Mycoremediation of Synthetic Dyes: An Insight into the Mechanism, Process Optimization and Reactor Design - Microbial Degradation of Synthetic Dyes in Wastewaters - page 4

cell wall i.e. amino, carboxyl, thiol and phosphate groups, can bind dye molecules
(Tan et al. 2011 ; Fan et al. 2012 ). Biosorption of dye molecules onto the surface of
fungal cells is a quick process and often gets completed in a few hours. Dye
biosorption process is also affected by various process parameters, such as pH,
temperature,

initial dye concentration and type of dye present in the solution

(Srinivasan and Viraraghavan 2010 ). Therefore, to obtain ef cient dye removal, it is

necessary to optimize various process parameters. Moreover, selection of a fungal
strain fordye biosorption should be made in a way that it is capable of removing
wide variety of dyes belonging to different classes.
The biosorption capacity of biomass can be further increased by certain physical
(drying, autoclaving) or chemical (organic, inorganic) pre-treatments (Viraraghavan
and Srinivasan 2011 ). Immobilization in alginate beads (Prigione et al. 2008 )or
loofa-sponge (Iqbal and Saeed 2007 ) has been reported to enhance biosorption
capacity. Biosorbent can be regenerated by treatment with certain chemicals, such
as alkalis, chelating agents etc. Recovery of the adsorbent and dye makes the
treatment process more economical. It is observed that most of the studies are
performed with the help of dye solutions. However, mixed ef uent from textile

industries containing mixtures of dyes and certain other chemicals may interfere
with the process of dye removal through biosorption. Therefore, more studies
should be performed utilizing the mixtures of dyes and industrial ef

uent.

2.2 Dye Bioaccumulation

Majority of the reports, that report bioaccumulation as the principle mechanism for
dye removal, are focused on the use of single cell fungi (Dias et al. 2010 ; Das et al.
2011 ) and cyanobacteria (Silva-Stenico et al. 2012 ). However, a few studies report
bioaccumulation by mycelial fungi, such as A. niger (Taskin and Erdal 2010 ) and P.
oxalicum (Xin et al. 2010 ). Bioaccumulation of dyes by fungi is mediated by initial
biosorption to the fungal cell wall which is metabolism-independent and then
accumulation into the cytoplasm which is metabolism-dependent (Wang and Hu
2008 ).

2.3 Dye Biodegradation

Biodegradation is described as the breakdown of chemical compounds which is
mediated by the action of biological enzymes. Complete biodegradation is the total
breakdown of organic molecules into water, carbon dioxide and/or any other
inorganic end products which is known as mineralization. White-rot fungi secrete
certain ligninolytic enzymes that bind non-speci cally to the substrate. Therefore,

they are capable of degrading a wide variety of recalcitrant compounds and com-
plex mixtures of pollutants, such as dyes. Since these ligninolytic enzymes secreted