Controlled by Liquiline Control

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.

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.

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.

• 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.