The WWTP of Piedras Negras is located in the state of Coahuila (Mexico).
The works began in 2000 in the framework of Cross-border cooperation between the USA and Mexico. The wastewater from the city of Piedras Negras was poured into the Rio Bravo, which in this area forms the natural border between the two countries and later, the river enters again in the USA territory, and at that moment carried with him the polluted waters due to its passage through Piedras Negras.
The WWTP of Piedras Negras has the following treatment steps, which are listed below following the water line: