German wastewater plant benefits from accurate and reliable polymer dosing

Qdos 60 PU metering pump helps water treatment plant meet environmental standards for sludge dewatering

• Strict sludge regulation challenges met with accurate and reliable polymer dosing
• Innovative Qdos 60 PU chemical metering pump reduces maintenance
• Pumphead delivers high performance and efficiency

The upgrade of chemical dosing equipment at a wastewater treatment plant in Germany is delivering high performance sludge dewatering through more reliable polymer dosing.

Safe and reliable chemical dosing helps wastewater treatment plant (WwTP) operators ensure the facilities they manage meet the required environmental standards every day of the year.

The operator of a facility in Heide, a small town in Schleswig-Holstein, Germany, has upgraded the polymer dosing pumps in its sludge conditioning process with specialist peristaltic pumps to reduce maintenance interventions and polymer leaks it experienced previously with screw pumps.

In Germany, strict regulations for harmful chemicals, pharmaceutical residues, and microplastics mean the opportunities for reusing wastewater sludge as agricultural fertiliser are being increasingly limited and sending it to landfill is usually not permitted. This means thermal recycling is becoming more and more accepted as a highly effective way of sludge disposal, but the required sludge dewatering and polymer dosing during the sludge conditioning process can add significant cost.

Identifying cost-efficiencies in the dewatering process can mean significant savings for wastewater treatment plant operations and reduce the amount of sludge produced. In the case of Heide WwTP, deploying a Qdos chemical metering pump from WMFTS to replace a screw pump has made a big difference.

High accuracy

The plant installed a Qdos 60 PU peristaltic pump, which has been specially designed to dose hard-to-process polymers, and other hydrocarbons, with high accuracy.

In most cases, polymers are used as a flocculant in the sludge dewatering process, binding together micro or nano-sized particulates to form larger ‘flakes’. This improves the effectiveness of the solid-liquid separation system later in the sludge conditioning process. Selecting the correct polymer and ensuring it is used efficiently achieves the best possible dewatering of the sludge.

Qdos 60 PU peristaltic pumps can achieve this high standard of polymer dosing and are crucial in this process. The low-maintenance pumps are easy, safe and quick to service, offering substantial benefits in terms of time-saving and onsite health and safety which produces a streamlined and reliable process.

Reduces sludge

Sludge conditioning happens daily at Heide WwTP, which has capacity to serve a 40,000 population.

“We’ve modernised our sludge conditioning process considerably in recent years,” said Peter Dohrn, wastewater treatment manager and technical department manager at Abwasserzweckverband Region Heide (AZV Heide).

The sludge is thickened by adding an oil-based polymer flocculating agent and then fed through a screw press, which removes the water. This thickened sludge is then transported into the digestion tank, where it stays for up to 25 days before being dewatered again. After this, it is transported to the storage site before being collected for use in agriculture.

Sludge is processed at a rate of 7m3/hour, and conditioning reduces the volume by 80%, increasing the dry residue from 0.71% at the beginning of the process to 4.83% at the end. Each polymer dose takes around five minutes and occurs six times a day.

The process needs a pump which can deliver this repeatability and is robust against the polymer’s viscosity and resistance to pumping. Therefore, the reliability of the dosing pumps is critical in ensuring thickening the sludge in a cost-effective and time efficient manner.

The new Qdos 60 PU has a pumphead with a polyurethane tube. The dosing process is regulated by an external control system.

Maintenance and operation

To dose polymers, the Heide WwTP previously used progressive cavity pumps that were difficult to operate and required frequent servicing. Since progressing cavity pumps cannot run dry, suction from the IBC (intermediate bulk container) had to take place via the outlet fitting on the bottom of the IBC. This made changing the IBC time-consuming and almost never happened without minor leaks. The most serious problem, however, was the lack of leak detection during operation, so if a tube failed the entire polymer contents in the container could leak out. This meant a loss of expensive polymer and additional maintenance.

“A slippery mess on the floor would require intensive cleaning,” said Dohrn.

Additionally, the amount of time and effort involved in servicing the screw pumps, due to the different parts that came into contact with the polymer, was a growing problem.

“Every servicing run involved several hours of work [with the screw pumps],” said Dohrn. “Also, the extremely heavy progressive cavity pump was hard to move around, and its working principle meant it couldn’t achieve the dosing accuracy of other pumps due to its design.”

The Qdos 60 PU peristaltic pump provided an effective solution, with no need for diaphragms, valves, or seals that could be clogged by the polymer.

It also has a highly innovative design principle as the only part on the pump that ever requires replacement is the patented ReNu 60 PU pumphead. It is simply removed as a single unit and a new one clicked into place.

As the pumphead is fully sealed, there is no risk of the polymer leaking or the operator coming into contact with chemicals during replacement.

Leak detection

The pumphead has an integrated leak detector which automatically stops the pump and displays an error message if the tube ruptures. This also eliminates the risk of contamination caused by leaking polymer.

“In comparison to our previous pump, the Qdos has a much higher level of safe chemical handling and operational safety”

Peter Dohrn, wastewater treatment manager and technical department manager at AZV Heide

The intermittent dosing process is regulated from an external control system and has an accuracy of ±1%.

“Thanks to its highly effective suction capability, the self-priming Qdos pump can extract polymer from the IBC from above by means of a suction tube,” reported Dohrn.

“The pump handles the suction height of just under a metre with ease. The pump can also empty the polymer almost completely reducing the risk of leakage during changeover.”

Operators at Heide wastewater treatment plant are also very happy with the durability of the new Qdos 60 PU.

“The first pumphead ran smoothly for a year before we had to replace it, purely as a preventive measure, and the second has been working without any trouble since,” said Dohrn.