Carbonized sewage sludge has more advantages in terms of storage and transportation than dewatered sewage sludge, but no detailed studies have so far been conducted on the former. Dewatered sewage sludge was collected from Gifu City and Takasu Village in Gifu Prefecture. The dewatered sewage sludge was heated to several temperature ranges (300-700 degreesC) to produce the carbonized sewage sludge. Then, their chemical and physical properties were measured. Total nitrogen, EC, C/N ratio, etc. were found to vary with the site and time of collection, and the carbonizing temperature. For example, the total nitrogen content varied from 3% to 7%. Furthermore, the carbonized sewage sludge from Takasu Village was two times harder and 1.5 times denser than that from Gifu City. Thus. the carbonized sewage sludge from Gifu City was higher in porosity than that obtained from Takasu Village. Upland rice, grown in 1/5000a Wagner pot, was used as an indicator for evaluating the effect of the fertilizer. The rice seeds were sown in the pots with different amounts of 300 degreesC carbonized sewage sludge, 3 g and 6 g of total nitrogen per pot. Thirty days after sowing, top dry weight and SPAD (Soil & Plant Analyzer Development: measurement apparatus for chlorophyll content) value were higher in the sewage sludge from Gifu City compared with that from Takasu Village. The observed difference in fertilizer effect between the two sewage sludges on rice growth may be explained by their difference in chemical properties and porosity amount.
