Policyclic Aromatic Hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are two or more fused benzene rings. They come from incomplete combustion and from pyrolysis of organic compounds. Besides, petroleum and petroleum-derived products release high quantities of PAHs into the environmental. The Environmental Protection Agency (EPA) reported that this is the most spread environmentally family of carcinogenic and mutagenic compounds and it made a priority list of 16 of them.

They are hydrophobic compounds, therefore they can be adsorbing to organic matter of the soil during many years. Because of this property they can migrate to the groundwater and contaminate it. Nowadays the most frequently used technologies to eliminate PAHs are thermal desorption and bioremediation, but they have advantages and disadvantages.

Thermal desorption eliminates the contamination but it is expensive and damages the soil (a non renewable natural resource). Bioremediation is cheap but it has some problems: 1) the concentration of the contaminant takes a long time to decrease and 2) when the soil is chronically contaminated, the low availability of the PAHs complicates the remediation.

Because of this, scientists study alternatives to avoid these problems. One option is chemical oxidation. In situ chemical oxidation (ISCO) is one of the newest technologies that can be used to treat soils with PAH. The idea is to inject the oxidant into the soil, not to transport it. The most commonly used oxidants are permanganate, Fenton reaction or persulfate. They can react with many organic contaminants in water or soil and generate less harmful products, and sometimes water and carbon dioxide. Chemical oxidation has the advantage of eliminating the contaminant in less time than bioremediation, but when an oxidant enters the soil or water it changes chemical properties like pH and electric conductivity and modifies the microbial community. The best technology for remediation is the combination of chemical and biological treatments. But the challenge is to discover how to do that.

References

Cerniglia, C.E., (1992). Biodegradation of polycyclic aromatic hydrocarbons. Biodegradation 3: 351-368.

de Souza e Silva P.T., da Silva V.L., de Barros Neto B., Simonnot MO. (2009). Potassium permanganate oxidation of phenanthrene and pyrene in contaminated soils. Journal of Hazardous Materials 168: 1269–1273.

Gan S., Laua E.V., Ng H.K., (2009). Remediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Journal of Hazardous Materials 172: 532–549.

Rivas F. J., (2006). Polycyclic aromatic hydrocarbons sorbed on soils: A short review of chemical oxidation based treatments. Journal of Hazardous Materials B138: 234–251