Which of the following is not an advantage of the land disposal of digested sewage (sludge)?

The option indicating the build-up of heavy metals in the soil is not considered an advantage of the land disposal of digested sewage sludge. This is because while the application of digested sludge can enhance soil nutrient content and improve soil structure—leading to better aeration and erosion control—heavy metal accumulation presents a significant environmental and health concern.

When sewage sludge contains heavy metals, repeated application to soil may lead to the bioaccumulation of these metals in plants and organisms, potentially entering the food chain and causing adverse health effects in humans and wildlife. Thus, while the beneficial aspects of land application, such as nutrient addition and soil improvement, are recognized, the accumulation of heavy metals highlights a critical disadvantage that overshadows the positive environmental impacts associated with the practice.