Flow Meter Accuracy Verification Using ADCP: A Wastewater Treatment Plant Case Study

Every measurement site is unique. During a recent assignment at a large wastewater treatment plant, Avizo’s Water Quality Measurement and Monitoring team adapted its method to verify the accuracy of flow meters installed in an effluent channel more than 14 metres wide.

The context: an annual regulatory requirement

In Quebec, the Regulation respecting municipal wastewater treatment works (ROMAEU) governs the monitoring of wastewater treatment plants. It requires the operator to measure the daily flow of treated wastewater with a system whose maximum deviation does not exceed 15% from a reference value. The accuracy of this system must be verified at least once a year (section 4).

Our client already had flow meters in place and knew its flows. Its need was to confirm that its instruments accurately reflected the hydraulic reality of its facility.

The challenge: an unusually large channel

Standard verification methods work well in pipes and channels of typical dimensions. However, the effluent channel at this plant is more than 14 metres wide and carries a large flow. Under these conditions, standard methods could not provide a reliable reference value.

The solution: flow measurement by ADCP

At Avizo, we regularly measure flow in natural watercourses. We therefore proposed an approach proven in rivers: the Acoustic Doppler Current Profiler, or ADCP.

The ADCP sends acoustic pulses into the water column and analyzes the echo returned by suspended particles. It simultaneously measures depth and flow velocity over the full water depth. As it crosses the channel, the instrument builds a complete profile of the cross-section and takes continuous measurements. The result is a highly accurate average flow, representative of the entire flow.

The results: reliable flow meters

Hydraulic conditions were particularly stable during the assignment, which supported excellent-quality measurements. The deviation between the flow recorded by the plant’s instruments and the flow measured by the ADCP was below the 15% regulatory threshold.

No flow meter adjustment was therefore required. The operator now has independent confirmation that its data is reliable.

No two measurements are alike

In flow measurement, there is no one-size-fits-all solution. The geometry of the structure, the magnitude of the flow and the flow conditions all guide the choice of method. Our role is to analyze each situation and deploy the right tools to obtain a reliable, compliant measurement.

Need to complete the annual verification of your flow measurement systems? Avizo’s Water Quality Measurement and Monitoring team can support you, whatever the configuration of your facilities.

Frequently asked questions

What does the ROMAEU require for flow measurement?

The Regulation respecting municipal wastewater treatment works (ROMAEU) requires the operator to measure the daily flow of treated wastewater with a system whose maximum deviation does not exceed 15% from a reference value. The accuracy of this system must be verified at least once a year, in accordance with section 4.

What is the difference between calibration and accuracy verification?

Accuracy verification compares the data from an installed flow meter with an independent reference measurement, to confirm that the deviation remains within permitted limits. Calibration, strictly speaking, means adjusting the instrument when an excessive deviation is found. When the ROMAEU uses the term “étalonnage” (calibration), it actually refers to an accuracy verification.

What is an ADCP?

An ADCP (Acoustic Doppler Current Profiler) is an instrument that measures water velocity and depth over the full height of the water column. As it crosses a flow section, it builds a complete velocity profile and calculates a highly accurate average flow.

Why use an ADCP at a wastewater treatment plant?

The ADCP is mainly used to measure river flow. However, it becomes the most suitable solution in wide or high-flow effluent channels, where standard verification methods cannot provide a reliable reference value.

How accurate is an ADCP measurement?

Under stable hydraulic conditions, the ADCP provides a highly accurate reference measurement. During a recent Avizo assignment in an effluent channel more than 14 metres wide, the deviation from the plant’s flow meters was about 5%, well below the 15% regulatory threshold.

What happens if the deviation exceeds 15%?

A deviation above the threshold indicates that the measurement system does not meet the ROMAEU accuracy requirement. The operator must then identify the cause (instrument, installation or flow conditions) and make the necessary corrections, such as adjusting or replacing the equipment.

Who can perform a flow meter accuracy verification?

The verification must be performed by a qualified team able to select a reference method suited to the configuration of the structure. Through its Water Quality Measurement and Monitoring team, Avizo supports municipalities and industries across Quebec in verifying their flow measurement systems.