Magmeters Measure Up

Is the magmeter half full or half empty? That interesting twist on an old cliché is an apt question to ask the people of a small city located in Schuylkill County, Pa. The town was experiencing a serious problem with wastewater overflow, caused in part by the design of its 1800s-era masonry sewers.

For many years, raw sewage was transported via the sewers’ 4-ft-diameter pipe system and dumped straight into an open creek. Eventually, due to environmental concerns, state and federal regulations required that the water be treated before being discharged. Consequently, in the 1970s, an interceptor pipe was installed, which would grab a portion of this flow and send it to a recently built wastewater treatment plant (WWTP).

Although the interceptor pipe remedied some of the problem, the solution was plagued by a serious flaw. Whenever there was a sizable rainstorm, the interceptor system would bring an overabundance of storm water flow to the plant, which could not handle the increased water volume. As a result, the plant would flood out, causing untreated or partially treated water to enter nearby streams. This resulted in fines from the state regulating agencies, as well as negative impacts on the environment.

The city was determined to find a solution that would control the flow of water to the WWTP, particularly during heavy storms. The key would be to regulate the initial flow of water into the interceptor system that feeds the WWTP.

Search for Solution
To begin designing a viable solution, the city turned to Buchart-Horn, a full-service engineering and architectural firm. The firm began by updating the city’s “537 Plan,” which is required under the Pennsylvania Sewage Facilities Act. Enacted in 1966 to correct existing sewage disposal problems and prevent future problems, the law requires proper planning in all types of sewage disposal situations.

“The 537 Plan is approved by the Pennsylvania Department of Environmental Protection,” said Bruce Hulshizer, a senior engineer with Buchart-Horn and a project manager for sewer and water projects. “That’s basically saying: ‘This is what we’re going to do for our sewer needs.’ Apparently, the DEP wasn’t satisfied with the way things were going, and they weren’t going to meet their consent order, so that pulled us in.”

As part of the solution, Buchart-Horn brought in Krohne, a developer, manufacturer and distributor of measurement instrumentation for the process industries. Its role was to suggest components that would effectively regulate the flow. The solution recommended was the use of partially filled electromagnetic flowmeters (magmeters) to measure the lower, normal flows and the higher flows during high-water events.

By using partially filled magmeters, the city can measure the normal flows, which would not keep a typical magmeter filled, and also handle the higher flow rates in very rainy conditions. This meant that the storm water flow in high-water events could be diverted away from the plant and into nearby waterways, solving the issue of plant overload. When the flow rates reach a preset flow, it is assumed that the flow consists mainly of storm water runoff and can be safely diverted away from the WWTP. When normal flow rates resume, the flow is then directed back to the WWTP.

“The city had a combined system, which includes both storm water and sanitary flow,” Hulshizer said. “In order to have such a system, you must have control structures that basically separate sanitary flow out away from a predesignated amount of flow. After that, it would be storm flow, so you’d have to have some way of dividing the two. That’s where partially full magmeters came in.”

Technology Selection
Electromagnetic flowmeters are used in almost all branches of industry for the measurement of liquids (with or without solids content), pulps, pastes and other fluids that have a specific minimum of electric conductivity. Furthermore, the sophisticated electronics provide reliable and repeatable results, even under difficult process conditions. All magmeters are wet-calibrated by direct comparison of volumes, the most accurate calibration method available. This translates to a high accuracy—up to ±0.2% of actual value.

For this project, Buchart-Horn chose 21 electromagnetic magmeters from Krohne’s Tidalflux line, which are combined with a capacitive flow-level measuring system, built into the wall of the measuring tube. This provides accurate flow measurements in partially filled pipelines, with levels between 10% and 100% of the pipe cross-section.

Tidalflux flowmeters offer precise factory calibration to ensure a high level of measurement accuracy in partially filled pipelines. Featuring excellent abrasion and chemical resistance, the flowmeters’ steady display of measured values is achieved regardless of rough product surfaces and distorted flow profiles.

Buchart-Horn selected Krohne for this project because it was able to supply magmeters in the larger diameters necessary.

Critical Element Provides Answers
In the end, the load on the WWTP was reduced substantially in high-water events, allowing the plant to operate within its specified ranges. In addition, the environmental impact of non-treated or under-treated water entering the streams from the plant has been reduced greatly.

“It’s been a long process to where the city has come in terms of its wastewater treatment, but it has been a very effective solution,” Hulshizer said. “The Krohne magmeters proved to be a critical element.”

So, when you ask the city whether the magmeters are half full or half empty, you now know what the answer will be.

Richard Lowrie is water and wastewater industry manager for Krohne. Lowrie can be reached at r.lowrie@krohne.com or 978.535.6060.

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