Environmental Engineering Reference
In-Depth Information
hydrogen peroxide (H
2
O
2
) or (boron)). Alcohol or peroxyl groups formed by one and
two O
2
atoms are easily fragmentable. The reactions are differentiated on the basis
of source of oxygen atom (water, H
2
O
2
or O
2
). The enzymes that utilise oxygen are
called oxygenases. Two types of oxidases have been identiied, namely, one that is
involved in hydroxylation and the other is involved in oxidation reactions [20, 21].
Lignins are considered to be natural three-dimensional polymers, associated with
cellulose and hemicelluloses. Lignin has macromolecular framework, which is dificult
to degrade by microorganisms. Only a lignolytic organism has the ability to degrade
this which is an oxidative process by the extracellular enzyme, lignin peroxidase, in
the presence of H
2
O
2
. Lignin peroxidase is a non-speciic enzyme produced by many
species including aerobic fungi and few aerobic bacteria. This is an oxidation process
and different oxidation reactions (
Table 3.2
)
are catalysed by various oxidative
enzymes.
Table 3.2 Different reactions catalysed by oxidative enzymes in biological
systems
Reaction
Product formed
Reference
AH
2
+ B
→ A + BH
2
[1]
AH
2
+ O
2
→ A+ H
2
O
2
(H
2
O
2
-forming oxidases)
[2]
AH
2
+ ½O
2
→ A+ H
2
O (H
2
O-forming oxidases)
[3]
A + H
2
O + B
→ AO + BH
2
[4]
A + H
2
O
2
→ AO + H
2
O
[5]
A + O
2
+ BH
2
→ AO + B + H
2
O (monooxygenases)
[6]
A + O
2
→ AO
2
(dioxygenases)
[7]
A: Cofactor
B: Electron acceptor
3.3.2 Abiotic Degradation
In most degradation processes, abiotic parameters (mechanical, light, humidity, heat
and so on) play a major role in weakening the polymeric structure [22]. These factors
act as an initiator or synergistic factor for the biodegradation process. These factors
vary depending upon the location, season, wind, ocean currents, distance from shore
line, anthropogenic activities and so on, these factors cannot be altered or controlled.
