Organic Carbon Leachability from Bottom Ash Samples by Conventional and Ultrasound Methods

Abstract

The organic carbon (DOC) leachability of bottom ash samples obtained from two different sources, municipal solid waste (MSW) and industrial solid waste (ISW) incineration facilities, were investigated aiming at enhancing the washing efficiency of DOC. The relationship of DOC leaching with minerals in bottom ash was also studied as a tool for the prevention of their impact on the environment. Furthermore, ultrasound was applied to enhance the efficiency of the conventional washing method and shorten the washing time of DOC from bottom ash. MSW incinerator bottom ash (M-ash) showed a DOC leaching pattern dependent on pH; the higher DOC leaching was observed at the lower pH, while ISW incinerator bottom ash (I-ash) showed DOC leaching independent of pH. DOC leaching in M-ash appeared to be trapped in the solid matrix by stable soluble calcium-aluminosilicate mineral species, identified by X-ray diffraction (XRD) measurements. Approximately 50% of additional DOC leaching could be achieved when pH was lowered from alkaline-neutral to the acid range due to the dissolution of these mineral species in acid pH. Calcium-aluminumsilicate species were not detected in I-ash and therefore ratified the liability of these species for blocking the DOC leaching from M-ash. Ultrasound significantly increased the efficiency of the conventional washing method as well as shortened the washing time of DOC from 60 to 5 min in M-ash. Moreover, ultrasound would be considered as a feasible treatment method to minimize environmental impacts of landfill sites over short- and long-term considerations.