Primary and Secondary sewage treatment are designed to improve the quality of wastewater. These processes reduce bacteria, suspended solids, biodegradable organics, and other materials to improve effluent quality. Flow measurement is used to control, manage, and optimize a wastewater treatment plant. Siemens offers a wide range of process instrumentation including a full line of flow measurement (Magnetic, Coriolis, DP, Open Channel, and Ultrasonic). This article will focus on the Clamp-on non-intrusive ultrasonic flowmeter and its applicability to wastewater flow measurement.