removal behavior drasti-
cally, and the new formulation works over a wider pH range of 3–12
with very high removal efficiency in pH 3–7.
Inorganic-organic coagulant formulations are therefore considered to be
ideal advanced materials in coagulation processes that allow expanding pH
range coupled with lowered dosage to bring out overall improvement in
process efficiency at reduced cost as compared to individual coagulants
(Lee et al., 2012).

2.3 ADVANCED ADSORPTION AND ION EXCHANGE
PROCESSES

Adsorption can be defined in simple terms as selective concentration of one
or more components (adsorbate(s)) of either a gas or a liquid mixture on the
surface of a material (adsorbent). By definition, adsorption is clearly a surface
phenomenon incorporating wide variation in the surface interactions that
range from very-low-strength van der Waals forces to strong bond forma-
tion. The number and density of adsorption sites, the strength of adsorption,
the nature of the adsorbing species, and the nature of the adsorbent material
are important parameters that dictate not just the overall adsorption process
but also the regeneration of the adsorbent by desorption of the adsorbed spe-
cies. In industrial wastewater treatment applications, adsorption is com-
monly performed as a column chromatography operation with adsorption