The process of wastewater treatment is commonly called treatment.

sewage

The correct answer is Option (1) - sewage

The process of wastewater treatment is commonly called sewage treatment. Wastewater treatment, often referred to as sewage treatment, is the process of removing contaminants and pollutants from wastewater before it is released back into the environment or reused for various purposes. This process involves several physical, chemical, and biological processes aimed at reducing the harmful effects of wastewater on the environment and public health.