Located in the town of Wells on Maine’s southern coast, the Wells Sanitary District provides treatment for up to 2.0 million gallons of wastewater per day.
Originally constructed in the late 1970s, the treatment facility underwent a major refurbishment in 2001 to update the facility and to ensure that it met all safety standards required by the Environmental Protection Agency and Maine’s Department of Environmental Protection.
To accomplish these objectives, the district contracted Wright-Pierce, a consulting engineering firm located in Maine to redesign many of the facility’s systems and processes.
As part of the refurbishment, it was deemed necessary to replace the electromagnetic flowmeters that measure the flow of waste throughout the facility.
“The existing meters had seen better days,” said Dennis Thayer, superintendent of the facility. “They were worn out and just needed to be replaced. Many people don’t realize that these meters operate 24/7, under demanding conditions, so they need to offer superior performance and reliability.”
Wright-Pierce recommended electromagnetic meters from Krohne, Inc., for the newly designed facility.
Role of magmeters
These electromagnetic meters, or magmeters, are being used for three different applications at the Wells Sanitary District, including sludge recirculation, total gallons of treated effluent and sludge wasting.
In the sludge recirculation area, two of the meters measure the sludge recirculation rates in gallons per minute to totalizing gallons per day. This is part of the facility’s inline, waste-activated sludge process.
Another meter is used in the wasting sludge area to measure the flow of sludge that is removed from the system. A fourth meter is used in the treated effluent area that measures the flow of all the treated wastewater that moves throughout the facility.
“The use of accurate and reliable meters in this environment cannot be overstated,” said Thayer. “Flowmeters are essential to the overall process here and at any treatment facility for that matter.
“Since the day that they were installed, the magmeters have been trouble-free, extremely accurate and reliable,” he added.
Accurate by design
The accuracy of the magmeters is no accident as every magnetic-inductive and ultrasound flowmeter has a calibration certificate. To achieve this high level of calibration accuracy, the manufacturer relies on a calibration rig that is not only the world’s largest and most accurate flow calibration rig, it is accurate up to 176,115 gal/min with measurement uncertainty less than 0.013%.
Nederland Meetinstituut B.V. (NMI), the Dutch calibration authority, has certified that the volume serving as the testing standard for this large-scale calibration rig is accurate to within ±0.013% when calibrating volume-flowmeters in the range from 79 to 176,115 gal/min.
This flow rate would be sufficient to fill a normal indoor swimming pool in less than one minute.
NMI’s test rig permits the precise calibration of flowmeters up to 120 in. in diameter—large enough for a small goods vehicle to pass through. The stainless steel calibration tower is 138 ft high and has a water volume of some 105,670 gal. High-precision level switches at various heights mark a series of partial volumes and these partial volumes and the total volume can be precisely calibrated by NMI.
The test rig itself is certified by the Netherlands Calibration Organization under EN 45001, ensuring that it conforms to both national and international standards.
For each calibration performed, the computer automatically produces a calibration report documenting flow values and measurement errors. Every flowmeter is wet-calibrated in a direct comparison with the volume calibrated by NMI.
NMI’s calibration method is actually 10 times more precise than the flowmeter being tested. This guarantees that the specified error limits of these devices are genuinely achieved under reference conditions. More importantly, it ensures that Krohne’s magmeters will provide true, verifiable data.
Maintaining performance
Recalibrating meters on a regular basis is an integral process to help maintain their high performance levels. Krohne’s MagCheck, a portable testing and verification device for electromagnetic flowmeters was incorporated by the Wells Sanitary District as means to ensure performance. The device enables complete functionality and accuracy verification of the magmeter’s flowhead, converter and cables without removal from the pipeline or interruption of the process.
An ISO 9001-compliant portable device that uses available line power at the flow tube, MagCheck can be used with most Krohne flowmeter converters as either an automatic verification instrument or as a manual flow signal calibrator. Simple to connect on-site, MagCheck verifies flowmeter performance while creating an archived calibration record accurate within 1% of the original factory calibration. Stored verifications can be imported into an advanced PC program for easy evaluation and analysis, adding even more functionality. MagCheck is directly traceable to international standards.
As mentioned above, Thayer’s own experience with the MagCheck device at the Wells Sanitary District confirms the units’ effectiveness. “We recently recalibrated the meters, which is required by both federal and state agencies on an annual basis, with the MagCheck and all of the meters were well within the accepted calibration limits.”
Pete Williams of Sullivan Associates, a Krohne distributor, explained that the accuracy and reliability of the testing and verification device provides customers with a high confidence level.
“MagCheck creates a significant comfort factor,” he said. “The calibration figures produced by the unit are certifiable and traceable. Ultimately, the device meets all government standards including the EPA.
“Customers can perform annual certifications on their magmeters without any interruption of the meters’ operation. And the customer will also have a ‘history’ of these certifications so the results can be viewed over time.”
Thayer’s satisfaction with the performance of the magmeters at the Wells Sanitary District translates to a willingness to employ them again in subsequent renovations.
“In the near future, the district’s two main pump stations will undergo a major overhaul and we plan to install Krohne’s meters. These meters have met and exceeded our expectations.”
