A wastewater association in Saxony-Anhalt, Germany, operates a central sewage treatment plant that receives effluent from several surrounding towns, treats it, and subsequently discharges it into a river serving as the receiving water body.

The wastewater treatment plant (WWTP) already has an aeration tank at the inlet. Downstream of this, there is a rectangular weir over which the wastewater can flow freely. The customer uses this as a measuring point for the regulatory monitoring of flow and other parameters.

The operator is obliged to provide evidence to the district’s lower water authority and must continuously record wastewater volumes and submit annual reports by a specified date. A reliable volumetric flow measurement and totalisation in cubic metres per hour (m³/h) was therefore required.

KROHNE recommended the use of the OPTIWAVE 1540 radar level transmitter for measuring wastewater flow. This compact 80 GHz radar provides a highly cost-effective solution for flow measurement in open channels where the installation of a flowmeter for partially filled pipes is not feasible for structural or economic reasons. The device was installed above the rectangular weir, directly next to a conductivity and pH sensor. It is mounted on a long bracket supplied as a complete solution by KROHNE.

The OPTIWAVE 1540 transmits the level signal to the control room via analogue output and also provides flow-converted values directly to the control system via HART^®. The 80 GHz radar enables particularly fast response to dynamically changing levels and flow conditions.

In addition to monitoring via the control room, the customer uses the local SHD 200 display on site. Measurement values can also be accessed at any time via a mobile device using Bluetooth^® and the OPTICHECK Level Mobile app. The device was also commissioned quickly and easily via the app, which includes preconfigured templates for various weir types, including rectangular notches in accordance with ISO 1438. Commissioning required only the entry of a few parameters such as measuring range and bottom distance. In addition, the operator can perform on-site verification of the OPTIWAVE 1540 at any time via the app.

The customer benefits from a reliable, cost-effective solution that provides comprehensive documentation of the wastewater loads at the inlet, in accordance with regulatory requirements. A complex and uneconomical redesign of the measuring point was not necessary. Likewise, no additional peripheral equipment for converting level into flow had to be procured.

As the rectangular weir is stored as a standard application in the OPTICHECK Level Mobile app, all functions required for flow calculation are already integrated in the measuring device. Unlike many radar level devices in its class, the OPTIWAVE 1540 supports the HART^® protocol and transmits totalised flow values digitally to the control system.

The OPTIWAVE 1540 also enables the customer to carry out on-site verification required under local self-monitoring regulations directly via the OPTICHECK Level Mobile app and Bluetooth^®. A corresponding verification report can be generated at the push of a button and, for example, stored in the control room. For this purpose, the device accesses data from its comprehensive self-diagnostics. With OPTICHECK technology built-in, the 80 GHz radar features continuous self-monitoring.

The radar level transmitter has proven to be a robust solution for open-channel applications and is ideally suited for outdoor conditions. With an IP68 rating, it is protected not only against heavy rainfall but also against continuous submersion. Unlike ultrasonic level devices, radar technology is unaffected by wind, weather influences or condensation. It provides long-term stable, drift-free measurement and does not require recalibration. A factory calibration certificate is supplied as standard with every OPTIWAVE 1540 to verify its accuracy (measuring error: ±2 mm) and support compliance with local regulatory requirements.