Building for the Future: A Commonsense Approach for Kalamazoo Water Reclamation Plants' Dewatering Facility Upgrade

Rising chemical and sludge disposal costs, an uncertain future for biosolids disposal, and operator shortages; are some issues shared by many wastewater utilities today. The Kalamazoo Water Reclamation Plant (KWRP) dewatering upgrade case study presents a road map for other utilities on how to address the pressing issues many utilities face today by incorporating pilot testing, and utilizing operations and maintenance staff input in the equipment selection and design process, selecting the equipment to produce the driest cake, configuring equipment in a way to minimize odor and maximize the potential for future expansions, and by visualizing data to fast track the operator training process. This presentation presents a history of the plant, its past and present concerns related to biosolids, and an overview of its dewatering facility commissioned in 2022. KWRP, located in western Michigan, serves approximately 190,000 people. KWRP previously used sludge incineration, but the incinerator was abandoned in 1999 due to the implementation Title V EPA, a stringent air quality regulation for flue gas from incinerators. Until the most recent upgrade discussed here, the gravity-thickened primary sludge and waste-activated sludge from the biological nutrient removal (BNR) process were combined and dewatered together using four belt filter presses. Because a sizable pharmaceutical production plant is in the service area, activated carbon is added to the BNR process to absorb micropollutants. In 2001, because of the closure of the incinerator, KWRP started to produce Class A biosolids using the RDP lime addition and pasteurization process. This class A sludge production process did not last long. The plant experienced too many difficulties with operating and controlling the installed RDP process for the required sludge production throughput. Michigan's rising costs for land application fees were another factor for discontinuing that process. In 2008, the utility moved to 100% landfilling sludge, taking advantage of relatively low disposal cost: $17.5/wet ton. From 2008 to the present, the plant has faced a steady rise in disposal costs, on average 13.0% /year; cake dryness requirements (%TS) have also tightened. Maximizing the dryness of the dewatered cake and reduction of disposal volume became a priority for the Dewatering Facility Upgrade. Additional objectives for the upgrade included minimizing the odor source and improving the operational environment in the sludge dewatering facility, designing a flexible set up to adapt future changes in post-dewatering solids-handling, and to ensure the selected equipment is intuitive for operators to dial-in and maintain. KWRP believes pilot testing provides the most accurate data for decision-making and solidifying the facility design. The city opened an invitation for paid pilot testing to all interested manufacturers in 2014. Eleven manufacturers and six technology alternatives participated. After testing was completed, centrifuges were selected as the equipment of choice, for being the lowest annualized cost option in present-worth with the possibility for simple future expansion. (Figure 1). Figure 1: Annualized Total Cost for Kalamazoo Sludge Dewatering Options After receiving proposals from vendors, the city organized operators' visits to other water reclamation facilities and equipment manufacturing and equipment service facilities to gather KWRP staff input during the selection process. Among the equipment evaluated, Centrisys was selected for several reasons: The central location for repairs was fundamental for the centrifuge manufacturer choice, along with access to their top technical and optimization leaders in the company. Simple operation and maintenance of the hydraulic scroll drive, in comparison to a gearbox drive, was also a critical factor for the equipment selection. The hydraulic scroll drive was also preferred for its ability to generates higher torque than gear box to maximize the cake dryness. Three Centrisys CS26-4 units were installed in 2021 and successfully started up in 2022 (Figure 2). The project design includes the necessary infrastructure to support the current installation along with the possibility of an additional fourth Centrisys CS26-4 if needed. The upgrade resulted in the immediate improvement in sludge dewaterability: before the upgrade a 2-meter Andritz belt filter press was generating 16-17% cake; after the upgrade, the centrifuges now generate cake in the range of 21-24%, which translates to a disposal sludge volume reduction of 20-30%. The timing was just right: When pilot testing began, disposal costs were $30.90 per ton. In 2022, it was raised by 44% over the previous year to $92.71/wet ton, making it one of the highest in the region. Figure 2: Centrisys CS26-4 Installation at Kalamazoo Water Reclamation Plant Working through the volatility of disposal costs and uncertainties in the regulatory climate, KWRP has selected ancillary equipment to accommodate future changes better. Instead of open-top conveyors, cake piston cake pumps are now used to move the dewatered biosolids. The piston pumps can generate operating pressures up to 1,500 psi. In the case of either future regulations of emerging contaminants like PFAS, or increasing disposal costs, where further processing of the dewatered cake by means of sludge drying are required, facility additions can be accommodated by a simple reconfiguring of the pipes. The selection of the cake pumps over open conveyors minimizes the source of odor. The small amount of odorous gas generated from the decanter centrifuges and the cake pumps is now treated through activated carbon filters to improve the operator environment. Another design consideration for ease of operation is the addition of Valmet total solid meters to the centrifuge feed lines (Figure 3). The centrifuges have forward control of the polymer dosing systems: taking the measurements from the TS meter and the flow meter and pacing the polymer rate by specifying the polymer dose in lb/dry ton, rather than just a pump speed, in the control panel. This setup makes training new operators easier by giving real-time trends for the operators to learn about the plant and specifically dewatering operations. Additionally, having the polymer dose input (lb./ton) at the centrifuge which resembles what the operators learned for the operator training exam aids staff in being able to visualize the data. This in turns helps KWRP to shorten the initial training period for dewatering operations and more quickly move operators to the next level of training: tuning the centrifuges and to take on tasks such as selecting better polymers to get more out of their new equipment. Figure 3: Installed Valmet Meter KWRP addressed these challenges via a data-driven, and operator-centric approach for their biosolids dewatering facility upgrade. The primary pieces of the KWRP story are: the support from the community in funding the pilot testing piece of the dewatering equipment evaluation, the operator site visits to learn about the equipment, and the inclusion of innovative technologies such as real time solids measurement and visualization. In close collaboration with the equipment suppliers, KWRP found the winning ticket for navigating uncertain regulatory market conditions and preparing the plant for the future.