https://www.nhbr.com/the-importance-of-local-limits-for-our-wastewater-systems/

Clean water is essential to our environment and quality of life. The National Pollutant Discharge Elimination System (NPDES) includes National Pretreatment Program elements developed by USEPA to control pollutant discharges from Publicly Owned Treatment Works (POTWs) into the nation’s waterways. In other words, the National Pretreatment Program is an important program which includes specific regulatory tools to keep our water clean all over the country.

POTWs must ensure compliance with federal pretreatment standards by regulating non-domestic (industrial and commercial) users, such as pharmaceutical manufacturers, metal finishers and breweries, to name a few. Local limits are intended to keep POTWs in compliance with NPDES permits and to prevent operational issues at wastewater treatment facilities and within the wastewater collection system. Pollutants incompatible with treatment works can cause major disruptions to the collection system and treatment works and contribute to permit violations.