The feasibility of planting on stabilized sludge-amended soil

The feasibility of growing plants on stabilized anaerobically-digested sludge from a local secondary sewage treatment plant (STP) and stabilized chemically-modified sludge from a pilot chemically-assisted primary treatment plant were studied. Apropyron elongatum (tall wheat grass) was used in this research study. A sandy soil obtained locally was amended by the addition of the lime/pulverized fuel ash (PFA) stabilized sewage sludge at the rates of 0, 25, 50, 100, and 200 g/kg. The total shoot yield of the grass harvested from the amended soil was significantly higher than that of the natural soil (except chemically-modified sludge 200 g/kg). The optimum application rates that achieved the highest yield for digested sludge and chemically-modified sludge-amended soils were 50 g/kg and 25 g/kg, respectively. Applying the stabilized digested sludge to the soil reduced Zn, Cr, and P but increased Cu, Cd, N, and K concentrations in the root tissues of the grass. The Ni, Cr, B, and K concentrations in the shoot were increased with the addition of stabilized digested sludge-amended soil. For the chemically-modified sludge samples, the concentrations of the metal contaminants as well as the nutrient levels of the crops (both in the shoot and root tissues) grown in the stabilized amended soil were increased as compared to the control. However, all the trace metal concentrations in the crop were below stipulated toxicity levels. The experimental results indicate that it is feasible to plant on a mixture of natural soil and stabilized sewage sludge provided the dosage applied is carefully controlled.