Final answer:
The statement is true. About 70 to 80% of primary sludge total solids are volatile, which are broken down in the sludge digestion process in wastewater treatment.
Step-by-step explanation:
The statement that 70 to 80% of primary sludge total solids are usually volatile is true. In the sedimentation tank or primary clarifier of a wastewater treatment process, solids settle to form sludge. This primary sludge is then sent to solids processing facilities like digesters, where it is held for 20-30 days. During the sludge digestion process, the volume of the material is reduced, odors are diminished, and potentially disease-causing organisms are destroyed. The volatile fraction of the sludge accounts for much of the material that is broken down and often includes organic substances that decompose under the action of bacteria. The fact that a significant portion of the primary sludge's total solids is volatile is an important aspect of the waste management and treatment process, as it affects how the sludge can be processed and repurposed, for example, as fertilizer after testing for contaminants.