Wastewater treatment process use flow measurement to ensure process efficiency, to provide information for hydraulic and organic loading, and for data needed to prepare regulatory compliance reports. Flow rates are measured by finding a physical measurement that can be related to the quantity of liquid moving past a given point in a specified length of time. The three most common methods are fill and draw, weir, and flumes.
The fill and draw method measures the time required for liquid to fill a container of kwon volume. Dividing the liquid volume by the required time provides the flow rate.
Weir and flumes both use the principle involved in placing a constriction or barrier in an open channel. The amount of water that passes over or though the constriction is directly proportional to the height of the water behind the constriction (The head) and the area of the flow opening in the constriction. The constriction’s opening area remains constant, so the only required measurement for calculating flow rate is the head behind the constriction