Mycoremediation of Synthetic Dyes: An Insight into the Mechanism, Process Optimization and Reactor Design - Microbial Degradation of Synthetic Dyes in Wastewaters - page 5

by fungi are extracellular, therefore, problem related to substrate diffusion limitation
into the cell, which is commonly encountered in bacteria, is not observed in fungi.
Also, enzyme secretion by white-rot fungi depends on nutrient limitation (nitrogen
or carbon) and is not altered by the presence of pollutants. This implies that for dye
removal through biodegradation as the principle mechanism, acclimatization of the
fungi with the pollutants may be skipped (Ge et al. 2004 ). Laccase, Manganese
Peroxidase (MnP), Manganese Independent Peroxidase (MIP), Lignin Peroxidase
(LiP), Tyrosinase etc. are the various enzymes that are involved in the degradation
of the dye.
For biodegradation, fungal cells have to be in their growing form. This limits
their application in treatment of toxic dye ef uents. Nevertheless, the enzyme

activity is often not altered by the presence of other pollutants, but biosorption as a
process is in

uenced by the factors, like ionic strength, ionic state of dye and
biosorbent. Thus, biodegradation, as a means for dye removal, has its own
advantages. The growth of the fungus, enzyme production and subsequent dye
decolorizationare effected by the culture conditions, like initial dye concentration,
pH, agitation, media components, presence of heavy metals etc. (Martorell et al.
2012 ;Da

â

ssi et al. 2013 ; Jin and Ning 2013 ; Moreira-Neto et al. 2013 ). Growth of
the fungus is also affected by the nutritional conditions of the environment. Table 2
summarizes the key differences among three principle mechanisms fordye removal
process. It is important to note that during the process of dye removal through
fungi, multiple mechanisms may be operative either simultaneously or sequentially.

Table 2 Comparison between biosorption, bioaccumulation and biodegradation process (mod-
i ed after Chojnacka 2010 )
Biosorption Bioaccumulation Biodegradation

Passive process Active process Active process

Biomass is not alive Biomass is alive Biomass is alive

Dye molecules are
bound with cellular
surface

Dye molecules are bound with
cellular surface and interior

Dye molecules are degraded by
enzymes

Adsorption Absorption Extracellular degradation/

adsorption followed by
degradation

Reversible process Partially reversible process Irreversible process

Nutrients are not
required

Nutrients are required Nutrients are required (nitrogen

limiting conditions favourable)

Single-stage process Double-stage process Double-stage process

The rate is quick The rate is slow The rate is slow

Not controlled by
metabolism

Controlled by metabolism Controlled by metabolism

No danger of toxic
effect

Danger of toxic effects caused
by contaminants

Interference by contaminants,
byproducts may be toxic

No cellular growth Cellular growth occurs Cellular growth occurs