PURPOSE: To inexpensively supply a deodorizing and dehumidifying treating agent for sludge, by using combustion fly ash as a stock material.

CONSTITUTION: Stock ash (consisting of SiO2, Fe and Fe2O3) is screened to remove carbon and other particles. Subsequently, Fe and Fe2O3 are removed by a plate shaped magnetic separator. In the next step, the treated ash is subjected to heat treatment at 1,000W1,050°C in a fluidized bed for 1.5W2hr while oxygen is sufficiently introduced. Thereafter, the heat treated ash is allowed to cool at once and 1N NH4Cl is added under stirring to obtain precipitated ash. This precipitated ash is sufficiently washed with water and, after dehydration, 10% Al2O3 is added while the resulting mixture is kneaded by a ball mill and vacuum dried.