Remediation of PAH-Contaminated Soils and Sediments: A ...

Biological Techniques for Enhancing PAH
Degradation (Bioremediation)
Biodegradation is the biological transformation of molecules into smaller
molecules with less toxicity (preferably water and carbon dioxide which is then
termed “mineralization”). Bioremediation is the application of biodegradation to
decrease pollutant concentrations (Olson et al., 2003). In this section, we will be
discussing techniques to enhance biodegradation of PAHs during
bioremediation.
Several factors may limit the biodegradation of PAH in contaminated soils
including (Alexander, 1999; Olson et al., 2003; Straube et al., 2003; Harmsen et
al., 2007):
� limited supply of bacterial nutrient or carbon sources
� nonoptimal abiotic conditions of temperature, pH, salts, oxygen
concentration and toxins
� lack of bacterial species that can degrade PAH compounds or low
microbial biomass in general
� low PAH bioavailability to degrading organisms
� physiochemical characteristics of PAH compound
Manipulations of the above limitations are the basis for bioremediation with the
subsequent goals of: (1) improving soil microbial habitat through fertilizer
additions, tillage, liming, and/or (2) plant establishment to promote microbial
functional groups capable of degrading PAHs, while at the same time (3)
increasing the bioavailability of the PAHs. Biostimulation techniques are used to
improve the soil microbial habitat and bioaugmentation strategies manipulate the
microbial community structure to make it more capable of degrading PAHs.
Biostimulation
Lack of sufficient carbon and nutrient sources to sustain the growth of
biodegrading microorganisms may affect bioremediation success (Odokuma and
Dickson, 2003; Ward and Singh, 2004). Nutrient and carbon additions can
enhance microbial activities which may promote cometabolism (Untermann et al.,
2000). Abiotic conditions can also affect ioremedation, since oxygen is often the
most limiting factor in microbial growth. Oxygen can be manipulated through
physical (landfarming, composting) and chemical (injection of manganese
peroxide) techniques to stimulate microbial communities (Ward and Singh,
2004).
45