Most municipal sewage in the United States is subjected to

The answer is 'sewage treatment'. Sewage treatment plants treat the municipal sewage produced by most large towns and cities. These treatment plants use biological systems to break down waste and remove some of the more damaging constituents, such as pathogens and certain chemicals, such as pharmaceuticals. Also removed as much as possible are nutrients such as nitrates and phosphates. Treatment is implemented as treated waste is most often released to the environment, usually into rivers or the ocean. Raw sewage or incompletely treated effluent can be hugely damaging to aquatic environments and human health. Diseases such as cholera can be spread by municipal waste.