Casas Viejas Wastewater Treatment Plant, San Pablo Tolimán, Querétaro, Mexico

Casas Viejas is a wastewater treatment plant located in San Pablo Tolimán, within the municipality of Tolimán, Querétaro, Mexico. The plant serves a population of 2,755 people, making it a small-scale facility in the region. It operates under Mexico's national water regulations, which require secondary treatment for municipal wastewater to protect public health and the environment. The plant provides secondary treatment, a standard biological process that removes organic matter and suspended solids. With a designed capacity of 691.20 m³/day and an actual discharge volume of 815.62 m³/day, the plant operates slightly above its nominal capacity, indicating potential stress on the system. As a small agglomeration, it is subject to Mexican Official Standards (NOM-001-SEMARNAT-1996) that set limits on pollutants in treated wastewater. The treated effluent is discharged into local water bodies, likely tributaries of the Moctezuma River, which flows into the Pánuco River and eventually reaches the Gulf of Mexico. The plant plays a crucial role in protecting the local watershed from untreated sewage, supporting downstream ecosystems and communities that rely on these water resources.

The plant discharges into the Moctezuma River basin, part of the larger Pánuco River system that drains into the Gulf of Mexico. This watershed supports diverse aquatic life and provides water for agriculture and human consumption in the semi-arid region of Querétaro. The secondary treatment reduces organic pollution, but the plant's operation above design capacity may pose risks to downstream water quality, particularly during low-flow periods.