Bioremediation: An Overview

By Dr. Priyom Bose, Ph.D.Reviewed by Emily Henderson, B.Sc.

Bioremediation is a technology that employs living organisms such as bacteria and fungi to remove harmful contaminants and toxins from the environment. This reliable and eco-friendly approach has rapidly gained popularity in environmental research. Scientists have been successful in developing different bioremediation techniques to restore contaminated sites.

Bioremediation. Image Credit: OpturaDesign/Shutterstock.com

Among various other applications, this technology is used to clean up oil spills and contaminated groundwater. The microbes used in this technology can be both indigenous or non-indigenous. These microorganisms take part in the degradation, immobilization, and detoxification of various harmful chemical wastes and contaminants.

The main mechanism behind this process is to detoxify, reduce, degrade, or transform toxic substances into less toxic substances. The microbes used for bioremediation solely depend on the nature of the contaminants, for example, type of pesticides, agrochemical, xenobiotic compounds, heavy metals, plastics, organic halogens, greenhouse gases, etc. This technology is also used to process nuclear waste.

Principles of Bioremediation

The main principle behind biotechnology is the use of living organisms, especially microbes, in remediating harmful contaminants to lesser toxic substances. This technology uses bacteria, fungi, and/or plants to detoxify or degrade hazardous substances from the environment. The living organisms convert pollutants via their metabolic processes (e.g., synthesis of enzymes). This technology involves several microbes to degrade pollutants from the contamination site.

Factors of Bioremediation

Several environmental factors such as type of soil, pH, temperature, nutrients, the presence of oxygen or other electron acceptors in the soil, and the type of microbial population present in a particular contamination site play an important role in the rate of bioremediation. Thereby, for the best bioremediation process, optimization of these conditions is important. Some of the factors are discussed in details below:

Environmental Factors

Microbial growth depends on several environmental factors such as pH, temperature, moisture, and nutrients. Scientists practice biostimulation that involves the addition of nutrients to the contamination site which enhances the growth of microbes that assist in bioremediation.

Most of the microbes grow best at optimal conditions, thereby, amending those nutritional or biochemical conditions (e.g., pH, temperature, etc.) would aid in the growth of particular microbes. Scientists deploy different processes to alter the growth conditions, for example, if a soil is too acidic (low pH), the condition can be reversed by adding lime.

Microbial Populations for Bioremediation Processes

Microbes such as bacteria and fungi can survive varied temperatures, i.e., sub-zero to extremely high temperatures. Some bacteria exhibit a chemotactic response, where they can sense the contaminant and move towards it, thereby, leading to bioremediation. Similarly, Several fungi, involved in this process, grow their filament in the contamination site. Some of the microbes involved in this process are discussed below:

Bacteria:

For bacterial degradation, they must be in contact with the contaminant. There are two types of bacteria, namely, aerobic and anaerobic, that are used for bioremediation. Aerobic bacteria can degrade complex compounds in the presence of oxygen. These bacteria can degrade hydrocarbons, pesticides, alkanes, and polyaromatic compounds.

Some of the examples of aerobic bacteria are Pseudomonas, Sphingomonas, Nocardia, Flavobacterium, and Mycobacterium. The anaerobic bacteria functions in absence of oxygen and are not popularly used for the bioremediation process. However, some anaerobic bacteria are used in the bioremediation of polychlorinated biphenyls (PCBs), chlorinated aromatic compounds, and dechlorination of the solvent trichloroethylene and chloroform.

Fungi:

Several fungi can degrade harmful heavy metals and other hazardous components. For instance, white-rot fungus Phanaerochaete chrysosporium can degrade persistent or toxic environmental pollutants and Aspergillus sp can degrade heavy metals present in the soil.

Bioremediation Strategies

Several bioremediation strategies are employed depending on the level of saturation and aeration of the soil. These techniques can be divided into two categories, i.e., in-situ and ex-situ. The in-situ techniques are employed for the treatments of the soil or groundwater, which require minimal disturbance. Whereas ex-situ techniques are employed away from the treatment site, i.e., the contaminated soil under consideration is removed via excavation for its treatment.

In-situ treatments are mostly concentrated in the soil. Some of the examples of in situ treatments are bioaugmentation, bioventing, and biosparging. Bioaugmentation is a type of in-situ bioremediation which involves the amendment of microbes to the polluted site to increase the rate of degradation.

Bioventing is one of the most common in-situ treatments which deals with providing air and nutrients to the contaminated site via wells to trigger the growth of indigenous bacteria. Bioventing is effective for hydrocarbon degradation. In biosparging, the air is injected under pressure below the water table to enhance the groundwater oxygen concentrations and, thereby, triggering the aerobic bacteria. Landfarming is one of the simple ex-situ bioremediation techniques. This technique deals with excavating contaminated soil which is subsequently spread over a prepared bed where the indigenous biodegradative microorganisms are stimulated.

Bioreactors (slurry reactor) are also used in the ex-situ bioremediation process. This bioreactor is used for the treatment of contaminated water and soil that have been pumped up from a polluted plume. Generally, the rate of biodegradation is high in a bioreactor system.

Advantages and Disadvantage of Bioremediation  

The main advantage of bioremediation is that it does not use any toxic chemicals. Typically, it utilizes nutrients such as fertilizers to activate the microbial population. Additionally, this process is less labor-intensive and is economical. Bioremediation is an eco-friendly and sustainable approach that can destroy a pollutant or convert harmful contaminants into harmless substances.

The main disadvantage of bioremediation technology is that it is restricted to biodegradable compounds. Further, researchers have revealed that sometimes the new product developed after biodegradation may be more toxic to the environment than the initial compound. Lastly, the process is time-consuming, especially for ex-situ bioremediation, which requires excavation and pumping.

Applications of Bioremediation

Bioremediation is appropriate for all states of matter, i.e., solid, liquid, and gases. This technology is highly efficient for the treatment of solids such as sediments, soil, and sludge.

In the case of liquid treatment, it is applied to remediate oil spills in the ocean, as well as, treatment of industrial wastewater and groundwater. Further, bioremediation is also widely used for the treatment of industrial air emissions.