Biodegradation Process, Meaning, Examples and Types

biodegradation plastic

Biodegradation is the process by which organic compounds are broken down into simpler compounds, by microbes. Stages of biodegradation include; biodeterioration, biofragmentation, bioassimilation, and mineralization. This article discusses biodegradation process, meaning, examples and types;  

 

-Biodegradation Meaning: What is Biodegradation?

-Examples of Biodegradation

-Biodegradation Process

1). Aerobic Biodegradation

2). Anaerobic Biodegradation

-Conclusion

 

 

 

Biodegradation Meaning: What is Biodegradation?

Biodegradation is the breakdown and conversion of organic matter into simpler compounds like carbon dioxide and sulfur dioxide.

The term ‘bio-degradation’ apparently derives from two sub-terms. These terms are bio; which can be seen as a short form of biological, and degradation; which refers to the process of conversion, deterioration, disintegration or breaking down.

Based on the analogy above, we can say that biodegradation is the breakdown, conversion or disintegration of matter under biological conditions.

The unique feature of biodegradation is its biological characteristics. Both the cause and effect of biodegradation are related to biological factors.

This is because biodegradation is a biological process, driven by biological components, and involving organic, biological matter, also known as biomass.

All materials capable of undergoing biodegradation are referred to as “biodegradable” materials.

With the use of a different set of terms, we can produce other definitions of biodegradation.

Biodegradation is the use of biological catalysts to decompose organic matter, thereby producing simpler compounds.

It is a natural process that leads to the disintegration of organic compounds to produce simpler materials that can be cycled easily in the environment.

Biodegradation is an important process with respect to the natural, biogeochemical cycles on Earth, such as the nitrogen, sulfur and carbon cycles [5].

 

Examples of Biodegradation

Plant Biomass

All organic matter includes carbon and hydrogen in its chemical composition. These elements are released when the organic matter breaks down, in the process of biodegradation.

For plant biomass, which includes parts of plants like leaves, biodegradation decomposes complex organic compounds like cellulose, to yield end-products such as water and carbon dioxide.

 

Hydrocarbons

Generally, hydrocarbons are organic compounds, composed primarily of carbon and hydrogen [2].

On of the most common natural forms of hydrocarbons include petroleum and natural gas. These compounds can be broken down by microorganisms, to yield simpler chemical compounds.

Biodegradation of hydrocarbons is facilitated by microbes like bacteria. fungi, archaea and algae [4]. Many of these organisms are ubiquitous, and can be found occurring across a wide range of environments.

The ability of hydrocarbons to undergo biodegradation, is the basis of bioremediation methods used in petroleum-spill cleanup projects.

 

Plastics

Plastics can be natural or synthetic [11].  

Natural plastics are more easily broken down through the process of biodegradation, than their synthetic counterparts.

Like hydrocarbons, biodegradation of plastics is driven by microorganisms. These organisms colonize the plastic material, reducing its molecular weight [7], and its complexity. Ultimately, less-complex chemical compounds are produced.

It is important to note that polyethene is also a form of plastic [10]. Because plastics occur as polymeric chemical compounds, their breakdown initially leads to the production of monomeric compounds or monomers.

The period of time required for complete decomposition of non-synthetic plastics is between three and six months [3]. For synthetic plastics, this period may be hundreds of years.

Various factors determine the rate and effectiveness of biodegradation of plastics. These factors include temperature, humidity, pH, and microorganisms present.

biodegradation plastic
Illustration of Biodegradation Process for Plastics (Credit: Polymersrock 2019 .CC BY-SA 4.0.)

 

Biodegradation Process

The process of biodegradation comprises of a set of stages. In some studies, these may be called the ‘phases’ of biodegradation.

Also, biodegradation occurs through different mechanisms or methods.

The two mechanisms of biodegradation are aerobic and anaerobic.

Aerobic biodegradation stages are biodeterioration, biofragmentation, bioassimilation, and mineralization [9].

Anaerobic biodegradation stages are non-methanogenic, methanogenic/unsteady-state, and methanogenic/steady-state.  

 

1). Aerobic Biodegradation

Aerobic biodegradation is the microbial breakdown of organic matter to form simpler chemical compounds, in the presence of oxygen.

It differs from anaerobic decomposition simply by the presence of oxygen. However, aerobic decomposition is composed of different stages, which are discussed as follows;

-Biodeterioration

Biodeterioration is the physical alteration of organic matter in the process of biodegradation [1].

It is the first stage of biodegradation, during which the organic matter begins to change in its physical, mechanical and chemical characteristics. It may therefore be also referred to as surface-level biodegradation.

