Dewatering and Utilization of Fly Ash Slurries Using Geotextile Tubes

Abstract

About one billion metric tons of coal ashes are produced annually around the world, among which 700 million tons are fly ash wastes that must be disposed of. The practice of wet fly ash disposal has increased environmental concerns due to fly ash leachate, ground water contamination, and the limitation of pond capacity. Therefore, alternatives to the current disposal methods should be addressed. Geotextile tube dewatering is an efficient dewatering method that can decrease the volume of fly ash slurry and at the same time provides containment of dry fly ash. In this study, pressure filtration tests were conducted to evaluate the dewatering performance of Class C fly ash with seven woven geotextiles having a wide range of hydraulic properties. Anionic polymer flocculant was used to evaluate the effect of polymer conditioning on dewatering performance. In addition, the increase in filter cake strength due to flocculants was evaluated. Lastly, chemical analysis of the effluent was performed to quantify the concentration of contaminants present in the geotextile tube effluent. The results of this study indicate that hydraulic properties of the geotextile do not have a significant effect on the dewatering performance of fly ash. It was found that polymer conditioning significantly increased the strength of the filter cake, making fly ash filled geotextile tubes suitable for use in geotechnical engineering applications. It was also found that geotextile tube dewatering does not retain fly ash trace elements that can leach out with effluent, meaning that proper safety measures must be taken in fly ash reutilization projects.