Primary treatment of wastewater is primarily a __________ process.

The primary treatment of wastewater is primarily a physical process. This stage typically involves the removal of large solids and debris from the wastewater through processes such as screening, sedimentation, and grit removal. These physical processes work to separate particles based on size and density. For instance, sedimentation allows heavier solids to settle at the bottom of a tank, while lighter materials may be removed through skimming.

In contrast, biological processes, which involve the breakdown of organic matter by microorganisms, occur primarily during secondary treatment. Chemical treatment methods also play a role in wastewater treatment but are generally involved later in the process or under specific circumstances for disinfecting or nutrient removal. Thermal processes are not commonly associated with primary wastewater treatment. Thus, identifying primary treatment as a physical process highlights its focus on mechanical and gravitational techniques to enhance the quality of wastewater before it undergoes further treatment stages.