Process Engineers at a water treatment works (WTW) are benefiting from accurate chemical dosing, reduced maintenance and reliable operation thanks to the replacement of rotor and stator pumps with peristaltic technology. The peristaltic pumps, supplied by specialists, Watson-Marlow were installed at Bamford Water Treatment Works as part of a project to optimise performance at the site.
The water treatment works at Bamford, near the historic Derwent Water Reservoir in the UK, pump 160 megalitres of water per day. Water from the works enters a large aquaduct, which flows down from North Derbyshire through Nottingham into Birmingham.
An integral part of the water treatment process at Bamford is the addition of lime slurry, to control the pH of the water. Water entering the works is dosed with ferric sulphate and a polyelectrolyte and brought to a pH of between 4.7 and 5.1. If the water is lower than this pH, it is dosed with lime in order to bring it up to the required level. The water is then fed from the clarifiers onto a bank of RG filters. At this stage Sodium Hypochlorite is added as a disinfectant.
Just before the water leaves the site, further alkaline lime slurry is metered to the supply in order to maintain the required pH level. The lime raises the pH to around 8/9, which assists in the removal of naturally occurring manganese.
Bamford WTW, which is owned and operated by Severn Trent Water, had previously been using rotor and stator pumps for this purpose – although two Watson-Marlow pumps had been used on the site for kalic dosing for several years. The rotor and stator pumps were removed as part of the AMP3 capital programme to upgrade the site and were replaced with a range of Watson-Marlow peristaltic hose pumps. The hose pumps have been in operation since the upgrading programme in approximately 1988.
According to the works manager at Bamford Works, the peristaltic pumps supplied by Watson-Marlow offer significant advantages over the previous pump types. “Because there are no glands – there are no leaks, which was always an issue with the rotor and stators. The other important thing for us is that when the tube needs replacing, it’s simply a case of a single step operation to complete the task.”
The process control engineers at Bamford WTW opted for a range of Watson-Marlow SPX hose pumps to handle the lime dosing. The larger SPX40's (maximum flow 6000 l/hr, discharge pressure 16 bar) and SPX32's (maximum flow 3400 l/hr, discharge pressure 16 bar) are situated at the north end of the site where the dosing demand is greatest. The smaller units, including the SPX10's (maximum flow 105 l/hr, discharge pressure 7.5 bar), SPX15's (maximum flow 375 l/hr, discharge pressure 7.5 bar) are used at the south end of the plant. The SPX25’s (maximum flow 1800l/hr, discharge pressure 16 bar) are used later in the system, when the pH is increased to between 8 and 9 for the removal of manganese.
The works manager is convinced of the benefits of peristaltic technology over alternative pumps types for demanding chemical dosing applications. “The Watson-Marlow pumps are capable of pumping viscous and high density fluids – which is not necessarily true of other pump types. It’s also vital for us that the unit doesn’t require high levels of maintenance. As the hose or tubing is the only wearing part it can be quickly replaced without dismantling the pump - and maintenance is therefore simple and cost-effective.”
The design of Watson-Marlow peristaltic pumps prevents backflow, and means that no valves are required, thereby significantly reducing blockages. Accuracy of the delivered volume and flow rate are parameters which can be fully tailored through the size of the pump, the rotor speed and the tube diameter. A number of safety features are incorporated at the Bamford WTW including pressure relief switches which ensure any excess force is pumped back into the suction system to do a full circle, and pressure sensors that will show if the system is running correctly.
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