The DePere Wastewater Treatment Plant (WWTP) is located on a 23-acre site on the west side of the Fox River at the north end of DePere, Wis., and services DePere and the city of Ashwaubenon, as well as part of the town of Hobart, and the Lawrence, Ledgeview and Oneida townships. The plant has a two-stage activated sludge process with tertiary filtration and UV disinfection designed to treat from an average of
9.5 million gal per day (mgd) up to a 30-mgd peak flow rate.
Since 1997, the plant has been undergoing a series of upgrades designed to enable it to provide the highest quality treatment at the lowest cost to its customers. The last of the planned upgrades was completed in October 2004 with an aeration system upgrade. The goals of the project were to increase the efficiency of the aeration system, increase the reliability of the power supply system by eliminating the need for medium voltage switchgear, reduce air supply system maintenance and reduce operating costs.
Turbocompressor replacement
Because 80% of the energy costs associated with an activated sludge plant is directly related to the blowers that furnish air to the aeration system, the plant’s five aging, multistage blowers that had reached the end of their useful life were targeted for either a major rebuild or replacement. The plant manager, Mike Kiersten, decided that replacement was the best option and began searching
for replacement blowers that would meet the project goals.
When the evaluation was completed, six model S9000-1-H-5 high-speed technology (HST) integral turbocompressors manufactured by High Speed Technology Oy (a company owned by ABS) were chosen. The evaluation included not only the blowers’ initial capital cost but also installation costs, energy usage costs, maintenance costs, system reliability and supply voltage. It was estimated that the turbocompressors would decrease the plant’s energy cost by $40,000 to $50,000 per year—a 35% reduction—and reduce maintenance costs by 45% while meeting or exceeding all other project goals. The turbocompressors could do this because they virtually eliminate maintenance and provide the highest available reliability through the use of a non-contact magnetic bearing design.
The units also have VFD speed control that automatically keeps the technology operating at optimum efficiency while meeting process demands, as well as real-time monitoring system that assures the HST will operate reliably.
As a result of installing the turbocompressors and other similar innovative equipment, the DePere WWTP has received five prestigious awards. They include the U.S. Environmental Protection Agency Regional Award for excellence in operation and maintenance, the WDNR Brogan Award for excellence in environmental achievement, the National Energy Watch Award, the Clean Bay Backer Award and the Brown County Conservation Alliance Award.
Additional benefits
Along with reduction in costs, the DePere WWTP has experienced a significant reduction in noise levels in the blower building since installing the six turbocompressors. The previous noise level was in excess of 100 dBA, and now it is less than 75 dBA with all six blowers operating. Magnetic bearing technology used in the turbocompressors eliminated the vibration that existed in the previous blowers that had conventional bearings, which made being in the blower building very difficult for any length of time.
Other benefits are the elimination of periodic lubrication system maintenance and an automated control system that assures the blowers will always operate at their best efficiency. Also, efficiency remains constant throughout the compressors’ useful life because there is no contact of rotating parts, eliminating wear of critical parts that reduced efficiency over the lifetime of previous blowers.
Meeting the goal
This new replacement technology has not only helped the DePere WWTP receive several awards but has also assisted in meeting its primary goal of providing its customers with the highest quality treatment at the lowest cost.
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