Name two common flow measurement devices used at wastewater plants.

• A. Weirs/open-channel devices (orifice/venturi) and magnetic flow meters
• B. Turbidity meters and pH meters
• C. Chlorine residuals and ORP sensors
• D. Weirs and ORP sensors

Answer: (A)

Flow measurement at wastewater plants relies on devices that translate a measurable signal into discharge. Weirs and other open-channel devices work in channels where the water surface height is related to flow rate, so measuring depth gives you the amount of wastewater flowing through. These are common at headworks and channel sections because they’re simple, reliable, and work well with open streams of wastewater. Magnetic flow meters, on the other hand, measure flow in closed pipes by sensing the velocity of the conductive wastewater as it passes a magnetic field; they have no moving parts and tolerate solids, making them a practical choice for many in-plant pipes. The other options focus on water quality (turbidity, pH, chlorine, ORP) rather than flow, and pairing a flow device with an ORP sensor isn’t how flow is typically measured.