Qdos peristaltic pump technology from Watson-Marlow Fluid Technology Group, is delivering a significant reduction in maintenance time - from 1.5 hours to just 5 minutes - at the local authority effluent plant in Selters (Westerwald), Germany. The Qdos pump is being used in preference to traditional diaphragm pumps for metering precipitants that help eliminate phosphate in wastewater.
"Wastewater is purified and discharged into a nearby stream – the Saynbach,” explains plant manager Achim Linder. "An important stage in the purification process is the elimination of phosphates, most of which come from domestic washing and cleaning products."
While the phosphate content of the water inflow is usually around 5-6 mg/l, the concentration after purification must not exceed 1.6 mg/l. To avoid this, a measured amount of precipitant is added (before the water enters the aeration tank) as soon as the concentration of phosphates in the wastewater reaches a concentration of 1.0 mg/l.
The addition of the precipitant converts the phosphate solution into insoluble phosphate compounds, which can then be isolated. The introduction of the ferric chloride from a large tank takes place at the precipitant metering station, with metered controlled using phosphate measurement. Depending on the phosphate content of the inflow water, delivery is between 60 and 250 ml of ferric chloride per minute. Until fairly recently, diaphragm metering pumps were used, but these proved insufficiently robust.
"The ferric chloride attacked the pump diaphragm, meaning it had to be changed every three to four months,” explains Mr Schenkelberg. “This took one of our technicians at least an hour every time and, because of the subsequent leakage of ferric chloride, almost as long again to clean the metering station."
For this reason, automation experts from Siershahn-based Jonas Schaltanlagenbau GmbH were invited to help find an alternative.
"In view of the susceptibility of diaphragm pumps we had to consider an alternative functioning principle, which brought us quickly to peristaltic pumps and the market leader Watson-Marlow, who recommended their Qdos pump,” says Benjamin Bullert, project Manager at Jonas Schaltanlagenbau.
"The simple but effective functioning principle did not take long to convince us of its suitability,” says Mr Schenkelberg. "Qdos is also intuitive to use and easy to operate."