Factors Affecting Biodegradation – It is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It can be divided into three stages: biodeterioration, fragmentation, and assimilation. It is sometimes described as surface-level degradation that alters the mechanical, physical, and chemical properties of materials. This stage occurs when the material is exposed to abiotic factors in the external environment, further deteriorating by weakening the material structure. Abiotic factors that influence these initial changes include compression (mechanical), light, temperature, and chemicals in the environment. Biodegradation usually occurs as the first step of biodegradation, but in some cases, it can occur in parallel with biodegradation.
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Factors Affecting Biodegradation
Factors affecting biodegradation can be classified into two main categories; biotic factors and abiotic factors.
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The biotic factors affecting biodegradation include microbe species, microbe population, and microbial enzymes.
1). Microbe Species:
The types of microorganisms present in each environment affect the rate and effectiveness of biodegradation. This is because different types of microorganisms have different metabolic capacities.
Moreover, the metabolic capacity of each microorganism species differs depending on the type of biodegradable substance to be decomposed. This means that a particular microbe may be more effective at breaking down one type of organic matter, but less effective at breaking down another.
2). Microbe Population:
Microbial population size is another factor that affects biodegradation rates. Even when the most suitable microbial species (based on metabolic capacity) are present, biodegradation can be slow and ineffective if these microorganisms are not present in sufficient numbers.
The biodegradation rate is proportional to the size of the microbial community and diversity of the microbial community. The higher the number of microorganisms, the faster the biodegradation rate. In general, as the size (area and volume) of the substrate (i.e. biodegradable material) increases the need for a large microbial population increases.
Enzymes are powerful and essential biochemical tools used for biodegradation. They are chemicals that act as catalysts to facilitate chemical reactions that degrade, transform, and ultimately mineralize biodegradable materials.
During biodegradation, enzymes from cells are supplied by microorganisms, which secrete these chemicals. The effectiveness of microbial enzymes depends primarily on the nature of the biodegradable material (substrate) involved. Certain microbial enzymes may be most effective at breaking down proteins, petroleum hydrocarbons, aromatics, halogenated compounds, detergents, heavy metals, bioplastics, and more. Biochemical reactions are the pathways through which biodegradation occurs. The three main biochemical reactions involved in the biodegradation process are reduction, oxidation, and hydrolysis. During adsorption, the enzyme comes into contact with a biodegradable substance (substrate). This results in an effective biochemical reaction (between enzyme and substrate) leading to biodegradation.
Examples of microbial enzymes which are useful for biodegradation include hydrolases, lipases, laccases, dehalogenases, lipases, dehydrogenases, and proteases.
Abiotic factors affecting biodegradation include temperature, pH, aeration, salinity, humidity, and nutrients. These abiotic factors are those factors that do not directly depend on biological conditions, organisms, or processes.
Temperature is one of the abiotic environmental factors that affect biodegradation.
In general, the biodegradation rate is proportional to temperature. This means that the biodegradation rate is generally low at low ambient temperatures and high at moderate/relatively high temperatures.
In bioreactors, increasing the temperature of the system has been found to increase the rate of biomass decomposition and conversion. Since the activity of microbial enzymes increases with temperature, an increase in temperature leads to an increase in biodegradation. This causes the biochemical reactions necessary for biodegradation to occur.
However, if it is extremely hot (above 50°C) or extremely cold. Microbial enzymes (and microbial communities) can be destroyed. Biomass can undergo thermal decomposition at such extreme temperatures.
pH affects biodegradation because microbial survival, growth, reproduction, and effectiveness depend on pH.
In general, moderate pH values are optimal for biodegradation. For bacteria, a pH range of 6.5-7.5 is optimal for optimal growth. Microbial population size and diversity are generally greater when the pH is adequate. This correlates with the high rate and effectiveness of biodegradation.
Aeration is the introduction of air into a material or medium. It also often involves the circulation and mixing of air in media such as soil, air, or water.
One of the most important components of air is oxygen. Aeration affects biodegradation because the microbial activity depends on oxygen. The supply of oxygen is essential for microbial survival. This means that microbial populations are likely to increase as oxygenation increases.
