Microbial Transformations at Aqueous-Solid Phase Interfaces: A Bioremediation Approach

Abstract

The application of state-of-the-science analytical techniques to environmental chemodynamics of organic contaminants has provided society with various information of concern. The air we breathe, the water we drink, the soil in which our crops are grown, and the environments where populations of humans, animals, and plants grow are contaminated with a variety of synthetic organic chemicals. Many of these contaminants are industrial chemicals that have been, deliberately or inadvertently, discharged into surface and ground waters, or onto soils and bottom sediments following their intended use. Others are by-products of manufacturing operations that do not utilize waste-treatment facilities or by-products that were inadequately treated.

Biodegradation is the most important fate and biotransformation mechanism for various organic compounds at aqueous-solid phase interfaces, compared to other abiotic chemodynamic processes (e.g., photolysis, volatilization, and hydrolysis). It frequently, although not necessarily, leads to the conversion of much of the organic C, N, P, S, and halogens in the original contaminant to inorganic products. Such a conversion of an organic substrate to inorganic products is known as mineralization or ultimate biodegradation. Thus, in the mineralization/biodegradation of organic compounds, CO₂ and inorganic forms of N, P, and S are released by the microorganisms in aqueous-solid phase environments. This biotransformation process appears to result largely, or entirely in some interfacial environments, from microbial activity. Indeed, microorganisms are the dominant means of converting synthetic chemicals to inorganic products in the ambient environment.

Accordingly, the present chapter is designed to present the basic principles of microbial associations at aqueous-solid phase interfaces, the types and mechanisms of biodegradation and biotransformation, and to show how those principles relate to bioremediation engineering technologies. It considers the microbiological, chemical, environmental, engineering, and technological aspects of biodegradation. However, it does not cover all facets because the information is too extensive and diverse, and the knowledge base is expanding too rapidly to be covered in a single chapter. Nevertheless, there are general key principles that underlie the science and engineering technology. Thus, the present chapter focuses mainly on state-of-the-knowledge about the major groups of microorganisms, the biodegradation processes and factors affecting them, and the microbial transformations of various toxic and carcinogenic organic contaminants at interfaces. In addition, several case studies showing the application of biodegradation concepts in bioremediation technology of contaminated environments are also presented and discussed.