Trenching of Digested Sludge

Effects of trenching digested sludge were evaluated for 4 yr. Digested sludge buried in trenches that were 2 ft (0.6m) wide by 2 ft (0.6m) deep and 2 ft (0.6m) apart was sampled along with the surrounding soil and analyzed for N, Cl, and heavy metals. Most of the Cl leached into the profile during the first 2 yr. After 4 yr, nearly all the Cl leached from the sludge and surrounding soil profile. More N leached from the sludge in the first 2 yr than the second 2 yr. After 4 yr, the sludge was nearly stabilized as judged from its mineralization rate. Zinc was the only heavy metal found in detectable levels in the soil profile beneath the trenches. The amount of Zn leached was minor as compared with the total Zn levels in the entrenched sludge.