Arla: Fieldbus controlled dosing at dairy.

Europe’s largest dairy ARLA Foods A/S, processes some 7,1 billion kilos of milk per year. The wastewater from the dairy’s cheese production is treated according to local standards before it
is discharged into the Gudenaa river. Recently, ARLA Foods A/S built a state-of-the-art wastewater treatment system in Rødkærsbro, Denmark, to take care of the wastewater from the cheese production.

The Situation
Treatment of wastewater according to limit values is crucial for the daily operation of ARLA Foods. If ARLA Foods do not respect the limit values for phosphorous in wastewater, it will lead to an expensive production standstill within 24 hours.
Therefore, the dairy has to follow the waste water treatment process closely. The monitoring and controlling is done by the means of a fieldbus-controlled treatment system, which ensures a steady and reliable flow of information and makes sure that the level of phosphorous do not exceed the limit values.

The Grundfos Solution
The Grundfos Digital Dosing pumps can easily be connected to multiple pump systems via the optional integrated Profibus interface on the DME range.The dosages of additives are performed with minor pulsations and high accuracy due to the unique dosing principle of the Digital Dosing pumps. The Digital Dosing pump’s diaphragm is mounted directly on the motor-driven connecting rod. This construction makes it possible to control the speed of the diaphragm through every discharge and suction phase. All the Grundfos Digital Dosing pumps operate at a maximum stroke length every time, and therefore the amount of additive discharged through the dosing head is always the maximum possible. ARLA Foods has installed 6 Grundfos DME Digital Dosing pumps at the wastewater treatment plant. 4 of them are used to dose different chemicals such as ferric chloride and 2 and them are used to dose acid and lye, all with the purpose of keeping the phosphorous content at a safe level. The Digital Dosing pumps are compatible with the Profibus network that ties the ARLA Food plant together. Thus, it is easy to follow the wastewater treatment process closely. Sensors monitor the phosphorous level in the wastewater system, and relay the information back to the controlling PC. If the phosphorous level rises above a certain limit, the PC automatically starts the dosing pumps, or increases the dosage in order to prevent a high concentration of phosphorous in the wastewater.