Thermal desorption of PCBs from contaminated soil with copper dichloride

Recent advances in PCB removal from historically contaminated environmental matrices

Despite being drastically restricted in the 1970s, polychlorinated biphenyls (PCBs) still belong among the most hazardous contaminants. The chemical stability and dielectric properties of PCBs made them suitable for a number of applications, which then lead to their ubiquitous presence in the environment. PCBs are highly bioaccumulative and persistent, and their teratogenic, carcinogenic, and endocrine-disrupting features have been widely reported in the literature. This review discusses recent advances in different techniques and approaches to remediate historically contaminated matrices, which are one of the most problematic in regard to decontamination feasibility and efficiency. The current knowledge published in the literature shows that PCBs are not sufficiently removed from the environment by natural processes, and thus, the suitability of some approaches (e.g., natural attenuation) is limited. Physicochemical processes are still the most effective; however, their extensive use is constrained by their high cost and often their destructiveness toward the matrices. Despite their limited reliability, biological methods and their application in combinations with other techniques could be promising. The literature reviewed in this paper documents that a combination of techniques differing in their principles should be a future research direction. Other aspects discussed in this work include the incompleteness of some studies. More attention should be given to the evaluation of toxicity during these processes, particularly in terms of monitoring different modes of toxic action. In addition, decomposition mechanisms and products need to be sufficiently clarified before combined, tailor-made approaches can be employed.

A review on the sustainability of thermal treatment for contaminated soils

Sustainable remediation is a goal in the remediation industry. Thermal treatment can remediate contaminated sites quickly and reliably, but its energy-intensive nature and potential to damage soil properties make it seemingly not sustainable. This review evaluates the potential for thermal treatment to become a sustainable remediation technology based on a comprehensive analysis of the scientific literature. The fundamentals, advantages, and limitations of single thermal treatment technologies are summarized. The compatibility and advantages of thermal treatment coupled with thermal, physicochemical, or biological technologies are reviewed. The results suggest that ingeniously designed coupled technologies can improve the availability and removal efficiency of contaminant, suppress the production of toxic byproduct, and reduce the required heating temperature and energy input. The sustainability of thermal treatment is then discussed from the perspectives of energy efficiency and land reuse. Approaches for improving energy efficiency include applying solar energy-based technologies, smoldering-based technologies, and coupled technologies. For land reuse, heating below 250 °C has negligible adverse impacts on most soil properties, and can increase nutrient availability and release dissolved organic carbon to support the growth of microorganisms and plants. Heating above 250 °C can significantly reduce soil organic matter and clay content, which decreases the soil cation exchange capacity and water holding capacity, and consequently damages the soil fertility. Some restoration strategies are also proposed for the recovery of soil quality. In addition, thermally remediated soil is considered to be a good candidate as an engineering medium for construction. This review concludes with an outlook of future research efforts that will further shift thermal treatment toward sustainable remediation.

Thermal desorption for remediation of contaminated soil: A review

Soil pollution has become a global environmental concern. Thermal desorption is one of the methods commonly used to remediate contaminated soil. This method has received increasing attention for remediating contaminated sites due to its advantages, such as suitability to different types of contaminants, short treatment period, high efficiency, high safety, and capability to recycle soil and contaminants. This paper provides a comprehensive review of studies on thermal desorption. Introduction of the mechanism, classification, and cost of thermal desorption is presented. Factors affecting the performance of thermal desorption (heating temperature, heating time, heating rate, carrier gas, soil particle size, moisture content, initial concentration of contaminants, and additives) are reviewed. Thermal desorption produces off-gases, which are mostly organic compounds and may result in secondary pollution. Thus far, treatment methods for off-gas have not been systematically investigated. This paper also summarizes current methods for treatment of off-gas in the soil field and of volatile organic compounds in atmospheric and water pollution fields. Several feasible off-gas treatment methods are also comparatively analyzed, and the corresponding principles, advantages, disadvantages, and application ranges are discussed.

Review of chemical and electrokinetic remediation of PCBs contaminated soils and sediments

Polychlorinated biphenyls (PCBs) are manmade organic compounds, and pollution due to PCBs has been a global environmental problem because of their persistence, long-range atmospheric transport and bioaccumulation. Many physical, chemical and biological technologies have been utilized to remediate PCBs contaminated soils and sediments, and there are some emerging new technologies and combined methods that may provide cost-effective alternatives to the existing remediation practice. This review provides a general overview on the recent developments in chemical treatment and electrokinetic remediation (EK) technologies related to PCBs remediation. In particular, four technologies including photocatalytic degradation of PCBs combined with soil washing, Fe-based reductive dechlorination, advanced oxidation process, and EK/integrated EK technology (e.g., EK coupled with chemical oxidation, nanotechnology and bioremediation) are reviewed in detail. We focus on the fundamental principles and governing factors of chemical technologies, and EK/integrated EK technologies. Comparative analysis of these technologies including their major advantages and disadvantages is summarized. The existing problems and future prospects of these technologies regarding PCBs remediation are further highlighted.