Biotreatment of Industrial Effluents
Intended for practicing environmental engineers and technologists from any industry, this book discusses the treatment procedures using biochemical means for all types of solid, liquid and gaseous contaminants.
TABLE OF CONTENTS Biotreatment of Industrial Effluents
Chapter 9: Degradation of Polymers
Introduction
Approximately 140 million tonnes of synthetic polymers are produced worldwide each year. Since polymers are extremely stable, their degradation cycles in the biosphere are limited. In Western Europe it is estimated that 7.4% of municipal solid waste is plastic; these plastics are classified as 65% polyethylene (PE)/polypropylene (PP), 15% polystyrene (PS), 10% polyvinyl chloride (PVC), 5% polyester terephthalate (PET), and miscellaneous others. Environmental pollution by synthetic polymers, such as waste plastics and water-soluble synthetic polymers in wastewater, has been recognized as a major problem. Degradation of polymers can be carried out by heat, radiation, or biochemical treatment. The radiant energy may be high-energy radiation from gamma rays, ion beams, and electrons or even low-energy radiation from ultraviolet (UV) light. UV stabilizers added to polymer products reduce the rate of degradation. Chemical degradation results from treatment with chemicals such as acids and alkalis. Biodegradation of polymers results from the use of microorganisms and enzymes.
Biodegradation
The biodegradability of a compound depends on its molecular weight, molecular form, and crystallinity. Biodegradability decreases with increase in molecular weight, while monomers, dimers, and repeating units degrade easily. Two types of depolymerases are involved in the process, namely, extracellular and intracellular. Microbial exoenzymes first break down the complex polymers in a process called depolymerization. The resulting short chains are small enough to permeate the cell walls, allowing them to be used as carbon and energy sources. When the end products are carbon dioxide, water, or methane, the process is called mineralization. Different end products...
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