Installment of small-scale on-site domestic wastewater treatment systems has been actively promoted as a part of the waste disposal management plan.
In this study, basic solid-liquid separation characteristics of waste excess sludge from small-scale on-site domestic wastewater treatment systems by cleaning were evaluated for disposal at night-soil treatment plants.
The values of various parameters of filtration efficiency in waste excess sludge were far lower than those in digested sludge. Dewaterability from the treatment systems was very poor, and efficient solid-liquid separation was considered to be difficult without sludge conditioning.
Characteristics of solid-liquid separation of waste excess sludge from the treatment systems were evaluated experimentally. Mechanical thickening was more effective than gravitational thickening. However, solid-liquid separation was nearly impossible without conditioning of sludge. Dewaterability was markedly improved by conditioning with a polymer coagulant.
Methods of sludge dewatering without chemicals were examined for sludge utilization for agriculture and landscape planting. The freezing-thawing process was the most effective, and its conditioning efficiency was comparable to that of chemical coagulation.

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A mathematical model was developed to estimate the dynamic performance of solid waste in the Nagasaki Water Disaster, where a large amount of disaster solid waste was generated and waste treatment facilities were both directly and indirectly damaged. To evaluate the effectiveness of each option, numerical simulations of solid waste flow/stock were tried for both cases when the waste treatment option was practised and when it was not.
Main results obtained in this study can be summarized as follows:
(1) The mathematical model proposed in this study is promising to estimate the dynamic performance of solid waste in a waste management system, even when some processes of the system are damaged.
(2) Increase of waste transportation capacity and temporal waste storage sites are effective in reducing waste accumulation at its generation site. However, open incineration is not effective among several options practised.
(3) Increase of waste treatment and transportation capacity can be most effective when their capacity is balanced among each process in the solid waste management system.

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Fly ashes containing 19 wt% chlorides with the waste sands and soda ashes were melted continuously in an electric melting furnace with a capacity of 150 kg, which has an exit for molten salt. Consumption of electricity and separation ratios of molten salt and transfer ratios of the harmful heavy metals were measured under fly ash disposal rates of 4.2-25.4 kg/h.
The wastes containing a lot of chlorides could be melted continuously when the arrival time (Ta) of marker of the tracer test was longer than 0.7 hr. In the steady condition of slag melting, the minimum consumption of electricity was 1.7 kWh/kg, and the maximum separation ratio of molten salt calculated from the chlorine concentration in the slag was 97%.
Transfer ratios of the heavy metals to the molten salt or the melted slag were different according to the kinds of heavy metals.

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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 Environ ment 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.

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Emissions of N₂O from 4 municipal solid waste incinerators were analyzed. The results showed that N₂O concentrations tended to be in reverse correlation to the furnace temperature. At low temperatures during start-up and burn-out, the emission rates of N₂O were high.
When CO concentrations in exhaust gas were high, there was a positive correlation between the concentrations of CO and N₂O. It was also confirmed that NO_xconcentrations have a negative correlation with N₂O concentrations at high furnace temperatures. This suggests that gas phase reactions may play a major role in N₂O formation with regard to municipal solid waste incinerators.
The total emission of N₂O from municipal solid waste incinerators in 1990 is estimated to be 2.0 -6.8 Gg a year. These emissions correspond to about 2 times that of sewage sludge incinerators.

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