Subsurface fire might occur in the waste pile due to the heat generated by biological decomposition and chemical oxidation process accumulates inside waste and elevates surrounding temperature, which will result in fire in combination with combustible material or gas from the waste. In this study, an investigation flow was proposed to identify this so-called “hot spot”. The investigation flow includes field survey, hearing, in-waste temperature distribution and gas concentration survey, determination of detailed investigation zone, create depth profile with continuous monitoring and locate core zone with simulation. In addition, a case study in an inappropriate landfill site was presented. The in-waste temperature and gas concentration were measured at 46 spots and 3 spots where total temperature above 65℃ was chosen for continuous monitoring. The temperature at the depth of 1 m was below 60℃ and the CO concentration at the depth of 50 cm was below 100 ppm, it can be considered that there is no risk of subsurface fire. In conclusion, it is important to collect and accumulate data of in-waste temperature and gas to determine proper trigger value on site for detailed investigation.

A closed semi-aerobic landfill in Hokkaido, Japan is studied to examine stabilization by passive aeration system. New landfill gas (LFG) extraction wells were installed to extract LFG and induce the air into the landfill body for controlling LFG passively. Observation of LFG component, temperature and LFG flux in three monitoring wells has been carried out for confirming the stabilization of this landfill. Through the survey of landfill gas components, flux and gas temperatures at monitoring wells were monitored for 15 years after closure. Methane concentrations at 3 monitoring wells were still high after closure. Only gas flux at B-M-1 reached 1000 ml/min as the critical value of gas flux for the end of aftercare. The relationship between gas flux and methane concentration show significant correlation, however, not between gas flux and gas temperature. Methane concentrations at 3 monitoring wells were still high, so the continuous monitoring is still important.

The primary treatment of municipal solid waste (MSW) in Japan is by using the thermal treatment that 80.3% of its MSW treated by using an incinerator in 2017. Municipal solid waste incineration (MSWI) fly ash that byproducts from the incineration process contain a high concentration of heavy metals and toxic organic compounds that can be harmful to the environment. Heavy metals are entrapped into mineral aggregate or as chlorides or sulfates condensed into fly ash particles. This study aims to estimate new possible metal speciation in the fly ash particle from the fluidized bed incinerator by using correlation analysis. Correlation analysis, is using an elemental mapping from SEM-EDX observation, can be useful for the comprehensive characterization of heavy metal speciation with other analyses such as XRD analysis. The crystalline and non-crystalline of Cr and Cu were incorporated into spinel structure in the fly ash particle. These metals also incorporated in Al/Ca/Si-based core component of fly ash particles. It suggested chromium and copper is not easily to leached out from fly ash particle because these metals entrapped into spinel structures and Al/Ca/Si-based core fly ash.

Incineration residues (bottom ash and fly ash) account for about 80% of waste disposed of in landfills. In recent years, the number of landfills which accept fly ash mainly has increased on the back of this situation. Since hazardous heavy metals contained in fly ash are in general easily soluble, leaching suppression treatment is performed in order to dispose it to the controlled-type landfill. The current mainstream is chemical treatment. However, it has been reported that the function of leaching suppression by a chelating agent deteriorates with time, and re-release of heavy metals occurs. The authors confirmed that Cs was specifically trapped in the glassy amorphous phase formed on the surface of alkali feldspar by investigating the incineration process of decontamination waste in previous studies. Thus, in this study, the possibility on whether this trapping mechanism could be applied to insolubilize various heavy metals in fly ash, was set to the target of study. As the results, it was confirmed that aluminosilicates can insolubilize lead in fly ash.

Waste incinerated fly ashes are considered hazardous waste worldwide. Current research focuses on the potential recycling of incinerated materials through cement solidification. The problem with this technique is the potential leaching of hazardous content when material is contact with water. In that sense leaching characterization and quantification from the material is needed for short and long-term application scenarios. In this research a multidisciplinary approach combining mineralogical analysis with different leaching tests was performed to predict the mobility of potentially hazardous substances from recycled roadbed aggregate produced from tire waste boiler fly ash. Utilizing the geochemical modeling tools leachate pH controlling mineral phases in the material were predicted and compared to column leaching test results. Results have shown the material high buffer capacity prevents leaching of heavy metals, and its release is solubility controlled.