Cost Effective and Efficient Sludge Cake Pump Design

Moving increasingly dry dewatered, sewage sludge cake efficiently and cost-effectively is a problem for many sewage treatment works. Many works use a belt or screw conveyor to move the cake from one point to another. These have several associated environmental and maintenance problems. Odour nuisance is common on open conveyors and cake spillage leads to environmental and safety concerns. Screw conveyors often break down and unscheduled maintenance costs rise accordingly. The answer in many cases is to use a progressing cavity (PC) pump.

However, due to the non-Newtonian nature of sludge cake, a pump will generally only fill around 50% of each cavity within the pumping element [this is referred to as Îvolumetric efficiencyâ].
Materials handling specialists Robbins & Myers, based in Chandlers Ford in Hampshire has solved this problem by designing the 2000 HS progressing cavity pump that combines performance and low life costs. This unit accepts dry sludge from a variety of sources - belt filter presses, silos, plate and frame presses, vacuum filters and centrifuges. Capital and operating costs are reduced and the unit requires a much lower level of maintenance compared to other sludge cake transport methods. The unitâs capital costs are a fraction of the price of a piston pump.
The whole unit is enclosed, reducing odour problems ö an important point when sewage treatment works are sited near to residential areas. The pump unit has five flexible installation options, saving a significant amount of space. Sludge cake can follow existing pipe routes, which saves interior building space. In tests, this unit has out-performed piston ram pumps, screw conveyors, serpentine and belt conveyors.
The new design combines reduced power demand with increased mechanical efficiency. This is an important point to consider as all UK water companies face increased electricity bills from April 2001, when the climate change levy is introduced. In order to offset the impact of the levy, water companies will need to reduce energy demand significantly to reduce the impact of a 10-15% increase in electricity charges. One way of doing this is by fitting energy efficient pumps wherever possible.