Severn Trent Water mulls switch to peristaltic pumps

London – Severn Trent Water is considering expanding its use of peristaltic pumping following the recent introduction of the technology on three chemical dosing schemes.

The peristaltic pumps, from Watson-Marlow, were deployed as part of a temporary dosing rig constructed by engineering group, Costain. Severn Trent had previously employed conventional metering pumps in this application.

“Until recently, Severn Trent Water consistently used a specialist manufacturer of chemical dosing systems, all of which featured metering pumps,” confirms Paul Pearson, process commissioning engineer at Costain.

“However, in the past few months, aware that there may be even greater savings available, this arrangement has been relaxed and it’s given us the opportunity to run trials at Severn Trent using a peristaltic pump.”

According to Pearson, there are at least a further half-dozen such applications planned for the coming 12 months, all of which will also use peristaltic technology supplied by Watson-Marlow.

Some of these, however, might demand a higher flow rate specification than the existing [Watson-Marlow] 520 DuN/REM model (108 litres/hour at 4.1 bar), the engineer pointed out.

The three schemes to date have seen the peristaltic pump used for ferrous chloride and ferric sulphate dosing. These coagulants bind with phosphates in wastewater so they can be removed as sludge.

Under the Urban Wastewater Treatment Directive, water companies have to be very stringent about the level of substances such as phosphates that are recorded in treated water. Accurate dosing is, therefore, a critical requirment of the pump, which has also been used to dose with lime for pH correction.

“There are so many things that can go wrong with a metering pump,” said Pearson. “With peristaltic, the potential for failure is reduced massively because there are no valves, stators, diaphragms, seals or glands. It makes maintenance extremely straightforward.

“Only the tubing requires replacement, which is quick and inexpensive, and provided this is done at the recommended intervals, there won’t be any problems. We’ve certainly had no issues so far.”

The Watson-Marlow 520REM pumphead features large swept volume with sprung rollers for high accuracy, while the NEMA 4X enclosure delivers wash-down protection for use in arduous conditions such as the wastewater industry.

With peristaltic pumps nothing but the hose or tube touches the fluid, eliminating the risk of the pump contaminating the fluid, or the fluid contaminating the pump.

Complete closure of the tube provides the pump with its action, preventing backflow and siphoning, and eliminating the need for check-valves when the pump is not running.