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Issue link: http://wateronline.epubxp.com/i/716370
CNP-Technology Water and Biosolids Corporation's PONDUS thermo-chemical hydrolysis process (TCHP), which uses chemicals and thermal energy to hydrolyze the WAS stream to achieve biogas production. Another critical step was the addition of a second THK 200 thickening centrifuge — one for primary sludge thickening to complement the one already installed (in 2013) for WAS thickening. Combined, the thickening technology would work to reduce the liquid volume within the sludge stream and thicken the sludge before entering the primary anaerobic digesters. This thickening technology would yield a concentration of 7 percent solids compared to the 3 to 4 percent solids produced by the older dissolved air flotation thickening (DAFT) system. With thicker sludge, less water would be sent to the digesters, reducing the number of tanks needed from six to three, lowering heat and energy costs. Combining these technologies, a pair of combined heat and power (CHP) cogeneration units from Kraft Power Corporation is powered by the biogas. Prior, the electricity needed to run the equipment at the treatment plant was purchased exclusively from the local utility. Any heat needed for the operations had to be provided by boilers using either natural gas or biogas as a fuel source. With the generators, each unit is capable of producing 330 kW of electrical energy and 422 kW of thermal energy. The electricity produced is being used to power the new system and supply excess electricity to the main plant power network for use elsewhere throughout the plant. Based on the design, the new system will eventually consume approximately 340 kW of electricity, leaving the remaining balance of 320 kW for reuse elsewhere at the plant and moving toward a longer-term goal of providing supplemental power to the rest of the plant. The thermal energy will feed the TCHP, the belt dryer, and the central plant's heating loop. Based on current plant loadings, the TCHP will consume 245 kW of thermal energy, while the dryer will consume 590 kW, leaving the remaining balance of roughly 10 kW for the central plant's heating loop. The goal through optimization is that the dryer will consume less than the rated 590 kW of thermal energy, leaving additional heat for the central plant's heating loop. Meanwhile, a biogas conditioning system was brought in to reduce maintenance and increase the longevity of the combined heat and power cogeneration units. This technology removes moisture and siloxane from methane gas in the digestion stage in preparation to fuel the CHP system. The other major goal at hand for achieving greater sustainability was to realize an eco-friendly Class A Biosolids designation while lowering disposal volume. Prior to the overhaul, dewatered biosolids were manually loaded into a truck and disposed of at a local landfill. To meet this goal, a compact belt dryer by Sülzle- Klein was also installed. With the new dryer, dewatered material leaving a dewatering centrifuge is dried using the waste heat from the cogeneration units as the thermal supply. The dryer achieves all the requirements of Class A material, including temperature, duration, and moisture content. A Greener Tomorrow While each technology plays a critical role individually, it is their unique integration that has worked to bring this forward-thinking project to life. The additions and upgrades are in the midst of a year-long optimization process. With the additions and upgrades finished in the fall of 2015, the optimization period is targeted for a fall 2016 completion. Today, the plant stands to save $750,000 annually with an anticipated return on investment of just eight years. The majority of those savings are attributed to energy reuse. Kenosha is currently pursuing options for the beneficial reuse of its biosolids, which potentially include land application on local farm fields, additive to the city's yard-waste compost product, fuel supplement at a local coal-fired power plant or other incineration process, or contract operations with an outside firm for distribution. The city is currently in the process of getting the final biosolids product reclassified as Class A Biosolids with the Wisconsin Department of Natural Resources. "We're proud to take a stance in the management of our wastewater treatment facilities that is fiscally responsible to our ratepayers but also supports long-term sustainability for ecological balance," said General Manager Ed St. Peter. "It goes to show that with the right critical thinking, commitment, and steps, sustainability can be achieved cost-effectively. We're very proud that the Kenosha treatment system demonstrates such a balance." n wateronline.com n Water Innovations BIOSOLIDSMANAGEMENT The centrifuge room at the Kenosha Water Utility Ed St. Peter is general manager of the Kenosha Water Utility (Kenosha, WI), and has been with the utility for his entire 45-year career. Along with being a leader in the municipal water and wastewater field, Ed believes his greatest accomplishment is the exceptional staff with which he has surrounded himself. About The Authors 40 Michael Kopper is the founder and CEO of Centrisys Corporation, leading a global team in dewatering and process innovation problem-solving for municipal, manure management, and industrial wastewater applications.