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PUMPS, VALVES & ACTUATORS PUMPS PROVE THEIR WORTH WITH POLYMERS
The operator of a WwTP facility in Heide, Germany, has upgraded the polymer dosing pumps in its sludge conditioning process with specialist peristaltic pumps from Watson-Marlow Fluid Technology Solutions
performance sludge dewatering through more reliable polymer dosing. Safe and reliable chemical dosing helps
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wastewater treatment plant (WwTP) operators ensure their facilities meet the required environmental standards every day of the year. 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 an effective way of sludge disposal, but sludge dewatering and polymer dosing during the sludge conditioning process can add cost. Identifying cost-efficiencies in the dewatering
process can result in savings and reduce the amount of sludge produced. In the case of Heide WwTP, deploying a Qdos chemical metering pump from Watson-Marlow Fluid Technology Solutions (WMFTS) to replace a screw pump has made a big difference. 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
he upgrade of chemical dosing equipment at a wastewater treatment plant in Germany is delivering high
The upgrade will reduce the maintenance interventions and polymer leaks the plant experienced previously with screw pumps
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 using it efficiently achieves the best possible dewatering of the sludge, making the Qdos 60 PU peristaltic pumps crucial in this process. These low-maintenance pumps are easy,
safe and quick to service, offering time-saving and onsite health and safety benefits. Sludge conditioning happens daily at Heide WwTP, which has capacity to serve 40,000 people. 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. 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 didn’t usually happen 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. 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 Peter Dohrn, wastewater treatment manager and technical department manager at Abwasserzweckverband Region Heide (AZV Heide). “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. 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 is 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. It 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. The intermittent dosing process has an accuracy of ±1%. “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,” said Dohrn. Operators are also very happy with the
durability of the new pump. “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.
WMFTS
www.wmfts.com
NOVEMBER 2023 | PROCESS & CONTROL 31
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