What happens to most digested sludge in the city sewage system?

The correct option indicates that most digested sludge is often utilized as soil fertilizer. After the sewage treatment process, the sludge, which contains nutrients, is commonly processed and treated to ensure safety and stability. This treated sludge, also known as biosolids, can then be applied to agricultural land or used in landscaping to enhance soil fertility and promote plant growth.

Using digested sludge as fertilizer is a sustainable practice that recycles nutrients back into the ecosystem and helps reduce the need for chemical fertilizers. This regenerative approach not only helps in managing waste but also contributes to soil health and agricultural productivity.

In contrast, while options such as landfill and ocean dumping may occur under specific circumstances, they are generally less favorable due to environmental concerns and regulatory guidelines. Processing into soap is not a typical application for digested sludge, as the characteristics of the material do not lend themselves to this use.