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Building a Diffuser Performance Monitoring Program
Ornella Sosa-Hernandez, Adrienne Menniti, Peter Schauer
Clean Water Services, United States of America;
Due to the logistics associated with bringing aeration basins off line, Clean Water Services (CWS) has historically chosen not to routinely clean diffusers. Also, the ultimate replacement of diffusers is done on a schedule of 10 years instead of being prompted by performance. CWS has embarked on an effort to establish a diffuser monitoring program to support decisions about how frequently to clean and replace diffusers.
Diffuser performance is being characterized by tracking changes in diffuser headloss and oxygen transfer efficiency (OTE) over time. Both parameters are monitored using two approaches:
Discrete measurements are used to monitor the performance of Sanitaire EPDM diffusers installed in March 2017. Diffuser headloss is measured bi-weekly at a fixed airflow rate using a pressure monitoring panel. OTE is estimated measuring oxygen uptake rate bi-weekly.
Continuous measurements are used to compare the performance of diffusers installed in March 2018 in two aeration basins, one with SSI PTFE-coated EPDM diffusers and the other with standard SSI EPDM diffusers. A commercial off-gas analyzer was used during the summer of 2018 to compare the OTE. Diffuser headloss is tracked continuously by having the pressure monitoring panel connected to the SCADA system.
Current data comparing the SSI diffusers suggests that two diffuser types show undistinguishable OTE performance. However, the PTFE-coated diffusers have higher initial headloss. The diurnal variability makes using both OTE evaluation methods challenging for long-term performance characterization. In addition, optimization of the headloss monitoring system is required to guarantee data reliability.
This presentation will include the CWS efforts to implement this program and to help answer the following questions:
Which are the best metrics to characterize long-term diffuser performance for decision making?
What are the challenges associated to the systematic implementation of these measurements?
What is the cost-benefit trade-off of having continuous versus discrete measurements?
3:45pm - 4:30pm
McMinnville WRF: Reliably Meeting Low TP Limits for 25 Years
William Leaf1, Jeff Swale2, Erik Grimstad2, Joshua Koch1
1Jacobs, United States of America; 2City of McMinnville, OR; , ,
The water reclamation facility (WRF) serving McMinnville, Oregon has reliably met one of the most stringent effluent total phosphorus (TP) limits in the Northwest for over 25 years. The WRF operates with an effluent TP limit from May 1 – October 31 for discharge into the South Yamhill River. The stringent effluent TP limit of 70 micrograms of phosphorus per liter (µg-P/L) must be met when the South Yamhill River monthly average flow drops below 100 cubic feet per second (cfs). This typically occurs during the summer months, July through September. The McMinnville WRF utilizes an Orbal™ oxidation ditch operating with enhanced biological phosphorus removal (EBPR) together with a tertiary treatment system that includes solids contact clarification, filtration (continuous upflow sand filters) and the associated chemical feed systems. The 6.6-mgd capacity tertiary treatment system was constructed in the mid-1990s and operates seasonally to address the TP limits at the facility.
The WRF’s reliability is a result of the City staff’s dedication to understanding and optimizing the system over the years. One example is the optimization of the oxidation ditch, implementing operational modifications to reliably develop and maintain EBPR during the permit season. Improvements and adjustments to the aerators and associated mixing system have been key. These changes have been informed by a high level of wastewater characterization completed at the facility over the years, providing valuable information to WRF staff. Teamwork among the City’s public works staff, particularly pretreatment and collection system staff, are also integral to the success of the WRF’s treatment process. Bridging the gap bewtween pretreatment, collections, and operations has been critical to meeting the WRF's stringent TP Limit. The cooperation and commitment of McMinnville staff for the last 25 years places the facility in a great position to meet the future challenges facing the City.