Sustainable remediation techniques for fly ash disposal sites and addressing challenges in implementing phytoremediation strategies at field scale: A review

Coal-fired thermal power plants occupy a significant amount of land for ash disposal. Too often, ash disposal sites are not properly designed, constructed, or operated, resulting in uncontrolled emissions of pollutants to the local and regional environment due to the accumulation of toxic elements and limited natural attenuation. This review describes current strategies for reclamation of ash disposal sites through various remediation and stabilization techniques. Application of in situ chemical stabilization methods, such as chemical column technique, has proven effective in immobilizing heavy metals, reducing leachability, and enhancing the engineering properties of the ash bed for subsequent land use. Furthermore, phytoremediation is a bio-remedial strategy that involves the use of various plant species to reduce contaminants and enhance nutrient content in ash beds as well as adjacent soil, presenting a long-term sustainable approach. The efficacy of phytoremediation through various plant species, aiming at its effectiveness in reducing contaminants through phytoextraction, phytostabilization, phytodegradation, and phytovolatilization, along with the associated challenges and limitations of these remediation techniques, has been discussed thoroughly. These combined methods mitigate the environmental impacts of ash disposal while reclaiming degraded land for subsequent reuse by optimizing land utilization while facilitating the construction of small structures: lightweight industrial shelters, temporary storage units, service sheds, and possibly generating revenue through the establishment of consumable vegetation. Moreover, this review highlights the global viability and scalability of ash stabilization by chemical column and phytoremediation techniques, aligning with various Sustainable Development Goals, while providing useful information to industry experts and researchers striving for sustainable management of ash disposal sites.