Basic characteristics of leachate produced by various washing processes for MSWI ashes in Taiwan

Approximately 19.2% of Taiwan’s municipal solid waste (MSW) that passes through incineration disposal is converted into ashes (including bottom ash and fly ash). Although bottom ash can pass nearly all of the standards of the toxicity characteristic leaching procedure (TCLP), its high chloride content makes its reuse limited; it generally cannot be used as a fine aggregate material in concrete applications. This research examined washing four types of bottom ash (BA) and fly ash (FA) with water to reduce their chloride content. The optimal water intensity for washing pretreated bottom ash was found to be 7–8 L of water per kg of bottom ash, and the optimal water intensity for washing untreated fly ash was found to be 20–25 L of water per kg of fly ash. Based on regression analyses of the chloride concentrations of the leachates and their electrical conductivity (EC) values, each MSW incineration plant has its own ash characteristics as well as a specific regression line in bottom or fly ash leachate. Clearly, it is possible to monitor the EC values of the leachates online by estimation from regression equations to determine the chloride concentrations in the leachates.

► Reducing the Cl− content in bottom ash is hard to achieve by water washing solely.
► The best L/S ratio values to wash fly ash are 20/1∼25/1.
►  Each MSW incineration plant has its own specific regression line in ashes.