Tar is a dark, viscous liquid composed mainly of hydrocarbons and free carbon, originating from the destructive distillation of organic materials like coal, wood, or petroleum. Its breakdown is a significant area of study due to its environmental persistence and cleanup challenges. Some forms, like coal tar, contain toxic components, posing risks to human health and ecosystems. Understanding its degradation processes is important for addressing contamination and for various industrial applications.
Physical and Chemical Methods
Solvents are frequently employed to dissolve or loosen tar, allowing for its removal. Common examples include petroleum distillates, hexane, and toluene, which solubilize tar’s hydrocarbon components and break them into smaller, more manageable particles. Specialized tar removers, including citrus-based ingredients, also function by dissolving the tar, making it easier to wipe away.
Applying heat aids in tar breakdown by increasing its temperature, which reduces its viscosity and breaks down complex molecules into smaller, less viscous forms. This softening effect makes the tar more amenable to removal.
Mechanical actions physically break down or remove tar. Scraping, pressure washing, and abrasion directly dislodge tar from surfaces. These methods are often used in conjunction with chemical solvents or heat to enhance efficiency; for instance, after a solvent loosens the tar, mechanical wiping or scrubbing can remove the softened residue.
Biological Processes
Biological processes, known as bioremediation, utilize living microorganisms to break down tar. Bacteria and fungi possess enzymes capable of transforming complex tar compounds into simpler, less harmful substances. This natural process, called biodegradation, involves microbes metabolizing hydrocarbons found in tar, ultimately converting them into compounds like carbon dioxide and water.
Many types of microorganisms are effective at degrading hydrocarbons. A diverse community of different microbial species working together is often more effective at degrading the complex mixture of compounds found in tar than individual strains.
The effectiveness of biological breakdown is influenced by several environmental conditions, including temperature, with higher temperatures generally leading to increased biodegradation rates.
Natural Environmental Degradation
Tar also undergoes degradation through passive, long-term processes in the natural environment. Photodegradation occurs when tar is exposed to ultraviolet (UV) light from the sun. The absorption of light energy can initiate chemical reactions that alter the tar’s molecular structure, leading to its breakdown and often involving oxidation.
Oxidation, the reaction of tar components with oxygen in the air, contributes to its natural degradation. This process often works in conjunction with photodegradation, as light can facilitate oxidative reactions. Weathering, which encompasses the physical breakdown of tar due to environmental elements like rain, wind, and temperature fluctuations, further contributes to its disintegration. These processes can involve physical abrasion, dissolution of some components, and transport of smaller particles.
While these natural mechanisms contribute to tar breakdown, they are generally very slow processes. Complete degradation of tar in the environment can take a very long time, as many of its complex components, particularly PAHs, are persistent. This persistence highlights the long-term environmental challenges posed by tar contamination.
Factors Influencing Breakdown
The efficiency and rate at which tar breaks down are influenced by several factors. The specific composition and type of tar significantly affect how easily it degrades. Tar with higher viscosity or a greater proportion of heavier, more complex hydrocarbons, such as high molecular weight PAHs, tends to be more resistant to breakdown compared to lighter, less viscous forms.
Environmental conditions play a substantial role in determining breakdown rates. Temperature is a key factor, with warmer conditions generally accelerating chemical reactions and microbial activity, thereby increasing the rate of tar degradation. The pH of the surrounding environment can also influence both chemical reactions and the viability of microorganisms. The availability of oxygen is particularly important for aerobic biological breakdown processes, as many hydrocarbon-degrading microbes require it.
For biological methods, the presence of essential nutrients like nitrogen and phosphorus can limit or enhance the rate of degradation. In chemical approaches, the concentration of the breakdown agent directly impacts its effectiveness; a sufficient concentration is necessary to solubilize or react with the tar. Additionally, the surface area of the tar exposed to the breakdown agent, whether it be a chemical, microbes, or sunlight, influences the rate of degradation. A larger exposed surface area allows for greater interaction and faster breakdown. Tar that is strongly bound to soil particles, for example, can have reduced bioavailability for microbes, slowing its degradation.