6.5 Methods Used in Bioremediation Process

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6.5.1

In Situ Method

6.5.1.1

Bioaugmentation

The process involves an addition of either indigenous or exogenous microorganisms

to contaminated locations [27]. It is favorable for the soils that are bioremediated, but

yet have risks, because microbes that are naturally occurring could not do their part

of work due to the unfavorable environmental factors (temperature, pH, salinity,

etc.) or the changes occur in the microbial population due to mutation. To apply

bioaugmentation method, there are few conditions which depend on site size and

availability of certain microbes.

6.5.1.2

Bioventing

This method comprises of utilizing native microorganisms for the biodegrada-

tion of organic pesticide content absorbed into the soil at the unsaturated zone.

Vacuum-enhanced soil vapor extraction method is used where pressure alterations

in the subsurface display an influx of oxygen supply which is required for aerobic

degradation of impurities. In the case of volatile contaminants, extraction of

soil vapor is carried out by the process of adsorption on activated carbon and

biodegradation within a biofilter [28].

6.5.1.3

Biosparging

It is a stimulation and exploitation of novel microorganisms for the biodegradation

of organic toxins in water-logged soil. To enhance the microbial activity by increas-

ing the oxygen dissolution, air is injected into the saturated region present beneath

the water table through the boreholes which will significantly upsurges the aerobic

biodegradation of pesticides. Moreover, it is also used to remove petroleum products

[29, 30]. An imperative feature for the effective elimination of contaminants is soil

porosity.

6.5.1.4

Biostimulation

It is the modification of natural habitat for the stimulation of the existing bacterial

population to carry out bioremediation process. Addition of phosphorus, oxygen,

carbon, and nitrogen will stimulate indigenous microbes in the soil which act as

rate-limiting nutrients and electron acceptors. The advantage of this method is that

the bioremediation will take place by natural native microbes [31]. Alternatively,

bioremediation of halogenated pesticide contaminants in anaerobic condition can

be stimulated by electron donors, thus indigenous microbes use the halogenated

contaminants as electron acceptors.

6.5.2

Ex Situ Methods

6.5.2.1

Composting

Soil will be treated with aerobic thermophilic microorganisms for the degradation

of pesticides. Periodic moistening and mixing are done to promote microbial activity

and to diminish the toxicity of metallic residues, pesticides, waste, and byproducts.