Examples of anaerobic microorganisms (bacteria) include Listeria, Escherichia Coli, and Shewanella oneidensis.
On the other hand, aerobic microorganisms include Bacillus, Nocardia asteroids, and Pseudomonas Actinomycetes.
4). Humidity and Moisture:
Humidity is the amount of water vapor in the air.
Moisture affects biodegradation by affecting microbial effectiveness. Studies have shown that the biodegradation rate tends to increase as the humidity of the biodegradable material (substrate) and/or the air in the degradation environment increases.
In some cases, moisture can enhance biodegradation rates when other environmental/abiotic factors such as temperature are low. Moisture and moisture have also been shown to increase the degradation rate of biodegradable plastics.
Nutrients affect biodegradation because nutrient availability determines the presence of microorganisms in any environment.
Nutrients are needed to support the growth of microorganisms, which are needed to break down substances in biodegradation processes. Higher concentrations of nutrients increase the number of microorganisms and increase their metabolic efficiency.
Microorganisms help in biodegradation:
Bacterial strains capable of degrading aromatic hydrocarbons have been repeatedly isolated mainly from the soil. These are usually Gram-negative bacteria, most of which belong to the genus Pseudomonas. Biodegradation pathways have also been described in bacteria of the genera Mycobacterium, Corynebacterium, Aeromonas, Rhodococcus, and Bacillus.
Many bacteria are capable of metabolizing organic pollutants, but no single bacterium possesses the enzymatic capacity to degrade all or most of the organic compounds in contaminated soil. It has the highest potential for biodegradation, as the genetic information of multiple organisms is required to degrade the complex mixture of organic compounds present in contaminated areas.
Reduction of metals may occur through dissimilatory metal reduction, through the use of metals as terminal electron acceptors for anaerobic respiration by bacteria. Additionally, bacteria may have reduction mechanisms unrelated to respiration but are thought to confer metal resistance. For example, reduction of Cr(VI) to Cr(III) under aerobic or anaerobic conditions, reduction of Se(VI) to elemental Se, reduction of U(VI) to U(IV), and Hg( 0 ) of Hg(II).
Fungi are an important part of the degradative microbiota because, like bacteria, they metabolize dissolved organic matter. They are the main organisms that break down the carbon in the biosphere. However, unlike bacteria, fungi can grow in low-moisture environments and in solutions with a low pH, making them useful for breaking down organic matter. Equipped with extracellular multienzyme complexes, fungi are particularly efficient when it comes to degrading natural macromolecular compounds. Through their hyphal system, they can not only rapidly colonize and penetrate substrates but also transport and redistribute nutrients within the hyphae. Mycorrhiza is a symbiotic relationship between fungi and the roots of vascular plants. In a mycorrhizal association, fungi colonize the roots of host plants either intracellularly, as in arbuscular mycorrhizal fungi (AMF), or extracellularly, as in ectomycorrhizal fungi. They are also an important part of soil life and soil chemistry. Bioremediation by mycorrhiza is called mycorrhizal remediation. Fungi have important degradative capacities that affect the recycling of stubborn polymers (such as lignin) and the removal of hazardous wastes from the environment.
Yeast is known to play an important role in removing toxic heavy metals. There are many reports on the biosorption of heavy metals by yeast. Several studies have shown that yeast can accumulate heavy metals such as Cu(II), Ni(II), Co(II), Cd(II), and Mg(II), which is superior to certain bacteria and indicates a metal accumulator. In the case of hexavalent chromium (Cr(VI)), P. anomala was able to scavenge Cr(VI)  and biosorbent Cr(VI) by live and dead cells of three yeast species. I understand.
Several yeast strains S. cerevisiae, P. guilliermondii, Rhodotorula pilimanae, Yarrowiali polytica, and Hansenula polymorpha have been reported to reduce Cr(VI) to Cr(III). Furthermore, P. Guilliermondii produces chromium in response to its ability to reduce Cr(VI) and Cr(III) chelation extracellularly. Most studies report the efficiency of immobilized yeast cells for metal removal. An example is Schizosaccharomyces pombe for copper removal.
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