Environmental Engineering Reference
In-Depth Information
3
Biodegradation of Polymers in Marine
Environment
Thangavelu Muthukumar and Mukesh Doble
3.1 An Introduction to Biodegradation
Biodegradation is the process of degrading an organic, i.e., carbon containing,
substance into simpler carbon containing substances (end products) by the action of
the environment and the surrounding microorganisms. The microorganisms utilise
these materials as their food. The biodegradation process differs depending on the
type of microorganism, polymer type, environmental conditions, type of additives
present and pretreatment conditions. The secondary metabolites or the end products
produced by one organism can become the nutrient source for others. Microbial
communities act in synergy and enhance the biodegradation process.
There are several reasons why this process is better when compared to other chemical
or physical processes. This method directly degrades the contaminants rather than
transforming them to the other form. There are numerous degradation mechanisms
that are combined synergistically in nature to degrade polymers. Biodegradation
by microorganisms can take place by the action of enzymes or by the by-products
(acids and peroxides) produced by it. In the marine environment macroorganisms
including barnacles, bryozoans, polychaetes and so on, also play a major role in the
biodegradation process. These macroorganisms may attack the polymer causing
mechanical, enzymic or chemical ageing or use it as its carbon source.
Polymers accumulate at a rate of 25 million tonnes per year in the terrestrial and in
the marine environment [1]. Dumping of this waste material in the sea is the reason
for major marine pollution. It has been estimated that more than a million marine
animals are being killed every year either because of choking on loating plastic items
or by becoming entangled in plastic debris. Fishing and shipping industries are a major
cause of plastic litter. A weight loss of only 0.75% was observed when pure high-
density polyethylene (HDPE) was immersed in sea water for a period of 6 months
[2]. Studies from our laboratory have reported a 2.5% weight loss in unblended
HDPE used in marine water for 12 months [3].
In vitro
degradation of starch blended
