Biodegradable
Biodegradable substances are those that can be decomposed quickly by the action of biological organisms, especially microorganisms. The term is a process by which materials or compounds are broken down to smaller components, and all living organisms participate to some degree. Foods, for instance, are degraded by living creatures to release energy and chemical constituents for growth. In the sense that the term is usually used, however, it has a more restricted meaning. It refers specifically to the breakdown of undesirable toxic and waste materials or compounds to harmless or tolerable ones. When breakdown results in the destruction of useful objects, it is referred to as biodeterioration.
Although the term has been in common use for only two or three decades, processes of biodegradation have been known and used for centuries. Some of the most familiar are sewage treatment of human wastes, composting of kitchen, garden and lawn wastes, and spreading of animal waste on farm fields. These processes, of course, all mitigate problems with common and ubiquitous byproducts of civilization. The variety of objectionable wastes has greatly increased as human society has become more complex. The waste stream now includes items such as plastic bottles, lubricants, and foam packaging. Many of the newer products are virtually non-biodegradable, or they degrade only at a very slow rate. In some instances biodegradability can be greatly enhanced by minor changes in the chemical composition of the product. Biodegradable containers and packaging have been developed that are just as functional for many purposes as their non-degradable counterparts.
Advances in the science of microbiology have greatly expanded the potential for biodegradation and have increased public interest. Examples of new developments include the discovery of hitherto unknown microorganisms capable of degrading crude oil, petroleum hydrocarbons, diesel fuel, gasoline, industrial solvents, and some forms of synthetic polymers and plastics. These discoveries have opened new approaches for cleansing the environment of the accumulating toxins and debris of human society. Unfortunately, the rate at which the new organisms attack exotic wastes is sometimes quite slow, and dependent on environmental conditions. Presumably, microorganisms have been exposed to common wastes of a very long time and have evolved efficient and rapid ways to attack and use them as food. On the other hand, there has not been sufficient time to develop equally efficient means for degrading the newer wastes.
Research continues on the surprising capabilities of the new microbes emphasizing opportunities for genetic control and manipulation of the unique metabolic pathways that make the organisms so valuable. The potential for biodegradation can be improved by increasing the rates at which wastes are attacked, and the range of environmental conditions in which degrading organisms can thrive. The advantages of biological cleanup agents are several. Non-biological techniques are often difficult and expensive. The traditional way of removing petroleum wastes from soil, for instance, has been to collect and incinerate it at high temperatures. This is very costly and sometimes impossible. The prospect of accomplishing the same thing by treating the contaminated soil with microorganisms without removing it from its location has much appeal. It should have less destructive impact on the contaminated site and be much less expensive.
Resources
Books
King, R. B., G. M. Long and J. K. Sheldon. Practical Environmental Bioremediation. Boca Raton, Florida: CRC Press, Inc., 1992.
Sharpley, J. M. and A. M. Kaplan. Proceedings of the Third International Biodegradation Symposium. London: Applied Science Publishers, 1976.
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