Hiroshi Eya

* Machinery Research Laboratory, The Japan Steel Works, Ltd.

+ Correspondence should be addressed to Hiroshi Eya
Research & Development Headquarters, The Japan Steel Works, Ltd.
(2-2-1 Fukuura, Kanazawa-ku, Yokohama-shi, Kanagawa, 236-0004 Japan)

Abstract

This study verified the most suitable conditions for static aeration and scooping up time in composting. Garbage was fed to a scoop-type fermentor, which could compost one ton of raw material per day. A first series of experiments was carried out to evaluate the effect of aeration with a constant scooping up time (5 times a day) . The experiments were conducted under the three aeration rates of zero, 370 and 900l/min for one dry-weight ton of garbage and paper, as the composition of the raw material. The experiment with the 900 l/min aeration rate showed the fastest rate of increase of temperature, pH and degradability of organic matter. However it was expected that the microorganism activity might be decreased by the excessive decline in moisture content under this condition. Furthermore the rate of increase of temperature and pH at the early stage of composting and the amount of degraded organic matter in the 370 l/min aeration experiment were not so different from those of the 900 l/min experiment. Hence, if we consider the plant investment and running costs of a practical plant, the most suitable condition for static aeration should be 370 l/min. In the next series of experiments, the effect of scooping up time was examined at a regular static aeration rate (370 l/min) . The experiments were carried out for six scooping up conditions; one, 3, and 5 times over a day, and 3, 6, and 12 times over a night and day. A faster rate of increase of temperature and pH at the early stage of composting was obtained in the higher scooping up frequency, although there was very little difference in the degradability of organic matter among the experiments. It seemed that the excessive high temperature in the later stage of the experiments depressed the microorganism activities. Since the excessive scooping up at this stage tends to cause temperature decrease, we should choose a suitable scooping up frequency.

Key words: composting, garbage, static aeration rate, scooping up time, aerobic fermentation