Source: http://www.marsh-mcbirney.com

A flow monitoring site located on the effluent of the Town of Erie Colorado’s Water Reclamation Facility had been problematic from the start due to a very steep fall designed into the system just in front of the metering location. Erie, Colorado’s Water Reclamation Facility was built in 1998 and is a 1.2 mgd activated sludge water reclamation facility. The water reclamation facility utilizes various physical and biological processes to remove the organic and inorganic constituents from wastewater generated by residential, commercial, and industrial sources.

Influent pumping, screening, grit removal, activated sludge, sedimentation, ultraviolet disinfection and aerobic sludge digestion are some components making up the water reclamation facility. An in-house laboratory program enables personnel to treat the wastewater to meet federal and state mandated regulations and to meet discharge permit limits.

The effluent monitoring site had been outfitted with a weir as well as an open channel flow meter that utilized a submerged style sensor. An ongoing sensor fouling issue, caused primarily by algae, required weekly maintenance as well as very unreliable flow data. When compared to readings on the magmeter on the influent side of the facility, accuracy discrepancies exceeded the 10% requirement mandated by their NPDES permit. It was clear that the effluent meter needed replacing.

Jon Mays, Chief Water Reclamation Facility Operator with the Town of Erie, states, “We originally put in a weir and later a flow meter that had a submerged sensor. The problem was that it was continually getting algae on it and required maintenance. We had to go in and clean that submerged sensor frequently and we still couldn’t keep good accuracy. The meter was also not accurate at low flows. There is a very steep fall on the pipe coming away from the meter site that also made it difficult for a submerged unit to accurately measure flow.” Because this was a permanent monitoring site that provided permit data it was very important to choose a meter that would be highly accurate under these less than desirable conditions and require little or not maintenance.

Mays mentions that he saw Marsh-McBirney’s product information on the web when he was looking for a solution to his flow monitoring application and that he was also familiar with the local Marsh rep, Brian Dieke of the Water Technology Group. During last years annual WEFTEC conference Mays also visited the Marsh-McBirney/Hach Flow booth at last years WEFTEC conference to learn more about possible monitoring options for the Town. Dieke recommended the Flo-Dar Radar Velocity/Area Flow Meter for the application and was confident that the meters ‘above-the-flow’ sensor would be unaffected by fouling and could provide the high accuracy Mays was looking for.

The Flo-Dar Open Channel Flow meter provides a revolutionary approach to open channel flow monitoring by measuring from above the flow stream eliminating confined space entry concerns and maintenance caused by fouled submerged sensors. Flo-Dar transmits a digital Doppler radar beam that interacts with the fluid surface and reflects back signals at a different frequency than that which was transmitted. The return frequency is compared with the transmitted frequency and the resulting frequency shift provides an accurate measure of the velocity and the direction of the flow. Depth is detected by an ultrasonic pulse echo sensor. Flow is then calculated based on the Continuity Equation: Q = V x A, Where Q = Flow, V = Average Velocity and A = Area.

A Flo-Dar sensor with Flo-Station electronics (permanent model) was ordered by the Town and was recently installed. “The Flo-Dar is in and it is working very, very well.” Mays adds. According to Mays, ‘accuracy’ was the main reason that he selected the Flo-Dar. He comments, “The state of Colorado wants my meters to be within 10% of each other. The previous meter would never come within 10%. However, with the Flo-Dar unit we have been having an accuracy of about 2%.” Additionally, Mays is glad to be free from regular flow meter maintenance and manhole entry which has been totally eliminated. He continues, “The other feature I like very well is that I am able to take my laptop out there, download a months worth of flow data and the software (Flo-Ware) allows me to keep flow charts that the state wants me to keep rather than having a separate chart or something else hooked up. I can simply go out there with my laptop and download that chart.” In the near future the meter will be tied to the Town’s Wonder-Ware SCADA system.

Recently awarded a grant to upgrade their Wastewater Facility, the Town of Erie will now to able to meet capacity loads for the future. Currently rated as a 1.2 mgd facility, plans call for a 1.6 mgd capacity in the near future. The entire plant will undergo a complete modernization. The investment in their Town’s all important infrastructure coupled with their investment in the accurate Flo-Dar flow meter will ensure that they continue to maintain the public health and safety of the Town of Erie and its citizens.