not required. It does not disturb the structure of the soil. However, the important
challenges of in situ techniques are the on-site installation of some complicated
equipment and cost of design to increase the activity of microbes during bioremediation (Jain et al. 2011). The type and the quality of the contaminants, the type and
the environmental situation of the contaminated site, and the cost of treatment
determine the best treatment method (Khan et al. 2004). It is also required that
before selecting the best method, a thorough investigation of the properties of the
contaminated site be conducted. This process is important especially for in situ
remediation since the performance of the treatment process is more complicated
for monitoring and controlling through treatment than the ex situ remediation
process (Morgan and Watkinson 1992). Achieving uniform remediation throughout
the treatment is an important challenge for in situ treatment. In situ bioremediation
methods were successfully applied to treat many contaminants like hydrocarbons in
crude oils (Kim et al. 2014). To achieve successful in situ bioremediation, the
important environmental conditions include the moisture content, status of electron
acceptor, pH, availability of nutrient and temperature (Philp and Atlas 2005).
Transferring the bioremediation methods, which have been tested in laboratory
with good results to the field is the specific challenge of in situ bioremediation.
The ex situ technology needs shorter time to treat than in situ technology and
because of the ability to monitor, homogenize, and screen, it provides more uniformity of treatment. It can be used for a wide range of pollutants and is controlled
easily. However, ex situ technology needs excavation that requires more cost and
engineering for equipment. The base of the ex situ methods is the cost of treatment,
type of contaminant, degree of pollution, depth of pollution, geographical location,
and geology of the contaminated site. Philp and Atlas (2005) have described the
performance criteria to select the ex situ method. In situ bioremediation includes
bioventing, biosparging, permeable reactive barrier, intrinsic bioremediation,
bioslurping, and phytoremediation. In conclusion, both in situ and ex situ technologies are beneficial in bioremediation; however, the type and the quality of the
pollutants, the type and the medium of the contaminated site, and the cost of
treatment determine the effective treatment method.
Bioventing
The method, which is also called soil vacuum extraction (Boopathy 2000), increases
the bioremediation and the activity of indigenous microorganisms in order to
microbial transformation of contaminants to safe state (Philp and Atlas 2005),
using controlled airflow to deliver oxygen to the unsaturated zone (Azubuike et al.
2016). It is useful to remove the oily phase contaminants above the water table.
Undissolved subsurface contaminants which get biodegraded contact with the oxygenated air. Appearance of CO 2 in an extraction well, which is near the contamination points but above the water table shows the biological activity. In comparison
with the use of electron acceptors such as nitrates and hydrogen peroxide, bioventing
468
M. Fatehi et al.
challenges of in situ techniques are the on-site installation of some complicated
equipment and cost of design to increase the activity of microbes during bioremediation (Jain et al. 2011). The type and the quality of the contaminants, the type and
the environmental situation of the contaminated site, and the cost of treatment
determine the best treatment method (Khan et al. 2004). It is also required that
before selecting the best method, a thorough investigation of the properties of the
contaminated site be conducted. This process is important especially for in situ
remediation since the performance of the treatment process is more complicated
for monitoring and controlling through treatment than the ex situ remediation
process (Morgan and Watkinson 1992). Achieving uniform remediation throughout
the treatment is an important challenge for in situ treatment. In situ bioremediation
methods were successfully applied to treat many contaminants like hydrocarbons in
crude oils (Kim et al. 2014). To achieve successful in situ bioremediation, the
important environmental conditions include the moisture content, status of electron
acceptor, pH, availability of nutrient and temperature (Philp and Atlas 2005).
Transferring the bioremediation methods, which have been tested in laboratory
with good results to the field is the specific challenge of in situ bioremediation.
The ex situ technology needs shorter time to treat than in situ technology and
because of the ability to monitor, homogenize, and screen, it provides more uniformity of treatment. It can be used for a wide range of pollutants and is controlled
easily. However, ex situ technology needs excavation that requires more cost and
engineering for equipment. The base of the ex situ methods is the cost of treatment,
type of contaminant, degree of pollution, depth of pollution, geographical location,
and geology of the contaminated site. Philp and Atlas (2005) have described the
performance criteria to select the ex situ method. In situ bioremediation includes
bioventing, biosparging, permeable reactive barrier, intrinsic bioremediation,
bioslurping, and phytoremediation. In conclusion, both in situ and ex situ technologies are beneficial in bioremediation; however, the type and the quality of the
pollutants, the type and the medium of the contaminated site, and the cost of
treatment determine the effective treatment method.
Bioventing
The method, which is also called soil vacuum extraction (Boopathy 2000), increases
the bioremediation and the activity of indigenous microorganisms in order to
microbial transformation of contaminants to safe state (Philp and Atlas 2005),
using controlled airflow to deliver oxygen to the unsaturated zone (Azubuike et al.
2016). It is useful to remove the oily phase contaminants above the water table.
Undissolved subsurface contaminants which get biodegraded contact with the oxygenated air. Appearance of CO 2 in an extraction well, which is near the contamination points but above the water table shows the biological activity. In comparison
with the use of electron acceptors such as nitrates and hydrogen peroxide, bioventing
468
M. Fatehi et al.