By incorporating methane-producing digesters into its municipal waste water treatment system, Chicago is looking to offset a large part of its energy consumption and the associated cost.

Smart City: Chicago developing an energy-neutral water treatment system

Chicago’s municipal authorities are working on plans to generate energy from the city’s waste water. Every day around 1.2 billion gallons pass through the pipes of the city’s Stickney water treatment plant, which is the largest in the world and requires large amounts of energy to operate. Now the engineering team at Chicago’s Metropolitan Water Reclamation District (MWRD) have set the goal of making their system completely energy neutral by 2023 and thus helping to reduce the city’s huge $50 million annual electricity bill.

L'usine Calumet aux abords de Chicago

The Calumet plant near Chicago, where the MWRD is developing its methane digesters (MWRD)

In order to do so, Chicago is planning first of all to invest $10 million at its smaller Calumet plant, expanding a system which combines water treatment with anaerobic bacterial digesters that produce biogas (methane) from the organic matter in the waste water. This methane will then be used to meet part of the MWRD’s onsite energy needs and surplus gas can potentially be sold to the local grid. Meanwhile the solid digestate produced from the process, in the form of dry compost, will be re-used as natural fertiliser for the city’s green spaces and farms in the vicinity. If the Calumet pilot project demonstrates the viability of this approach, the Chicago authorities intend to extend it to other water treatment plants, with the prospect that the biogas could eventually be used to meet up to three-quarters of the MWRD’s energy needs.

In similar vein to the HORSE portable composting unit, this initiative is designed to help optimise municipal resources and is thus a significant further step towards the Smart City. 

By Pauline Canteneur