FERREIRA, J. M.; http://lattes.cnpq.br/1966216398901568; FERREIRA, Joelma Morais.
Résumé:
The industrial activities have introduced metals in waters in quantities which are
greater than those found naturally, thereby causing heavy pollutions. The
conventional treatments (chemical reduction, ionic exchange, ultrafiltration and
inverse osmosis), normally used for the metal removal of the liquid effluents,
present some disadvantages, because majority of them apart from being
expensive processes are not capable to remove metal ions compleatly. The
necessity of efficient and economic treatments for removal of metallic ions from
effluents has resulted in the development of new technologies. Many of these
techniques are based on the use of bacteria, fungi, microseaweed, and
macroseaweed. The biosorption is a process in which solids of natural origin or
its derivatives are used in the retention of metallic ions from an aqueous
medium. The biosorption process has as main advantages the low operational
cost and high selectivity when compared to the conventional methods for the
removal of metallic ions from industrial effluents. Amongst the used
microorganisms fungi are more distinguished, as these are used in a variety of
industrial processes and serves as constant and economic source of
supplement of biomass for removal of metallic ions. Brazil being a world-wide
big producer of ethyl alcohol by a fermentative process that uses the
Saccharomyces cerevisiae (ferment) as the microorganism, it is a common
practice in the industries of alcohol to remove the excess of the ferment cream
by centrifuging. This way, the excessive Saccharomyces cerevisiae of the
fermentation process is a source that can be used, for example, as biosorbent
of metallic íons for the decontamination of environment. Experiments of
biosorption of metallic íons using the Saccharomyces cerevisiae for removal of
the Cd2+ and Pb2+ had been carried out to investigate the factors that
influence and optimize the biosorption process. Through the study of the static
kinetics it was verified that a period of 48 hours is enough for the process to
reach the equilibrium. For the dynamic kinetics after 90 min no more change in
the final concentration of the two metallic ions occurred. Therefore, this time is
enough for the system to reach the equilibrium when the process is operating in
dynamic conditions. The design of experiment technique was used to evaluate
the effect of the variables: biomass amount, metallic ions concentrations,
temperature, pH and state of the biomass (alive or dead). The effects of the
amount of biomass amount and initial metallic ion concentration were the
variables that presented more significant effects when compared with the effect
of pH and state of the biomass (alive or dead) under the evaluated conditions.
The Langmuir and Freundlich models were used to adjust to the experimental
data of the adsorption isotherms of metal ions studied. The model that adjusted
better the adsorption isotherms was of Langmuir having qmax values as 210.5
mg.g-1 for cadmium and 1486.88 mg.g-1 (Langmuir not linearized) for the lead.
The immobilized ferment presented a decrease in its efficiency of metal ion
removal. In the study for the immobilized ferment an average efficiency of the
adsorbed amount per unit of mass of 78.5% for the Cd2+ and 73.92% for the
Pb2+ was observed.
