Recovering Gas from Digesters in Wastewater Treatment Using Thermal Flow Meters

Fox Thermal Flow Meters used to recover gas from digesters

Wastewater Treatment Plants (WWTPs) use large, heated digester tanks to remove and dispose of solid waste material. Here, bacteria break down the material, producing digester gas in the process. A Thermal Mass Flow Meter from Fox can monitor the flow of the gas.

Methane is a primary component of anaerobic digester gas (ADG) and a large wastewater treatment plant can produce roughly one million cubic feet of this gas each day.

Most WWTPs utilize recovered gas to fuel boilers and flare off the excess. Other biogas uses include fuel for combustion engines to generate electricity, fuel for natural gas vehicles, and sale and distribution to neighboring industries and communities.

ADG is a wet, dirty gas, often containing trace levels of contaminates such as hydrogen sulfides and volatile siloxanes, which may condense and accumulate on pipe walls or equipment inside of the pipe. Selecting a flow meter with no moving parts can dramatically reduce costs associated with maintenance and repair.

Most digester gas applications operate at relatively low pressure. Fox Flowmeters create virtually no pressure drop and can be used to accurately measure these flow rates. They are widely used in WWTPs to optimize digester processes, comply with environmental regulations (40 CFR Part 98 Subpart II) and control fuel and air flow ratios in combustion processes.

Read more about Wastewater and Biogas applications.

Aeration Systems in Wastewater Treatment

Fox Thermal Flow Meters for Aeration Systems

In wastewater aeration, one of the most important factors for proper treatment is the determination of how much air volume in standard cubic feet per minute (SCFM) will be needed to deliver the mass of air required for optimal bacterial biodegradation of organic matter.

The oxygen transfer efficiency of aeration systems in wastewater treatment is the ratio of dissolved oxygen to the total amount of air fed into the system. Oxygen that is not dissolved in the wastewater is lost and the biodegradation process is compromised. In order to avoid this, the flow of oxygen fed into the system must be monitored and then compared to water sample data to find oxygen transfer inefficiencies.

Another common problem associated with aeration systems is clogging of the diffusers which interrupt the flow of air in the system. Fox flow meters may be used to monitor flow and configured to trigger alarms when flow goes above or below a given flow range. These alarms signal that there are potential problems with diffusers on a given air line that can be quickly serviced in order to keep the system running optimally.

Sludge disposal regulations, EPA values for oxygen transfer, and growing disposal site scarcity are all motivating factors for improving aeration systems by locating and eliminating inefficiencies. Fox Meters can accurately measure air or oxygen flow rates in aeration systems to help solve inefficiency problems.

With aging wastewater facilities across the United States, there will be an increase in the need to upgrade or improve existing wastewater system inefficiencies.


Fox flow meters are often calibrated to measure air flow. Please review the product features for Models FT1, FT2A and FT3 for further information about our thermal mass flow meter products. If you’re not sure which meter is right for your coal emission application, use our Help Me Choose app to find the ideal meter or Contact Us today!

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