equivalent inhabitants

World's largest single-phase wastewater treatment plant

The treatment of wastewater produced in the Valley of Mexico, Mexico City.

Forming part of the Valley of Mexico Water Treatment Consortium (ATVM), the ACCIONA Agua division designed, constructed, and will operate the Atotonilco Wastewater Treatment Plant for 22 years.


The Atotonilco WWTP has a nominal average treatment capacity of 35m3 per second and a maximum treatment capacity of 50m3 per second, including the final disposal of all solid waste and sludge generated. The plant is also be equipped with a cogeneration system to take advantage of the biogas produced in the digester for maximum energy saving.

The plant was designed for a maximum flow rate of 50 m3 per second during the rainy season, with its average flow rate of 42 m3 per second during the rainy season, and for 35 m3 per second during the low flow season, representing an average flow rate of 3,628,800 m3 per day and 3,024,000 m3 per day during each of the stated periods. It can treat wastewater from a population equivalent to 12,600,000 of Mexico City's inhabitants.


The plant was designed with two treatment lines in order to be able to treat water during both the low flow and rainy seasons. It has a physico-chemical treatment line for treating an average flow rate of 14.4 m3 per second during the rainy season and a conventional biological treatment line for treating an average flow rate of 27.6 m3 per second.

The sludges produced during the first settling thicken in 16 x 23 m diameter gravity thickeners, and the excess biological sludges thicken in 12 x 18 m diameter flotation thickeners. The mix of thickened sludges plus those from the physico-chemical treatment line are stabilised using 30 x 13,000 m3 unit capacity anaerobic digesters, and are then dehydrated using 12 x 100 m3 per hectare capacity centrifuges before being located in the 100 hectare single filling pond.

The plant is completed with a gas network to make use of the energy, with 7 x 8000 m3 capacity membrane gasometers and 12 x 2.7 mW electric motogenerators.

General Information

  • Location: Atotonilco, Hidalgo (Mexico)
  • Capacity: 35 m3 per second and a maximum treatment capacity of 50 m3 per second
  • Type of contract: D&C and O&M
  • Equivalent population: Over 10.5 million people

Key figures


equivalent inhabitants


m3/per day


years of D&C and O&M contract


hectares reused to irrigate


€ of total investment


At ACCIONA we are committed to innovation and we use new digital tools to communicate our projects. We take you to our facilities and show you how we care for and manage water in a sustainable way, to guarantee access to this fundamental resource in any part of the world. Discover the process that wastewater follows to be treated and the operation of one of the largest wastewater treatment facilities in the world.

Technology and innovation


ACCIONA developed a lamellar settling device with sludge recirculation in a contact turbine (DECLAMER®), which can provide high settling yields due to the formation of the right size and weight of flocs.

The settled sludge is concentrated using a centrally driven sludge scraper, fitted with thickening rods. The synergy deriving from suitable flocculation, along with a calculated percentage of recirculated sludge, applied with an adjustable speed contact turbine and lamellar settling with lamellas selected for each specific case, means that the solution can be adapted to the specific pollutant requiring removal, aiming for the best possible performance.

    Awards and recognitions

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