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Issue link: http://wateronline.epubxp.com/i/716370
By Ed St. Peter and Michael Kopper T he Kenosha Water Utility has long been a forward thinker for sustainable technology and solutions in the water and wastewater industry — in fact, on the very leading edge. In 1997 it installed what was then the largest water microfiltration purification system in the world. The installation put Kenosha ahead of regulatory requirements concerning surface water and disinfection byproducts without the use of pretreatment chemicals. Like many plants in the U.S., Kenosha's collective wastewater infrastructure was also aging. The plant first went online in 1940, with the addition of secondary treatment in 1967 and upgrades to expand capacity in 1987. More recently, due to aging infrastructure as well as an effort to combat ever-rising natural gas and electric utility costs and landfill disposal fees, the Kenosha Water Utility began to explore emerging technologies as a means of becoming more energy independent by looking to transform "waste to energy" while also reducing the volume of biosolids in need of disposal. When it came time to make critical upgrades, Kenosha set out with the confidence to venture into a state-of-the-art wastewater treatment process. That decision is already paying off. Meeting Complex Integration Challenges In all, the project would have to deliver a cost-effective and eco- friendly solution to biosolids handling, processing, and disposal. But the task was anything but simple. The biosolids handling process was to be the biggest project at the plant since the 1980s and called for a range of new technologies and their integration to: • Increase the generation of methane gas from the anaerobic digestion of sludge. • Generate electricity from the methane gas to produce greater than 500 kW of continuous power for the plant. • Use the electricity generated to offset peak energy pricing during high-demand periods. • Use electric and thermal energies to dry the biosolids to reduce the volume of biosolid cakes to 90 percent. • Reduce the volume and cost of biosolids that are land filled. • Produce high-quality biosolids that meet the criteria for Class A Biosolids for beneficial reuse. • Recover and utilize waste heat as the main thermal energy supply for the facility. At the same time, the new process and individual technologies would have to maintain the existing effluent quality and not increase the ambient noise level, odor, or particulates beyond the area of the plant. Steps To Becoming More Sustainable Over the years, initial portions of the biosolids handling process underwent rebuilds or upgrades. These included the grit system in 2009, bar screens in 2010, and three of four final clarifier drive units with the final tank being completely rebuilt in 2015. As is typical for municipal contracts, a design-bid-build model was used to complete these upgrades. But to meet the goal of becoming energy efficient while drastically reducing biosolids disposal, a design-build approach was solicited for the latest major biosolids overhaul due to the complexity of the project and varying technologies necessary to accomplish the monumental task at hand. In the request for proposal (RFP), the design/builder was tasked with preparing of the design, assisting Kenosha with all necessary permits, procuring, constructing, and installing all components, integrating of the new system with the existing plant supervisory and control data acquisition (SCADA) network, and startup and commissioning. Centrisys, a U.S. manufacturer of decanter and thickening centrifuges and dewatering systems, was awarded the contract along with J.F. Ahern, CD Smith, and Pieper as the contractors, and Donohue & Associates as the consulting engineer. The proposed plan would incorporate some technologies never before used in North America. One of the biggest challenges was procuring and integrating the varying technologies. Also adding to the complexity was the need to generate enough biogas production to meet energy-resource needs. While some biogas would be recovered through primary sludge, Centrisys offered a solution to generate additional biogas needed through waste-activated sludge (WAS). The solution came by way of sister company 38 wateronline.com n Water Innovations The Journey Toward A Sustainable Biosolids Handling Process A Kenosha, WI wastewater treatment plant leveraged innovative upgrades to become more sustainable — and save $750,000 per year.