Chitosan-based Materials in Waste Water Treatment––Recent Developments - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 28

Fibers
Scanty information is available onto the use of chitosan in fiber forms for wastewater
treatment. Chitosan fibers were tested with aqueous solutions of copper sulfate and
zinc sulfate for different periods of time to prepare samples containing different levels
of metal ion contents. On chelation of metal ions the chitosan fibers gained substantial
increase in the both dry and wet strength. The metal ions were readily removed from
the chitosan fibers by treatment with an aqueous EDTA solution (Yimin Qin, 1993).
The recovery of direct dye by adsorption on cross-linked fiber was developed and
appeared technically feasible. The concentration of amino group fixed in the adsorbent
phase was 3.30 mol/kg dry fibers. A typical direct dye, brilliant yellow was used. The
breakthrough curves for adsorption of the dye were measured for different flow rates,
bed heights, influent concentration of the dye, and temperature (Hiroyuki et al., 1997).
Chitosan fibers have been studied for the recovery of dyes and amino acids (Yoshido,
1993) but less attention has been paid to the use of this conditioning of the polymer for
the recovery of metal ions.
Hollow Fibers
Hollow fibers have recently received attention with the objective of performing the
simultaneous sorption and desorption of the target metal. Hollow chitosan fibers were
prepared and the system was used for the recovery of chromate anions. The hollow
fibers were immersed in the chromate solution while an extractant was flowed through
the lumen of the fiber. Chromate anions adsorbed on the fiber were re-extracted by the
solvent extractant. The hollow fiber acts simultaneously as a physical barrier that can
make the extraction process more selective. (Vincent, 2000, 2001)
ChemiCal modiFiCatioNs
Recently, there has been growing interest in the chemical modifications of chitosan in
order to improve its solubility and widen its applications (Heras et al., 2002; Kurita et al.,
1998; Sashiwa and Shigemasa, 1999). Chitin and chitosan have been modified via a
variety of chemical modifications. Some authors have reviewed the methods (Kurita,
2001; Van Luyen and Huong, 1996). Robert has explained the modifications reactions
in his source-topic, Chitin Chemistry . Of the various possible modifications, a few
to mention are nitration, phosphorylation, sulphonation, xanthation (De Smedt
et al., 2000), acylation, hydroxyalkylation (Van Luyen and Huong, 1996), Schiff's
base formation and alkylation (Avadi et al., 2003, 2004). These modification tech-
niques, as foreseen by Kurita will likely find new applications in some fields includ-
ing water treatment, metal cation adsorption, toiletries, medicine, agriculture, food
processing, and separation (Kurita, 2001).
Derivatives of Chitosan
The high sorption capacities of modified chitosan for metal ions can be of great use for
the recovery of valuable metals (or) the treatment of contaminated effluents. A great
number of chitosan derivatives have been obtained with the aim of adsorbing metal
ions by introducing new functional groups onto the chitosan backbone. The new func-
tional groups are incorporated into chitosan to increase the density of sorption sites,