Contaminated soil is an environmental problem caused by the release of hazardous substances into the environment. The contaminants include heavy metals, volatile organic compounds, petroleum hydrocarbons, pesticides, herbicides, and other hazardous materials. Contaminants in soil can adversely affect human health and the environment, so soil remediation is often necessary to protect the affected area.
Soil remediation refers to various processes that decontaminate contaminated soil, providing for the removal of contaminants to low levels. There are various remediation methods, among which, remediation technique based on cyclodextrin (CD) has attracted much attention. In soil remediation, CD can be used for the joint removal of heavy metals and organic pollutants, the improvement of the bioavailability of pollutants, and the enhancement of electrokinetic remediation of heavy metals.
Joint Removal of Heavy Metals and Organic Pollutants
Composite pollution of organic matter and heavy metals coexists in many contaminated soils. CDs modified functional groups not only form inclusion complexes with a variety of metal ions, but also encapsulate weakly polar organic pollutants, which jointly remove heavy metals and weakly polar organic pollutants from soil.
Chatain et al. found that not only the cationic metals can be chelated by the oxygen atoms on the rim of the carboxylmethyl-β-CD (CMCD), but the hydrophobic organic pollutants can also be included within the nonpolar cavity of the CD.
It was found that CMCD aqueous solution significantly promoted the removal of arsenic, copper, and iron in mining soil, and significantly increased the extraction rate of 2,3,4,6 tetrachlorophenol (TeCP) in soil, which is beneficial for the remediation of contaminated soil with both metal ions and organic pollutants [1].
Improvement of Pollutants' Bioavailability
Bioavailability affects the degree of biodegradation. Hydrocarbons are a class of pollutants that are poorly soluble in water and are easily adsorbed in clay and humus. They are mainly decomposed through microbial metabolism. Through their complexation with CD, the bioavailability of these pollutants can be effectively improved, which is beneficial to the remediation of contaminated soil.
Garon et al. studied the effect of maltosyl-CD amendment on fluorene (FL) in soil slurries. FL is a polycyclic aromatic hydrocarbon (PAH) pollutant present in soil. The study indicated that maltosyl-CD enhanced the bioavailability of FL. The reason for increasing FL bioavailability may be that the formed CD inclusion complexes increase the apparent solubility of FL, as low water solubility may limit its bioavailability and thus its biodegradability [2].
Enhancement of Electrokinetic Remediation of Heavy Metals
The electrokinetic remediation process involves using direct current to remove contaminants from the soil. This method can be performed as an in-situ remediation and does not require excavation of the soil, resulting in minimal disturbance to the soil surface. It has the advantages of strong controllability and a good remediation effect. CD can be used as a cosolvent to improve the electromigration ability of pollutants in clay composite pollution systems and may not cause secondary pollution to the soil [3].
Ko et al. studied the removal of hydrophobic organic contaminants (HOCs) from contaminated soil through electrokinetic remediation using hydroxypropyl-β-CD (HPCD) as a solubility-enhancing agent. The results showed that the addition of HPCD increased the osmotic current and promoted the removal of phenanthrene which is a typical soil HOC. In the control group where 6.85 mmol/L HPCD was added to the kaolinite sample, the phenanthrene removal rate increased to 56% from 25% before adding HPCD [4].
Alfa Chemistry is dedicated to the manufacture of CDs. We offer high-quality native CDs, CD derivatives, and CD inclusion complexes. We have strong supply capabilities and can provide products at the kilogram level. Please feel free to contact us and we will serve you wholeheartedly.
References
- Chatain, V.; et al. Enhanced solubilization of arsenic and 2, 3, 4, 6 tetrachlorophenol from soils by a cyclodextrin derivative. Chemosphere. 2004, 57(3): 197-206.
- Garon, D.; et al. Effects of fungal bioaugmentation and eyclodextrin amendment on fluorene degradation in soil slurry. Biodegradation. 2004, 15(1): 1-8.
- Maturi, K.; Reddy, K. R. Cosolvent-enhanced desorption and transport of heavy metals and organic contaminants in soils during electrokinetic remediation. Water, Air, and Soil Pollution. 2008, 189: 199–211.
- Ko, S. O.; et al. Cyclodextrin-enhanced electrokinetic removal of phenanthrene from a model clay soil. Environ Sci Technol. 2000, 34(8): 1535-1541.
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