Helena Joyce
Soil pollution is a pressing issue, with a third of the world's arable land degraded due to human activities such as industrial spills, intensive agriculture, and urbanization. Soil remediation is the practice of cleaning contaminated land to reduce pollutant concentrations and prevent their spread. Various methods include soil washing, thermal treatment, bioremediation, biodegradation, phytoremediation, and the use of fungi, bacteria, and polymers. While remediation is crucial, prevention is ideal, achieved through proper waste disposal and minimizing chemical pesticides and fertilizers.
Techniques to clean soil pollution
| Characteristics | Values |
|---|---|
| Phytoremediation | Using plants and trees to remove harmful elements from the soil. For example, willows, birches, and leguminous plants can suck up pollutants, which are then harvested and destroyed off-site. |
| Bioremediation | Treating the soil using naturally-occurring organisms. For example, certain types of fungi and bacteria can break down pollutants into a safer state. |
| Soil washing | Physically separating soil from contaminants by passing a solution of cleaning fluid and water through the contaminated soil. |
| Soil containment | Preventing the spread of contaminants by placing heavy-duty liners under and around contaminated soil. |
| Thermal treatment | Using heat to move contaminants in the soil. Some contaminants are destroyed, while others are moved to another place and collected. |
| Air sparging | An in-situ remediation method where contaminated soil does not need to be removed. This is more environmentally friendly than ex-situ methods. |
| Air injection | Pumping air into the ground to remove contaminants. |
| Soil remediation | Reducing the concentration of pollutants to a safe level. |
| Soil replacement | Removing and replacing contaminated soil with clean soil or soil-like material. |
| Soil capping | Covering contaminated soil with a barrier layer of varying materials, such as asphalt concrete or vegetated soil, to prevent toxic effects on nearby areas. |
| Soil dilution | Mixing contaminated soil with clean soil or soil-like materials to dilute concentrations of pollutants. |
| Soil paving | Covering contaminated soil with pavement to reduce the risk of incidental ingestion of pollutants. |
| Soil fertilisation | Treating lead-contaminated soils with phosphorus fertilizer. |
| Soil lining | Using a root-impenetrable layer, such as landscape fabric, to prevent the spread of contaminants. |
| Soil enrichment | Using polymers to improve water and nutrient retention in soil, enhancing its health and cleanliness. |
| Soil biodegradation | Accelerating the natural biodegradation process by injecting zero-valent iron and organic matter into the soil. |
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What You'll Learn
Using plants and trees to remove harmful elements
Phytoremediation is a process that uses plants and trees to reduce, degrade, or remove toxic residues from the soil. This natural process is a cheap, eco-friendly, and effective way to clean contaminated soil.
Plants and trees have different bioaccumulation capabilities, which allow them to extract and concentrate metals and other harmful elements from the soil. For example, sunflowers are known to remove lead and arsenic, while Indian mustard is a powerful hyperaccumulator of lead, cadmium, and zinc. Other plants, such as the Chinese brake fern and Cretan brake fern, are effective arsenic hyperaccumulators.
Willow trees are excellent phytoremediators, capable of accumulating heavy metals and absorbing toxins like diesel fuel and carbon tetrachloride, a known carcinogen. Poplar trees are also effective phytoremediators, able to absorb large quantities of water contaminated with petroleum hydrocarbons like benzene or paint thinners.
Some organic toxins can be metabolized by trees and dispersed into the atmosphere, where they are eventually broken down by UV radiation. However, it is important to note that metallic contaminants cannot be destroyed and must be properly disposed of. The plants used in phytoremediation should not be used for food or composted, as the toxins remain within them.
Phytoremediation is a progressive and sustainable process that reduces the need for heavy machinery or additional contaminants. It is a useful alternative to other soil remediation methods, such as soil washing, thermal treatment, or soil containment, which may involve the use of machinery or the physical extraction of contaminated soil.
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Soil washing
The clean coarse-grained soils are then separated from the contaminated fine-grained soils and washwater. The contaminated portions can be treated or disposed of as required. The washed soils may be reused as backfill on-site if all contaminants are removed. This technique is particularly effective for removing volatile organic compounds (VOCs) and metals from sandy and gravelly soils.
However, a drawback of soil washing is its inability to remediate fine-particle substrates and treat wash water in a cost-effective manner. Newer surfactants have been developed to address this issue, forming a separate phase that can be easily separated from the soil-water phase. Mechanical separation may also be used to remove water from the soil if it contains many fine particles.
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Soil containment
Soil pollution is a serious issue, often caused by human activities such as industrial waste, agricultural chemicals, and improper disposal of sewage and other liquid wastes. The consequences of soil pollution are far-reaching, affecting all living beings, including plants, groundwater, surface water, and ambient air. It is essential to address soil pollution through effective remediation techniques to mitigate its impact on the environment and human health. One such technique is soil containment, which plays a crucial role in preventing the spread of contaminants and protecting the environment.
