Utilization of recycled charcoal as a thermal source and adsorbent for the treatment of PCDD/Fs contaminated sediment

Abstract

A novel heat treatment process in which charcoal was used as both a thermal source and an adsorbent was investigated as a low-cost method for removal of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from solids. Three laboratory scale experiments involving various ratios of charcoal to contaminated sediment and air superficial velocities were performed. The results indicated that the total and toxic equivalency quantities (TEQ) concentrations of PCDD/Fs decreased significantly in the treated sediment of all runs with removal efficiencies greater than 96% and 90%, which resulted in residual concentrations below the Japanese standard limit of 0.15ng-TEQg(-1). The charcoal/contaminated sediment ratio and air superficial velocity were determinant factors controlling the PCDD/Fs concentrations and homologue profiles in effluent. As the air superficial velocity increased and charcoal/contaminated sediment ratio decreased, more PCDD/Fs were released from the sediment as fly ash, making them less likely to remain in the treated sediment. These phenomena were likely a result of the vapor pressure of PCDD/Fs, contact time with effluent gas and amount of PCDD/Fs adsorbed by charcoal. The developed process would promise an alternative to a conventional remediation process for PCDD/Fs contaminated solids.