Biosorption of Organic Dyes: Research Opportunities and Challenges - Green Chemistry for Dyes Removal from Wastewater - page 322

second part was assigned to the intraparticle diffusion step, and the third
linearity was related to the equilibrium. Dotto and Pinto [68] observed
multilinearity with two distinct phases in the biosorption of Acid Blue 9
and Food Yellow 3 onto chitosan. The initial portion was related to the
boundary layer diffusion (film diffusion). The second portion was assigned
to the gradual biosorption step, where intraparticle diffusion control is rate
limiting. So, they assumed that film diffusion and intraparticle diffusion
were simultaneously operating during the biosorption process.

8.5 Future Perspectives and Challenges

The biosorption of organic dyes is a crescent research area and many efforts
have been made for this technology to become an alternative to the con-
ventional treatment processes. Several biomasses have been successfully
employed and the factors affecting biosorption are known. Furthermore,
equilibrium, thermodynamics and the kinetic aspects have also been well
studied. Nevertheless, these efforts have not been sufficient to apply bio-
sorption on a full industrial scale. Thus, to assist future research in the
biosorption field, some of the studies listed below are still necessary.

i. Despite the fact that several biomasses were successfully
employed for the biosorption of organic dyes, the search for
new, low-cost, efficient, eco-friendly and alternative biosor-
bents is always necessary.
ii. It is know that specific compounds and functional groups on
biomasses are responsible for dyes binding. Thus, in order
to apply as biosorbents, the identification and extraction of
these specific compounds from biomasses are another per-
spective in the biosorption field.
iii. A relevant way of investigation is relative to fungi, bacteria
and algae. These biomasses can be obtained from cultiva-
tions, and their characteristics and properties are directly
related with the culture conditions. To this end, it is nec-
essary to control the culture conditions (temperature, pH,
lightness, stirring rate, cell concentration, nutrients) in
order to obtain biosorbents with specific functionalities.

iv. The majority of biosorption studies use synthetic aqueous

solutions, with only one dye, in batch systems. However,
from a realistic viewpoint, the dye-containing effluents
are composed of more than one dye. In addition, other