Page 137 - Industrial Wastewater Treatment, Recycling and Reuse

Advanced Physico-chemical Methods of Treatment for Industrial Wastewaters 111

removal or separation, is an important consideration. A number of experi-
mental and theoretical studies have been reported on the sorption of various
acids (Helfferich, 1962; Adams et al., 1969; Ho ¨ll and Sontheimer, 1977;
Hu ¨bner et al., 1978; Rao and Gupta, 1982a,b; Helfferich and Hwang,
1985; Bhandari et al., 1992a,b, 1993, 1996, 1997, 2000; Cloete and Marais,
1995; Juang and Chou, 1996; Bhandari, 1998; Husson and King, 1999;
Sonawane et al., 2009). The anomalous nature of sorption equilibria has also
been indicated with polybasic acids (Bhandari et al., 1997). The experimen-
tal and theoretical information on acid sorption is rather incomplete due to
the following:
1. The majority of the studies have been reported on a single component
acid, not on acid mixtures, and there is little information on wastewater
treatments containing acids.
2. The selection of a resin for any acid removal/separation in wastewater
treatment has not been discussed. Not many new materials have been
investigated, developed, reported, or discussed.
3. Less information is available on experimental and theoretical aspects of
sorption equilibria, especially with reference to the differences in the
sorption behavior and behavior modifications.
4. Not much information is available in open literature on adsorption/ion
exchange in industrial wastewater treatment and techno-economic fea-
sibility analysis.
For the removal of acids from dilute solutions, weak base resins have been
recommended due to their high capacity of removal and ease of regenera-
tion. It has also been suggested that the resins with high basicity are more
suitable in this regard because a near rectangular type of sorption isotherm
can be expected, indicating total sorption of acids corresponding to theoret-
ical resin capacity, especially for stronger acids (Bhandari et al., 2000). Com-
mercial weak base resins are classified into weak, medium, and high basicity
on the basis of ion exchange equilibria.
The importance of basicity depends on type of acid and is found to be less
pronounced for very weak acids, implying that for removal of weak acids
such as phenols and cresols, the capacity and the basicity of resin are equally
important considerations in selection.
It is necessary to know how material selection and material modification
can affect the removal of acids. This is briefly explained here for both adsorp-
tion and ion exchange using the example of lactic acid removal (Bhandari
et al., 2006), where it was found that resins like Dowex MWA-1 can provide
an excellent option for acid removal, especially at low concentrations typical