Peristaltic Pumps for Disinfectant/Coagulant Tasks

Watson-Marlow Pumps has revealed how its 520 and 620 series peristaltic pumps have been selected by Black and Veatch for use at Thames Water's Advanced Water Treatment Works in Walton, Surrey. Black and Veatch was tasked with replacing ageing pumps for disinfectant and coagulant processes at the works. The Watson-Marlow pumps offer continuous high pressure and quick-release functionality. Several processes reliant on pumping operations are vital to the advanced water treatment process at Walton.

For example, pre-ozonated water is mixed with a coagulant in the flocculators to aid the production of large flocs, which are floated more easily in the subsequent counter-current dissolved air flotation and filtration (CocoDAFF) process. The addition of coagulant is now facilitated by 620 series pumps from Watson-Marlow. 'While the previous 504 series pumps for the coagulant process were reaching the end of their natural life, they had performed well so it was decided to continue with this type of pump,' said Black and Veatch's project MandE co-ordinator at the Walton site.

Watson-Marlow 620 series close-coupled pumps are pumping inorganic polymer coagulants, such as ferric sulphate, which perform well with thick flocs and offers fast sedimentation. The water is then treated using CocoDAFF and passes through post-ozone and granular activated carbon (GAC) contactors, as well as slow sand filters, before arriving at the disinfection stage, where sodium hypochlorite is introduced to contact tanks in doses using 520 series Watson-Marlow pumps. The residual is controlled into the supply by adding a further dose of either more hypochlorite to increase the residual, or sodium bisulphate to reduce the residual to a set point.

Ammonium sulphate is then added to combine with the residual to form chloramine before being pumped into the supply. Sodium hypochlorite is a corrosive chemical that has disinfection and bleaching properties. It is used in the purification of wastewater and the disinfection of drinking water. However, dealing with the chemical can be difficult as it is toxic and emits chlorine when in contact with acids. It naturally releases tiny bubbles of gas, which have a tendency to collect on the small ball valves found in conventional diaphragm dosing pumps.

This can cause gas locks in the system, which prevent the pumps from functioning. Because peristaltic pumps retain the fluid completely within the tube and have no valves that can leak or corrode, they can be used for the accurate metering of substances as challenging as sodium hypochlorite, without the associated gas locking and maintenance problems. Peristaltic technology therefore helps to keep costly downtime at the site to a minimum. A total of 10 Watson-Marlow 520 and 620 series pumps have been in use at Walton since June 2009.

Watson-Marlow 520 pumps are designed for the specific needs of the process sector. The models at Walton feature Loadsure elements, which fit into position for simple, error-free tube loading. Using the Loadsure D-connectors and easy-grip clutched rotor, the element can be changed in less than one minute without the need for special skills. These pumps also facilitate analogue signals for automated control and feedback purposes, accepting/providing 0-10V, 4-20mA, 5V TTL and 24V industrial logic inputs/outputs.

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