4.2.1. In situ Bioremediation Techniques

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4.2.1. In situ Bioremediation Techniques

Bioremediation technologies that are used “in place” without removal of the contaminated matrix from air, water and soil. The advantages and disadvantages of these techniques are given in Table 4.1. Commonly used in situ treatments are:

Bioventing

Bioventing involves supplying air and nutrients through wells to contaminated soil to stimulate the local bacteria. If the contamination is deep under the surface, this technique can be used for environmental cleaning. Bioventing supply low air flow rates and provides only the amount of oxygen necessary for the biodegradation while minimizing volatilization and release of contaminants to the atmosphere.

Biodegradation

Biodegradation involves supplying oxygen and nutrients by circulating aqueous solutions through contaminated soils to stimulate indigenously occuring multiple organisms to degrade organic contaminants. Generally, this technique can be used for contaminated soil and groundwater.

Biosparging

This method is one of the in situ remediation technologies that use local microorganisms to biodegrade organic ingredient in the saturated site. In order to increase the biological activity of the naturally occuring microorganisms, air and nutrients are injected into the saturated zone. Biosparging is used to clean groundwater and soil contaminated with petroleum constituents. The ease and low cost of installing smalldiameter air injection points allows considerable flexibility in the design and construction of the system.

Bioaugmentation

This method involves the addition of microorganisms naturally occuring or exogenous to the contaminated sites. This method is especially useful for contaminated soil with inorganic compounds.

Biostimulation

Biostimulation is a type of natural remediation that can improve pollutant degradation by optimizing conditions such as aeration, addition of nutrients, pH and temperature control. This method can be considered as an appropriate remediation technique for petroleum pollutant’s removal in soil and requires the evaluation of both the intrinsic degradation capacities of the autochthonous microflora and the environmental parameters involved in the kinetics of the in situ process.

Table 4.1. Advantages and disadvantages of in situ techniques

Advantages

Disadvantages

•No need to excavate & transport soils - typically less expensive

•Can treat a large volume of soil at once

•Causes less contaminants to be released than ex situ techniques

•Creates less dust

•Most effective if the soil is permeable sandy soil (uncompacted)

•Least effective in clays/highly layered subsurface environments - oxygen cannot be evenly distributed throughout the treatment area

•May be slower to reach cleanup goal (if less easily degradable contaminant, requires years)

•May be more difficult to manage (than ex situ techniques)

•The seasonal variation of microbial activity exists

•The sites are directly exposed to environmental factors like temperature, oxygen supply etc.

•Problematic application of treatment additives like nutrients, surfactants, oxygen etc.

•It is a very tedious and time consuming process.