South West Water is using peristaltic pumps from Watson-Marlow for dosing coagulant into raw reservoir water. It is thought to be the first time peristaltic technology has been used on a coagulant application, certainly within the South West region.
Originally the purification plant employed two conventional diaphragm pumps for this duty but the suffered from blocking due to crystallisation of the coagulant chemical. Following discussion with Watson-Marlow Bredel, South West Water employed two 520DuN/R2 peristaltic pumps on a trial basis.
“It was a ground breaking trial in that we had not used large peristaltic technology for coagulant dosing before,” explains water treatment supervisor, Michael Galligan. “The only peristaltic pumps we had experienced were very low flow units used for buffer applications on chlorine analysers. Clarification of raw reservoir water is obviously a highly critical part of the process, but we hoped peristaltic would be the answer.”
Sure enough the trial pumps performed without problem over the trial period and the two NEMA4X rated (IP66) Watson-Marlow pumps were subsequently purchased – one duty and one standby.
Within the treatment hall, raw reservoir water is processed through dual stream dissolved air flotation tanks and coagulant (polyaluminium chloride solution) is applied at the front end. The coagulant is dosed by the 520DuN/R2 pump at between 100-1500ml/min.
The pump doses at variable rates that are driven by the raw water conditions, and the process is monitored continuously so that the optimum amount of coagulant is applied. For instance, in springtime, algae levels in the raw reservoir water are higher due to increasing sunlight levels and the coagulant requires adjusting accordingly, which is where the variable dosing capability of the 520DuN pump is invaluable.
“As a result of this project, our in-house technical standards officer, who is responsible for reviewing technology suitable for company use, has now added peristaltic pumps to the list" commented Galligan.
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