Organic pollution loads in municipal solid waste incineration fly ash derived from highly reactive slaked lime in leachate from landfill site

High levels of total organic carbon (TOC) are often detected in leachate from landfill sites in Japan, which is problematic for proper leachate treatment. The chelating agent for stabilizing heavy metals has often been... [ view full abstract ]

High levels of total organic carbon (TOC) are often detected in leachate from landfill sites in Japan, which is problematic for proper leachate treatment. The chelating agent for stabilizing heavy metals has often been reported as the origin of organic matter in landfill sites. However, some types of raw fly ash, which do not contain chelating agents, also show high levels of TOC leaching. In this study, TOC and chemical oxygen demand (COD_Mn) of leachate from fly ash and slaked lime in Japanese landfill sites were determined.

The TOC in leachates from 13 kinds of incineration fly ash from municipal solid waste was measured. Ignition loss (IL) of each type of fly ash was also measured to determine the content of organic matter. There was no relationship between TOC and IL. Higher TOC levels were detected in leachate from fly ash from incinerators with dry-acid gas treatment systems. This suggests that the TOC of the leachate from the abovementioned fly ash was derived from slaked lime for the neutralization of acid gas.

Subsequently, 13 kinds of highly reactive slaked lime were obtained. The TOC of their leachates was measured and was in the range of 600–5,680 mg/kg. In contrast, normal industrial lime and Ca(OH)₂ reagent do not contain organic materials. Generally, there was a positive correlation between COD and TOC in slaked lime. TOC showed 60–80% of COD_Mn values.

Furthermore, we conducted a questionnaire survey on the acid gas neutralization method in municipal solid waste incineration plants, and obtained data from 68 incineration facilities. Based on the results of the survey, approximately 50% of municipal waste incinerators used highly reactive slaked lime for acid gas neutralization. From these results, it is considered the organic materials from highly reactive slake lime account for a significant proportion in the organic pollution loads in the leachate from landfill sites mainly disposed of incineration ash.