Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds: A review

doi:10.1016/j.cej.2015.09.001

Chemical Engineering Journal

Volume 284, 15 January 2016, Pages 582-598

https://doi.org/10.1016/j.cej.2015.09.001 Get rights and content

Highlights

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The main drawback of conventional Fenton treatment is the reduction in soil pH.
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Modified Fenton treatments can produce OH at a pH near neutral.
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The lack of visible light activity hinders the practical applications of photocatalysis.
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Ozonation is suitable to treat soils with large pore spaces and low moisture.
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Plasma oxidation is able to treat soils with high concentration pollutants.

Abstract

Advanced oxidation processes (AOPs) constitute a promising technology for the remediation of soils contaminated with non-easily removable organic compounds. This review provides the reader with a general overview on the application of AOPs to pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and total petroleum hydrocarbons (TPHs) contaminated soils remediation. Four types of AOPs including Fenton processes, TiO₂ photocatalysis, plasma oxidation and ozonation were discussed. In particular, this paper focuses on the fundamental principles and governing factors of the two typical techniques – Fenton oxidations and TiO₂ photocatalysis. Apart from the effect of chemical’s dosage as a major influencing factor, selected information such as pollutant characteristics, light intensity, soil characteristics and pH are presented. Some innovations (e.g., chelating agents, surfactants) on the traditional AOPs and the combined utilization of AOPs with other techniques (e.g., bioremediation, soil washing) are also documented and discussed. This review also highlights the effects of AOPs treatments on soil properties.

Graphical abstract

Introduction

As an important component of the ecological environment, soil is one of the main resources that human beings rely on to survive, and also the material repository of bio-geochemical cycles. Nowadays, extensive use of pesticides and fertilizers constantly damage farmland. In addition, accidental emissions of harmful pollutants, the industrial wastewater and the landfill leachate have been causing serious soil pollution and deteriorating soil quality [1]. Government and the public now have recognized the potential dangers that organic pollutants such as pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and total petroleum hydrocarbons (TPHs) posed to human health and the environment [2], [3], [4]. Remediating the contaminated soil, in order to protect human health and achieve sustainable development, has become the common view of both government and public.

Extensive work has been devoted to the development of soil remediation techniques, and several new and innovative solutions for efficient contaminants removal from soils have been investigated to reduce the contaminants contents to a safe and acceptable level [5], [6]. Among these treatment techniques, chemical oxidation has the potential for rapidly treating or pretreating soils contaminated with toxic and biorefractory organic compounds [7]. Chemical oxidation aims to mineralize the pollutants to carbon dioxide (CO₂), water (H₂O) and inorganics or, at least, transform them into harmless or biodegradable products [8]. In last two decades a lot of researches have been addressed to this aim and pointed out the prominent role of a special class of oxidation techniques defined as advanced oxidation processes (AOPs), which usually operated at or near ambient temperature and pressure [9], [10].

The advantage of AOPs over all chemical and biological processes is that they are totally “environmental-friendly” as they neither transfer pollutants from one phase to the other (as in chemical precipitation and adsorption) nor produce massive amounts of hazardous sludge [10]. AOPs are capable of degrading nearly all types of organic contaminants into harmless products [11] and almost all rely on the production of reactive hydroxyl radicals (OH) with a redox potential of 2.8 V [12]. OH is the second most reactive species next to fluorine atom, they attack the most part of organic pollutants molecules with rate constants usually in the order of 10⁶–10⁹ M⁻¹ s⁻¹, which is 10⁶–10¹² times faster than ozone [13], [14]. In these process, OH initiate a series of oxidation reactions then leading to the ultimate mineralization products of CO₂ and H₂O [15]. Due to these characteristics, numerous works have been done to investigate the applications of AOPs to treat different types of contaminated soils. However, they have concentrated solely on one technology employed in treating one kind of pollution, and to date, an evaluation of all currently available AOPs for different types of contaminated soils remediation has not been reported. With this in mind, the review attempts to summarize and discuss the state of the art in the treatment of pesticides, PAHs, PCBs and TPHs contaminated soils by using OH based AOPs.

