Temperature
Temperature is a significant factor that affects bioremediation via its effect on the
chemical and physical compositions of contaminants (Zhang et al. 2019). The
activity of enzymes and the degradation rate are reduced at low temperatures
(Bisht et al. 2015). At high temperature from 30 to 40
C, the hydrocarbon metabolism reaches the maximum level (Al-Hawash et al. 2018). The ranges of temperature with the greatest rate of degradation are 30–40, 15–20, and 20–30
C in soil,
marine, and freshwaterenvironments, respectively (Al-Hawash et al. 2018).
Oxygen
One of the factors to limit the rate of crude oilhydrocarbons degradation is the
concentration of oxygen (Von Wedel et al. 1988). According to the report of
Haritash and Kaushik (2009), anaerobic degradation of crude oilhydrocarbons
using microorganisms can be at insignificant rates. Based on the study of McNally
et al. (1998), the aerobic biodegradation of crude oilhydrocarbons is higher than their
anaerobic biodegradation. For the catabolism of all aromatic and aliphatic and cyclic
materials by microorganisms, substrate oxidation by oxygenases is a key step in the
biodegradation process.
Nutrients
Nutrients including nitrogen, phosphorus, and iron in some cases have an important
role in successful biodegradation and act as a limiting factor for this process (Atlas
1995). Carbon can be provided from organic materials. Oxygen and hydrogen can be
supplied from H 2 O (Kalantary et al. 2014). Oil spills in freshwater and marine
environment increase the amounts of carbon and reduces the phosphorus and
nitrogen levels and thus affects biodegradation. There are low levels of nitrogen
and phosphorus in marine environments. Moreover, nutrients cannot be provided by
wetlands since there is a high nutrients demand by plants. Therefore, adding
nutrients is essential to increase the biodegradation of pollutants (Hesnawi and
Adbeib 2013). It should be noted that the extra nutrients concentration can inhibit
the biodegradation activity. Mineki et al. (2015) investigated the degradation of
polycyclic aromatic hydrocarbons by Trichoderma/Hypocrea applying pyrene as a
source of carbon. The strains growth and pyrene-degrading efficiency were
increased in comparison with the control sample after 1 and 2 weeks of incubation
when 0.1% of lactose or 0.1% of sucrose and 0.02% of yeast extraction were added.
478
M. Fatehi et al.
Temperature is a significant factor that affects bioremediation via its effect on the
chemical and physical compositions of contaminants (Zhang et al. 2019). The
activity of enzymes and the degradation rate are reduced at low temperatures
(Bisht et al. 2015). At high temperature from 30 to 40
C, the hydrocarbon metabolism reaches the maximum level (Al-Hawash et al. 2018). The ranges of temperature with the greatest rate of degradation are 30–40, 15–20, and 20–30
C in soil,
marine, and freshwaterenvironments, respectively (Al-Hawash et al. 2018).
Oxygen
One of the factors to limit the rate of crude oilhydrocarbons degradation is the
concentration of oxygen (Von Wedel et al. 1988). According to the report of
Haritash and Kaushik (2009), anaerobic degradation of crude oilhydrocarbons
using microorganisms can be at insignificant rates. Based on the study of McNally
et al. (1998), the aerobic biodegradation of crude oilhydrocarbons is higher than their
anaerobic biodegradation. For the catabolism of all aromatic and aliphatic and cyclic
materials by microorganisms, substrate oxidation by oxygenases is a key step in the
biodegradation process.
Nutrients
Nutrients including nitrogen, phosphorus, and iron in some cases have an important
role in successful biodegradation and act as a limiting factor for this process (Atlas
1995). Carbon can be provided from organic materials. Oxygen and hydrogen can be
supplied from H 2 O (Kalantary et al. 2014). Oil spills in freshwater and marine
environment increase the amounts of carbon and reduces the phosphorus and
nitrogen levels and thus affects biodegradation. There are low levels of nitrogen
and phosphorus in marine environments. Moreover, nutrients cannot be provided by
wetlands since there is a high nutrients demand by plants. Therefore, adding
nutrients is essential to increase the biodegradation of pollutants (Hesnawi and
Adbeib 2013). It should be noted that the extra nutrients concentration can inhibit
the biodegradation activity. Mineki et al. (2015) investigated the degradation of
polycyclic aromatic hydrocarbons by Trichoderma/Hypocrea applying pyrene as a
source of carbon. The strains growth and pyrene-degrading efficiency were
increased in comparison with the control sample after 1 and 2 weeks of incubation
when 0.1% of lactose or 0.1% of sucrose and 0.02% of yeast extraction were added.
478
M. Fatehi et al.