Factors Affecting the Decomposition of an Anaerobically Digested Sewage Sludge in Soil
1974
Carbon dioxide evolution was used as a measure of the rate at which anaerobically digested sewage sludge is decomposed in soils. Variables included soil texture, moisture content (1/3 bar and saturated), loading rate (90 and 224/metric ton of dry sludge per ha), incubation time (1, 3, and 6 months), and temperature. Incubation temperatures were programmed to provide both diurnal and seasonal temperature variations. Sewage sludge was rather resistant to further decomposition with a maximum of 20% of the added carbon evolved as CO₂ during a 6 months incubation. At the high rates employed, the rate of decomposition of sewage sludge was largely independent of differences in soil texture or chemical properties. Soil moisture content did not affect sludge decomposition in a sandy soil, but saturated conditions reduced it moderately in a silt loam soil and almost completely stopped decomposition in a clay soil. Soil temperature was the major factor influencing the rate of sewage sludge decomposition. A plot of the percentage sludge carbon evolved as CO₂ vs monthly degree days was used to predict the amount of sewage sludge which would be decomposed per unit time at different soil temperatures.
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