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The method for selecting the appropriate treatment system in low-density areas was studied by statistical data analyses and questionnaire surveys. The main results obtained are as follows.(l) The efficiency of sewerage service has been decreasing. With decrease of the population density in served areas, treatment cost is increasing from 7,000 yen/household in 1961 to near 40,000 in 1989.(2) By considering the external cost of treated water quality, the marginal house density beyond which collective systems become advantageous, was estimated to be 9.5 houses/ha compared to the original value of 13 houses/ha.(3) Improvement of water quality, saving energy, and efficient uses of sludge are considered to be important for the environmental impact of sewerage systems. Suitable allocation of optional treatment systems, energy saving technology and prevention of sludge contamination must be the important issues for the sewerage service on a small scale.

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ABSTRACT;In this paper, we studied the present situation of refuse recycling in Ube City and analyze the collection cost by scenario-analyses.Resource recovery has been done mainly by the volunteer works of children circles and so forth. However, the activity has been suppressed by the low price of resources nowadays. Almost 1/3 of community circles has not been involved in the volunteer works for refuse recycling. In new residential areas with many children, the frequency of the volunteer works and the recovery rate of resources tend to be high. As the result of scenario-analyses, the collection cost of refuse recycling by the municipality amounts to be 4 times of the cost for recycling by volunteer works. In case of newspaper refuse, the collection by municipality was estimated to be feasible only if the recovery rate was higher than 70%, otherwise it is more advantageous for the municipality to collect and incinerate the newspaper refuse together with garbage.

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