Abstract
Sewage sludge was collected from four wastewater treatment plants in Sapporo city; respective two plants treated the sewage with and without chemical precipitation by lime and ferric chloride. In the following, these sludges are designated as"limed sludge"and"no-limed sludge."Ashes were made from these sludge samples by 800℃ incineration. In addition to these materials, one compost derived from limed sludge was provided. Various chemical properties, especially the status of phosphorus and heavy metals, were analyzed to determine the effect of the incineration process. 1) pH was higher in limed sludges than n no-limed sludges, and lower in compost than in limed sludge. There was, however, no change in pH by the incineration treatment. 2) EC were higher in limed sludges than in no-limed sludge because of elution both of alkali and alkali-earth metals. By the incineration treatment, EC did not change in limed sludge, but were slightly increased in no-limed sludges. 3) Sewage sludges and compost contained 2.4 to 3.5% of total P_2O_5. By the incineration treatment, water-soluble P_2O_5 was decreased but acetic acid-soluble P_2O_5 and citric acid-soluble P_2O_5 were increased 1.2-4.8 and 1.1-1.8 times, respectively. 4) Some heavy metals which possess relative low-boiling point were evaporated by incineration treatment. Heavy metal which possess relative low-boiling point were ashes were, however, in the order of Fe>Al>Mn>Zn>Cu>Cr>Pb≒Ni>Co>Dd, in general. 5) The incineration treatment was very effective in insolubilization of heavy metals contained in sewage sludge, since it decreased significantly water-soluble, exchangeable and absorbed fractions, except Cr, and increased insoluble fraction.
