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Controlled by Liquiline Control

Automated phosphate removal in Stadtlohn wastewater treatment plant

The Stadtlohn WWTP regulates phosphate elimination using the Liquiline Control. This control system doses the precipitant into the clarifiers depending on the current concentration of phosphate in the wastewater.

WWTP in the town of Stadtlohn, North Rhine-Westphalia ©Endress+Hauser

WWTP in the town of Stadtlohn, North Rhine-Westphalia.

Precipitant tank at Stadtlohn WWTP ©Endress+Hauser

Precipitant tank at Stadtlohn WWTP: An iron(III) chloride (FeCl3) precipitant is used in summer, while an iron-aluminum combination product is used in the winter months.

The results

  • Uniform phosphate concentration in outlet of only 0.5 - 0.6 mg/l.

  • Optimized precipitant usage.

  • High level of process transparency combined with ease of use.

  • The switching of the basins from parallel to cascade operation during a plant upgrade posed no problem for the control system.

Ewald Rathmer

We can always rely on the Liquiline Control control system. Even in difficult inflow conditions, it works as specified, thus ensuring that the outlet parameters are always adhered to.

Ewald Rathmer, Plant Manager
WWTP Stadtlohn (Germany)

The challenge

The customer required a control system that automated phosphate precipitation while also ensuring compliance with the phosphate limit value of the plant (1 mg/l), as stipulated by regulations. The phosphate concentration in the outlet had to be as constant as possible during both peak- and low-load phases. The control system also had to be able to comply with much lower limit values, since a more stringent limit value of 0.3 mg/l is expected in the next few years.

An additional requirement was the ability of the control system to function after the clarifiers were switched from parallel to sequential operation. Furthermore, the solution had to be easy to operate, to ensure that staff could make settings quickly and easily when on standby duty during the night and at weekends.

Our solution

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

  • State-of-the-art, low-maintenance phosphate analyzer.

  • Programmable logic controller (PLC) with Liquiline Control software.

  • 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.

Load-dependent precipitant dosage in Stadtlohn

The customer wanted phosphate measurement to take place at three measuring points. A phosphate analyzer was therefore installed in a centrally located measuring container. The analyzer automatically analyzes samples from the measuring points every 10 minutes. The Liquiline Control uses the measured value from the inlet of the biological stage to adapt to the incoming load, thus balancing out peak- and low-load phases.

Based on the measured value from the outlet of the biological stage, the Liquiline Control regulates precipitant dosage until such point as the desired residual outlet concentration of 0.5 - 0.6 mg/l has been reached. In this way, precipitant usage is optimized.

Phosphate measuring points at Stadtlohn WWTP

  • Inlet of biological stage: Measurement of incoming load.

  • Outlet of biological stage: The effectiveness of phosphate precipitation is tested here.

  • Outlet of WWTP: Final check to verify if limit value has been observed.