Figure 1. Biodegradation of aromatic compounds and n-alkanes.

Figure 2. (a) Leakage from an underground storage tank. The contaminated soil and groundwater can be bioremediated in situ or ex situ. (b) Diagram of in situ bioremediation of subsurface hydrocarbon-contaminated soil and groundwater. (c) In situ bioremediation of hydrocarbon-contaminated aquifer by injection of hydrogen peroxide to provide a source of molecular oxygen and nitrate and phosphate to provide nutrients for the growth of hydrocarbon degraders.

Figure 3. Bioremediation of polychlorinated biphenyl (PCB)-contaminated river sediments. (a) Placement of steel caissons into sediments; chromatographic tracing showing full range of contaminating PCB congeners. (b) Nutrients added to sealed caissons lead to creation of anaerobic conditions: anaerobic dehalogenation converts higher molecular weight congeners to ones with fewer chlorines; chromatographic tracing shows disappearance of higher molecular weight congeners with 4–6 chlorines and increased concentrations of lower molecular weight PCBs with 2–3 chlorines. (c) Forced aeration and stirring create aerobic conditions; biodegradation of lower molecular weight congeners leads to cleaner sediments.

Figure 4. Bioremediation of trichloroethylene (TCE)-contaminated groundwater based upon injection of air and the cosubstrate methane to stimulate a bacterial consortium that can utilize methane and co-metabolize TCE. Much of the TCE is biodegraded in the treatment zone. Residues in the extracted air are destroyed in a catalytic oxidizer.

Figure 5. Permeable reactive barrier. Redrawn from U.S. EPA. 2004. Treatment Technologies for Site Cleanup: Annual Status Report (eleventh edition). EPA-542-R-03-009.

Figure 6. Bioremediation techniques. (a) Landfarming and (b) windrows, at a large bioremediation site in the UK (courtesy of WSP Remediation.) This windrow is being turned, and it is evident that the heat generated by microbial action can be considerable.