Page 129 - Industrial Wastewater Treatment, Recycling and Reuse

Advanced Physico-chemical Methods of Treatment for Industrial Wastewaters 103

structure and porosity of the material, ionic species, and reaction conditions
apart from further modifications, for example by exchanging different ions.
In addition to engineering key modifications in the existing process, process
integration is an interesting and fairly wide open area for research and devel-
opment wherein there is huge opportunity for studying intelligent combi-
nations of two or more operations. The advent of nanomaterials has also
increased the scope of investigating advanced adsorptive separations with
altogether new dimensions. In the future, new adsorbent materials are
required to have high capacity, high selectivity, improved stability, and more
favorable geometries (Adler et al., 2000). The technical challenges for waste-
water treatment applications include:
1. Developing newer, efficient, and cost-effective adsorbents for better
performance.
2. Developing efficient ways to regenerate and reuse adsorbents.
3. Developing tailor-made adsorbents for complex systems, especially for
the removal of refractory pollutants.
4. Predicting adsorption behavior through modeling and simulation.
As far as adsorptive process advances are concerned, it is believed that cost
and efficacy of pollutant removal will drive further growth in this area.

2.3.4 Ion Exchange

The ion exchange process is mainly used to separate ionized molecules
(organic as well as inorganic) from aqueous solutions as well as contaminants
in organic streams. Ion exchange has been used industrially for many years in
the form of cationic or anionic resins with strong or weak acidic or basic
groups to remove ions from dilute solutions (Helfferich, 1962). In wastewa-
ter treatment, this process is commonly employed as a tertiary or polishing
method for the removal of specific pollutants to desired levels.
For industrial wastewater treatment, the ion exchange process mostly
employs synthetic ion exchange resins in bead form (Figure 2.7). The resin
beads are spherical, by and large, with size typically ranging from 0.1 to
1 mm in radius. The backbone can be made of polymers such as polystyrene,
epoxy, phenol-formaldehyde, or polyacrylate-polystyrene; polyacrylates are
most widely used in practice. The bead contains a large network of pores,
similar to that discussed in Section 2.3.1. On the basis of pore size, the resins
are classified as microporous, mesoporous, or macroporous. The polymer
backbone in resin is essentially hydrophobic, while the pore phase, due to
the presence of ionic/ionogenic functional groups, is essentially hydrophilic.