What is Bioremediation?

By Reginald DaveyReviewed by Sophia Coveney

Humans have an impact on the world around them. From greenhouse emissions to the waste and pollution we produce every day, the activity of each person and communities and nations as a whole has wide-reaching effects on the natural world and our civilization itself. This article will discuss bioremediation, which is one method that can be utilized to mitigate environmental damage.

Image Credit: BigBearCamera / Shutterstock.com

Bioremediation – An overview

One environmental issue that human society faces is pollution and poorly managed waste. This can come from everyday domestic and industrial processes and can impact every environment on Earth. From effluent runoff into rivers and oceans to industrial waste disposal or oil spills, human activity is having a real and lasting effect. Once waste and pollution have entered natural cycles, it has the potential to proliferate for decades to come, causing lasting damage.

In areas with less stringent environmental controls, and even in those with tight regulations that control the storage and disposal of waste, and the risk of site contamination, the environmental repercussions of incorrect management and mitigation can be disastrous. Microbes that feed on waste can produce harmful by-products, not the least of which can be the release of greenhouse gases and toxic effluence entering soil or the water table.

Bioremediation is one process for handling waste and toxic pollutants. It works by altering environmental conditions in a way favorable to the stimulation of microorganisms and thus promote the degradation of target pollutants. By treating contaminated media (for example, water, soil, and subsurface material) the effect upon the environment by these factors can be neutralized.

How does bioremediation work?

There are two general categories of bioremediation methods: in situ and ex situ. In situ techniques can treat the contaminant in place (this includes bioventing and biostimulation) and ex situ techniques require the physical removal of contaminants and transporting them to other controlled environments. This includes bioreactors, farming, and composting.

In terms of chemistry, most bioremediation processes involve redox reactions. By far the most common bioremediation techniques are aerobic, as oxygen is a superior oxidizer. Common electron acceptors in these processes include manganese III and IV, iron (III) sulfate, nitrate, carbon dioxide, as well as pollutants including oxidized metals and chlorinated solvents. Electron donors in bioremediation processes include fuel hydrocarbons, organic pollutants, sugars, alcohols, and fats.

Bioremediation processes must be tightly controlled. Nutrients such as phosphorous and oxygen are added to improve treatment effectiveness. Bioremediation processes can also be pH controlled to provide a more favorable environment using certain additives.

Aerobic processes

Aerobic bioremediation processes are by far the most commonly applied methods. Using oxygen as an electron acceptor provides a higher energy yield and enzymes require it to initiate degradation processes.

Aerobic processes are especially suited to the oxidation of reduced pollutants such as petroleum and phenols. Microorganisms have been shown in studies to be effective in the degradation of a wide variety of hydrocarbons.

Anaerobic processes

Anaerobic bioremediation processes are employed when there is a need for the treatment of pollutants that aerobic processes are not suited for. These include chlorinated ethenes, chlorinated ethanes, chlorinated cyclical hydrocarbons, and various energetics.

Electron donors are added to deplete background electron acceptors (for example, oxygen, oxidized iron, manganese, and sulfate) and stimulate biological and chemical reduction of oxidized pollutants.

Bioremediation methods for dealing with heavy metals

Bioremediation processes can also utilize microbes to reduce the mobility of heavy metals (for example, uranium, cadmium, and lead.) Microorganisms are used to catalyze the usually slow reduction rate of these heavy elements.

Bioremediation processes can be used to remove metals from water through enhanced sorption of metals to cell walls of the microbes utilized. This has potentially powerful applications for the removal of lead and cadmium from water tables. Contaminants can also be concentrated within biomass by phytoextraction processes for easy removal.

Advantages of using bioremediation processes

Bioremediation is a technology with many advantages over traditional methods of pollution control. These include reduced cost compared to more traditional methods and sustainability. Also, the lack of toxic chemicals in these processes is particularly advantageous for researchers and companies who are concerned about adverse, unexpected environmental damage from pollution control methods.

Limitations

There are, however, limitations to this technology. Bioremediation is highly dependent on specific microbial and environmental conditions. The microbial population present must have the metabolic capacity to degrade a target pollutant.

The environment must have the right conditions for microbial growth, and it also depends heavily on nutrient and contaminant amounts. As contaminated sites can vary in many of these factors, bioremediation processes must be tailored specifically to them.

Small-scale tests must be performed before carrying out bioremediation procedures at contaminated sites. This is due to many of the factors being inter-dependent. It can be difficult to scale these small-scale tests to large field operations as it can be hard to accurately extrapolate data from them. Thus, bioremediation can take more time than alternative processes (for example, incineration.)

There is also the very real risk of untoward toxic compounds being produced by microbes used due to factors such as insufficient mineralization of pollutants. This can be mitigated by using further microbial populations known to degrade any harmful side-products of bioremediation.

A thorough knowledge of metabolic and chemical pathways within the microbes employed can mitigate this and avoid any untoward complications which may arise.

In conclusion

Bioremediation is a powerful, advantageous technology that makes effective use of biotechnology to remove potentially harmful pollutants from a variety of environments. However, it is not a perfect solution.

It must be tightly controlled to avoid any untoward side-effects which may arise from the treatment of pollutants in this manner. Clearly, more research is needed in the field but it is a technology that is changing the way we deal with the environmental harm caused by human society.

Further Reading

• All Microbiology Content
• Microbiology and Food Security
• What Can Microbiology Tell Us About Extraterrestrial Life?
• How Intelligent are Microbes?
• How Could Microbes Help to Solve Climate Change?