Energy Management Techniques and Outcomes at the Metropolitan Water Reclamation District of Greater Chicago

Implementation of an aggressive energy management program has always been a priority of the Metropolitan Water Reclamation District of Greater Chicago (District). The District is a large consumer of energy in order to conduct its mandated operations of wastewater treatment, flood control and waterway management for the Cook County area. The District, as a municipal entity, is responsible to the taxpayer for fiscal management and operation; and energy conservation is one way to do that. Energy conservation has taken on a new significance and sense of urgency with the recently recognized threat of global warming. Energy conservation at the District facilities also results in a reduction of pollutant emissions that threaten air quality and helps to conserve our natural resources, which are being depleted. Many of the energy management techniques already in place at the District produce desired outcomes for promoting sustainability and reducing the potential for global warming.While purposeful reduction of energy is one method to conserve resources, the District also looks to finding internal energy sources to use or reuse. The anaerobic sludge digestion process used by the District produces a significant amount of digester gas that is captured and distributed to boilers for use in heating District buildings. The production of digester gas can be maximized by careful control of time and temperature in the digestion process.Better control of treatment processes can result in energy conservation. The process control system at the Egan Water Reclamation Plant (WRP) was upgraded with a state-of-the-art Distributed Control System (DCS) enabling automatic dissolved oxygen control to be reestablished in the aeration process. This has resulted in a more efficient process, with lower air usage and consequently, less energy required for blower operation. Modifications of existing dissolved oxygen controls together with installation of state of the art blowers at the Stickney, North Side and Calumet Water Reclamation Plants, will result in a more efficient blower operation, thus reducing power requirements in the near future.Diligent maintenance of infrastructure can avoid energy loss. A leaking air main at the Hanover Park WRP resulted in increased air demand and associated electrical usage and cost. Installing new seals in the joints of air mains has eliminated air main leaks. This has also resulted in the ability to operate only two blowers, rather than the previously required three, with the consequent energy reduction. It is important to recognize the huge role that proper maintenance and a little ingenuity can have on energy usage.Since 1997, the District has participated in the Energy Cooperative Programs offered by the Commonwealth Edison Company (ComEd), a local electric utility. By voluntarily curtailing usage during short-lived peak demands, ComEd is able to defer the need for additional generating capacity. In return, the District receives monetary compensation based on the load curtailed.