Isao Fukunaga*, Hisao Itoh* and Minoru Sawachi**

* Osaka City Institute of Public Health and Environmental Sciences
** Osaka City Environmental Management Bureau

+ Correspondence should be addressed to Isao Fukunaga:
Osaka City Institute of Public Health and Environmental Sciences
(Tohjou-cho 8-34, Tennoji-ku, Osaka 543, Japan)

Abstract

In the newly amended Waste Management and Public Cleansing Law, fly ash from a municipal general waste incinerater is designated as specially controlled municipal waste. Therefore, in the new plant it should be treated by the four methods decided by the Minister of Health and Welfare before final disposal. Osaka City is also planning to control the fly ash from plants that were constructed before the new law went into effect, according to the spirit of the new law. We have been investigating to find new methods and already presented the possibility of the water-washing method as one of detoxification of fly ash. The water-washing method means to wash fly ash by ash quench water, its final treated water or industrial water. The washed fly ash is then dewatered and finally disposed of. The wastewater that is generated by dewatering washed fly ash should involve heavy metals and be treated at existing wastewater treatment facilities. The dewatered fly ash passed the leaching test of the Japan Environment Agency Notification No.13. and pH of the leachate is about 9's. It was concluded that this washing method is more simple and economical than others such as cement solidification method and other designated methods. In this report, for practical use, we had laboratory investigation about various leaching factors effecting leaching test, such as pH, leaching time, leaching ratio and others and plant research. From those results our findings were as follows. (1) pH of washed fly ash was from 9 to 11 and almost no heavy metal was leached from the ash. (2) Even after about one year in fresh water or marine water almost no heavy metal was leached from the washed fly ash. (3) For detoxication, 15-minutes washing time is enough. (4) Ash to water ratio requires less than 1:5. (5) This water-washing method would be applicable to all types of fly ash from incineration plants.

Key words: fly ash from municipal waste incinerators, detoxification treatment, leaching test, specially controlled municipal waste, water-washing method, heavy metal