Peristaltic pumps from Watson-Marlow Bredel are being used by South West Water for dosing coagulant into raw reservoir water for the purpose of purification.
The peristaltic pumps dose coagulant into the water at variable rates that are driven by the condition of the raw water.
Located near Falmouth in Cornwall, the water purification plant had earlier employed two conventional diaphragm pumps for the purpose but faced blockage problems caused by crystallisation.
The plant decided to explore alternative options since it involved the critical process of coagulant dosing.
Following discussions with Watson-Marlow, South West Water took two 520DuN/R2 peristaltic pumps on a trial basis.
Peristaltic pumps have no valves, seals or glands with the fluid only contacting the bore of the hose or tube. This eliminates the risk of the pump contaminating the fluid or the fluid contaminating the pump.
Water treatment supervisor, Michael Galligan commented that they were using peristaltic technology for coagulant dosing for the first time. They had only used peristaltic pumps for buffer applications on chlorine analysers.
The trial pumps performed well during the trial period and the plant purchased a 520DuN/R2 pump from Watson-Marlow for installation at the treatment hall near Falmouth, one of 30 plants in the South West region.
Considering the high process criticality, South West Water purchased two pumps for operation and back-up.
Each day South West Water supplies more than 100 million gallons of water to approximately 1.5 million residents, so there is no margin for error or failure.
Raw reservoir water is processed through dual stream dissolved air flotation tanks and coagulant (polyaluminium chloride solution) is applied at the front end.
A Watson-Marlow 520DuN peristaltic pump doses coagulant at variable rates of 100-1500ml/minute through a ½-inch clear braided hose into the first stage of the purification process via a flowmeter.
The variable dosing is driven by raw water conditions and the process is monitored continuously so that an optimum amount of coagulant is applied.
The new 520DuN pumps have a set speed accuracy of 0.1% and can be calibrated by weight or volume for accurate metering.
The pumps provide user feedback via a display and have dual analogue input to control and scale speed.
The 520 series peristaltic pumps provide industry with a 'drop-in' alternative for diaphragm or piston pumps with variable stroke control.