Water & Wastewater Treatment

6 The PumPing STaTion - PumP and ValVe SuPPlemenT 2017 Case study Peristaltic pumps prove the right dose for Welsh Water plants T o help overcome the repeated blockage of diaphragm pumps when dosing ferric sulphate at wastewater treatment plants, a number of Welsh Water sites now feature Qdos 30 peristaltic pumps from Watson-Mar- low Fluid Technology Group (WMFTG). The investment is expected to achieve a quick return thanks to significant savings in maintenance associated with stripping down and cleaning the diaphragm pumps. Moreover, the Qdos pumps are helping Welsh Water meet increasingly strict phosphorus limits. With ever-tightening Water Frame- work Directive (WFD) standards, phosphorus limits are under close scrutiny. WFD Directive 2000/60/EC demands that rivers, lakes, coastal waters and groundwater be in a "good ecological and chemical condition" by 2027. Excessive nutrients such as phosphorus in the watercourse work against this aim as they lead to excessive algal growth and eutrophica- tion - a form of water pollution. To reduce the ingress of phosphorus through municipal wastewater treat- ment plants, chemical coagulation is required. The addition of a coagulant such as ferric sulphate converts the phosphate solution into insoluble phosphate compounds which can then be isolated. The continuous dosing of ferric sulphate at wastewater treatment works requires the application of reliable, high performance pumps. For Welsh Water, the traditional pump type of choice has been based on diaphragm technology. However, this has had its issues. Blocked diaphragm pumps "Our diaphragm pumps were blocking on a repetitive basis," explains Ronnie Swain, Process Technician at Welsh Water. "Almost every time I visited one of our sites there would be problems with the diaphragm pumps. We would start off by turning them up to achieve the same flow, but eventually we'd have little option but to get our maintenance team involved to open up the pumps and remove the blockage. However, this obviously involves time and cost, and it was happening year-round. Diaphragm pumps have a lot of components, such as non-return valves and springs, which can clog. We had to carry a whole array of replacement parts in stock. It was clearly time to look for another solution." Having witnessed the benefits of peristaltic pump technology first hand when a Qdos model was recently installed at Welsh Water's Eign plant in Hereford for the back-end dosing of polyaluminium chloride at 12 l/h, the company thought this might also be a good solution for front-end ferric sulphate dosing. Initially, Welsh Water opted to install a Qdos 120 pump for dosing ferric sulphate at its Rotherwas wastewater treatment plant in Hereford. Here, the pump has been set to work operating at a flow rate of 50-60 l/h. However, Qdos pumps are reliable at flows as low as 0.1 l/min. "The difference compared with the Switching from diaphragm to peristaltic pumps for chemical dosing helped Dwr Cymru Welsh Water save Opex costs while maintaining phosphorus standards

• Cover