An innovative technology for sewage treatment systems is proposed. A mixture of sewage sludge and char particle is subjected to drying in the progress of composting in an updraft column. Exothermic heat generated during composting is utilized for energy of sludge drying. The char particle in the mixture contributes to enhancement of composting and drying rate. This study presents drying and composting behaviors of sludge to examine the effect of char addition. A fundamental drying experiment was carried out by hot-air heating of the sample in a small vessel. The drying characteristic curve for a mixture of sludge and char was greater than the sample of only sludge over a whole period if the drying rates were compared with the same moisture content. The drying behavior could be analyzed with a reasonable agreement by the water front receding model. The enhancement effect of drying and composting of sludge by char addition was confirmed by examination using a pilot scale of the updraft column whose volume was 50 m 3 . Sludge with 400% dry base (80% wet base) in moisture content could be dried successfully to lower moisture content than 67% dry base (40% wet base) only by exothermic heat during composting without supplying any auxiliary energy from the outside, and the treatment time was reduced by mixing char in sludge. The behavior was analyzed with a satisfactory agreement by a theoretical model employing moisture diffusion parameters determined from the drying characteristic curve.
In order to evaluate nitrogen and sulfur behavior during carbonization, carbonization experiment with bio-dried sludge was conducted in a horizontal lab-scale reactor and rotary kiln. Bio-dried sludge dried by using fermentation was used as the carbonization material. Carbonization temperature was changed from 573 to 1173K, and the effect of steam introduction on the elements behavior during the carbonization process was revealed. Nitrogen in the bio-dried sludge decomposed linearly with rising treatment temperature, and more than 90% of nitrogen decomposed at the 1173 K temperature. Sulfur in bio-dried sludge decreased slowly with increasing treatment temperature, but the decreasing ratio was insignificant against the carbonization temperature. Around 70 % of sulfur remained in the char after the carbonization at 1173 K. Sulfur behavior was changed when the steam was introduced during the carbonization. Sulfur content in the char was decreased significantly.
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