At the biodeterioration stage, the organic matter has not necessarily been acted upon by microorganisms. Rather, the abiotic components of the environment have altered the characteristics of this organic matter, causing it to change in its structure.

Biodeterioration may occur in the form of structural weakening, swelling or compression. Abiotic factors that contribute to this stage include pressure, temperature, chemical composition and humidity.

In some cases, microbes are present in the biodeterioration stage. When present, these microbes may release enzymes that act upon organic matter to form carbonyl-groups.

-Biofragmemtation

Biofragmentation is the microbial separation of polymeric chemical bonds in organic matter to generate monomers and oligomers [8].

It may be seen as the most significant stage of biodegradation since it is the stage at which the complex organic compounds are first broken down.

In order for biofragmentation to occur, some organisms and enzymes must be present. In most cases, biofragmentation involves hydrolysis, which uses the hydrogen and oxygen present in organic matter, to cause its breakdown.

However, biofragmentation is no always an aerobic process. This means that it may also be categorized under the anaerobic phase of biodegradation.

Aerobic biofragmentation does not produce methane, whereas anaerobic biofragmentation produces methane. Also, anaerobic biofragmentation leads to a greater degree of mass and volume decrease than aerobic biofragmentation. This is why anaerobic digestion technology is used go treat organic waste.

-Bioassimilation

Bioassimilation is the absorption of organic matter by microbes.

It occurs after the organic matter has been broken down through biodeterioration and biofragmentation. The simpler chemical compounds which result from this breakdown is then absorbed/assimilated by bacteria and fungi.

Based on the explanation above, we can consider bioassimilation to be a result of metabolic processes in the digestive system of microbes.

Although the products of biodeterioratoon and biofragmentation may be absorbed by the microorganisms, it is often necessary for organic matter to undergo further biotransformation reactions before it can be transported into the cells of microbes.

The materials absorbed in the bioassimilation stage, contribute to the production of chemical energy in the form of Adenosine Triphosphate (ATP), which is used by the microorganism.

-Mineralisation (or Biomineralisation)

Mineralization or biomineralization, is the conversion of organic matter to inorganic minerals.

The concept of mineralization is common in crop and soil science. It is the final stage of aerobic biodegradation and its products include minerals which ultimately enter into the soil.

The inorganic minerals produced during mineralization, are by-products of hydrolysis of organic matter by enzymes secreted from the cells of microbes. These cells themselves may release inorganic materials after they have completely absorbed the organic matter in the bioassimilation stage.

The minerals released are usually taken up and absorbed by plants, to which they serve as nutrients that support growth and development.

 

2). Anaerobic Biodegradation

Anaerobic biodegradation is the breakdown of organic matter by microorganisms, in the absence of oxygen.

Another term used for this mechanism of biodegradation, is ‘anaerobic digestion’.

It leads to significant decrease in mass and volume of the decomposed organic matter. For this reason, anaerobic biodegradation is widely used to treat solid and liquid organic waste (sewage, sludge, wastewater) [6].

There are three phases of anaerobic biodegradation, namely; non-methanogenic; steady/methanogenic; unsteady/methanogenic respectively.

 

-Anaerobic, Non-Methanogenic Biodegradation

Anaerobic, Non-methanogenic biodegradation is the breakdown of organic matter by microbes, through acidogenesis and hydrolysis, with the production of CO2.

The term methanogenic, relates to methanogenesis, which signifies the production of methane or biogas. In the non-methanogenic phase of biodegradation, there is usually no significant production of biogas.

Hydrolysis is the primary procedure which causes the breakdown of organic matter in anaerobic, non-methanogenic phase of biodegradation.

In this process, microorganisms break down polymeric organic compounds through enzymatic biochemical mechanisms, to form monomers.

As a result of hydrolysis, organic acids are usually produced. The production of these acids is known as acidogenesis.

Carbon dioxide (CO2) is produced in relatively large volumes during anaerobic, non-methanogenic biodegradation.

This is accompanied by hydrogen production. The rate of nitrogen oxide production also decreases, in comparison to the rate at which it is produced in the aerobic stage of biodegradation.

 

-Anaerobic, Methanogenic, Unsteady Biodegradation

Anaerobic, methanogenic, unsteady biodegradation is the phase of biodegradation in which acetic acid is produced.

Acetogenesis is a prominent chemical reaction which occurs in the anaerobic, methanogenic, unsteady phase of biodegradation. It involves the conversion of fatty acids to acetic acid.

