Peristaltic pump technology for wastewater treatment

Technology replaces timer-controlled valves

Two Watson-Marlow SPX50 hose pumps have been installed at Dwr Cymru - Welsh Water’s Lavister Waste Water Treatment Works in North Wales in the UK, significantly improving system performance at the site. The pumps were installed during October 2006 and have delivered trouble-free operation since installation.

Prior to the installation of the pumps, auto desludging of the primary tanks at the site was operated by timer-controlled automatic actuated valves. Engineers at Lavister, which serves a population of 5500, found the valve technology difficult to control and sludge quality was far from consistent.

“By their very nature, the timer-controlled actuated valves opened fully for the set time period resulting in variable sludge consistency. Either too much water content resulted at the primary sludge holding tank or insufficient desludging resulted in blanket carry over at the primary tanks,” said Dave Hughes working on behalf of Dwr Cymru - Welsh Water. “We took the decision to replace the valves with two SPX50 hose pumps, one for each tank - each of which currently produces approximately 7 m³ of sludge/day.”

The mechanical installation was carried out by Smart Liquid Systems, the electrical by Lloyd Morris Electrical, and the civil work by E Jones and Son, all local contractors.

Since installation, the SPX50 pumps have not only required minimal routine maintenance, but have desludged at the specified rate without interruption to flow or ‘rat holing”.

The hose pumps installed at Lavister handle 3-5% dry solids content primary sludge at a transfer rate of 2500 L/h. Each pump runs at 16 rpm and has a discharge pressure of less than 5 bar.

They are also fitted with WIMES Efficiency1 1.5 kW cast iron frame motors with fixed-speed gearboxes.

The pumps were installed complete with associated pipework and valves, and are fitted with automatic cut-out switches to protect against blockages in the suction or discharge lines and burst hose protection. Suction and delivery lines are also fitted with surge dampers.

The success of the pumps on abrasive sewage sludge pumping, and other similar applications, stems from a combination of the gentle peristaltic pumping action, low operating speeds, and the abrasion-resistant characteristics of the hose itself. Designed to deliver continuous flow rates of up to 5000 L/h and pressures up to 16 bar, the Watson-Marlow SPX50 hose pump is suited for auto desludging applications. Its composite, braided nylon reinforced hose element is designed to handle sewage sludge as well as other viscous, fibrous and abrasive materials. It also incorporates an internal reinforcing element for enhanced mechanical strength, and its elasticity is maintained by passing it continually through a bath of lubricant.

The SPX design allows rapid hose changing when required, as well as simple maintenance. The pumps also feature overload protection and enhanced corrosion resistance. The ability to achieve and maintain accuracy to within ±1% and to handle additives such as lime slurry and easily damaged filamentous flocculants, has led to the pump’s widespread adoption for dosing duties in sewage and water-treatment processes.