Dewatering Technology Selection for the "2nd Most Difficult-to-Dewater Sludge in the World"

The City of Bend, Oregon, and Carollo Engineers, Inc. worked together to select a new dewatering technology to replace the City’s aging, poorly performing belt filter press. While the selection process included economic and non-economic analyses, the project team also assessed solids dewaterability through testing by third-party experts and incorporated criteria specific to the City’s Water Reclamation Facility (WRF) to identify the most suitable technology for the plant. The WRF’s digested solids are extremely difficult to dewater so dewaterability testing was used to determine the underlying reasons for poor dewaterability and the realistically achievable performance from different technologies. Belt filter presses, screw presses, centrifuges, and drying beds were considered, and centrifuges were ultimately selected as the most appropriate technology for the City’s Water Reclamation Facility (WRF). In-person site visits and telephone surveys of operating facilities allowed staff to hear about different equipment directly from other operators and maintenance personnel, which proved essential in building consensus around technology selection. Performance criteria and ultimate design features were based on the plant’s specific O&M needs and the results of the third-party dewaterability testing and on-site pilot tests.