Factors Affecting the Stabilization Period of Sewage Sludge in Soil with Reference to the Gel Chromatographic Pattern

Abstract

Effects of the sludge loading rate, soil properties, dewatering agent in sludge, and incubation temperature on the stabiIization period of dewatered sewage sludge in soil were investigated with reference to the gel chromatographic patterns of the water extracts from the soil-sludge mixtures. The stabiIization period was defined as the period until which a specific pattern of the gel chromatogram appears, indicating both the presence of small amounts of free ammonia and the accumulation of nitrate nitrogen in soil. A high sludge loading rate above 5% resulted in a longer stabilization period, especially in the Fujimi loamy coarse sand soil. The stabiIization period was shorter in the Hiratsuka coarse sandy loam soil than in the other two kinds of soils (Fujimi loamy coarse sand soil and Sekiya fine sandy loam soil). Lime, used as a dewatering agent, shortened the stabiIization period at low sludge loading rates, but prolonged it at high sludge loading rates, compared with a polymeric organic coagulant. Temperature was the most significant factor to affect the stabilization period. As the temperature decreased from 25 to 5°C, the period of stabilization increased drastically. The stabiIization process of sewage sludge in soil was interpreted as a process of nitrogen transformation consisting of ammonification and nitrification. The limiting step in the stabiIization process was the nitrification step. The period was prolonged whenever nitrification was inhibited, while ammonification was little inhibited except at a low temperature.