Elsevier

Journal of Hazardous Materials

Volume 355, 5 August 2018, Pages 34-49
Journal of Hazardous Materials

The electrochemical regeneration of granular activated carbons: A review

https://doi.org/10.1016/j.jhazmat.2018.04.079Get rights and content

Highlights

  • Overview of research conducted surrounding the electrochemical regeneration of GAC.

  • Discusses the regenerative mechanism and theory behind electrochemical regeneration.

  • Varying reactor configuration and operating conditions affect regeneration outcomes.

  • Specifies industrial applications for which this technology may be used.

Abstract

The electrochemical treatment of exhausted granular activated carbon (GAC) has been identified as an effective alternative to traditional adsorbent regeneration methods (e.g. thermal, chemical, and microbial). However, despite its proven potential and initial investigation over two decades ago, the development of this technology has been progressing slowly, hindering its deployment in industrial applications. Thus, a review has been conducted that aims to present the fundamentals of GAC electrochemical regenerative methods, what research has been conducted to develop the technology to the present day, and lastly, identify limitations and future prospects associated with electrochemical methods. The regenerative mechanism is firstly discussed, followed by a presentation of the varying reactor configurations and operating parameters utilized during the electrochemical treatment of GAC materials exhausted with a broad range of wastewater contaminants. Finally, emerging electrochemical technologies used for the commercial treatment of exhausted adsorbent materials and contaminated soils are discussed.

Introduction

The large surface area, microporous structure, and increased surface reactivity associated with granular activated carbon (GAC) [1,2] makes it one of the most powerful adsorbent materials used in purification processes. In the present day, industries such as oil and gas, pharmaceutical, and waste water treatment are now incorporating increasing amounts of GAC into their manufacturing processes. With increasing amounts of legislation being placed on environmental protection, product quality, and liquid and gas emissions, the global demand for activated carbon continues to increase nearly 10% annually from its global consumption of 4.28 million tons in 2012 [3].

Although proven to be highly effective, the leading shortcoming of GAC is the limited lifetime for which it can perform. Upon reaching its adsorptive capacity, it is no longer effective and is most often sent for disposal and replaced with fresh material. However, the continuous material change out that results is not financially viable, and the disposal of exhausted material into landfill leads to the possibility of toxic contaminants leaching into the environment [4]. A more economical and environmentally friendly option is to regenerate the material such that it can be used for several cycles of adsorption and regeneration.

The regeneration of GAC aims to restore the original adsorptive capacity of the GAC by removing contaminants that have accumulated onto the carbon surface, while damaging the carbon as little as possible [5]. Several regenerative techniques are extensively covered in the literature and currently applied in industrial applications; this includes thermal [6], chemical [7,8], and microbial methods [9]. However, these methods are met with limitations such as high energy consumption and carbon attrition [10], pore blockage and oftentimes the requirement for secondary treatments [11], and slow regeneration rates [12] respectively.

In an attempt to overcome these restrictions, attention is being turned towards a relatively newer technology, electrochemical regeneration, at which saturated GAC is placed between two oppositely charged electrodes. Upon application of an electric current, both desorption and degradation processes of the adsorbed contaminants are observed. Narbaitz and Cen [13] were one of the first to study this technique, utilizing a 1-litre electrochemical reactor to regenerate 1.2 g of phenol saturated GAC. Following 5 h of treatment, the GAC was 95% regenerated, with consecutive treatments resulting in only a 2% loss in adsorptive capacity per cycle due to minimal carbon losses. As these results exceeded the outcomes of other regenerative methods, in terms of adsorptive capability and prolonged use, it gave merit to conduct further research in the field.

Despite the recent application of electrochemical technology, it has had limited discussion within the literature. Thus, a review has been conducted that aims to present 1) the theory of electrochemical regeneration, 2) what research has been done related to the electrochemical treatment of activated carbon, and 3) identify limitations and future engineering prospects associated with the technology.

Section snippets

Regenerative mechanism

The application of an electric current across and exhausted bed of granular activated carbon results in two main regenerative processes. First, enhanced desorption from the GAC surface commences, Fig. 1(A)–(C), and results in an adsorbent free of contaminant species. Second, electrochemical reactions occurring at the electrodes and polarized GAC particles stimulate the degradation of contaminant species, completely removing them from the system, Fig. 1(D). An ideal electrochemical regenerative

Operational considerations

Although the electrochemical regeneration of GAC is known to be a functional treatment, research to date has greatly varied in reactor configuration and operating parameters, with research groups utilizing different types of GAC and model contaminants. Although this makes it difficult to gain an understanding of the underlying mechanism, kinetics, and possibility of scale up, the following section aims to encapsulate and compare how different reactor configurations used during the

Industrial application

The large-scale implementation for the electrochemical regeneration of GAC has not yet been implemented, largely due to a lack of understanding and optimisation of the treatment process. However, a technology operating on a similar principle has recently been developed by Arvia Technology Ltd., whereby contaminant adsorption and electrochemical destruction occur within a single cell. The Arvia Organics Destruction Cell™ (ODC), depicted in Fig. 7, passes contaminated wastewater through a bed of

Conclusion

The literature demonstrates that electrochemical treatments are an effective method for the regeneration of exhausted GAC, with high regeneration efficiencies being obtained within a few hours. Even so, the development and application of this technology has progressed slowly since its initial exploration over two decades ago. Research to date has predominantly focused on variations in reactor configurations and operating parameters, with research groups utilizing different types of GAC and

Declarations of interest

None.

Acknowledgments

The authors acknowledge the research financial support provided from the Australian Antarctic Science Project 4029 and The Particulate Fluids Processing Centre.

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