The Ejby Mølle Wastewater Treatment Plant (EMWWTP) is the largest treatment facility in Odense, Denmark with a treatment capacity of 385,000 population equivalents. The load to the plant is mainly of domestic origin and it discharges to a small river with very stringent effluent requirements. VandCenter Syd (VCS) Denmark is the provider of water and wastewater services for Odense and operates the EMWWTP.

VCS is a very progressive utility, striving to become a model for the incorporation of sustainability principles in discharging its responsibilities. To this end, it has adopted a goal of achieving CO2 neutrality firm-wide by 2014. Through its own efforts, VCS was able to implement changes in the facilities and operations of the EMWWTP and achieve a very impressive level of 77% energy self-sufficiency.

In 2012, VCS selected CH2M HILL along with another global engineering firm to execute a project aimed at identifying additional energy optimization opportunities (EOOs) at the EMWWTP that would further facilitate the achievement of their declared corporate goal. The adopted approach by the combined utility/consultant team aimed to develop a comprehensive electrical energy consumption profile and identify EOOs that relied primarily on relatively quick-to-implement process modifications, which would significantly reduce electrical power consumption and/or increase power generation from cogeneration. The approach also identified (but did not fully develop) more complex improvements that could be considered for future implementation.

Ejby Molle WWTP 2011 Annual Average Electrical Consumption

The team relied on the CH2M HILL Pro2D tool (which incorporates ASM and ADM modeling relationships) to facilitate a whole-plant integrated model for the identification, prioritization, and eventual development of the selected EOOs. With this tool, the project team quickly and thoroughly evaluated multiple process re-configuration scenarios as well as the impact of implementing operational modifications to existing systems – making sure that the stringent effluent requirements were always met, while also measuring improvements against pre-established metrics for energy demand, energy generation, and carbon footprint.

A list of 35 potential EOOs was identified using the Pro2D tool. The EOOs were broadly grouped under the general categories of process modifications, equipment improvements, and increased power generation. The EOOs identified were not only readily implemented (some requiring minor facility modifications), but placed the EMWWTP essentially in an energy self-sufficient status – a significant contribution towards the realization of VCS’s aggressive corporate environmental goal.

Implementation of these recommendations have confirmed the predictions made by the model, and for some months even have resulted in a slight net positive energy balance (approximately 104%) for the plant. The Ejby Mølle project serves as an example of how to approach similar energy optimization projects: relying on modeling tools to facilitate comprehensive alterative evaluations, concentrating on maximizing the use of existing valuable assets and focusing in the modification of operational strategies – without sacrificing effluent quality.