Environmental Engineering Reference
In-Depth Information
3.1.5.11
Chitin and Chitosan
Braconnot i rst described chitin in 1811 upon isolating a substance he
called “fungine,” from fungi. h e i rst scientii c reference to chitin was
taken from the Greek word “Chiton,” meaning an “oat of mail,” for the
material obtained from the elytra of May beetles [113]. Chitin is i rst pre-
pared from shells of Crustacea at low-cost by removing other components,
such as calcium and proteins, by treatment with acids and alkalines. Chitin
and chitosan are excellent natural adsorbents [114-116] with high selec-
tivities due to the following reasons:
• Large numbers of hydroxyl and amino groups give chitosan
high hydrophilicity.
• Primary amino groups provide high reactivity.
• h e polymer chains of chitosan provide suitable coni gura-
tions for ei cient completion with metal ions
All of the results obtained from these adsorbents are given in Table 3.8.
3.1.5.12 Biomass
Removal of trivalent arsenic from solution was assessed by Kamala
et al.
[117]. h e As(III) removal capability of fresh and immobilized G. cambo-
gia biomass was estimated. h e As(III) uptake was not greatly af ected by
pH, with optimal biosorption occurring at around pH 6-8. Common ions
such as Ca(II) and Mg(II) did not inhibit As(III) removal at concentra-
tions up to 100 mg/L, but 100 mg/L of Fe(II) caused a noticeable drop in
the extent of As(III) removal. Immobilized biomass columns were recy-
cled i ve times. Water lettuce (
Pistia stratiotes L.
) is an aquatic plant also
used for the removal of arsenate [118] in water. Young plants were har-
vested from a pollution-free pond and hydroponically cultured, ef ectively
absorbing arsenic in a range from 0.25 to 5.0 mg/L. From 22.8% to 82.0%
of the As was removed for a biomass loading of 20 g/L at pH 7.0 at er 144
h. Ridvan
et al.
[119] examined the fungus, Penicillium purpurogenum,
for cadmium, lead, mercury, and arsenic ion removal from water. Heavy
metal loading capacity increased with increasing pH under acidic condi-
tions, presumably as a function of heavy metal speciation versus the H+
competition at the same binding sites. h e adsorption of heavy metal ions
reached a plateau at
pH 5.0. h e fungus adsorption capacity for As(III)
was 35.6 mg/g (Table 3.5). Metal ion elution was achieved using 0.5M HCl.
h is fungus was recycled through 10 adsorption cycles. h e biosorption
∼
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