Section snippets

Advanced oxidation processes

The versatility of AOPs is also enhanced by the fact that they offer different possible processes for OH generation, thus allowing a better compliance with the specific treatment requirements. The following techniques are most often used in AOPs (Fig. 1): (i) Fenton oxidations, (ii) photocatalysis, (iii) plasma oxidation, and (iv) ozonation. As shown in Fig. 2, the interest of researchers for AOPs began only around 1995 [12] and continues nowadays since the number of investigations devoted to

AOPs for remediation of pesticides contaminated soils

Soil contamination by pesticides is a widespread occurrence [73]. Pesticides have been used to mitigate or repel pests such as insects, bacteria, nematodes, mites and other organisms that affect food production or human health since Second World War [74], and many times irresponsible use has made them an environmental problem [75]. This is mainly due to their properties, such as hard-biodegraded and high retention time in soil [76]. Furthermore, some pesticides, such as

AOPs for remediation of PAHs contaminated soils

PAHs are ubiquitous environmental contaminants, which are by-products of fossil fuels processing or combustion [103]. PAHs are included in the European Community and in the Environmental Protection Agency priority pollutant list mainly due to their mutagenic and carcinogenic properties [104], [105], [106]. Because of hydrophobic and recalcitrant characteristics, PAHs tend to be adsorbed on solid particles and these characteristics make it as one of the major soil pollutants [107]. Since most

AOPs for remediation of PCBs contaminated soils

PCBs are toxic and persistent pollutants that have been used in a variety of applications such as transformers, capacitors, coolants, and lubricants since 1930s [132]. Due to their hazardous nature and chemical stability, they are categorized as persistent organic pollutants [133]. Their extreme persistence in the environment and ability to bioconcentrate in the food chain present a great environmental risk [134]. Although incineration and land-filling are proven and widely used technologies

AOPs for remediation of TPHs contaminated soils

Nowadays petroleum hydrocarbon pollution has been one of the major environmental problems, not only by their toxicity but also by the significant amounts released. Soil contaminated with petroleum hydrocarbon is adverse to plant growth and is also a potential source of groundwater pollution [151]. Bioremediation has proven to be successful in many case studies [152]. However, bioremediation usually requires a long treatment period, and it is often inefficient to lower the contamination level

Plasma oxidation

The first study that uses LTPs discharges to treat polluted soil was carried out by Redolfi et al. [172] who evaluated kerosene components oxidation in a soil matrix by a DBD reactor at atmospheric pressure. Results showed that the total kerosene components abatement can reaches 90%, and the removal mechanism was determined as the oxidation of kerosene in the soil matrix [172]. In the sequent studies [62], [173], [174], Wang et al. studied the remediation of PCP contaminated soil using PCD

Conclusions and prospects

This review provides the reader with a general overview on the treatments of pesticides and PAHs, PCBs and TPHs contaminated soils by using AOPs, with a special address to the two mainly applied methods Fenton processes and photocatalytic processes. Fenton process has become popular because of the following reasons: (1) easy to implement, (2) able to degrade a wide range of contaminants, (3) sub-products are usually harmless or biodegradable. The main drawback of conventional Fenton treatment

Acknowledgments

This study was financially supported by the National Natural Science Foundation of China (51378190, 51278176, 51408206), the Environmental Protection Technology Research Program of Hunan (2007185), the Fundamental Research Funds for the Central Universities, the Hunan University Fund for Multidisciplinary Developing (531107040762), the Program for New Century Excellent Talents in University (NCET-13-0186), the Program for Changjiang Scholars and Innovative Research Team in University

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ReviewHydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds: A review

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Advanced oxidation processes

AOPs for remediation of pesticides contaminated soils

AOPs for remediation of PAHs contaminated soils

AOPs for remediation of PCBs contaminated soils

AOPs for remediation of TPHs contaminated soils

Plasma oxidation

Conclusions and prospects

Acknowledgments

Sci. Total Environ.

Chem. Eng. J.

J. Environ. Manage.

Chemosphere

Water Res.

Water Res.

Catal. Today

Chem. Eng. J.

J. Hazard. Mater.

Water Res.

Water Res.

Chem. Eng. J.

Chemosphere

Chemosphere

Water Res.

Chem. Eng. J.

Chem. Eng. J.

J. Hazard. Mater.

Chemosphere

J. Hazard. Mater.

J. Photochem. Photobiol. A: Chem.

J. Ind. Eng. Chem.

Chemosphere

Water Res.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

Chemosphere

Appl. Catal. B: Environ.

J. Environ. Sci.

J. Colloid Interface Sci.

J. Photochem. Photobiol. C: Photochem. Rev.

Chem. Eng. J.

J. Photochem. Photobiol. A: Chem.

J. Photochem. Photobiol. C: Photochem. Rev.

Surf. Sci. Rep.

J. Photochem. Photobiol. C: Photochem. Rev.

Appl. Catal. B: Environ.

Chemosphere

Appl. Catal. B: Environ.

Appl. Catal. B: Environ.

J. Hazard. Mater.

Sep. Purif. Technol.

Chem. Eng. J.

Chem. Eng. J.

Sep. Purif. Technol.

Vacuum

Water Res.

Chemosphere

Chemosphere

Review
Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds: A review