Abstract

Bioremediation involves the utilization of microorganisms to degrade environmental pollutants. This technology therefore involves the exploitation of biochemical capabilities of microbial-based processes already functioning in nature. That is, the dangers and consequences of the use of bioremediation processes should be more predictable than if such processes were based on novel technologies. The role of regulatory agencies in the utilization and exploitation of bioremediation technologies will be discussed. Factors influencing the public acceptance of bioremediation as a tool for cleaning up the environment will be reviewed relative to developments in other areas of biotechnology.

Introduction
Bioremediation

Bioremediation involves the use of living microorganisms or their enzymes to enhance the rate or extent of destruction of environmental pollutants which could be toxic or lethal to other life forms. Microorganisms, both aerobes and anaerobes, are responsible for the natural mineralization of organic matter and biochemical nutrient cycling which takes place in soils and waters. That is, they form a "microbial reservoir" which contains organisms with the genetic information for the degradation of many different natural compounds and pollutants, including those from anthropogenic sources (i.e. xenobiotics). Microbial growth in natural environments, if it takes place at all, will be very slow as there is usually a lack of growth-supporting carbon sources and/or essential nutrients such as nitrogen and phosphate, and for aerobic bacteria oxygen. The microbial population in most environments can be considered to be in a state of "dormancy" where the cells are very small in size and are referred to ultramicrobacteria.

If a pollutant such as gasoline was introduced into soil via a rupture of a storage tank it would support the growth of that portion of the "dormant"microbial population which could use gasoline hydrocarbons as a source of cell carbon and energy. This potential for gasoline degradation however can only be fully expressed if conditions are suitable for growth. Therefore the addition of nutrients, (i.e. nitrogen and phosphate) and oxygen are required to stimulate aerobic microbial growth on hydrocarbons. The first successful use of nutrient/aeration stimulated bacterial clean-up of a gasoline contaminated aquifer was reported (1). After it was no longer economical to remove residual gasoline by physical means, the growth of the gasoline-degrading bacteria was initiated by adding a source of nitrogen, phosphate and oxygen. Within two years this microbial stimulation procedure resulted in a water source which was free of gasoline as detected by taste, odor and UV spectrometry and was suitable for human consumption.

Bioremediation processes can be carried out in situ as in the above example, or, if the pollutant can be recovered, ex situ bioremediation processes can be utilized. Under ex situ conditions it is possible to take advantage of "fermentation style" technologies where aeration, temperature, pH etc. can be controlled thus optimizing microbial activity Microbial cells in such reactors can be immobilized on inert support material which results in enhanced oxidizing activity and stability of microbial catalysts. For example, in a commercial detoxification process (2) the bacterial strain used normally grew at a pH slightly above 7 and was sensitive to acid pH when grown in liquid culture.

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