Question

what is the main purpose of preliminary treatment in sewage treatment plants?
to remove large objects and debris
to disinfect the water
to add nutrients to the water
to increase water flow rate

Explanation:

Preliminary treatment in sewage - treatment plants aims to remove large objects like rags, sticks, and debris that could damage downstream equipment. Disinfection is a later - stage process, adding nutrients is not a goal of preliminary treatment, and increasing water flow rate is not the main purpose.

Answer:

to remove large objects and debris