Technology 2005: 2nd Joint Specialty Conference for Sustainable Management of Water Quality Systems for the 21st Century: Development of New Technologies to Suppress Leachate of Heavy Metals from Sewage Sludge Incineration Ash
Sewage sludge incineration ash (“incineration ash”) contains trace amounts of heavy metals, and leachate of arsenic (As) and selenium (Se) that often exceeds the level specified in the Environmental Quality Standards for Soil Contamination of Japan (hereinafter called the
“Japanese Standard”) is one reason for the flagging rate of incineration ash recycling. To help expand recycling of incineration ash, the Bureau of Sewerage of the Tokyo Metropolitan Government promoted development of technologies to suppress leachate of heavy metals from incineration
ash and methods to reduce heavy metal contents in incineration ash, so as to alleviate the effects of heavy metals generated in the course of application of incineration ash. Adding iron(II) sulfate and sodium thiosulfate to the ash, then
heating it to chemically transform it into a form that hinders the leachate of heavy metals (Reagent Addition Method) Adding slaked lime to the incineration ash to create a hydrothermal reaction that causes crystals to form on the surface of the ash that
will physically seal the heavy metals. (Hydrothermal Treating Method) Utilizing the fact that heavy metal compounds remain in a gaseous state at the temperature inside the incinerator, to collect the incineration ash with low heavy metal content from
the area near the incinerator outlet where the temperature is high. (High-temperature Dust Collection Method) Each of these methods is introduced below because they have been used successfully to produce incineration ash that meets the requirements of the Japanese Standard
by leachate of arsenic and selenium.
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