2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
P28 APLICATION OF ChITOSAN FOR wATER
TREATMENT
ZUZAnA KLíMOVáa , PETR DOLEJŠa,b and MILADA
VáVROVáa aInstitute of Chemistry and Technology of Environmental
Protection, Faculty of Chemistry, Brno University of Technology,
Purkyňova 118, 612 00 Brno, Czech Republic,
bW&ET Team, box 27, Písecká 2, 370 11 České Budějovice,
Czech Republic,
klimova-z@fch.vutbr.cz
Abstract
Results of experimental study focused on the removal
of humic substances and turbidity by cationic biopolymer
chitosan are presented. Chitosan is a natural high-molecular-weight
polymer prepared from chitin, which is a polysaccharide
found in the exoskeleton of shellfish like shrimps
or crabs. The high content of amino groups provides very
interesting heavy metals chelating properties to chitosan.
Chitosan is partially soluble in diluted mineral acids such as
HnO 3 , HCl, H 3 PO 4 . We have used 0.5% solutions of chitosan
diluted in 0.1M HCl. Aggregates of humic substances after
inorganic coagulant or chitosan addition were separated by
centrifugation. Tests were made with model humic water.
The aim of this work was to found optimal use of chitosan
and to compare its coagulative effectivity with that of standard
coagulants – ferrous and clayey sulphate.
Introduction
Chitosan is a derivative of chitin, a polysaccharide that is
the major component of the shells of crustaceans and insects.
Chitin consists of long chains of acetylated D-glucosamine,
that is, glucosamine with acetyl groups on the amino groups
(n-acetylglucosamine). Chitosan is n-deacetylated chitin,
although the deacetylation in most chitosan preparations
is not complete (see Fig. 1.). Chitin itself is usually prepared
from crab or shrimp shells or fungal mycelia. Treatment with
an alkali then produces chitosan with about 70% deacetylation
1,2 .
Fig. 1. Structure of chitosan
Chitosan as cationic polysaccharide is an important
polymer flocculant in water treatment. It is known that in
chitosan’s molecular structure contains many amino groups
s392
(–nH 2 ) and hydroxyl groups (–OH) on the molecular chain.
These –OH and –nH 2 groups contain single-pair electrons
that can offer the electron pair to empty d-trajectories of
metal ions. Chitosan can therefore be used for removal of
many unwanted metal ions from water such as Al 3+ , Zn 2+ ,
Cr 3+ , Hg 2+ , Ag + , Pb 2+ , Ca 2+ and Cu 2+ etc. Because the active
amino groups in chitosan molecule can be protonated with H +
in water into a cationic polyelectrolyte 3 the molecule shows
effects of static attraction and adsorption. Thus chitosan can
also flocculate particles into digger flocs which become deposited.
Chitosan can be effectively used for removing COD
(organic contaminant) and SS (solid suspending substances)
in water treatment.
Compared with traditional chemical flocculants, chitosan
has the following advantages: the required dosage is
lower, a the depositing velocity is higher, also the efficiency
of removing COD, SS and metal ions is better, sludge treatment
is easier and there is no further pollution. Chitosan
as a flocculant for treating of water will be more expensive
than traditional flocculants. The objective opf our work was
to prepare a cheaper composite based on the chitosan flocculant
material and to make this up from lobster shells 4 and
other chemical flocculants. This composite chitosan flocculant
was planned not only to reduce flocculation cost but also
to improve flocculating function, in comparison with single
chitosan flocculant and traditional chemical flocculant polyaluminium
chloride (PAC) 5 .
Impurities present in the raw water are in suspended,
colloidal, and dissolved form. These impurities are dissolved
organic and inorganic substances, microscopic organisms,
and various suspended inorganic materials. It is necessary to
destabilize and bring together (coagulate) the suspended and
colloidal material to form particles. Afterwards these particles
are removed by filtration.
Coagulation is accomplished by the addition of ions
having the opposite charge to that of the colloidal particles.
Since the colloidal particles are almost always negatively
charged, the ions which are added should be cations or
positively charged. Typically, two major types of coagulants
are added to water. These are aluminium salts and iron salts.
The most common aluminium salt is aluminium sulphate, the
most common iron salt is ferric sulphate. Iron and aluminium
salts are used as primary coagulants and the reactions that
occur after addition of these coagulants are fairly well elucidated.
More recently, organic polyelectrolyte coagulants
have become also used. Organic coagulants are sometimes
used in combination with inorganic coagulants. Depending
on the specific chemistry of the target water, polymer use can
vary from as little as 5 % of the total coagulant dosage to as
much as 100 % ref. 6 .
Chitosan has been widely used in vastly diverse fields,
ranging from waste management to food processing, medicine
and biotechnology. It becomes an interesting material
in pharmaceutical applications due to its biodegradability
and biocompatibility, and low toxicity. The protonization
of amino groups in solution makes chitosan positively char-