Bioavailability
The effect of the microbial, physical, and chemical factors on the extent and rate of
biodegradation is defined as bioavailability. It refers to the amount of a soil contaminant that is transformed and taken up using microorganisms. Other factors like the
extent of hydrocarbons deterioration, microbial community, and pH may be widely
influenced by the limitations in the hydrocarbons bioavailability. The bioavailable
component of the hydrocarbons is the accessible part to microorganism (Semple
et al. 2003). Hydrocarbonorganic pollutants have little water solubility and therefore
they are stable to chemical biological and photolytic breakdown. The reducing of
bioavailability with time is often referred to as weathering or aging. It may result
from the chemical oxidation reactions incorporating pollutants into natural organic
materials, slow diffusion into very small pores and absorption into organic materials
as well as the formation of semi-rigid films close to non-aqueous-phase liquids with
a good stability toward non-aqueous-phase liquids-water mass transfer (Boopathy
2000). Using of food-grade surfactants that enhance the availability of pollutants for
microbial degradation overcomes bioavailability problems (Boopathy et al. 1998).
Table 12.24 lists all the main factors affecting bioremediation.
Degradation Mechanism of Crude Oil Hydrocarbons
Most organic contaminants need aerobic conditions for a rapid and complete degradation. The primary intracellular organic contaminant attack takes the form of
oxidation and activation. The key enzymatic catalyst by oxygenates and peroxidases
needs integration of oxygen. The key degradation pathways transform organic
contaminants in intermediates of the main intermediary metabolism. The biosynthesis of cell biomass occurs from the central precursors metabolites like the succinate,
pyruvate, and Acetyl-CoA. The essential saccharide for various biosynthesis and
growth is synthesized using gluconeogenesis. Crude oilhydrocarbons treatment can
be performed by a specific enzyme system, attaching microbial cell to substrates and
biosurfactant production (Rahman et al. 2003). Cytochrome P450 hydroxylases,
which is isolated form Candida species like C. maltose, C. tropicalis and Candida
apicola attends in the biodegradation of chlorinated compounds and other materials
(Van Beilen and Funhoff 2007). The system of extracellular enzymes in Aspergillus
spp., isolated from crude oil contaminated soil, efficiently treats crude oil (Zhang
et al. 2016). The efficiency of anthracene degradation of ligninolytic and
non-ligninolytic fungi was studied by Jové et al. (2016). They reported less efficiency of anthracene degradation for Irpex lacteus and Pleurotus ostreatus than
those for Phanerochaete chrysosporium. As a conclusion, aerobic situations provide
the best medium for a quick and complete degradation of organic pollutants.
480
M. Fatehi et al.
The effect of the microbial, physical, and chemical factors on the extent and rate of
biodegradation is defined as bioavailability. It refers to the amount of a soil contaminant that is transformed and taken up using microorganisms. Other factors like the
extent of hydrocarbons deterioration, microbial community, and pH may be widely
influenced by the limitations in the hydrocarbons bioavailability. The bioavailable
component of the hydrocarbons is the accessible part to microorganism (Semple
et al. 2003). Hydrocarbonorganic pollutants have little water solubility and therefore
they are stable to chemical biological and photolytic breakdown. The reducing of
bioavailability with time is often referred to as weathering or aging. It may result
from the chemical oxidation reactions incorporating pollutants into natural organic
materials, slow diffusion into very small pores and absorption into organic materials
as well as the formation of semi-rigid films close to non-aqueous-phase liquids with
a good stability toward non-aqueous-phase liquids-water mass transfer (Boopathy
2000). Using of food-grade surfactants that enhance the availability of pollutants for
microbial degradation overcomes bioavailability problems (Boopathy et al. 1998).
Table 12.24 lists all the main factors affecting bioremediation.
Degradation Mechanism of Crude Oil Hydrocarbons
Most organic contaminants need aerobic conditions for a rapid and complete degradation. The primary intracellular organic contaminant attack takes the form of
oxidation and activation. The key enzymatic catalyst by oxygenates and peroxidases
needs integration of oxygen. The key degradation pathways transform organic
contaminants in intermediates of the main intermediary metabolism. The biosynthesis of cell biomass occurs from the central precursors metabolites like the succinate,
pyruvate, and Acetyl-CoA. The essential saccharide for various biosynthesis and
growth is synthesized using gluconeogenesis. Crude oilhydrocarbons treatment can
be performed by a specific enzyme system, attaching microbial cell to substrates and
biosurfactant production (Rahman et al. 2003). Cytochrome P450 hydroxylases,
which is isolated form Candida species like C. maltose, C. tropicalis and Candida
apicola attends in the biodegradation of chlorinated compounds and other materials
(Van Beilen and Funhoff 2007). The system of extracellular enzymes in Aspergillus
spp., isolated from crude oil contaminated soil, efficiently treats crude oil (Zhang
et al. 2016). The efficiency of anthracene degradation of ligninolytic and
non-ligninolytic fungi was studied by Jové et al. (2016). They reported less efficiency of anthracene degradation for Irpex lacteus and Pleurotus ostreatus than
those for Phanerochaete chrysosporium. As a conclusion, aerobic situations provide
the best medium for a quick and complete degradation of organic pollutants.
480
M. Fatehi et al.