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Digester Mixer Performance Comparison in Caldwell, ID
Eric Roundy1, Kaitlin Chattin2, Katy Keeton2, Jason King1
1Keller Associates, Inc., United States of America; 2City of Caldwell, United States of America; , ,
After both of their 65-year old digesters broke down, the City of Caldwell needed additional solids treatment capacity at its wastewater resource recovery facility. Rather than copy their other digesters, the City wanted to maximize its investment by investigating new technologies. The project objectives were to construct a new facility that provided the needed capacity, maximized their use of digester biogas, and saved the City energy. The result was a $7.0 million solids handling and digestion improvement project.
As part of the improvements, an innovative linear motion mixing system was selected and installed on the new digester. The linear motion mixer had the potential to use significantly less electricity than the previously used pump mixing technology. The City has a similar size digester at the plant that utilizes a pump mixed system. This presentation will present findings comparing the digester performance using the new linear motion mixer and the pump mixed system.
8:45am - 9:30am
Sticky Business - Thickened Solids Pumping 101
MURRAYSMITH, United States of America;
The difficult job of pumping thickened solids has plagued wastewater treatment plant designers and operators for decades. While numerous studies have proposed various methods for the design of thickened solids pumping systems, what method to use should be chosen carefully as there is not one universally accepted method to address all the various solids types and pumping scenarios.
When the solids content of a flow stream is below 2-3%, it is typically considered “dilute” and special design considerations are not typically required. Solids streams at a wastewater treatment plant, however, are commonly thickened to higher concentrations to optimize the operation and the capacity of downstream processes. In doing so, the conveyance of this thickened sludge becomes considerably more difficult. The thickened solids streams no longer behave like water when pumped, but still contain enough moisture to preclude the use of conveyance mechanisms used for dewatered solids streams. This can lead to both design and operational problems that must be thoughtfully addressed.
This presentation will provide an overview of:
· how and why thickened solids stream pumping varies from dilute streams
· the most common methods used to design pumping systems for thickened solids and when to use them
· point out a faulty methodology in two very commonly used reference books that can result in significantly undersized pumps
· compare the methods against each other and with real-world data
· equipment and operational factors to consider in facility design.