An Overview of Chemical Oxidation Based Remediation technologies for Non-Aqueous Phase Liquids Removal from Soil

Abstract

<p>This review provides a general overview of the application of chemical oxidation to hydrophobic contaminants in the form of non-aqueous phase liquids (NAPLs). Three types of chemical oxidation processes, conventional activated persulfate, permanganate, and ozonation, along with three advanced oxidation processes (AOPs), the Fenton process, photocatalysis, and plasma oxidation are presented discussed. In addition, this paper provides a brief insight into the combination of chemical oxidation with other remediation technologies for the efficient removal of NAPLs. The common and wide use of activated persulfate for soil remediation is hindered by the fact that it needs heat activation, whereas the main drawback of using permanganate is the precipitation of manganese oxide at the NAPLs face. In addition, the high cost of equipment at the site restricts the ozone application for in-suit soil remediation. The application of AOPs processes such as Fenton and plasma oxidation has received great attention due to its high removal efficiency. However, photocatalysis technology in the field is difficult because it needs photo energy to run the oxidation process. Although plasma oxidation can degrade contaminants in minutes, some active species have short-lived time that could disappear before entering the soil layer. Ozonation is efficient in treat soils with low moisture and large pore spaces. Nevertheless, the optimal pH for ozonation oxidation is 3, which is hard to achieve in real-world applications. Combining chemical oxidation with other remediation technology is a valuable technique of soil remediation as the synergetic effects may increase the sustainability of the applied process towards green technology for soil remediation.</p>

Current Trends and Future Perspectives in the Remediation of Polluted Water, Soil and Air—A Review

“…It implies the use of reducing or oxidizing agents for the complete removal of pollutants or their conversion into a less toxic form. Reduction/oxidation reactions lead to the precipitation of compounds or the generation of free radicals that act on pollutants, whereby they are degraded or converted into a less toxic form [56,58,59]. Reduction is often used to convert toxic chromates into less toxic Cr 3+ , as well as organic compounds into less harmful products such as methane and ethane.…”

“…Reduction is often used to convert toxic chromates into less toxic Cr 3+ , as well as organic compounds into less harmful products such as methane and ethane. Chemical oxidation is used to degrade organic contaminants such as PAHs, chlorinated hydrocarbons and inorganic contaminants such as cyanide [56,58]. Chemical extraction combined with oxidation can be very effective for removing organic and inorganic contaminants.…”

“…Hydrogen peroxide (H 2 O 2 ) is a strong oxidant, and its effectiveness increases in the presence of Fe 2+ ions, where it is activated by the formation of free hydroxyl radicals that are effective for the decomposition of organic pollutants. The reaction of generating free hydroxyl radicals from the Fe 2+ /H 2 O 2 system is also known as the Fenton reaction and is the basis for the development of advanced oxidation techniques (AOTs) [38,56,58,59].…”

“…The aforementioned Fenton oxidation involves the formation of hydroxyl radicals by the reaction of hydrogen peroxide (H 2 O 2 ) with a liquid catalyst, Fe 2+ (Fenton's reagent, Fe 2+ /H 2 O 2 ). The generated hydroxyl radical is considered one of the strongest oxidants (E • = 2.8 V) compared to classic oxidants such as ozone (E • = 2.10 V), persulfate (E • = 2.01 V), hydrogen peroxide (E • = 1.80 V) and permanganate (E • = 1.70 V) [57][58][59][60][61]. Fenton's process depends on acidic pH (pH < 3) because the catalytic power of Fe 2+ decreases in an alkaline medium due to its oxidation and precipitation in the form of Fe(OH) 3 .…”

“…For this purpose, external energy in the form of UV light, electricity and/or ultrasound is added to the Fenton process, resulting in photo-Fenton, electro-Fenton and sono-Fenton processes, as well as their combinations sono-photo-Fenton, photo-electro-Fenton and sono-electro-Fenton. Thus, free radicals are generated with the help of UV radiation, electrochemical oxidation, ultrasound and their combinations [38,[56][57][58][60][61][62].…”