Degradation of Polycyclic Aromatic Hydrocarbons: A Review

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are hydrocarbons composed of two or more benzene rings, and they are widely found in nature. The degradation of PAHs remains in a dynamic equilibrium, which has suffered from the increasing PAHs emissions under the continuous development of society. Therefore, the environmental pollution is getting increasingly serious. Many scholars have conducted researches on the degradation of PAHs. In this paper, the origin and properties of PAHs are introduced. Besides, the physical, chemical and biological methods for the degradation of PAHs were reviewed. Among them the biodegradation of PAHs has been especially analyzed. Meanwhile, the advantages and disadvantages of each method were described through comparison.

Polycyclic Aromatic Hydrocarbons: Sources, Toxicity, and Remediation Approaches

“…Due to the hydrophobic property of PAHs, they are soluble in organic solvents like acetone, alcohol, hexane, dichloromethane, methyl ethyl ketone, toluene, etc. Therefore, the use of suitable individual solvents or a mixture of solvents can be used to remove PAHs from water, sludge, and soil (Peng X. et al, 2018). Soil washing with solvent is a suitable approach for the removal of HMW PAHs, which are difficult to remove from the soil due to their low bioavailability and strong affinity to soil (Kuppusamy et al, 2017).…”

“…The PAH removal rate is highly affected by factors like reaction temperature, pH, humidity, concentration of adsorbent, etc. (Peng X. et al, 2018).…”

“…Most physical methods simply transfer PAHs from water and soil, but there are no structural changes in PAHs; therefore, physical methods cannot completely remove PAHs from the environment. Due to time-consuming and inefficient role of physical methods for PAH removal, chemical methods have been gaining attention (Peng X. et al, 2018). The most common approach for PAH removal by chemical methods is oxidation processes using common oxidants like ozone (O 3 ) and Fenton reagent (Fe 2+ + H 2 O 2 ) as well as other oxidants like potassium permanganate (KMnO 4 ), peroxy-acid (R-COOH), hydrogen peroxide (H 2 O 2 ), and activated sodium persulfate (Na 2 S 2 O 8 ) (Ukiwe et al, 2013;Das and Das, 2015;Peng X. et al, 2018).…”

“…Due to time-consuming and inefficient role of physical methods for PAH removal, chemical methods have been gaining attention (Peng X. et al, 2018). The most common approach for PAH removal by chemical methods is oxidation processes using common oxidants like ozone (O 3 ) and Fenton reagent (Fe 2+ + H 2 O 2 ) as well as other oxidants like potassium permanganate (KMnO 4 ), peroxy-acid (R-COOH), hydrogen peroxide (H 2 O 2 ), and activated sodium persulfate (Na 2 S 2 O 8 ) (Ukiwe et al, 2013;Das and Das, 2015;Peng X. et al, 2018). During oxidation through the Fenton reagent, unstable hydroxyl radicals (•OH) are generated in the presence of ferrous iron (Fe 2+ ), which are utilized to degrade PAHs either by hydrogen abstraction or by hydroxyl addition (equations 1-3) (Gong et al, 2017).…”

“…Therefore, most of the recent studies emphasized on mixed bacterial culture-and consortia-assisted PAH degradation (Vaidya et al, 2018;Haleyur et al, 2019;Patel et al, 2019). Degradation by immobilized bacteria and genetically modified bacteria is also a considerable approach (Peng X. et al, 2018). One of the major difficulties for degradation in soil/sediment is a dispersion of inoculum; it is easy for surface soil, however, challenging for subsurface soil due to limited microbial transport as cells adhere strongly to soil organic matter.…”