Bioremediation is the process of decontaminating polluted sites through the usage of either endogenous or external microorganism. In situ is a term utilized within a variety of fields meaning "on site" and refers to the location of an event. Within the context of bioremediation, in situ indicates that the location of the bioremediation has occurred at the site of contamination without the translocation of the polluted materials. Bioremediation is used to neutralize pollutants including Hydrocarbons, chlorinated compounds, nitrates, toxic metals and other pollutants through a variety of chemical mechanisms. Microorganism used in the process of bioremediation can either be implanted or cultivated within the site through the application of fertilizers and other nutrients. Common polluted sites targeted by bioremediation are groundwater/aquifers and polluted soils. Aquatic ecosystems affected by oil spills have also shown improvement through the application of bioremediation. The most notable cases being the Deepwater Horizon oil spill in 2010 and the Exxon Valdez oil spill in 1989. Two variations of bioremediation exist defined by the location where the process occurs. Ex situ bioremediation occurs at a location separate from the contaminated site and involves the translocation of the contaminated material. In situ occurs within the site of contamination In situ bioremediation can further be categorized by the metabolism occurring, aerobic and anaerobic, and by the level of human involvement.
History
The Sun Oil pipeline spill in Ambler, Pennsylvania spurred the first commercial usage of in situ bioremediation in 1972 to remove hydrocarbons from contaminated sites. A patent was filed in 1974 by Richard Raymond, Reclamation of Hydrocarbon Contaminated Ground Waters, which provided the basis for the commercialization of in situ bioremediation.
Classifications of In situ Bioremediation
Accelerated
Accelerated in situ bioremediation is defined when a specified microorganism is targeted for growth through the application of either nutrients or an electron donor to the contaminated site. Within aerobic metabolism the nutrient added to the soil can be solely Oxygen. Anaerobic in situ bioremediation often requires a variety of electron donors or acceptors such as benzoate and lactate. Besides nutrients, microorganisms can also be introduced directly to the site within accelerated in situ bioremediation. The addition of extraneous microorganisms to a site is termed bioaugmentation and is used when a particular microorganism is effective at degrading the pollutant at the site and is not found either naturally or at a high enough population to be effective. Accelerated in situ bioremediation is utilized when the desired population of microorganisms within a site is not naturally present at a sufficient level to effectively degrade the pollutants. It also is used when the required nutrients within the site are either not at a concentration sufficient to support growth or are unavailable.
Raymond Process
The Raymond Process is a type of accelerated in situ bioremediation that was developed by Richard Raymond and involves the introduction of nutrients and electron acceptors to a contaminated site. This process is primarily used to treat polluted groundwater. In the Raymond process a loop system is created. Contaminated Groundwater from downstream of the groundwater flow is pumped to the surface and infused with nutrients and an electron donor, often oxygen. This treated water is then pumped back down below the water table upstream of where it was originally taken. This process introduces nutrients and electron donors into the site allowing for the growth of a determined microbial population.
Oxygen Injection
In contaminated sites where the desired microbial metabolism is aerobic the introduction of oxygen to the site can be used to increase the population of targeted microorganisms. The injection of Oxygen can occur through a variety of processes. Oxygen can be injected into the subsurface through injection wells. It can also be introduced through an injection gallery. The presence of oxygen within a site is often the limiting factor when determining the time frame and efficacy of a proposed in situ bioremediation process.