In Japan, the yearly production of sewage sludge amounted to 1.50 million tons in 1992 and about eighty percent of the sludge produced has been treated by landfill disposal.
Studies of effective utilization and recovery of sewage sludge have become important and urgent problems as a necessary consequence of limited landfill sites.
We developed the new production method for high adsorptive activated charcoal from organic sludge containing sewage and food industrial waste water treatment, etc.
The dried sludge was carbonized for 2 hours at 650°C under wrapping vessels with aluminium foil without nitrogen gas flow. The carbonized substances were heated for 10 min. at 650°C with potasium hydroxide flake and washed with hot water. The activated ones were treated for 30 min. at 100°C with 35% hydrochloric acid and then the high adsorptive activated charcoal was produced. The characteristic values of this activated charcoal were as follows: methylene blue number was 160 -250 ml/g; specific surface area was 793-1, 771 m²/g. The developed charcoal can be utilized for the advanced waste water treatment and/or environmental purification such as deodorization and decolorization.

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In Japan more than 70% of municipal solid waste (MSW) has been incinerated. Since the heavy metal content is high in incinerator ash, there is a potential hazard of releasing heavy metals to the environment. In this paper, we did experimental studies on biological sulfate reduction in leachate from ash to know the possibility of heavy metal insolubilization.
In this experiment, the influence of environmental conditions on the activity sulfate-reducing bacteria (SRB) was almost the same as reported by other researchers. Once those conditions were met, sulfide was produced by SRB in leachate from ash. Sulfate reduction was stopped even though sulfate and TOC still remain in leachate, because SRB in the authors' experiment utilized mainly lactate. Only 25% of TOC was transformed into lactate.

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Recently, with the rapid progress of the incineration technique, the landfill volume of incineration residues is increasing. Therefore, the salinity of leachate from landfill sites is increasing.
On the effect of the high salinity of the landfill layer, we investigated the microbial degradation of solid wastes using the small-scaled lysimeters. The biodegradation of solid wastes and the purification of leachate were retarded under the high salinity condition. But it did not show up clearly because narrow pores like soil aggregates existed in the landfill layer. Also, the bacteria flora of leachate succeeded to the flora, in which the halophilic bacteria dominated, with the increase in the concentration of chloride in leachate. As a result, the number of NB organisms hardly decreased. On the other hand, the enzyme activities for biodegradation of organic compounds in leachate declined and the growth of the organisms which participated in the nitrogen compounds catabolism were inhibited, especially on the denitrification. Consequently, the concentration of inorganic nitrogen compounds in leachate decreased less than that of organic carbon compounds under the high salinity of the landfill layer.

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Toxicity of leachate of municipal solid waste combustion fly ash was examined by quantitative analysis of heavy metals and the Daphnia toxicity test.
Comparing the concentrations of heavy metals with the regulatory levels for landfill restriction, it was expected that cadmium and lead would be the dominating causes for the toxicity of leachate. Zinc, which was not regulatory constituent, was also expected to be one of them because its concentration was much higher than other metals.
The Daphnia test, however, showed that the toxicity of the leachate was much higher than the toxicity expected form cadmium, lead and zinc concentrations.
These facts show that, in addition to chemical analysis, it is useful to conduct biological toxicity test to evaluate the toxicity of wastes.

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