Controlled by Liquiline Control

The customer required a control system that automated nitrogen reduction while also ensuring compliance with the official nitrogen value in the plant outlet (TN ≤ 8 or 12 mg/l, depending on the time of year). It was also important that the control system would be able to function after the clarifiers were switched from parallel to sequential operation. The upstream basin is now used at the peak-load stage, while the second basin is subsequently used at the low-load stage.

The WWTP operator opted for a complete solution comprised of several different components:

• One oxygen sensor per basin as well as an ion-selective sensor for ammonium and nitrate.

• Programmable logic controller (PLC) with Liquiline Control software, which controls both basins individually.

• Touchscreen display used to operate the system from the control room.

• Various services, such as consulting, design and configuration of the controller, process integration, system training.

The customer wanted the two aeration basins in the plant to be aerated individually. Sensors in both basins measure the parameters ammonium, nitrate and oxygen. Using the measured values, the Liquiline Control control system configures a dynamic set point for oxygen: depending on the ammonium concentration, the exact amount of air required for complete removal of the ammonium (NH4-N) is injected. This results in process stability while also optimizing the energy efficiency of the blowers.

In addition, the controller dynamically adjusts the duration of the nitrification and denitrification phases. This improves the reduction of total nitrogen (TN), ensuring that it remains at a constant level in the plant outlet.

For the Stadtlohn WWTP, the controller was fitted with a remote control unit. This means that staff on standby duty are able to monitor the process and intervene if necessary from the comfort of their own homes.