Dover Wastewater Treatment Facility Generates Green Energy
Treated effluent is more than water in a pipeline; it’s a potential source of clean renewable energy. While conventional-design hydro turbine generators have been considered for years as a means to scavenge and harvest this potential power source, the challenge posed by the fluctuating flow environment and has more often than not rendered this technology impractical and not cost effective. However, preliminary project data compiled at the City of Dover Wastewater Treatment Facility relating to the power production of a new hydrokinetic turbine generator is providing a reason to consider treated effluent as a cost-effective source of clean, renewable electrical energy for smaller and mid-size operations.
Background
Since the mid-1990s, the City of Dover has been actively engaged in an overall energy upgrade program, which has included measures to increase efficiency and promote the use of clean, renewable sources. In 2011, in alignment with the city’s overall green energy improvement efforts, the management of the wastewater treatment facility decided to consider the installation of a hydro turbine generator to attempt to cost-effectively capture the potential power contained in the moving treated effluent. The facility is comprised of primary clarifiers, conventional activated sludge secondary treatment, secondary clarifiers, and ultraviolet disinfection. The system discharges approximately 2.95 million gallons daily of treated effluent through its outfall pipe, which has a vertical drop of nearly 60 feet. The intention was to utilize any generated electricity on site for operational use.
During the project evaluation process, the city was presented with the opportunity to pilot test a new type of hydro turbine generator design, known as the W4e. Walker Wellington LLC, an equipment supplier to treatment facilities for more than 25 years, developed the technology in conjunction with the inventor, Benjamin Brickett, for use in wastewater treatment effluent lines and related applications with low-head/variable flow conditions in order to provide smaller and mid-size operations the opportunity to generate cost-effective, clean, renewable energy.
This project received grant funding through the State of New Hampshire’s 2011 Green Launching Pad.
Technology
The W4e has been recognized as an innovative small-hydro power technology by the U.S. Department of Energy. It is an inline, direct drive, hydrokinetic turbine generator. Features include:
Variable pitch control mechanism. As flow rates and head pressure change throughout the day, the turbine blades automatically open and close optimizing the production of energy from the power available from the water stream.
Variable force generator. The level of generator engagement is regulated by the automatic adjustment of the proximity of the magnet embedded rotor to the stator in response to water flow conditions in the pipeline. This eliminates high start-up torque and allows the turbine to maintain safe operational generator speed.
Simplicity/Robustness. The W4e is a simple electro/mechanical (essentially one moving part) technology designed with the goal of low operational and maintenance requirements as well as low life-cycle costs.
Modular/Scaleable. The W4e can be customized to match various pipe sizes and flow conditions found at most facilities by varying the number and size of blades, coils, magnets, and generator rings.
Initial Results
The W4e was installed during the first week of December 2011 in the outfall pipe at the second of three manholes, with an approximate elevation of 15 feet below the disinfection building. Due to existing space constraints, only two generator rings have been mounted on the unit for the initial installation phase. Nevertheless, preliminary results are encouraging.
Now that the unit has met certain initial installation phase objectives, consideration is being given to either (1) relocating the unit to the end of the outfall pipe or (2) keeping the unit at the existing manhole location and installing a second unit at the end of the outfall pipe to explore the efficacy of two units operating in tandem. It is projected that either of these approaches would result in a minimum yield of 14-16 kilowatts with a corresponding minimum annual savings of $14,000 to $16,000 based on current electricity pricing.
Moving Forward
The City of Dover Wastewater Treatment Facility has been very pleased to allow this project to be implemented at its site. The obvious reasons include the anticipated annual electricity cost savings and the contribution toward the city’s green energy initiative. But there is more. Through the use of viable advanced hydro turbine generator technology, small to mid-sized treatment facilities can cost-effectively scavenge and harvest clean, renewable energy resulting in utility savings for countless communities and reduction in carbon emissions to the benefit of us all.
Raymond Vermette is the Supervisor for the City of Dover’s Wastewater Treatment Facility. To view turbine specifications, photographs and diagrams, visit www.W4ehydropower.com.