ABSTRACT
The large-scale buildup, dispensation, and handling of chemicals have led to serious surface and subsurface soil contamination with a wide variety of harmful and toxic hydrocarbons. Many of the chemicals that have been synthesized in great volume, including polychlorinated biphenyls (PCBs), trichloroethylene, and others, differ substantially in chemical structure from natural organic compounds and are designated as xenobiotics because of their relative recalcitrance to biodegradation. Other
11.1 Introduction .................................................................................................. 321 11.2 Biodegradation .............................................................................................. 323 11.3 Contaminants ................................................................................................ 324
11.3.1 Contaminant Types and Their Biodegradation Potentials ................ 325 11.3.2 Effect of Chemical Structures on Biodegradation ............................ 325
11.4 Environmental Factors for Biodegradations ................................................. 326 11.4.1 Subsurface Heterogeneity and Abiotic Factors ................................. 326 11.4.2 Sorption and Bioavailability ............................................................. 326 11.4.3 Moisture Content .............................................................................. 327
11.5 Bioremediation .............................................................................................. 327 11.5.1 Biostimulation ................................................................................... 327 11.5.2 Bioaugmentation ............................................................................... 328 11.5.3 Intrinsic Bioremediation ................................................................... 328 11.5.4 Land Farming ................................................................................... 329 11.5.5 Compost ............................................................................................ 329 11.5.6 Bioventing ......................................................................................... 329 11.5.7 Rhizofiltration ................................................................................... 330
11.6 Factors Affecting Bioremediation ................................................................ 330 11.6.1 Energy Sources ................................................................................. 330 11.6.2 Bioavailability ................................................................................... 331
11.7 Advantages and Disadvantages of Bioremediation ...................................... 332 References .............................................................................................................. 332 Suggested Readings ............................................................................................... 332
compounds, for example, the polycyclic aromatic hydrocarbons (PAHs), are also toxic and are typically intractable to biodegradation. Intensification of energy-related and other industrial processes with associated production of wastes and by-products, rich in PAHs, has led to soil contamination in most of the industrial sites. The resultant accumulations of the various organic chemicals in the environment, particularly in soil, are of significant concern because of their toxicity, carcinogenicity, and potential to bioaccumulate in living systems. A wide variety of nitrogen-containing industrial chemicals are produced for use in petroleum products, dyes, polymers, pesticides, explosives, and pharmaceuticals. Major chemical groups involved include different nitro-aromatics, nitrate-esters, and nitrogen-containing hetero-cycles. Most of these chemicals are toxic and adversely affect human health and are classified as hazardous by the United States Environmental Protection Agency (EPA).
