In-Situ Bioremediation

 

       IN-Situ Bioremediation

Q: What is Bioremediation?

Q: What is In-situ Bioremediation?

 

·       Bioremediation:

1:  Bioremediation is a process used to treat contaminated media, including water, soil and subsurface material, by altering environmental conditions to stimulate growth of microorganisms and degrade the target pollutants.

2: Bioremediation is a process that uses mainly microorganisms, plants, or microbial or plant enzymes to detoxify contaminants in the soil and other environments.

     

Ø  There are two types of bioremediation:

Ø  1:  In situ bioremediation. 

Ø  2: Ex situ bioremediation.

 

·       In situ bioremediation:

Definition:

In Situ Bioremediation is the use of microorganisms (e.g., bacteria, fungi), plants (termed phytoremediation), or biological enzymes to achieve treatment of hazardous waste.

Explanation:

In situ bioremediation is an attractive option for groundwater with lower contaminant concentrations because the treatment occurs directly in the subsurface aquifer.

In situ is a term utilized within a variety of fields meaning "on site" and refers to the location of an event.

Ideally, in situ bioremediation only requires injection of an electron donor to stimulate activity of indigenous dissimilatory metal reducing or sulfate reducing bacterial communities. This is often achieved by injecting an organic carbon source such as acetate, ethanol, or molasses. The process of stimulating microbial growth in this manner is called in situ “Bio stimulation”.

In situ bioremediation is the application of a biological treatment to clean up hazardous compounds present in the environment. The optimization and control of microbial transformations of organic contaminants requires the integration of many scientific and engineering disciplines. Some of the in situ bioremediation practices have been discussed below.

1: Biosparging:

 This involves the injection of air under pressure below the water table to increase ground water oxygen concentrations and to enhance the rate of biological degradation of contaminants by naturally occurring bacteria. Biosparging increases the mixing in the saturated zone and thereby increases the contact between soil and ground water. The ease and low cost of installing small-diameter air injection points allow considerable flexibility in the design and construction of the system.

2: Bioventing:

 Bioventing is a promising new technology that stimulates the natural in situ biodegradation of any aerobically degradable compounds by providing oxygen to the existing soil microorganisms. It uses low air flow rates to provide only enough oxygen to sustain microbial activity. Oxygen is most commonly supplied through direct air injection into residual contamination in soil by means of wells. Henceforth, the adsorbed fuel residuals are biodegraded and volatile compounds are also biodegraded as vapors move slowly through biologically active soil.

 

3: Bio piling:

This is a full-scale technology in which excavated soils are mixed with soil amendments, placed on a treatment area, and further bio-remediated using forced aeration. The contaminants are reduced to carbon dioxide and water.

 

Process of In-Situ Bioremediation:

 

Microorganisms used in the process of bio-remediation can be implanted or cultivated within the site common polluted sites targeted by bio0-remediation are ground water \ aquifers and polluted soils.

 Aquatic ecosystems affected by the oils spills. The most notable cases being the “Deep water Horizon” oil spills  in the 2010 and the “Exxon valdez” in 1998.

The process of In-Situ bioremediation may be:

 “Aerobic”  and   “An-aerobic”.  

Advantages of In Situ Bioremediation:

Ø  It may be possible to completely transform organic contaminants to innocuous substances (e.g., carbon dioxide, water, ethane).

Ø  Accelerated ISB can provide volumetric treatment, treating both dissolved and sorbed contaminant.

Ø  The time required to treat subsurface pollution using accelerated in situ bioremediation can often be faster than pump-and-treat processes.

Ø  In situ bioremediation often costs less than other remedial options.

Ø  As an In situ there is reduced risk of human exposure to contaminated media

Limitations of In Situ Bioremediation:

Ø  Depending on the particular site, some contaminants may not be completely transformed to innocuous products.

Ø  If biotransformation halts at an intermediate compound, the intermediate may be more toxic and/or mobile than the parent compound.

Ø  Some contaminants cannot be biodegraded (i.e., they are recalcitrant).

Ø  Accelerated In situ bioremediation relies on appropriate distribution of amendments and thus, may be difficult to implement completely in low-permeability or heterogeneous aquifers.

Ø  Heavy metals and toxic concentrations of organic compounds may inhibit activity of indigenous microorganisms.