Atotonilco Wastewater Treatment Project, Mexico


On 7 January 2010, the National Water Commission of Mexico, Conagua, signed agreements with a consortium of companies to construct a new wastewater treatment plant in Atotonilco, Hidalgo, Mexico. The plant will be the largest wastewater treatment project in Mexico and one of largest of its kind in the world.

The $710m (MXN9.3bn) wastewater treatment plant will be built in two phases on a build-operate-transfer (BOT) basis at Atotonilco town, about 60km from Mexico City. The installed treatment capacity in the Atotonilco area is currently 11.6% per day.

The new plant will be able to treat 3.6m tons of water per day, raising the installed treatment capacity of the town to 60%. In the first phase, the plant will treat wastewater at the rate of 23m3/s. The treatment capacity will be increased by 12m3/s in the second phase.

Preliminary construction works commenced in 2010. First phase of the project was completed in 2013 and the second phase construction is expected to be completed in the second half of 2014. The commercial operation of the wastewater treatment plant will start is expected to begin in early 2015.

Mexico wastewater project background

The Hidalgo state is one of the principal sources of agriculture in Mexico. The alfalfa fields in the region are irrigated by using the untreated wastewater released from the metropolitan areas of Mexico City, which has been a major concern causing health problems and environmental pollution. To overcome these problems, the Atotonilco project was taken up as part of the Sustainable Water Programme for the Mexico Valley.

The Sustainable Water Programme also includes the construction of another five water treatment plants in the Valley of Mexico to attain its goal to treat 100% of the wastewaters of municipalities by 2020 and of industries by 2025.

Atotonilco wastewater treatment project

The Atotonilco project will provide treated water for irrigation of around 80,000ha in the Tula Valley of Hidalgo. It will improve living conditions of approximately 300,000 inhabitants in the region, who do not have access to treated water.

"The Atotonilco wastewater plant will raise the installed treatment capacity of the town to 60%."

The project will also hygienise 60% of wastewater from the metropolitan areas of Mexico City, which has a population of 20m. The Atotonilco project will thus significantly improve the environmental conditions and raise the overall water treatment rate of the country from 36% to 60%.

The contracts for the BOT project were awarded to an IDEAL-led consortium through international bidding in December 2009 against the OHL Medio Ambiente consortium.

The consortium is responsible to design, execute, construct and install all electromechanical equipment, as well as test the operations. The construction will take approximately three years and the consortium will operate, conserve and maintain the water treatment plant for 22 years. The scope of work also includes the cogeneration of electricity at the plant and the disposal of sludge. The project is estimated to generate 7,000 direct and indirect jobs during the construction phase.

Wastewater biological treatment

The plant will use biological treatment to treat around 1.99m m³ a day. It will have a primary treatment capacity of 1m m³ a day for use in wet weather conditions, which is expandable to 2.5m m³. The plant's total design capacity is around 4.5m m³ a day.

The average wastewater treatment capacity of the plant will be up to 42m³/s. The average dry season treatment capacity is expected to be 23m³/s and during wet conditions, the capacity will be increased to 35m³/s using a physical-chemical process. The plant's operations will also include evacuation of the solid waste and the sludge generated.

The plant will have a cogeneration system to convert the biogas (methane) produced during the digestion process for maximum energy efficiency.

Atotonilco plant key players

Aguas Tratadas del Valle de Mexico (ATVM) is the consortium formed to implement the project. The consortium will construct and operate the Atotonilco wastewater treatment plant for 22 years as per an agreement with the National Water Commission of Mexico (CONAGUA), an agency under the Ministry of the Environment and Natural Resources (SEMARNAT).

"The Atotonilco project will hygienise 60% of wastewater from the metropolitan areas."

The consortium is led by Impulsora del Desarrollo y el Empleo en America Latina (IDEAL), which holds a 40.8% stake in ATVM. IDEAL will realise the Atotonilco wastewater treatment project through its Promotora del Desarrollo de América Latina unit.

The stake holders in ATVM include Acciona Agua (24.26%), Atlatec (24.26%), which is a subsidiary of Mitsui & Co and Toyo Engineering, and ICA subsidiary Controladora de Operaciones de Infraestructura (10.2%), DYCUS and other minority investors.

The project is being funded by Mexico's national development fund, FONADIN, which will finance around 46% of the total cost, 51.66% by the consortium partners and the remaining through commercial bank credit.

On 18 January 2010, Green Gas was awarded the contract for the construction, operation and maintenance of combined heat and power (CHP) plants at the wastewater treatment plant. The greenhouse gas methane released by the wastewater will be used for generating heat and electricity through the CHP plants. The plants will have a 33MW capacity and will help to reduce greenhouse gas emissions by around 1m tons of CO2 per year.

In December 2010, Conagua awarded a $14.5m contract to a consortium of Ayesa, Exito, FOA and Canal de Isabel II. Under the contract, the consortium will undertake supervision, engineering and commissioning works of the plant.