Atotonilco Wastewater Treatment Plan

The Atotonilco Wastewater Treatment Plant (WWTP) is located in Atotonilco de Tula, in Hidalgo, Mexico and occupies an area of 158.5ha. The WWTP is the world’s third largest in water treatment capacity and the largest sewage and wastewater treatment project in Mexico.

The WWTP has been designed for a treatment flow of 35 (med) to 50 (max) cubic meters per second from a population of 12.6 million people in Mexico City. This capacity corresponds to the 60% of the total wastewater generated in the Valley of Mexico.

The treatment is comprised by two systems:

• The Chemical Physical Treatment line consists of pre-treatment, sedimentation with coagulation/flocculation and chlorination.
• The Conventional Biological Treatment line consists of pre-treatment, primary sedimentation, activated sludge, secondary sedimentation and chlorination.

The WWTP reports significant benefits for the region through the sanitation and ecological restoration of the Tula river and the Endho dam reservoir. Historically, the region has received the wastewater and without undergoing any treatment, has been utilised in agriculture thorough the flood irrigation method, which poses serious health and environmental risks.

The Atotonilco WWTP provides better health conditions for over 700’000 people from the surrounding communities, reducing contamination and improving epidemiological control, allowing cleaner cultivation practices and the recharge of the aquifers with higher quality water.

The WWTP was designed to be self-sustaining, through generation of its own energy, minimising energy required from the public network, reducing CO2 emissions by an estimated 400,000 ton/year.

A specialised network collects the biogas generated in the solid’s stabilization process carried out in digesters through 12 generators:

• Consumption: 245 GWh/year
• Generation: 197 GWh/year

Furthermore, the generated solid waste produced during treatment is sent to a landfill. This waste material has suitable characteristics for agriculture soil enhancement and is provided free of charge to the local communities. Management has also promoted the efficient use of water, including stormwater collection and reuse for the WWTP operations, cutting external supply requirements by an estimated 92.5%. Efforts were also placed in reforestation, which mitigates soil erosion.