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ABSTRACT
IMMOBILIZATION OF LACCASE AND ITS USE IN PAPER MILL EFFLUENTS
BIOTRANSFORMATION
Paper mill effluents are formed by several toxic phenol compounds. Among such
compounds, some of them of high molecular-mass (MM) are biotransformaded only by some
organisms such as fungi from Basidiomycota type. Several studies prove that wood
biodegradation by these fungi mainly depends on its capacity of producing extracellular
ligninolytic enzymes such as laccase ones. Laccase enzymes catalyze oxidation of a variety of
aromatic compounds, especially phenol ones. Several applications have been suggested for
these enzymes, among them, its use in bioremediation of phenol compounds, thus, effluents
which contain such compounds. Nevertheless, these applications and any other involving
enzymes in its free form are not possible because of its peculiarities, as for example, they lose
activity under denaturants means and conditions. Thus, to increase enzymes operational
stability, they can be immobilized in solid supports which supply more resistance to activity
loss. Considering this, the present essay, has as main aim to immobilize a laccase enzyme in
chitosan spheres and evaluate its biotransformating potential of a paper mill effluent sample.
Initially it was possible to observe that, in spite of the enzyme had acquired operational
stability low values, it became more resistant to many conditions and denaturant means, such
as: high pH and temperature, inhibitors and solvents presence. In a second stage, some
biotransformations tests were performed with effluent samples and the immobilized enzyme.
Biotransformation process was surveyed during different periods of time according to the
following patterns: total phenols, low MM phenols, color and DQO. With basis in obtained
results it was possible to notice that after 24 incubation hours of the immobilized enzyme and
the effluent, 65% of MM phenols were removed and 60% of the color ones. Although
statistically significant changes in DQO levels were not observed after enzymatic treatment, it
was possible to conclude that the immobilized enzyme in quitosane spheres have a great
biodegrading potential of phenol compounds which, at the same time, are the ones which stop
chemical agents, responsible for such kind of effluent high toxicity.
Keywords: Laccase, immobilization, paper mill effluents, phenol compounds, chitosan, paper
and cellulose.
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