Staying inside the lines
Racine, Wis., more than doubled its peak wastewater treatment capacity last fall without expanding the boundaries of its treatment plant site. By changing its wastewater treatment method, adding a computer management system, redesigning buildings and squeezing new components onto the property, the city is prepared to accommodate future growth over the next two decades.
Racine, a community of 81,500 residents on the shores of Lake Michigan between Milwaukee and Chicago, has been growing at an average rate of 1.25 percent per year in the last 40 years, and that trend is expected to increase to a rate of 2 percent per year for the next 20 years. The Racine Wastewater Utility serves 127,600 residents in six communities, including Racine, Mount Pleasant, Yorkville, Caledonia, Sturtevant and North Park. Faced with increasing wastewater treatment flows, the utility sought to expand its peak system capacity from 70 million gallons per day (mgd) to nearly 200 mgd. However, confined by neighborhoods on two sides and the lake on the other two, the treatment plant facilities did not have any room to grow beyond their existing boundaries.
In March 2001, the utility contracted with the local office of Long Beach, Calif.-based Earth Tech and Brookfield, Wis.-based Applied Technologies to design an expansion on the already crowded site. Then, Racine signed an intergovernmental agreement with its neighboring communities to allocate capacities and costs for the new $45 million facility. To pay for the project, the communities increased sewer user charges by an average of 10 percent and took out low-interest, revolving fund loans from the state.
Finding a spot for a new anaerobic digester tank (the part of the decomposition process where solids are broken down) was the primary challenge with the expansion. The tight space that was available in the anaerobic digestion area could not accommodate a new tank with common dimensions and construction techniques. So, designers called for a smaller diameter, but much taller, tank to reduce the volume of remaining residuals. They chose a pre-stressed tank, which helped during construction because it could be partially fabricated off-site.
The facility’s chlorine gas disinfection system was converted to one using ultraviolet light, which eliminated on-site storage of hazardous chlorine gas. The change improved safety for treatment plant staff and nearby residents, and saved site space as well.
Buildings were reused, and some were transformed from their original purpose. Administrative offices and the main facility control room were moved to a building that previously housed the first stage of the treatment system — the bar screens and grit removal facilities — which was moved to a new, 15,000-square-foot structure to better contain odors. To accommodate a new on-site laboratory, the garage and maintenance facility was redesigned, and the garage was moved to a new building a few blocks away.
The plant added a new supervisory control of data acquisition computer system to consolidate plant operations in one control room. The software connects all plant functions on a fiber optic backbone, so operational changes can be made from one location, as well as other satellite stations throughout the plant.
Dedicated in August 2005, the plant so far has successfully treated peak flows of up to 100 mgd, which is 30 percent greater than the previous peak flow capacity of the plant. Process improvements and enhancements have improved overall treatment performance, and computer automation has reduced operating costs. “The true success of this project was the buy-in from my senior level staff,” said Keith Haas, chief of operations for Racine Wastewater. “They made the plant perform day to day during adverse construction issues for the three-year effort. Because of their involvement in the design and construction phases, the completed project met with their approval and continues to be a pleasure to operate and maintain.”