Page 48 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse: An Overview 31

is relatively small, hundreds of these products are being produced commer-
cially with differences in performance, surface/pore characteristics, func-
tionalities, activation procedures, and other features. There is a wide
scope for the development and characterization of new materials and mod-
ification of materials and process development with the ultimate aim of
recovering valuable components or mitigating environmental concerns.
Specialty materials pose difficulty in evaluating them in terms of actual
surface interactions they offer in effluent treatment and for the removal of
pollutants simply on the basis of fundamental parameters such as surface area,
pore size, and size distribution. However, laboratory data in terms of capac-
ity, extent of removal, and regeneration of the adsorbent is usually sufficient
for suitable design. The selection and design procedure is similar to that for
ion exchange resins, which are discussed in the following section.

1.4.3 Ion Exchange
Ion exchange is commercially carried out for water softening/treatment and
various ion removal applications for dilute solutions.
The conventional ion exchange process depends upon the metathetical
exchange of ionic species and the capacity of resin to exchange; this is an
important parameter in the process design. However, for wastewater treat-
ment, it is quite attractive to employ weak base ion exchange resins that,
although they do not work in accordance with the conventional ion
exchange mechanism, remove both organics and acidic ionic species,
thereby resulting in COD reduction to a great extent. The mechanism in
the case of acid removal proceeds through protonation of ionogenic species
on the weak base resins by the proton of the acid and subsequent addition of
anion to the exchange site through electrostatic interaction (Bhandari et al.,
1992a,b, 1993, 2000).

+
R+H ! RH +
+
+
RH +A ! RH A

+

Where A is the anion of the acid, HA. R is a resin group. RH and
+
RH A are protonated species and acid salt of the resin respectively.
The treatment with a base, such as sodium hydroxide, regenerates the resin
in original free base form. The removal of non-ionics/organics, however,
takes place mainly through surface interaction with the polymer matrix
and does not involve any ionic interaction as such. The design of the ion
exchange process thus involves the efficient combination of cation and anion