Page 128 - Industrial Wastewater Treatment, Recycling and Reuse

102 Industrial Wastewater Treatment, Recycling, and Reuse

B. Surface modification
– Acids/base/specialty materials
(Often undisclosed)
The adsorption process and its application to wastewater treat-
ment is also a relatively mature technology. At present, there is rea-
sonably good understanding of the following aspects:
– Fundamentals of adsorption and adsorption processes (forces respon-
sible for adsorption, factors favoring adsorption, adsorption equilib-
ria and kinetics, temperature/pressure dependence, heat of
adsorption, molecular simulation pressure drop, cost)
– Synthesis and characterization: materials and methods
– Regeneration: chemicals and cost
– Process scheme: fixed bed/fluidized bed operation
– Advantages and disadvantages of adsorption separation
– Selection of adsorbents (listing of guidelines)
– Economic evaluations and comparison with other competing
processes.
Significant improvements can be obtained for most of the adsorption pro-
cesses with proper scientific modifications, either through material modifi-
cations or through process modifications. Surface modification of inorganic/
organic materials has a fundamental role in industrial and environmental
processes. The surface chemical modification of carbon is of great interest
in order to produce materials with specificity and essentially control the type
of pollutants that are adsorbed. This modification has been mainly carried
out by oxidative methods, producing a more hydrophilic structure with a
large number of oxygen-containing groups (Rios et al., 2003). The surface
modification of adsorbent materials is believed to improve quantity and
quality of the adsorbing sites and also at times alter functionality of the sur-
face or impart ion exchange properties. Zeolite is an excellent example
where huge benefits can be obtained through material modifications. A pro-
cess like pressure-swing adsorption is an excellent example of a huge trans-
formation in separation science through process modification wherein
adsorption and desorption can take place by swinging pressure alone. While
pressure-swing adsorption is established in gas separations, it finds little or no
applications in wastewater treatment, although thermal swing operations
have been investigated and tried. Zeolites typically have useful properties
through their cage-like defined pore structures and ionic framework. The
functional properties and advancement in the zeolites can be obtained in
the production process through change in parameters such as Si/Al ratio,