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 .Microbes are very small organisms , such as bacteria , that live naturally in the environment . Bioremediation stimulates growth of certain microbes that use contaminants as a source of food and energy . Contaminants treated using bioremediation include oil and other petroleum products , solvents , and pesticides .

 How does it work ?

Some microbes  consume and digest pollutants, converting them to small amounts of water and inert gases such as carbon dioxide and ethane . If soil and groundwater do not have enough of the right microbes, they can be added in a process called “bioaugmentation . For bioremediation to be effective , the right temperature , nutrients , and food also must be present. The correct microorganisms can thrive and proliferate in the right conditions—and eat additional pollutants. Microbes grow too slowly or die if the conditions aren't appropriate, and toxins don't get cleaned up. “Amendments” can help to improve the situation. Household goods such as molasses and vegetable oil, as well as air and chemicals that produce oxygen, are all examples of amendments. To treat soil and groundwater in situ, amendments are frequently pumped underground through wells (in place).

However, the conditions required for bioremediation in soil cannot always be met in situ. The environment may be too cold for bacteria to thrive, or the soil may be too compacted for additives to distribute evenly underground at some locations. The EPA may dig up the soil at such sites and clean it “ex situ” (above ground) on a pad or in tanks. To enhance conditions, the soil might be heated, agitated, or combined with amendments. When soil is mixed, pollutants may evaporate before the bacteria have a chance to devour them. The soil can be blended inside a dedicated tank or building where vapors from chemicals that evaporate can be collected and processed, preventing the vapors from contaminating the air. Wells are drilled to pump part of the contaminated groundwater into above-ground tanks in order to clean it up in situ. Before being pumped back into the earth, the water is mixed with amendments. Microbes can bioremediate the rest of the contaminated groundwater underground using the amended groundwater. Ex situ treatment can also be accomplished by pumping groundwater into a "bioreactor." Bioreactors are tanks in which groundwater is treated by mixing it with bacteria and additives. The treated water may be pumped back into the earth, discharged to surface water, or discharged to a municipal wastewater system, depending on the site.

Is Bioremediation safe ?

Microbes that exist naturally in soil and groundwater are used in bioremediation. People at the site or in the surrounding community are not at risk from these bacteria. Once contaminants and the conditions required for bioremediation are removed, microbes brought to the site for bioaugmentation often die off. Chemicals used to boost bioremediation are completely safe. The nutrients used to make bacteria thrive, for example, are routinely utilized on lawns and gardens, and only enough nutrients are provided to encourage bioremediation. Regular soil and groundwater samples are analyzed to check that the treatment is functioning and to track progress.

Why to use bioremediation ?

Bioremediation provides the advantage of cleaning contaminated places utilizing natural processes. It may be less expensive because it does not require as much equipment, personnel, or energy as other cleanup procedures. Another benefit is that contaminated soil and groundwater are treated on-site rather than being dug up, pumped, and transported to a treatment facility. Few if any waste byproducts are produced because bacteria convert hazardous compounds into modest amounts of water and gases. Bioremediation has been chosen or is being employed at over 100 Superfund sites across the US, and has effectively cleaned up many polluted sites.

source: 

https://clu-in.org/download/citizens/a_citizens_guide_to_bioremediation.pdf