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is a property of certain types of inactive, dead, microbial biomass to
bind and concentrate heavy metals from even very dilute aqueous solutions.
Biomass exhibits this property, acting just as a chemical substance, as
an ion exchanger of biological origin. It is particularly the cell
wall structure of certain algae, fungi and bacteria which was found responsible
for this phenomenon. Opposite to biosorption is metabolically driven
active bioaccumulation by living cells. That is an altogether
different phenomenon requiring a different approach for its exploration.
Pioneering research on biosorption of heavy metals at McGill University in Montreal has led to identification of a number of microbial biomass types which are extremely effective in concentrating metals. Some of the biomass types come as a waste by-product of large-scale industrial fermentations (the mold Rhizopus or the bacterium Bacillus subtilis ). Other metal-binding biomass types, certain abundant seaweeds (particularly brown algae e.g. Sargassum, Ecklonia ), can be readily collected from the oceans. These biomass types, serving as a basis for metal biosorption processes, can accumulate in excess of 25% of their dry weight in deposited heavy metals: Pb, Cd, U, Cu, Zn, even Cr and others. Research on biosorption is revealing that it is sometimes a complex phenomenon where the metallic species could be deposited in the solid biosorbent through different sorption processes of ion exchange, complexation, chelation, microprecipitation, etc.
A whole new family of suitably
"formulated" biosorbents can be used in the process of metal removal and
detoxification of industrial metal-bearing effluents. The sorption
packed-column configuration is the most effective mode of application for
the purpose. Recovery of the deposited metals from saturated biosorbent
can be accomplished because they can often be easily released from the
biosorbent in a concentrated wash solution which also regenerates the biosorbent
for subsequent multiple reuse. This and extremely low cost of biosorbents
makes the process highly economical and competitive particularly for environmental
applications in detoxifying effluents of e.g.
Different types of science background,
from engineering to biochemistry, can make a significant contribution in
elucidating the biosorption phenomenon. Interdisciplinary efforts
are mandatory and represent quite a challenge. Preparing biosorption
for application as a process requires mainly chemical engineering
background. Good understanding of the sorption operation is mandatory.