What is Phytoremediation?
Phytoremediation uses the natural ability of plants to contain, break down, or eliminate toxic chemicals and pollutants from soil or water. This process can be applied to clean up metals, pesticides, solvents, explosives, crude oil, and contaminants that are potentially harmful to the environment.
How does Phytoremediation Work?
Plants absorb and metabolize certain organic chemicals and metals, some of which are essential for plant growth, including zinc, copper, and iron. Some plants, absorb more metal than others, including metals that appear unnecessary for plant function, these are known as hyperaccumulators.
Types of Phytoremediation.
The first two examples are for organic metals and the last three for metal contamination.
Phytotransformation – Through the plants own metabolic processes organic compounds in contaminated soils and groundwater are absorbed and degraded.
Rhizosphere Bioremediation – Microorganisms are found in the area surrounding the roots of plants (rhizosphere) and are stimulated by natural substances released by the plant. These microorganisms aid the break down of the contaminants through their own metabolic processes.
Phytoextraction -- The plant absorbs metal contaminants through the roots and moves them into the stems and the leaves. The plants are harvested and then suitably discarded.
Rhizofiltration – This process concentrates on surface and groundwater remediation whereby the roots directly absorb the contaminants or indirectly, by attracting and containing them. When the roots become saturated, the plants are harvested and then replaced. An example of this process is the use of constructed wetlands to treat wastewater and landfill leachate.
Phytostabilization -- Plants are used to reduce the mobility of soil or water contaminants and contain them in a limited area. This can be accomplished by the plant roots, as detailed above or by decreasing soil erosion and wind-blown dust. For metals, which do not biodegrade, this is an effective method for preventing their spread to ground or surface water.
Advantages and Disadvantages of Phytoremediation.
Advantages
• Environmentally friendly, cost-effective, and aesthetically pleasing.
• Metals absorbed by the plants may be extracted from harvested plant biomass and then recycled. Phytoremediation can be used to clean up a large variety of contaminants.
• May reduce the entry of contaminants into the environment by preventing their leakage into the groundwater systems.
Disadvantages
• Slow process as it relies on natural cycle of plants.
• Limited by distance, phytoremediation works best when the contamination is within reach of the plant roots, 3-6ft underground for herbaceous plants and 10-15 feet for trees.
• Some plants absorb a lot of poisonous metals, making them a potential risk to the food chain if animals feed upon them.
Harvest and Disposal of Plants
When the plants have absorbed and accumulated contaminants, they can be harvested and discarded. If organic chemical contaminants are degraded into molecules like water and carbon dioxide, the plants may not require any special method of disposal. Controlled incineration is the standard method of disposal and then appropriate disposal of the ashes. Recovery of the original metals from the ashes is being investigated.
Sustainable Development and Phytoremediation
Sustainable technologies should be economically viable and environmentally compatible. Phytoremediation can be seen as an effective sustainable technology being more cost effective than traditional remediation methods, less laborious and does not disturb the natural surrounding of the contaminated site. Although this process takes time to gain results, it is one of the best demonstrations of using naturally existing resources to clean up contaminants.
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