The process of soil containment involves the strategic use of heavy-duty liners placed under and around the contaminated soil. These liners act as a protective barrier, preventing the downward migration of contaminants into the underlying soil or groundwater. The liners are carefully selected and designed to be impermeable to the specific pollutants present at the site. Regular inspections of the liners are crucial to ensure their integrity and effectiveness in containing the contamination. Any damage to the liners must be promptly addressed to maintain the integrity of the containment system.
In addition to liners, another crucial component of soil containment is the implementation of a landfill cap. This cap serves as a secondary barrier, providing an extra layer of protection to prevent toxic effects on nearby areas. The composition of the cap can vary depending on the nature of the soil contamination. For example, it could be constructed using a layering system of vegetated soil, plants, or asphalt concrete. The choice of capping material depends on factors such as the type of pollutants, the surrounding environment, and the long-term goals for the site.
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Thermal treatment
Soil contamination is a pressing environmental concern due to increasing anthropogenic activity. Thermal treatment is a method of cleaning contaminated soil by using heat to move contaminants. This process can be conducted at fixed facilities or remediation sites with portable units.
There are several types of thermal treatment methods, including thermal desorption and high-temperature electrothermal (HET) processes. Thermal desorption is a physical process that relies on volatilization as the main mechanism for removing contaminants. It is often referred to as "low-temp" thermal desorption to differentiate it from high-temperature incineration. This method is suitable for treating a broad range of hydrocarbon contamination and is particularly effective for soil with high levels of contaminants. The process involves heating the soil in a rotating dryer to remove or separate the contaminants.
The HET process, on the other hand, is a rapid and energy-efficient electrothermal process that simultaneously removes heavy metals and organic pollutants from the soil. It achieves this by ramping up the temperature of the contaminated soil with carbon additives to 1000 to 3000 °C within seconds, enabling the vaporization of heavy metals and the destruction of organic contaminants. The high temperature of the HET process significantly accelerates both the reaction and diffusion kinetics, allowing remediation to be completed in seconds, which is much faster than low- to mid-temperature processes.
Another thermal treatment method is chemical oxidation, or "chemox," which is particularly useful for treating soils that are difficult or expensive to access, such as those located beneath buildings. Chemox involves using heat in a Primary Treatment Unit (PTU) to evaporate hydrocarbons and other impurities in the soil. The PTU can reach temperatures of up to 480 °C, serving as a giant oven for baking the soil. After heating, the soil is cooled and then tested and recycled.
When selecting a thermal treatment method, several factors should be considered, including the property layout, location, available utilities, quantity of material to be treated, material characteristics, and timeframe for treatment. For large quantities of contaminated soil, typically over 30,000 tons, onsite thermal treatment may be the most cost-effective solution.
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Preventative measures
Preventing soil pollution is a far more effective strategy than attempting to clean it up after the fact. Soil pollution is largely the result of unsustainable agricultural practices, the improper disposal of waste, mining, illegal dumping, and littering.
Proper Waste Disposal: The proper disposal of waste is essential to preventing soil contamination. This includes the treatment of solid waste before releasing it into the environment. For instance, highly acidic or alkaline waste must be neutralized before disposal. Hazardous materials and pharmaceuticals should never be thrown in the trash or poured down the drain. Contact your local sanitation department to learn how to dispose of these items responsibly.
Minimize Chemical Usage: Reduce the use of chemical pesticides and fertilizers, as these can have long-term detrimental effects on soil quality. Opt for natural alternatives whenever possible, such as using manure instead of bio-fertilizers.
Sustainable Consumption: As a consumer, you can prevent soil pollution by buying sustainable and organic food products. This sends a message to producers and encourages a shift towards organic methods in the industry. Additionally, only buy as much food as you need to avoid food wastage, which can lead to soil pollution during disposal.
Land Management: Protecting and managing land effectively can help reduce the risk of soil pollution. This includes learning about sustainable land and water management practices and investing in these services.
Waste-to-Energy Initiatives: Supporting and advocating for waste-to-energy initiatives can help address soil pollution. These initiatives involve using waste treatment processes to generate energy, powering facilities and running power stations without greenhouse gas emissions.
Education and Awareness: Educate yourself and others about the causes and impacts of soil pollution. Spread awareness about preventive measures and sustainable alternatives to harmful products.
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Frequently asked questions
Soil remediation is the practice of cleaning up contaminated soil to reduce the concentration of pollutants to a safe level and prevent them from spreading.
Soil remediation techniques include soil washing, soil containment, thermal treatment, phytoremediation, bioremediation, biodegradation, and air sparging.
Phytoremediation involves planting deep-rooted plants and trees, such as willows, birches, and leguminous plants, to absorb and remove contaminants from the soil.
To prevent soil pollution, minimize the use of chemical pesticides and fertilizers, ensure proper waste disposal, and treat the soil with polymers to improve water and nutrient retention.