Other products of acetogenesis at this stage include hydrogen and carbon dioxide (CO2). However, the rates of CO2 and hydrogen production are much less than the non-methanogenic phase.

By the end of the unsteady-state phase (as it is also called), hydrogen usually ceases to be produced.

 

-Anaerobic, Methanogenic, Steady Biodegradation

Anaerobic, methanogenic, steady biodegradation is the final stage of biodegradation, in which methane is produced.

The dominant process involved in anaerobic, methanogenic, steady phase of biodegradation is methanogenesis.

In this phase, also called the steady-state phase, the activities of microbes cause acetic acids, which were produced in the preceding phase, to be further broken down, thereby producing carbon dioxide (CO2) and methane.

Hydrogen is usually consumed during methanogenesis, and the end product is humus, which ultimately becomes a part of soil.

 

Conclusion

Biodegradation is the breakdown of complex organic compounds to simpler, inorganic compounds by microorganisms.

The two mechanisms or methods of biodegradation are aerobic and anaerobic. These mechanisms differ by the presence or absence of oxygen.

 Aerobic biodegradation has four stages. The four stages of aerobic biodegradation are biodeterioration, biofragmentation, bioassimilation and mineralization.

Anaerobic biodegradation has three main stages. The three stages of anaerobic biodegradation are non-methanogenic, steady methanogenic, and unsteady methanogenic.

Generally, the products of biodegradation are inorganic materials like methane, carbon dioxide, nitrogen, hydrogen and sulfur dioxide. Biodegradation produces humus and inorganic nutrients that enrich the soil and support plant growth.

 

References

1). Cappitelli, F.; Catto, C.; Villa, F. (2020). “The Control of Cultural Heritage Microbial Deterioration.” Microorganisms 2020, 8(10), 1542. Available at: https://doi.org/10.3390/microorganisms8101542. (Accessed 17 March 2022).

2). Fernando, J. (2021). “Hydrocarbon.” Available at: https://www.investopedia.com/terms/h/hydrocarbon.asp. (Accessed 17 March 2022).

3). Gammage, E. (2022). “How long does it take for plastic to biodegrade?” Available at: https://www.savemoneycutcarbon.com/learn-save/how-long-does-it-take-for-plastic-to-biodegrade/. (Accessed 17 March 2022).

4). Ghosal, D.; Gosh, S.; Dutta, T.; Ahn, Y. (2016). “Current State of Knowledge in Microbial Degradation of Polycyclic Aromatic Hydrocarbons (PAHs): A Review.” Front. Microbiol., 31 Available at: https://doi.org/10.3389/fmicb.2016.01369. (Accessed 17 March 2021).

5). Hodzic, A. (2004). “Re-use, recycling and degradation of composites.” Green Composites: Polymer Composites and the Environment. Woodhead Publishing Series in Composites Science and Engineering, pp 252-271. Available at: https://doi.org/10.1016/C2013-0-17863-4. (Accessed 17 March 2022).

6). Kang, J. A.; and Yuan, Q. (2017). “Enhanced Anaerobic Digestion of Organic Waste.” IntechOpen. Available at: https://doi.org/10.5772/intechopen.70148. (Accessed 17 March 2022).

7). Krause, S., Molari, M., Gorb, E.V., Gorb, S.N., Kossel, E., Haeckel, M. (2020). “Persistence of plastic debris and its colonization by bacterial communities after two decades on the abyssal seafloor.” Sci Rep 10, 9484. Available at: https://doi.org/10.1038/s41598-020-66361-7. (Accessed 17 March 2022).

8). Majeed, Z., Ramli, N., Mansor, N. & Man, Z. (2015). “A comprehensive review on biodegradable polymers and their blends used in controlled-release fertilizer processes.” Reviews in Chemical Engineering, 31(1), 69-95. Available at: https://doi.org/10.1515/revce-2014-0021. (Accessed 17 March 2022).

9). Montazer, Z.; Najafi, H.B.M.; Levin, D.B. (2020). “Challenges with Verifying Microbial Degradation of Polyethylene.” Polymers 2020, 12, 123; Available at: https://doi.org/10.3390/polym12010123. (Accessed 17 March 2022).

10). Rogers, T. (2015). “Everything You Need To Know About Polyethylene (PE).” Available at: https://www.creativemechanisms.com/blog/polyethylene-pe-for-prototypes-3d-printing-and-cnc. (Accessed 17 March 2022).

11). Woodford, C. (2020). “Plastics.” Available at: https://www.explainthatstuff.com/plastics.html. (Accessed 17 March 2022).

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