How to Optimize Airflows to Aeration Basins

By design, Sierra’s proprietary “dry” sensor technology is extremely accurate, stable and holds calibration accuracy for the life of the product

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How to Optimize Airflows to Aeration Basins

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As a result of clean-energy mandates and the rising cost of energy, wastewater treatment facilities around the country are retrofitting their instrumentation to run highly efficient, cost-effective, clean facilities. To reduce emissions and produce clean energy, solid wastes are often digested in large digester tanks to reduce the volume of waste and produce more biogas, which is then used as fuel in the cogeneration process. However, a clean environment calls for not just clean air and clean energy, but clean water as well.

In the critical secondary stage of wastewater treatment, blowers aerate the basins, removing about 85 percent of organic matter by making use of the bacteria living within it. Municipalities need precise mass flow measurement instrumentation to bubble the exact amount of air into these aeration basins for the bacteria to flourish.

Sierra's solution
In the 1980s, many municipalities used differential pressure devices to measure the mass flow rate of air delivered to their aeration basins, but these devices proved to be expensive to maintain, clogged easily, measured only volumetric flow, and required a separate pressure and temperature transducer and flow computer to deliver true mass flow. Because of these pitfalls, municipalities began searching in the 1990s for an alternative to these costly and inefficient dP devices.

In 2003, a large western city retrofitted its aeration basins with Sierra’s SteelMass 640S to precisely measure the mass flow rate of air bubbling into the aeration basins in its secondary stage of waste treatment. By automating the aeration with the 640S as a key input into the control loop in a 7.8 mgd plant, the company saved about $50,000 a year in aeration costs and reduced chlorination and pH adjustment costs as an added benefit. Nearly total nitrogen removal was accomplished, resulting in improved effluent suspended solids.

Sierra differentiates its thermal mass flowmeters with patented Dry-Sense Sensor Technology. Unlike other thermal mass flowmeters, Sierra’s sensors use no organic fillers or cements in device construction. With the thermal expansion and contraction that is common to thermal mass flow technology, organic or “wet” sensors crack and shift over time, changing the “skin resistance” of the thermal sensor, and thereby causing drift or outright failure.

By design, Sierra’s proprietary dry sensor technology is extremely accurate, stable and holds calibration accuracy for the life of the product. Sierra has backed up those claims by being the only company to offer a lifetime warranty on its thermal sensor. Sierra’s validation software also lets the end user validate instrument accuracy on site periodically. If the validation ever fails, Sierra will replace the sensors and recalibrate the instrument free of charge.

With an installed base of more than 10,000 instruments in wastewater applications globally, Sierra is a proven leader in helping cities around the country measure true mass flow directly with one instrument that provides greater turndown, improved accuracy and a lower cost-of-ownership.

Here’s what makes Sierra’s SteelMass 640S an ideal choice:

  • Highly accurate calibration to precisely match the application conditions
  • Installed base of 10,000 instruments in wastewater applications
  • Provides savings up to $50,000 a year in aeration costs
  • Patented Dry-Sense Sensor Technology prevents sensor drift
  • Field validation of accuracy and instrument health
  • Lifetime sensor warranty

About Sierra Instruments
Sierra’s Flow Measurement and Control Division designs and manufactures flow instruments to cover nearly any gas, liquid and steam application spanning across global industries as diverse as oil and gas, scientific research, energy management, semicon, clean energy, aerospace and biotech. For more information, please visit


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